CA1062820A - Process for the purification of waste water - Google Patents
Process for the purification of waste waterInfo
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- CA1062820A CA1062820A CA234,524A CA234524A CA1062820A CA 1062820 A CA1062820 A CA 1062820A CA 234524 A CA234524 A CA 234524A CA 1062820 A CA1062820 A CA 1062820A
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Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed is a continuous process for purifying contaminated waste water. First the water passes through an equalization zone including at least two separate compartments, in one of which the pH of the water is adjusted to a range of from about 6.5 to 9.5. The water flows through the separate compartments such that the concentration of contaminants in the water exiting the equalization zone will approach about constant concentration which changes only gradually even though influent contaminant concentration changes rapidly.
Water in at least one compartment of the equalization zone is aerated so that the dissolved oxygen in the water is at least three parts of dissolved oxygen per million parts of water. Solids are skimmed from the surface of the water in the zone, and coagulant is added to the effluent water from the equal-ization zone so that colloidal particles in the water flocculate. The water from this equalization zone is then filtered to remove flocculated particles.
The effluent from the filter will have less than about ten parts of suspended solids per million parts of water and less than about ten parts of hydrocarbon per million parts of water. This effluent is aerated, preferably by aspiration, and is treated in a four stage biological treating zone. In the first stage, the water contacts an activated sludge which decontaminates the water by biodegrading contaminants. In the second stage, water from the first stage is clarified to separate suspended sludge particles from decontaminated water.
The bulk of the separated sludge particles is recycled to the first stage, and the bulk of the clarified, decontaminated water is withdrawn. In the third stage, that portion of the separated sludge particles not recycled is concen-trated by removing additional residual water. In the fourth stage, the concen-trated sludge particles are digested. In accordance with an important feature of our invention, the water-sludge mix as it flows between the first and second stages is aerated by aspirating air into the water-sludge mix and then sub-jecting thix mix to a high hydrostatic pressure. Preferably the sludge flowing between the second, third and fourth stages is also serated. The water sep-arated from the second stage is filtered to remove any minute suspended sludge particles which may be present. The preferred filter medium is sand or combinations of sand and coal, and may be followed by treatment with activated carbon. Interstage seration is conducted at pressures above atmos-pheric. This ensures substantial transfer of oxygen to the water. Also, activated sludge-water mixture that exited the first stage. The average age of the sludge in the system is greater than ten days. The dissolved oxygen concentration in the water flowing from the biological treating zone is at least about five parts of dissolved oxygen per million parts of water.
Disclosed is a continuous process for purifying contaminated waste water. First the water passes through an equalization zone including at least two separate compartments, in one of which the pH of the water is adjusted to a range of from about 6.5 to 9.5. The water flows through the separate compartments such that the concentration of contaminants in the water exiting the equalization zone will approach about constant concentration which changes only gradually even though influent contaminant concentration changes rapidly.
Water in at least one compartment of the equalization zone is aerated so that the dissolved oxygen in the water is at least three parts of dissolved oxygen per million parts of water. Solids are skimmed from the surface of the water in the zone, and coagulant is added to the effluent water from the equal-ization zone so that colloidal particles in the water flocculate. The water from this equalization zone is then filtered to remove flocculated particles.
The effluent from the filter will have less than about ten parts of suspended solids per million parts of water and less than about ten parts of hydrocarbon per million parts of water. This effluent is aerated, preferably by aspiration, and is treated in a four stage biological treating zone. In the first stage, the water contacts an activated sludge which decontaminates the water by biodegrading contaminants. In the second stage, water from the first stage is clarified to separate suspended sludge particles from decontaminated water.
The bulk of the separated sludge particles is recycled to the first stage, and the bulk of the clarified, decontaminated water is withdrawn. In the third stage, that portion of the separated sludge particles not recycled is concen-trated by removing additional residual water. In the fourth stage, the concen-trated sludge particles are digested. In accordance with an important feature of our invention, the water-sludge mix as it flows between the first and second stages is aerated by aspirating air into the water-sludge mix and then sub-jecting thix mix to a high hydrostatic pressure. Preferably the sludge flowing between the second, third and fourth stages is also serated. The water sep-arated from the second stage is filtered to remove any minute suspended sludge particles which may be present. The preferred filter medium is sand or combinations of sand and coal, and may be followed by treatment with activated carbon. Interstage seration is conducted at pressures above atmos-pheric. This ensures substantial transfer of oxygen to the water. Also, activated sludge-water mixture that exited the first stage. The average age of the sludge in the system is greater than ten days. The dissolved oxygen concentration in the water flowing from the biological treating zone is at least about five parts of dissolved oxygen per million parts of water.
Description
~C~6Z8Z() BACKGROUND
I'lle cre.~ enc of contnminat~ wnxte watet involvcs a seq~lcnce of processing steps for maximizing water purification at minimum costs. Indus-trial effluents, particularly waste water from oil refineries, include a broad spectrum of contaminants and, consequently, such waste water is usually more difficult to decontaminate than waste water from municipal sewage sys-tems. Four main sequential process treatments are used to decontaminate such industrial effluents. These are a primary, intermediate, secondary, and tertiary treatments, The primary treatment calls for removal of gross amounts of hydrocarbons and solids from the waste water. In the oil industry, usually separators of American ~etroleum Institute design are employed for removal of free, separable oil and solids. The intermediate treatment is the next process and it is designed to adjust water conditions so that the water entering the secondary treatment zone will not impair the operation of the secondary treatment processes. In other words, intermediate treatment is designed to optimize water conditions so that the secondary treatment process will operate most efficiently. The secondary treatment calls for biologically degrading dissolved organics and ammonia in the water.
One of the most common biological treatment processes employed is the acti-vated sludge process discussed below in greater detail. The tertiary treat-ment calls for removing residual biological solids present in the effluent from the secondary treatment zone and removing contaminants which contri-bute to impairing water clarity or adversely affecting water taste and odor.
This is usually a filtration of the water, preferably through beds of sand, or combinations of sand and coal, followed by treatment with activated carbon.
The acLivated sludge process is a conventional waste water treating process which produces the highest degree of biological treatment in reason-ably compact facilities at the present time. The application of this process to the treatment of industrial waste water has, however, been slow compared ~ ' - 1 - q~
1~6;28ZO
with municipal applications. Industrial applications of this process are nevertheless increasing rapidly, Currently, the activated sludge process is capable of achieving about 85% to 93% reduction in the five-day biological oxygen demand (BOD5). However, the BOD5 contaminants present in indus-trial waste water are relatively small compared with the total oxygen demand-ing contaminants present in such waste water, For example, the BOD5 con-taminants present in the effluent from an activated sludge process typically ranges from 10 to 20 parts per million parts of water It is not uncommon to also find present in such effluent 10 to 20 times this amount of other oxygen demanding contaminants.
The activated sludge process has four stages of treatment, In the first stage, contaminated water is contacted with the activated sludge. The sludge includes micro-organisms which feed on the contaminants in the wa~er and metabolize these contaminants to form cellular structure. This decon-taminated water flows into a second clarifier stage where suspended sludge particles are separated from the decontaminated water. A portion of the sludge is recycled to the first stage and the remainder is forwarded to the third and fourth stages. This sludge forwarded to the third and fourth stages includes water. In the.third stage the sludge is thickened to remove excess water and in the fourth stage the thickened sludge is permitted to digest. That is, the micro-organisms feed upon their own cellular structure and are stabilized, Normally, the average age of these micro-organisms in the sludge is substantially less than ten days.
THE INVENTION
We have now invented an improved process for treating waste water including high concentrations of BOD5 contaminants, COD contaminants, hydro-carbons, inert solids, ammonia, phenolics, and other contaminants which are relatively refractory. Our process is specially adapted to treat waste water 10~2820 from oil refineries and chemical complexes where the waste water from the refining oil is mixed with waste water from chemical plants. As conventional, our process calls for primary, inter-mediate, secondary and tertiary water treatment. We have, however, made important and novel modifications in the inter-mediate and secondary treatment steps which result in substantial improvement in effluent water quality.
In a broad aspect the present invention provides, in a multi-stage activated sludge process wherein in a first stage contaminated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising reducing the oil and grease, and solids content of the contaminated water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first stage. Preferably, the oil and grease, and solids content are reduced to less than about 10 ppm each.
In another aspect, the present invention provides, in an activated sludge process wherein in a first stage contami-nated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising treating the contaminated water prior to the first stage to reduce oil and grease, and solids to less than about 20 ppm oil and grease and less than about 20 ppm solids and maintaining the average sludge age in the first and second stages in excess of about ten days.
In another aspect, the present invention provides, in an activated sludge process wherein in a first stage con-taminated water is contacted with activated sludge for a period ~ - 3 -~06Z8Z() of time to degrade contaminants in the water, and in a second stage decontaminated water is separated from the activated sludge, and in a third stage a portion of the sludge from the second stage is thickened, the improvement comprising reducing the oil and grease, and solids content of the contaminated water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first staye, and recycling a portion of the thickened sludge from the third stage to the first or second stages.
In another aspect, the present invention provides such a process as described in the immediately proceeding para-graph wherein, prior to recycling the portion of the thickened sludge from the third stage to the first or second stages, the portion of the thickened sludge is digested. Preferably, the reduction of the oil and grease and solid contents of the contaminated water is carried out by filtration and a coagulant or flocculant is added to the waste water prior to filtration.
In another aspect, the present invention provides, in the activated sludge process wherein in a first stage con-taminated water is contacted with activated sludge for a periodof time sufficient to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, a first portion of said separated sludge being recycled for recontact with the water in the first stage and a second portion of said separated sludge being treated in downstream operations, the improvement comprising:
reducing the oil and grease, and solids content of the con-taminated water to less than about 20 ppm of oil and grease and less than about 20 ppm of solids prior to the first stage; and introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second zone is maintained in an aerobic state and separated decontaminated water from ~ - 3a -1~6Z8210 said second stage contains at least about three parts of dis-solved oxygen per million parts of water. Preferably, the oxygen is introduced into the water and sludge mix entering the second stage by aspirating air into a stream of the water and sludge mix flowing between the first and second stages.
In a further aspect, the present invention provides a method of pretreating waste water including from about 25 to about 150 parts per million of solids per million parts of water and/or from about 25 to about 300 parts of oil and grease per million parts of water upstream of activated sludge treat-ment including a first stage of contacting the pretreated waste water with activated sludge for a period of time to biologically degrade contaminants in the water and a second stage of separating the decontaminated water from the activated sludge comprising, passing the water through an equalization zone including at least two separate water retention compart-ments in series so that the water is mixed in each compartment and flows from one compartment to the next compartment and a given quantity of water is retained for predetermined period in each of said compartments, introducing air into the water in at least one of the compartments so that the water in the compartment is vigorously agitated and the effluent in the aerated compartment includes at least three parts of dissolved oxygen per million parts of water, adjusting the pH of the water in the equalization zone so that the pH of the water in one of the compartments and in the effluent from said zone ranges between about 6.5 and about 9.5, destabilizing colloidal particles suspended in the water, and filtering the effluent water from the equalization zone so that said filtered water includes no more than about twenty parts of oil and grease per million parts of water and no more than about twenty parts of suspended solids per million parts of water.
~ - 3b -In a still further aspect, the present invention provides a continuous process for purifying contaminated water including solids, oil and grease, comprising (a) passing the water through an equalization zone where-in the pH of the water is adjusted to a range from about 6.5 to about 9.5 and the contaminated water is distributed in a larger body of water so that the changes in concentration of contaminants in the effluent water to the equalization zone will produce gradual changes in concentration of contaminants in effluent water from said zone, (b) aerating the water in the equalization zone so that the dissolved oxygen in the water is at least about three parts of dissolved oxygen per million parts of water, (c) adding a destabilizing agent to the water so that colloidal particles in the water aggregate, (d) passing the water from the equalization zone through a filter so that particles and hydrocarbons will be removed therefrom and the effluent from the filter will have less than about ten parts of suspended solids per million parts of water and less than about ten parts of oil and grease per million parts of water, (e) passing effluent from the filter through a multi-stage biological treating zone having a first stage where the water flows into a contact zone and contacts activated sludge which decontaminates the water by biodegradation of contaminants, a second stage where the water from the first stage is clari-fied to separate suspended sludge particles from decontaminated water, a portion of said separated sludge particles being recycled to the first stage and the bulk of the clarified decontaminated water being withdrawn from the second stage, a third stage where that portion of the separated sludge particles not recycled are concentrated by removing the bulk of the ~ - 3c -residual water therefrom, and a fourth stage where said con-centrated sludge particles are digested, (f) aspirating air into the water and sludge mix as it flows between the first and second stages, so that the sludge in the second stage is maintained in an aerobic state and clari-fied water from said second stage contains at least about five parts of dissolved oxygen per million parts of water, and (g) filtering separated water withdrawn from the second stage to remove minute suspended sludge particles not separated from this water in said second stage.
Primary Treatment As conventional, gross amounts of oil and solids are removed from the oil refinery waste water by means of American Petroleum Institute separators. The effluent from this primary treatment typically includes from about 25 to about 150 parts of suspended solids per million parts of water and from about 25 to about 300 parts of hydrocarbon per million parts of water.
As is not commonly recognized, such waste water containing relatively large amounts of oil and solids, cannot be fed directly into an activated sludge process where the sludge aae is in excess of about ten days without upsetting the activated sludge process. Based on pilot plant studies and theoretical calculations, if the water entering the activated sludge pro-cess contains more than about ten parts of oily solids per million parts of water and more than about ten parts of hydro-carbon per million parts of water, gross quantities of oily, emulsified material collect in the first stage or mix liquor tank of the activated sludge process. Such oily, emulsified solids impair or prevent the activated sludge from decontaminat-ing the water, causing the effectiveness of the activated sludgeprocess to be substantially diminished. In accordance with an important feature of our invention excessive oil and solids ~ - 3d -are removed from the waste water by our intermediate treatment.
Intermediate Treatment Oil refinery waste water and waste water from a chemical plant are combined and subjected to intermediate treatment where excessive solids and hydrocarbons are removed and contaminant concentrations are equalized so that such concentrations of contaminants remains more or less constant even hollgll ~ contnlllinl)llr eollc~llt~r~ltion in tlle infl~ n~ to th(` etlll.lli~.,l~iOIl II(`~
ment stage sharpIy changcs from time to tlmc. If contaminant concen~ration in the influent changes and such change is sustained, this will ultimately result in a change in the contaminant concentration in the effluent from the e~ualiza-tion section. But because of the design of our equalization section, this changeinitially will occur gradually over a relatively long time interval. This per-mits the micro-organisms in the downstream activated sludge process to adapt or acclimate to this change in contaminant concentration.
In our process, intermediate treatment includes equalization and fil-tration. Equalization is conducted in a basin having two, preferably three or four compartments. These compartments are mixed and arranged in series so that water flows from one compartment to the next succeeding compartment.
The total retention time of water in the basin is less than about 10 to 15 hours preferably 2 to 15 hours maximum. Consequently7 heat loss/minimized.
Normally, the difference in temperature between the influent and effluent water is 20F or less. Preferably the retention time in each compartment is 30 to 90 minutes.
Waste waters from the various sources are mixed in the first compart-ment, and the contaminant concentration is monitored. Usually pH, toxic met-als, COD contaminants, phenolic, and ammonia concentrations are measured either manually or automatically. Since waste waters from multiple sources are fed into the relatively confined space in the first compartment, several ad-vantages occur. First it is easy to monitor contaminant concentration and readily detect any drastic change in concentration indicating, for example, a break in a chemical line. The reason is because the first compartment in a multiple compartment system will more rapidly increase in concentration to more readily detectable levels than a single CQmpartment system. Also neutral-ization is achieved. For example, one source of water may be highly acidic and 1062~32~) another highIy basic. Ncutralization occurs as these streams mix in the fi rst compa rtment.
It is important to adjust the pTI in the equalization basin in order to maximize oxidation of certain contaminants, particularly sulfides. pl-I is adjusted by adding acid or base to the water in the second compartment until the water has a p~I ranging from about 6. S to about 9, 5, preferably between 7. 5 and 8. 5. Our experiments indicate that at least about three parts of dis-solved oxygen per million parts of water must be present tO satisfy the immediate oxygen demand (IOD) of the contaminants in the water at a reason-able rate of oxidation. Preferably hydroquinone or gallic acid is added to the water to catalyze the oxidation of IOD contaminants. If this IOD is not satis-fied, the downstream activated sludge process can be adversely affected.
Consequently, the water in the equalization basin is aerated. Conventional floating aerators may be used. We have found that aeration is more effective in a confined zone. About 0.15 or more horsepower per thousand gallons of water provides excellent aeration. Aeration also thoroughly agitates and mixes the water with the result that floating solids accumulate on the water surface. These solids are removed by skimming. In order to ensure that the water to the activated sludge process includes less than about ten parts of hydrocarbon per million parts of water and less than about ten parts of solids per million parts of water, we add a coagulating and/or flocculating agent to the water in the equalization basin or to the stream of water flowing to the activated sludge process. The coagulating and/or flocculating agent destabil-izes colloidal particles which then aggregate. The aggregates are carried with the effluent stream to a filter and removed prior to introduction to the activated sludge process. wc ~ preferably intro-duce air into the stream of water flowing into the downstream activated sludge process to ensure that the immediate oxygen demand to the water is satisfied.
Seconcla ry I reatment -In .lc~ordancc witll anotller le.ltlll~c of our invcntion w.ltcr from inter-m~diate treatment flows through a conventional activated sludgc plant which has been modified in two important ways: (1) the sludge-water mix flowing between stages of the activated sludge process is aerated, and (2) the sludge of different ages from different stages is recycled to one or more upstream stages of the activated sludge process. In our process, oxygen either pure or most preferable in air is introduced, for example pressurized or most pre-ferably by aspiration into the stream of sludge and water flowing between the mix liquor tank of the first stage and the clarifier tank of the second stage.
This stream of sludge, water and air or oxygen is subjected to the increased pressure created by the hydrostatic heads of water in the mix liquor and clar-ifier tanks. Consequently, this stream is saturated or supersaturated with dissolved oxygen. The dissolved oxygen maintains the sludge in the clarifier tank aerobic and ensures that the effluent water to the subsequent tertiary treatment section includes at least five parts of dissolved oxygen per million parts of water. We also inject oxygen either in air or pure form under pres-sure into the sludge and water streams flowing between the second and third stages and the third and fourth stages of the activated sludge process. Con-sequently, the sludge in the thickener and digester can be retained for a longer period of time. This aged sludge from the thickener and digester is recycled to the first stage or mix liquor tank either directly or preferably by mixing with the stream of sludge and water flowing between the first and second stages.
Tertiary Treatment In our process, the effluent from the clarifier or second stage of the activated sludgeprocess is filtered to remove biological solids in the effluent m~y be and then/contacted with activated carbon to remove odor causing and other residual trace components by adsorption. Chemical agents may be added to the clarifier effluent to de~billZecolloidal suspensions and assist filtration.
;Z820 I-lowev-~r, be~ausc of the intcrstagc a~ration, thc water has at least five part~s of di~soIved oxygen pcr million parts of water ancl cons~ cntly or~anisms collected in the filter and on the carbon are maintained in an aerobic condition, avoiding odor and any degradation in quality of the filtered effluent. Further, the effluent water to the receiving stream has a high level of oxygen in it.
Thus, it does not contribute to deterioration of the water quality of the receiv-ing stream.
DETAILED DESCRIPTION
A waste water treating facility 10 embodying our improved process is schematically illustrated in the attached Figure. Typical contaminant water is the waste water from an oil refinery and waste water from a chemical plant. Table I below illustrates common characteristics of oil refinery waste water and Table 11 below illustrates common characteristics of waste water from a chemical plant.
TABLE I
REFINERY WASTE WATER CHARACTERISTICS AFTER
PRIMARY TREATMENT IN API SEPARATOR
Median Values for Class C Refineries (USA~
. _ Parameters Concentration, mg/liter Biochemical Oxygen Demand, 5-day 163 Chemical Oxygen Demand 473 Total Organic Carbon 160 Oil and Grease 51 Phenolics 1 1 Suspended Solids 52 Ammonia 48 Sulfide 2 _ _ ;Z820 TABLE II
~()MI` CI II MI('AI, I'I,AN I' W/~,S I ~' WA rli R (~I IA I~C"I~ I,'; I`IC,~
lER INPLANT PRET~E~ rML~N T
Parameters Concentration Range, mg~liter Biochemical Oxygen Demand, 5-day 50 - 5000 Chemical Oxygen Demand 500 - 20, 000 Suspended Solids 30-- 100 Ammonia 50 - 250 As shown in the Figure, the oil refining and chemical plant waste waters are mixed t~gether in the first compartment 29 of a multiple compart-ment equalization basin 12. The efflucnt from this basin 12 flows throu~h valved lines 13 and 14 into a bank of pressure filters/and through a head tank 18 into a biological treating plant 20. The oil refinery waste water first flows into a sump 22 and then into a conventional API separator 24 where gross amounts of oil and solids are removed. Under normal conditions, the treat-ment facility 10 can handle a maximum design quantity of water per day. For example, a large facility may have a capacity of 25, 000, 000 gallons of water per day. Heavy rain storms could, however, overload this facility. Conse-quently, a compartmented surge basin 26 is provided for holding abnormal]y large quantities of water, and as will be explained in detail below, for storing shock loads of contaminants such as acids or alkalis. A pump 28 forwards any excess water from the sump 22 to this surge basin 26.
In accordance with one feature of our invention, the concentration of contaminants in the water flowing to the downstream biological treating plant 20 is controlled so that variations in contaminant levels are equalized. The equalization basin 12 serves to level out or equalize contaminant concentration by passing the waste water through three separate compartments 29, 30 and 31 in the basin 12. When a sharp increase in the noxious contaminant is exper-ienced in the influent to the basin 12, the initial effluent concentration from 1~628ZO
the third compartment 31 is lower or changes less than from a single compart-ment basin. ~his provides time for acclimation of the micro-organisms in the biological treating plant 20.
Any sharp increase in contaminant concentration or any drastic change in the type of contaminants entering basin 12 has the greatest and most imme-diate impact on water quality conditions in compartment 29. When water from this first compartment 29 is mixed with the body of water in the second com-partment 30, contaminant concentration is reduced. When the water from the second compartment 30 is mixed with the body of water in the third compart-ment 31, contaminant concentration in the third compartment is substantially reduced again. Mixing the water in this manner tends to dilute the contamin-ants so that their initial effluent concentration from the third compartment 31 is lower than if a single basin is used. Thus, if a slug of contaminants flows into the first compartment 29, this slug would be blended gradually in the quantities of water in the second and third compartments 30 and 31, be diluted and therefore initially would not increase or otherwise change the contaminant concentration or character by any substantial amount in the third compartment 31. As a consequence, the micro-organisms in the downstream biological treating plan 20 acclimate to the slow exposure of the changes in contaminant concentration or character and adapt to biologically degrade this higher concen-tration of contaminants or different character of contaminants.
In accordance with another feature of our invention, we maintain at a minimum the average time the water is retained in the equalization basin 12.
Thus, the heat in the water is retained at a maximum. High heat in water fosters increased biodegradation of contaminants in the treating plant 20.
Average water temperature entering the plant 20 preferably ranges between 90F and 100F.
The water in the first compartment 29 is monitored to determine the presence of especially noxious contaminants, for example, ammonia, phen-- 1~6Z820 olics, BUlrl~-, acids, callstics, etc., so that their source may b~ traced ancl col r ~et-iv~ acli~ll taken. In tll~ secoIld compartmell~ 30 pH is contl-oIIc(l by addition of acids or alkalis so that it is in thc rangc (~f about ( . 5 Lo ~ but prc-ferably from about 7. 5 to 8. 5 when air oxidation of contaminants is required.
This pH range is optimal for the oxidation reactions to occur and when desired the reactions are accelerated by adding hydroquinone or gallic acids.
Conventional floating aerators (not shown) float on the surface of the water in each compartment 29 through 31 and introduce air into the water to aerate and thoroughly mix the waste water. Such aerators (not shown) in com-partment 30 mix and aerate to maintain dissolved oxygen levels in the preferred range of 3 mg 02/liter or greater. The preferred ratio of the aerators is 0. 2 horsepower aeration or more per 1000 gallons compartment volume.
If for any reason the equalization pond 12 is flooded with an extremely high concentration of contaminant beyond handling capability, for example, if a line carrying acid broke, a valve 34 in a recycle line 36 is opened and the valve 38 in the filter inlet line 14 is closed. A pump 40 then pumps this highly acidic water to the shock load compartment 26a of a surge basin 26 where it is retained and gradually reintroduced into the first compartment 29 of the basin 12 through a valved line 42. This protects the downstream biological treating plant 20 from being poisoned by shock loads of contaminants.
The mixing, aeration, pH control, chemical reactions, etc., taking place in equalization basin 12 causes coagulation and flotation of considerable contaminant matter. This matter is skimmed from the surface of the basin 12.
Conventional slotted skim pipe (not shown) at the surface of the water in com-partment 31 may be used.
The effluent from the final compartment 31 contains colloidal matter to which coagulants or flocculants such as aluminum or iron salts, and/or high molecular weight organic polyelectrolytes are added. The coagulants or floc-culants destabilize, for removal by filtration the colloidal particles which are 1~)62820 carried by the effluent from the basin 12 to the bank of filters 16. The filtered water passing into the head tank 18 is lifted by thc pump 40. The preferre(I
filtcr mcdium u9cd in thc bank of filtcrs 16 i9 Sall(l 0r Ll COmbill~ l)ll ol` sand and coal. It is important that the water flowing to the downstream biological treating plant 20 be filtered to reduce suspended solids and oil to levels which do not interfere with the process. Under most conditions, the water flowing into the biological treating plant 20 preferably must contain no more than ten parts of oil or hydrocarbons per million parts of water and no more than ten parts of oily suspended solids per million parts of water. Periodically, a fil-ter unit in the bank of filters 16 must be backwashed. This is achieved by closing a valve in the feed line to the filter unit being backwashed and opening a valvc in a backwash waste line (not shown) such that the effluents from the onstrcam filters are used for backwash water. One function of the head tank 18 is to provide a constant back pressure on the filtered water thereby pro-viding a constant pressure backwash water source. The backwash water washes out the solids trapped in the filters, carrying them with the water into a sludge surge basin (not shown).
The biological treating plant 20 has four process stages. A contact stage 44 where the contaminated water contacts a biologically active sludge 46.
A clarifier stage 48 where sludge is separated from decontaminated water.
A thickening stage 50 where separated sludge is thickened to remove excess water. And a digestion stage 52 where thickened sludge is digested. In the first stage 44 water essentially free of solid and oily matter contacts the acti-vated sludge mass 46 in a contact tank 54 called a mixed liquor tank. This sludge 46 includes micro-organisms which feed on the contaminants in the water. The metabolic processes of the micro-organisms convert the contam-inants to cellular structure of the organisms, carbon dioxide, and various intermediate products. In the second stage 48, water and activated sludge from the mixed liquor tank 54 flows into a clarifier tank 56 via a line 72.
~ iZ8zO
~ s will be explained further below, activated sludge from a second source is added to line 72 via line 100 and the combined sludges and water flows to clar-ifier tank 56. The line 72 and an isolated zone 84 of the clarifier tank 56 pro-vide for contact of the second activated sludge recycle component and the resid-ual contaminants in the water leaving the mixed liquor tank 54. This results in furtherpurification of the water. Water is separated from these sludge particles by allowing the sludge particles 46 to settle on the bottom of the clar-ifier tank 56. Decontaminated water flows from the top of ~he clarifier through a second bank of filters 58 into a receiving stream 60, Preferably through a bed of activated carbon 66 for removal of trace solublc contaminants before discharge to the receiving stream.
In the third stage S0, the sludge 4 6 withdrawn from the bottom of the clarifier tank 56 is concentrated and the bulk of any water retained by the sludge is separated and withdrawn, In the fourth stage 52, thickened sludge is held in a tank 62 for a period of time sufficient to allow the micro-organisms to metab-olize stored food material. This digested sludge is then spread over land and permitted to decompose and serve as a fertilizer. Alternately, the sludge can be incinerated.
In accordance with our invention, interstage aeration is provided to aerate the water as it flows into the biological treating plant 20 and between the four stages of the plant 20. The most important interstage aeration is the aeration of the streams of water and sludge flowing in lines 72 and 74 between the first and second stages 44 and 48. Because of this aeration, the water leaving the clarifier tank 56 and being discharged into a receiving body of water contains at least about five parts of dissolved oxygen per million parts of water.
This is highly desirable especially when carbon adsorption is employed. The oxygen in the discharged water from the clarifier tank 56 maintains any micro-organisms trapped in ~he filter 58 or following carbon bed aerobic. If there is insufficient air in this discharge water, the micro-organisms trapped in the filter go anaerobic producing hydrogen sulfide which would contaminate 11~6ZB20 thc dischar~ed water In addition, the dissolved oxy~en in the water in the clal if iel- tallk ~'i( m.~ t.liIls thc ~lu~ 46 otl tl)~ Ottolll of tl~is l.ulk .I( l ol-ic, pcrmit~:ing tlIc slll-lgc to be retaincd in lhc tl~ickcnel 5() ~lnd cl.l~ ilicl ~,Y lollgcl than conventional. This provides more effective thickener and clarifier oper-ation.
We achieve interstage aeration by aspirating air into water flowing between tanks or positively injecting pressurized air into the transfer line.
In addition to backwashing the bank of filters 16, the head of the water in the tank 18 can be utilized advantageously to aspirate air into the water flowing into the mixed liquor tank 54. The water level in the head tank 18 ls above the water level of the mixed liquor tank 54. Water thus flows from the top of the head tank 18 downwardly through a line 64 and along a long generally horizontal line 66 which turns upwardly into a line 68 leading into the center of the mixed liquor tank 54. The horizontal line 66 is either at ground level or preferably below ground level to maximize the hydrostatic pressure. Thus, the air aspirated into the water is subjected to high pressure due to the water standing in the head and mixed liquor tanks 18 and 54. The horizontal line 66 can have a larger diameter than the downwardly extending line 64 or purposely be extended by looping, for example, so that the dwell time of the water and air mix can be extended. This substantially saturates or even supersaturates with respect to atmospheric pressure the water entering the mixed liquor tank 54 with dissolved oxygen. Normally this water flowing into the mixed liquor tank 54 will contain at least about 6 to 8 parts of dissolved oxygen per million parts of water and typically can reach levels above saturation of about 12 parts of dissolved oxygen per million parts of water. In a similar manner, air is aspirated or pressured into the water flowing from the mixed liquor tank 54 into the clarifier tank 56. The vertical line 72 transfers the water and suspended sludge particles downwardly to the horizontal line 74 which turns upward into a line 76 terminating near the surface of the clarifier tank 1~6Z8ZO
S(. An aspi rator 78 sucks air into thc downward flowing water in the line 72.
I hc water elevation in tl~e tanks 54 and 56 subject the ~ir-water mixture ~o higl prcssure as it flows through the line 74. This can saturate or supersaturate the water with dissolved oxygen.
The clarifier tank 56 is designed to receive the water from the upwardly extending line 76 into a confined mixing region formed by cylindrical baffle 82 concentric with the side walls of the tank. The diameter of cylindrical baffle 82 is preferably about 1/2 the diameter of the clarifier 56 and extending to about six feet from the bottom. Line 76 upwardly extends to well within the circular baffle 82 and, as the air-water mix exits line 76, the air lift pumping action creates a turbulent zone 84 in the center of the clarifier tank 56 that provides for further activated sludge-water contact, oxygen transfer and floc-culation, The preferred contact time in line 76 and turbulent zone 8~ is at least 20 minutes, The clarifier tank 56 includes weirs 80 at the top of the tank that maintains the water level and provides for discharge of clarified water from the quiescent zone 86. Activated sludge particles settle to the bottom of the tank where they are withdrawn by a conveyor and pump 88 system In our process, air under pressure from sources 90 and 92 is injected into the sludge flowing between the clarifier tank 56 and thickener 50 and between the thickener 50 and the digester 52. This high pressure aeration of ~ lld sludge permits the sludge to be maintained in the clarifier tank 56/ thickener for periods in excess of what is normally considered feas-ible in the activated sludge process. For example, the activated sludge-water mass in the feed to the thickener and clarifier in the normal system contains 1 mg 02/liter or less. As the sludge blanket settles the dissolved oxygen in the interstitial water is rapidly depleted by the respiration of the micro-organ-isms and the facultative organisms start to remove oxygen from the nitrogen and sulfur compounds present in the water. This released hydrogen sulfide and nitrogen gas upsets the sludge settling process and seriously degrades 1~62820 water quality. In our process about ten times the dissolved oxygen concentra-tion can be provicled compared to conventional practice. This greatly decreases the rate at whicll septicity occurs and alleviates substantially the problems associated with retaining the sludge in the clarifier and thickener until the excess water is substantially removed, Another aspect of our invention relates to the use of sludges with differ-ent properties recycled to different points to achieve different functions, all in a single activated sludge plant 20. As conventional, sludge wi thdrawn from the elarifier tank 56 is reeyeled through valved branehed line 94 into the mixed liquor tank 54 with exeess sludge to the thickener 50. A portion of this recycled sludge is introduced through braneh 96 into the sludge-water mix flowing between the mixec3 liquor tank 54 and the elarifier 56. This absorptive sludge portion entering via line 96 has capacity to absorb and store residual soluble contaminants and improve the floeculating properties of the total sludge mass for improved separation in elarifier 56. The interstage aeration and elarifier design provides for eontaet time, mixing and aeration to optimize the eapacity of this system. Similarly, the recycle sludge could be routed through the thiekener 50 and via line 98 into the sludge-water mix flowing between the mixed liquor tank 54 and the elarifier tank 56 Sludge from the thickener 50 has been without food longer and therefore has greater absorptive and storage capacity and is cOntained in a reduced volume because of the c3ewatering aetion of the thiekener, Maintaining the thiekener sludge aerobie using interstage aeration is a requisite for satisfactory sludge quality for recycle from the thiekener 50.
Another souree in our proeess of the reeyele sludge is obtained by routing that sludge through the thiekener 50, the aerobie digester 52, and valved line 100 into the sludge-water mix flowing in lines 72 and 74 between the mixed liquor tank 54 and the elarifier tank 56. The sludge eomponent from the aerobie digester 52 has had typically one to four weeks to acclimate to the residual refractory substrate contaminants. This acelimated sludge is 1C)62820 especially effective for absorbing and biodegrading the residual ~ub~trate in thc watcr exitln~ mixcd liquor tank S4. When the combined sllIdgc m~ss enters clarifier 56, the acclimated sludge combines with sludge in the clar-ifier tank 56 and seeds the sludge being recycled to the mixed liquor tank 54 via line 94. Seeding the main recycle sllldge mass continuously with sludge acclimated to residual, refractory materials shifts the equilibrium to increase removal of these contaminants by the main sludge mass in the mixed liquor tank 54. After equilibrium is attained there is no longer high concentrations of refractory substrate in the water leaving the clarifier tank 54. Introduction of any new refractory materials into the system causes the rapid development of acclimsted organisms.
As evident to those skilled in the art, modifications can be made in our process without departing from the principles of our invention claimed herein. For example, oxygen may be substituted for air in the interstage aeration system.
I'lle cre.~ enc of contnminat~ wnxte watet involvcs a seq~lcnce of processing steps for maximizing water purification at minimum costs. Indus-trial effluents, particularly waste water from oil refineries, include a broad spectrum of contaminants and, consequently, such waste water is usually more difficult to decontaminate than waste water from municipal sewage sys-tems. Four main sequential process treatments are used to decontaminate such industrial effluents. These are a primary, intermediate, secondary, and tertiary treatments, The primary treatment calls for removal of gross amounts of hydrocarbons and solids from the waste water. In the oil industry, usually separators of American ~etroleum Institute design are employed for removal of free, separable oil and solids. The intermediate treatment is the next process and it is designed to adjust water conditions so that the water entering the secondary treatment zone will not impair the operation of the secondary treatment processes. In other words, intermediate treatment is designed to optimize water conditions so that the secondary treatment process will operate most efficiently. The secondary treatment calls for biologically degrading dissolved organics and ammonia in the water.
One of the most common biological treatment processes employed is the acti-vated sludge process discussed below in greater detail. The tertiary treat-ment calls for removing residual biological solids present in the effluent from the secondary treatment zone and removing contaminants which contri-bute to impairing water clarity or adversely affecting water taste and odor.
This is usually a filtration of the water, preferably through beds of sand, or combinations of sand and coal, followed by treatment with activated carbon.
The acLivated sludge process is a conventional waste water treating process which produces the highest degree of biological treatment in reason-ably compact facilities at the present time. The application of this process to the treatment of industrial waste water has, however, been slow compared ~ ' - 1 - q~
1~6;28ZO
with municipal applications. Industrial applications of this process are nevertheless increasing rapidly, Currently, the activated sludge process is capable of achieving about 85% to 93% reduction in the five-day biological oxygen demand (BOD5). However, the BOD5 contaminants present in indus-trial waste water are relatively small compared with the total oxygen demand-ing contaminants present in such waste water, For example, the BOD5 con-taminants present in the effluent from an activated sludge process typically ranges from 10 to 20 parts per million parts of water It is not uncommon to also find present in such effluent 10 to 20 times this amount of other oxygen demanding contaminants.
The activated sludge process has four stages of treatment, In the first stage, contaminated water is contacted with the activated sludge. The sludge includes micro-organisms which feed on the contaminants in the wa~er and metabolize these contaminants to form cellular structure. This decon-taminated water flows into a second clarifier stage where suspended sludge particles are separated from the decontaminated water. A portion of the sludge is recycled to the first stage and the remainder is forwarded to the third and fourth stages. This sludge forwarded to the third and fourth stages includes water. In the.third stage the sludge is thickened to remove excess water and in the fourth stage the thickened sludge is permitted to digest. That is, the micro-organisms feed upon their own cellular structure and are stabilized, Normally, the average age of these micro-organisms in the sludge is substantially less than ten days.
THE INVENTION
We have now invented an improved process for treating waste water including high concentrations of BOD5 contaminants, COD contaminants, hydro-carbons, inert solids, ammonia, phenolics, and other contaminants which are relatively refractory. Our process is specially adapted to treat waste water 10~2820 from oil refineries and chemical complexes where the waste water from the refining oil is mixed with waste water from chemical plants. As conventional, our process calls for primary, inter-mediate, secondary and tertiary water treatment. We have, however, made important and novel modifications in the inter-mediate and secondary treatment steps which result in substantial improvement in effluent water quality.
In a broad aspect the present invention provides, in a multi-stage activated sludge process wherein in a first stage contaminated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising reducing the oil and grease, and solids content of the contaminated water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first stage. Preferably, the oil and grease, and solids content are reduced to less than about 10 ppm each.
In another aspect, the present invention provides, in an activated sludge process wherein in a first stage contami-nated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising treating the contaminated water prior to the first stage to reduce oil and grease, and solids to less than about 20 ppm oil and grease and less than about 20 ppm solids and maintaining the average sludge age in the first and second stages in excess of about ten days.
In another aspect, the present invention provides, in an activated sludge process wherein in a first stage con-taminated water is contacted with activated sludge for a period ~ - 3 -~06Z8Z() of time to degrade contaminants in the water, and in a second stage decontaminated water is separated from the activated sludge, and in a third stage a portion of the sludge from the second stage is thickened, the improvement comprising reducing the oil and grease, and solids content of the contaminated water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first staye, and recycling a portion of the thickened sludge from the third stage to the first or second stages.
In another aspect, the present invention provides such a process as described in the immediately proceeding para-graph wherein, prior to recycling the portion of the thickened sludge from the third stage to the first or second stages, the portion of the thickened sludge is digested. Preferably, the reduction of the oil and grease and solid contents of the contaminated water is carried out by filtration and a coagulant or flocculant is added to the waste water prior to filtration.
In another aspect, the present invention provides, in the activated sludge process wherein in a first stage con-taminated water is contacted with activated sludge for a periodof time sufficient to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, a first portion of said separated sludge being recycled for recontact with the water in the first stage and a second portion of said separated sludge being treated in downstream operations, the improvement comprising:
reducing the oil and grease, and solids content of the con-taminated water to less than about 20 ppm of oil and grease and less than about 20 ppm of solids prior to the first stage; and introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second zone is maintained in an aerobic state and separated decontaminated water from ~ - 3a -1~6Z8210 said second stage contains at least about three parts of dis-solved oxygen per million parts of water. Preferably, the oxygen is introduced into the water and sludge mix entering the second stage by aspirating air into a stream of the water and sludge mix flowing between the first and second stages.
In a further aspect, the present invention provides a method of pretreating waste water including from about 25 to about 150 parts per million of solids per million parts of water and/or from about 25 to about 300 parts of oil and grease per million parts of water upstream of activated sludge treat-ment including a first stage of contacting the pretreated waste water with activated sludge for a period of time to biologically degrade contaminants in the water and a second stage of separating the decontaminated water from the activated sludge comprising, passing the water through an equalization zone including at least two separate water retention compart-ments in series so that the water is mixed in each compartment and flows from one compartment to the next compartment and a given quantity of water is retained for predetermined period in each of said compartments, introducing air into the water in at least one of the compartments so that the water in the compartment is vigorously agitated and the effluent in the aerated compartment includes at least three parts of dissolved oxygen per million parts of water, adjusting the pH of the water in the equalization zone so that the pH of the water in one of the compartments and in the effluent from said zone ranges between about 6.5 and about 9.5, destabilizing colloidal particles suspended in the water, and filtering the effluent water from the equalization zone so that said filtered water includes no more than about twenty parts of oil and grease per million parts of water and no more than about twenty parts of suspended solids per million parts of water.
~ - 3b -In a still further aspect, the present invention provides a continuous process for purifying contaminated water including solids, oil and grease, comprising (a) passing the water through an equalization zone where-in the pH of the water is adjusted to a range from about 6.5 to about 9.5 and the contaminated water is distributed in a larger body of water so that the changes in concentration of contaminants in the effluent water to the equalization zone will produce gradual changes in concentration of contaminants in effluent water from said zone, (b) aerating the water in the equalization zone so that the dissolved oxygen in the water is at least about three parts of dissolved oxygen per million parts of water, (c) adding a destabilizing agent to the water so that colloidal particles in the water aggregate, (d) passing the water from the equalization zone through a filter so that particles and hydrocarbons will be removed therefrom and the effluent from the filter will have less than about ten parts of suspended solids per million parts of water and less than about ten parts of oil and grease per million parts of water, (e) passing effluent from the filter through a multi-stage biological treating zone having a first stage where the water flows into a contact zone and contacts activated sludge which decontaminates the water by biodegradation of contaminants, a second stage where the water from the first stage is clari-fied to separate suspended sludge particles from decontaminated water, a portion of said separated sludge particles being recycled to the first stage and the bulk of the clarified decontaminated water being withdrawn from the second stage, a third stage where that portion of the separated sludge particles not recycled are concentrated by removing the bulk of the ~ - 3c -residual water therefrom, and a fourth stage where said con-centrated sludge particles are digested, (f) aspirating air into the water and sludge mix as it flows between the first and second stages, so that the sludge in the second stage is maintained in an aerobic state and clari-fied water from said second stage contains at least about five parts of dissolved oxygen per million parts of water, and (g) filtering separated water withdrawn from the second stage to remove minute suspended sludge particles not separated from this water in said second stage.
Primary Treatment As conventional, gross amounts of oil and solids are removed from the oil refinery waste water by means of American Petroleum Institute separators. The effluent from this primary treatment typically includes from about 25 to about 150 parts of suspended solids per million parts of water and from about 25 to about 300 parts of hydrocarbon per million parts of water.
As is not commonly recognized, such waste water containing relatively large amounts of oil and solids, cannot be fed directly into an activated sludge process where the sludge aae is in excess of about ten days without upsetting the activated sludge process. Based on pilot plant studies and theoretical calculations, if the water entering the activated sludge pro-cess contains more than about ten parts of oily solids per million parts of water and more than about ten parts of hydro-carbon per million parts of water, gross quantities of oily, emulsified material collect in the first stage or mix liquor tank of the activated sludge process. Such oily, emulsified solids impair or prevent the activated sludge from decontaminat-ing the water, causing the effectiveness of the activated sludgeprocess to be substantially diminished. In accordance with an important feature of our invention excessive oil and solids ~ - 3d -are removed from the waste water by our intermediate treatment.
Intermediate Treatment Oil refinery waste water and waste water from a chemical plant are combined and subjected to intermediate treatment where excessive solids and hydrocarbons are removed and contaminant concentrations are equalized so that such concentrations of contaminants remains more or less constant even hollgll ~ contnlllinl)llr eollc~llt~r~ltion in tlle infl~ n~ to th(` etlll.lli~.,l~iOIl II(`~
ment stage sharpIy changcs from time to tlmc. If contaminant concen~ration in the influent changes and such change is sustained, this will ultimately result in a change in the contaminant concentration in the effluent from the e~ualiza-tion section. But because of the design of our equalization section, this changeinitially will occur gradually over a relatively long time interval. This per-mits the micro-organisms in the downstream activated sludge process to adapt or acclimate to this change in contaminant concentration.
In our process, intermediate treatment includes equalization and fil-tration. Equalization is conducted in a basin having two, preferably three or four compartments. These compartments are mixed and arranged in series so that water flows from one compartment to the next succeeding compartment.
The total retention time of water in the basin is less than about 10 to 15 hours preferably 2 to 15 hours maximum. Consequently7 heat loss/minimized.
Normally, the difference in temperature between the influent and effluent water is 20F or less. Preferably the retention time in each compartment is 30 to 90 minutes.
Waste waters from the various sources are mixed in the first compart-ment, and the contaminant concentration is monitored. Usually pH, toxic met-als, COD contaminants, phenolic, and ammonia concentrations are measured either manually or automatically. Since waste waters from multiple sources are fed into the relatively confined space in the first compartment, several ad-vantages occur. First it is easy to monitor contaminant concentration and readily detect any drastic change in concentration indicating, for example, a break in a chemical line. The reason is because the first compartment in a multiple compartment system will more rapidly increase in concentration to more readily detectable levels than a single CQmpartment system. Also neutral-ization is achieved. For example, one source of water may be highly acidic and 1062~32~) another highIy basic. Ncutralization occurs as these streams mix in the fi rst compa rtment.
It is important to adjust the pTI in the equalization basin in order to maximize oxidation of certain contaminants, particularly sulfides. pl-I is adjusted by adding acid or base to the water in the second compartment until the water has a p~I ranging from about 6. S to about 9, 5, preferably between 7. 5 and 8. 5. Our experiments indicate that at least about three parts of dis-solved oxygen per million parts of water must be present tO satisfy the immediate oxygen demand (IOD) of the contaminants in the water at a reason-able rate of oxidation. Preferably hydroquinone or gallic acid is added to the water to catalyze the oxidation of IOD contaminants. If this IOD is not satis-fied, the downstream activated sludge process can be adversely affected.
Consequently, the water in the equalization basin is aerated. Conventional floating aerators may be used. We have found that aeration is more effective in a confined zone. About 0.15 or more horsepower per thousand gallons of water provides excellent aeration. Aeration also thoroughly agitates and mixes the water with the result that floating solids accumulate on the water surface. These solids are removed by skimming. In order to ensure that the water to the activated sludge process includes less than about ten parts of hydrocarbon per million parts of water and less than about ten parts of solids per million parts of water, we add a coagulating and/or flocculating agent to the water in the equalization basin or to the stream of water flowing to the activated sludge process. The coagulating and/or flocculating agent destabil-izes colloidal particles which then aggregate. The aggregates are carried with the effluent stream to a filter and removed prior to introduction to the activated sludge process. wc ~ preferably intro-duce air into the stream of water flowing into the downstream activated sludge process to ensure that the immediate oxygen demand to the water is satisfied.
Seconcla ry I reatment -In .lc~ordancc witll anotller le.ltlll~c of our invcntion w.ltcr from inter-m~diate treatment flows through a conventional activated sludgc plant which has been modified in two important ways: (1) the sludge-water mix flowing between stages of the activated sludge process is aerated, and (2) the sludge of different ages from different stages is recycled to one or more upstream stages of the activated sludge process. In our process, oxygen either pure or most preferable in air is introduced, for example pressurized or most pre-ferably by aspiration into the stream of sludge and water flowing between the mix liquor tank of the first stage and the clarifier tank of the second stage.
This stream of sludge, water and air or oxygen is subjected to the increased pressure created by the hydrostatic heads of water in the mix liquor and clar-ifier tanks. Consequently, this stream is saturated or supersaturated with dissolved oxygen. The dissolved oxygen maintains the sludge in the clarifier tank aerobic and ensures that the effluent water to the subsequent tertiary treatment section includes at least five parts of dissolved oxygen per million parts of water. We also inject oxygen either in air or pure form under pres-sure into the sludge and water streams flowing between the second and third stages and the third and fourth stages of the activated sludge process. Con-sequently, the sludge in the thickener and digester can be retained for a longer period of time. This aged sludge from the thickener and digester is recycled to the first stage or mix liquor tank either directly or preferably by mixing with the stream of sludge and water flowing between the first and second stages.
Tertiary Treatment In our process, the effluent from the clarifier or second stage of the activated sludgeprocess is filtered to remove biological solids in the effluent m~y be and then/contacted with activated carbon to remove odor causing and other residual trace components by adsorption. Chemical agents may be added to the clarifier effluent to de~billZecolloidal suspensions and assist filtration.
;Z820 I-lowev-~r, be~ausc of the intcrstagc a~ration, thc water has at least five part~s of di~soIved oxygen pcr million parts of water ancl cons~ cntly or~anisms collected in the filter and on the carbon are maintained in an aerobic condition, avoiding odor and any degradation in quality of the filtered effluent. Further, the effluent water to the receiving stream has a high level of oxygen in it.
Thus, it does not contribute to deterioration of the water quality of the receiv-ing stream.
DETAILED DESCRIPTION
A waste water treating facility 10 embodying our improved process is schematically illustrated in the attached Figure. Typical contaminant water is the waste water from an oil refinery and waste water from a chemical plant. Table I below illustrates common characteristics of oil refinery waste water and Table 11 below illustrates common characteristics of waste water from a chemical plant.
TABLE I
REFINERY WASTE WATER CHARACTERISTICS AFTER
PRIMARY TREATMENT IN API SEPARATOR
Median Values for Class C Refineries (USA~
. _ Parameters Concentration, mg/liter Biochemical Oxygen Demand, 5-day 163 Chemical Oxygen Demand 473 Total Organic Carbon 160 Oil and Grease 51 Phenolics 1 1 Suspended Solids 52 Ammonia 48 Sulfide 2 _ _ ;Z820 TABLE II
~()MI` CI II MI('AI, I'I,AN I' W/~,S I ~' WA rli R (~I IA I~C"I~ I,'; I`IC,~
lER INPLANT PRET~E~ rML~N T
Parameters Concentration Range, mg~liter Biochemical Oxygen Demand, 5-day 50 - 5000 Chemical Oxygen Demand 500 - 20, 000 Suspended Solids 30-- 100 Ammonia 50 - 250 As shown in the Figure, the oil refining and chemical plant waste waters are mixed t~gether in the first compartment 29 of a multiple compart-ment equalization basin 12. The efflucnt from this basin 12 flows throu~h valved lines 13 and 14 into a bank of pressure filters/and through a head tank 18 into a biological treating plant 20. The oil refinery waste water first flows into a sump 22 and then into a conventional API separator 24 where gross amounts of oil and solids are removed. Under normal conditions, the treat-ment facility 10 can handle a maximum design quantity of water per day. For example, a large facility may have a capacity of 25, 000, 000 gallons of water per day. Heavy rain storms could, however, overload this facility. Conse-quently, a compartmented surge basin 26 is provided for holding abnormal]y large quantities of water, and as will be explained in detail below, for storing shock loads of contaminants such as acids or alkalis. A pump 28 forwards any excess water from the sump 22 to this surge basin 26.
In accordance with one feature of our invention, the concentration of contaminants in the water flowing to the downstream biological treating plant 20 is controlled so that variations in contaminant levels are equalized. The equalization basin 12 serves to level out or equalize contaminant concentration by passing the waste water through three separate compartments 29, 30 and 31 in the basin 12. When a sharp increase in the noxious contaminant is exper-ienced in the influent to the basin 12, the initial effluent concentration from 1~628ZO
the third compartment 31 is lower or changes less than from a single compart-ment basin. ~his provides time for acclimation of the micro-organisms in the biological treating plant 20.
Any sharp increase in contaminant concentration or any drastic change in the type of contaminants entering basin 12 has the greatest and most imme-diate impact on water quality conditions in compartment 29. When water from this first compartment 29 is mixed with the body of water in the second com-partment 30, contaminant concentration is reduced. When the water from the second compartment 30 is mixed with the body of water in the third compart-ment 31, contaminant concentration in the third compartment is substantially reduced again. Mixing the water in this manner tends to dilute the contamin-ants so that their initial effluent concentration from the third compartment 31 is lower than if a single basin is used. Thus, if a slug of contaminants flows into the first compartment 29, this slug would be blended gradually in the quantities of water in the second and third compartments 30 and 31, be diluted and therefore initially would not increase or otherwise change the contaminant concentration or character by any substantial amount in the third compartment 31. As a consequence, the micro-organisms in the downstream biological treating plan 20 acclimate to the slow exposure of the changes in contaminant concentration or character and adapt to biologically degrade this higher concen-tration of contaminants or different character of contaminants.
In accordance with another feature of our invention, we maintain at a minimum the average time the water is retained in the equalization basin 12.
Thus, the heat in the water is retained at a maximum. High heat in water fosters increased biodegradation of contaminants in the treating plant 20.
Average water temperature entering the plant 20 preferably ranges between 90F and 100F.
The water in the first compartment 29 is monitored to determine the presence of especially noxious contaminants, for example, ammonia, phen-- 1~6Z820 olics, BUlrl~-, acids, callstics, etc., so that their source may b~ traced ancl col r ~et-iv~ acli~ll taken. In tll~ secoIld compartmell~ 30 pH is contl-oIIc(l by addition of acids or alkalis so that it is in thc rangc (~f about ( . 5 Lo ~ but prc-ferably from about 7. 5 to 8. 5 when air oxidation of contaminants is required.
This pH range is optimal for the oxidation reactions to occur and when desired the reactions are accelerated by adding hydroquinone or gallic acids.
Conventional floating aerators (not shown) float on the surface of the water in each compartment 29 through 31 and introduce air into the water to aerate and thoroughly mix the waste water. Such aerators (not shown) in com-partment 30 mix and aerate to maintain dissolved oxygen levels in the preferred range of 3 mg 02/liter or greater. The preferred ratio of the aerators is 0. 2 horsepower aeration or more per 1000 gallons compartment volume.
If for any reason the equalization pond 12 is flooded with an extremely high concentration of contaminant beyond handling capability, for example, if a line carrying acid broke, a valve 34 in a recycle line 36 is opened and the valve 38 in the filter inlet line 14 is closed. A pump 40 then pumps this highly acidic water to the shock load compartment 26a of a surge basin 26 where it is retained and gradually reintroduced into the first compartment 29 of the basin 12 through a valved line 42. This protects the downstream biological treating plant 20 from being poisoned by shock loads of contaminants.
The mixing, aeration, pH control, chemical reactions, etc., taking place in equalization basin 12 causes coagulation and flotation of considerable contaminant matter. This matter is skimmed from the surface of the basin 12.
Conventional slotted skim pipe (not shown) at the surface of the water in com-partment 31 may be used.
The effluent from the final compartment 31 contains colloidal matter to which coagulants or flocculants such as aluminum or iron salts, and/or high molecular weight organic polyelectrolytes are added. The coagulants or floc-culants destabilize, for removal by filtration the colloidal particles which are 1~)62820 carried by the effluent from the basin 12 to the bank of filters 16. The filtered water passing into the head tank 18 is lifted by thc pump 40. The preferre(I
filtcr mcdium u9cd in thc bank of filtcrs 16 i9 Sall(l 0r Ll COmbill~ l)ll ol` sand and coal. It is important that the water flowing to the downstream biological treating plant 20 be filtered to reduce suspended solids and oil to levels which do not interfere with the process. Under most conditions, the water flowing into the biological treating plant 20 preferably must contain no more than ten parts of oil or hydrocarbons per million parts of water and no more than ten parts of oily suspended solids per million parts of water. Periodically, a fil-ter unit in the bank of filters 16 must be backwashed. This is achieved by closing a valve in the feed line to the filter unit being backwashed and opening a valvc in a backwash waste line (not shown) such that the effluents from the onstrcam filters are used for backwash water. One function of the head tank 18 is to provide a constant back pressure on the filtered water thereby pro-viding a constant pressure backwash water source. The backwash water washes out the solids trapped in the filters, carrying them with the water into a sludge surge basin (not shown).
The biological treating plant 20 has four process stages. A contact stage 44 where the contaminated water contacts a biologically active sludge 46.
A clarifier stage 48 where sludge is separated from decontaminated water.
A thickening stage 50 where separated sludge is thickened to remove excess water. And a digestion stage 52 where thickened sludge is digested. In the first stage 44 water essentially free of solid and oily matter contacts the acti-vated sludge mass 46 in a contact tank 54 called a mixed liquor tank. This sludge 46 includes micro-organisms which feed on the contaminants in the water. The metabolic processes of the micro-organisms convert the contam-inants to cellular structure of the organisms, carbon dioxide, and various intermediate products. In the second stage 48, water and activated sludge from the mixed liquor tank 54 flows into a clarifier tank 56 via a line 72.
~ iZ8zO
~ s will be explained further below, activated sludge from a second source is added to line 72 via line 100 and the combined sludges and water flows to clar-ifier tank 56. The line 72 and an isolated zone 84 of the clarifier tank 56 pro-vide for contact of the second activated sludge recycle component and the resid-ual contaminants in the water leaving the mixed liquor tank 54. This results in furtherpurification of the water. Water is separated from these sludge particles by allowing the sludge particles 46 to settle on the bottom of the clar-ifier tank 56. Decontaminated water flows from the top of ~he clarifier through a second bank of filters 58 into a receiving stream 60, Preferably through a bed of activated carbon 66 for removal of trace solublc contaminants before discharge to the receiving stream.
In the third stage S0, the sludge 4 6 withdrawn from the bottom of the clarifier tank 56 is concentrated and the bulk of any water retained by the sludge is separated and withdrawn, In the fourth stage 52, thickened sludge is held in a tank 62 for a period of time sufficient to allow the micro-organisms to metab-olize stored food material. This digested sludge is then spread over land and permitted to decompose and serve as a fertilizer. Alternately, the sludge can be incinerated.
In accordance with our invention, interstage aeration is provided to aerate the water as it flows into the biological treating plant 20 and between the four stages of the plant 20. The most important interstage aeration is the aeration of the streams of water and sludge flowing in lines 72 and 74 between the first and second stages 44 and 48. Because of this aeration, the water leaving the clarifier tank 56 and being discharged into a receiving body of water contains at least about five parts of dissolved oxygen per million parts of water.
This is highly desirable especially when carbon adsorption is employed. The oxygen in the discharged water from the clarifier tank 56 maintains any micro-organisms trapped in ~he filter 58 or following carbon bed aerobic. If there is insufficient air in this discharge water, the micro-organisms trapped in the filter go anaerobic producing hydrogen sulfide which would contaminate 11~6ZB20 thc dischar~ed water In addition, the dissolved oxy~en in the water in the clal if iel- tallk ~'i( m.~ t.liIls thc ~lu~ 46 otl tl)~ Ottolll of tl~is l.ulk .I( l ol-ic, pcrmit~:ing tlIc slll-lgc to be retaincd in lhc tl~ickcnel 5() ~lnd cl.l~ ilicl ~,Y lollgcl than conventional. This provides more effective thickener and clarifier oper-ation.
We achieve interstage aeration by aspirating air into water flowing between tanks or positively injecting pressurized air into the transfer line.
In addition to backwashing the bank of filters 16, the head of the water in the tank 18 can be utilized advantageously to aspirate air into the water flowing into the mixed liquor tank 54. The water level in the head tank 18 ls above the water level of the mixed liquor tank 54. Water thus flows from the top of the head tank 18 downwardly through a line 64 and along a long generally horizontal line 66 which turns upwardly into a line 68 leading into the center of the mixed liquor tank 54. The horizontal line 66 is either at ground level or preferably below ground level to maximize the hydrostatic pressure. Thus, the air aspirated into the water is subjected to high pressure due to the water standing in the head and mixed liquor tanks 18 and 54. The horizontal line 66 can have a larger diameter than the downwardly extending line 64 or purposely be extended by looping, for example, so that the dwell time of the water and air mix can be extended. This substantially saturates or even supersaturates with respect to atmospheric pressure the water entering the mixed liquor tank 54 with dissolved oxygen. Normally this water flowing into the mixed liquor tank 54 will contain at least about 6 to 8 parts of dissolved oxygen per million parts of water and typically can reach levels above saturation of about 12 parts of dissolved oxygen per million parts of water. In a similar manner, air is aspirated or pressured into the water flowing from the mixed liquor tank 54 into the clarifier tank 56. The vertical line 72 transfers the water and suspended sludge particles downwardly to the horizontal line 74 which turns upward into a line 76 terminating near the surface of the clarifier tank 1~6Z8ZO
S(. An aspi rator 78 sucks air into thc downward flowing water in the line 72.
I hc water elevation in tl~e tanks 54 and 56 subject the ~ir-water mixture ~o higl prcssure as it flows through the line 74. This can saturate or supersaturate the water with dissolved oxygen.
The clarifier tank 56 is designed to receive the water from the upwardly extending line 76 into a confined mixing region formed by cylindrical baffle 82 concentric with the side walls of the tank. The diameter of cylindrical baffle 82 is preferably about 1/2 the diameter of the clarifier 56 and extending to about six feet from the bottom. Line 76 upwardly extends to well within the circular baffle 82 and, as the air-water mix exits line 76, the air lift pumping action creates a turbulent zone 84 in the center of the clarifier tank 56 that provides for further activated sludge-water contact, oxygen transfer and floc-culation, The preferred contact time in line 76 and turbulent zone 8~ is at least 20 minutes, The clarifier tank 56 includes weirs 80 at the top of the tank that maintains the water level and provides for discharge of clarified water from the quiescent zone 86. Activated sludge particles settle to the bottom of the tank where they are withdrawn by a conveyor and pump 88 system In our process, air under pressure from sources 90 and 92 is injected into the sludge flowing between the clarifier tank 56 and thickener 50 and between the thickener 50 and the digester 52. This high pressure aeration of ~ lld sludge permits the sludge to be maintained in the clarifier tank 56/ thickener for periods in excess of what is normally considered feas-ible in the activated sludge process. For example, the activated sludge-water mass in the feed to the thickener and clarifier in the normal system contains 1 mg 02/liter or less. As the sludge blanket settles the dissolved oxygen in the interstitial water is rapidly depleted by the respiration of the micro-organ-isms and the facultative organisms start to remove oxygen from the nitrogen and sulfur compounds present in the water. This released hydrogen sulfide and nitrogen gas upsets the sludge settling process and seriously degrades 1~62820 water quality. In our process about ten times the dissolved oxygen concentra-tion can be provicled compared to conventional practice. This greatly decreases the rate at whicll septicity occurs and alleviates substantially the problems associated with retaining the sludge in the clarifier and thickener until the excess water is substantially removed, Another aspect of our invention relates to the use of sludges with differ-ent properties recycled to different points to achieve different functions, all in a single activated sludge plant 20. As conventional, sludge wi thdrawn from the elarifier tank 56 is reeyeled through valved branehed line 94 into the mixed liquor tank 54 with exeess sludge to the thickener 50. A portion of this recycled sludge is introduced through braneh 96 into the sludge-water mix flowing between the mixec3 liquor tank 54 and the elarifier 56. This absorptive sludge portion entering via line 96 has capacity to absorb and store residual soluble contaminants and improve the floeculating properties of the total sludge mass for improved separation in elarifier 56. The interstage aeration and elarifier design provides for eontaet time, mixing and aeration to optimize the eapacity of this system. Similarly, the recycle sludge could be routed through the thiekener 50 and via line 98 into the sludge-water mix flowing between the mixed liquor tank 54 and the elarifier tank 56 Sludge from the thickener 50 has been without food longer and therefore has greater absorptive and storage capacity and is cOntained in a reduced volume because of the c3ewatering aetion of the thiekener, Maintaining the thiekener sludge aerobie using interstage aeration is a requisite for satisfactory sludge quality for recycle from the thiekener 50.
Another souree in our proeess of the reeyele sludge is obtained by routing that sludge through the thiekener 50, the aerobie digester 52, and valved line 100 into the sludge-water mix flowing in lines 72 and 74 between the mixed liquor tank 54 and the elarifier tank 56. The sludge eomponent from the aerobie digester 52 has had typically one to four weeks to acclimate to the residual refractory substrate contaminants. This acelimated sludge is 1C)62820 especially effective for absorbing and biodegrading the residual ~ub~trate in thc watcr exitln~ mixcd liquor tank S4. When the combined sllIdgc m~ss enters clarifier 56, the acclimated sludge combines with sludge in the clar-ifier tank 56 and seeds the sludge being recycled to the mixed liquor tank 54 via line 94. Seeding the main recycle sllldge mass continuously with sludge acclimated to residual, refractory materials shifts the equilibrium to increase removal of these contaminants by the main sludge mass in the mixed liquor tank 54. After equilibrium is attained there is no longer high concentrations of refractory substrate in the water leaving the clarifier tank 54. Introduction of any new refractory materials into the system causes the rapid development of acclimsted organisms.
As evident to those skilled in the art, modifications can be made in our process without departing from the principles of our invention claimed herein. For example, oxygen may be substituted for air in the interstage aeration system.
Claims (33)
1. In a multi-stage activated sludge process wherein in a first stage contaminated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising reducing the oil and grease, and solids content of the con-taminated water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first stage.
2. The process according to Claim 1 wherein the oil and grease, and solids content are reduced to less than about 10 ppm each.
3. In an activated sludge process wherein in a first stage contaminated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising treating the con-taminated water prior to the first stage to reduce oil and grease and solids to less than about 20 ppm oil and grease and less than about 20 ppm solids and maintaining the average sludge age in the first and second stages in excess of about ten days.
4. In an activated sludge process wherein in a first stage contaminated water is contacted with activated sludge for a period of time to degrade contaminants in the water, and in a second stage decontaminated water is separated from the activated sludge, and in a third stage a portion of the sludge from the second stage is thickened, the improvement comprising reducing the oil and grease, and solids content of the con-taminated water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first stage, recycling a portion of the thickened sludge from the third stage to the first or second stages.
5. The process according to claim 4 wherein, prior to recycling the portion of the thickened sludge from the third stage to the first or second stages, the portion of the thickened sludge is digested.
6. The process according to claim 1, 3 or 4 wherein the reduction of the oil and grease, and solid contents of the contaminated water is carried out by filtration and a coagulant or flocculant is added to the contaminated water prior to the filtration.
7. In the activated sludge process wherein in a first stage contaminated water is contacted with activated sludge for a period of time sufficient to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, a first portion of said separated sludge being recycled for recontact with the water in the first stage and a second portion of said separated sludge being treated in downstream operations, the improvement com-prising: reducing the oil and grease, and solids content of the contaminated water to less than about 20 ppm of oil and grease and less than about 20 ppm of solids prior to the first stage; and introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second stage is maintained in an aerobic state and separated decontaminated water from said second stage contains at least about three parts of dissolved oxygen per million parts of water.
8. The process according to claim 7 wherein the oxygen is introduced into the water and sludge mix entering the second stage by aspirating air into a stream of the water and sludge mix flowing between the first and second stages.
9. The process according to claim 8 wherein the oxygen in the stream of water and sludge mix flowing between the first and second stage is subjected to a high pressure produced by hydrostatic heads of liquid in the first and second stages.
10. The process according to claim 7 wherein the average age of the activated sludge in the first and second stages exceeds ten days.
11. The process according to claim 10 wherein the con-taminated water entering the first stage has been pretreated so that it contains no more than 10 parts of hydrocarbons per million parts of water and no more than 10 parts of solids per million parts of water.
12. The process according to claim 7 wherein a part of the first portion of the separated recycled sludge is mixed with the stream of water and sludge mix flowing between the first and second stages.
13. The process according to claim 7 wherein said second portion of the sludge treated in downstream operations is forwarded through a third stage for thickening, and the thickened sludge from the third stage is forwarded to a fourth stage for digestion.
14. The process according to claim 13 wherein a portion of the thickened sludge from the third stage is mixed with the water and sludge mix entering the second stage.
15. The process according to claim 13 wherein a portion of the digested sludge from the fourth stage is mixed with the water and sludge mix entering the second stage.
16. The process according to claim 7 wherein oxygen is introduced into the contaminated water entering the first stage by aspirating air into a stream of said water.
17. The process according to claim 16 wherein the oxygen in the stream of water entering the first stage is subjected to high pressure produced by a hydrostatic head of liquor.
18. The process according to claim 13 wherein oxygen is introduced into the sludge flowing between the second and third stages, and between the third and fourth stages.
19. A method of pretreating waste water including from about 25 to about 150 parts per million of solids per million parts of water and/or from about 25 to about 300 parts of and grease per million parts of water upstream of activated sludge treatment including a first stage of contacting the pre-treated waste water with activated sludge for a period of time to biologically degrade contaminants in the water and a second stage of separating the decontaminated water from the activated sludge comprising, passing the water through a equalization zone including at least two separate water retention compart-ments in series so that the water is mixed in each compartment and flows from one compartment to the next compartment and a given quantity of water is retained for predetermined period in each of said compartments, introducing air into the water in at least one of the compartments so that the water in the compartment is vigorously agitated and the effluent in the aerated compartment includes at least three parts of dissolved oxygen per million parts of water, adjusting the pH of the water in the equalization zone so that the pH of the water in one of the compartments and in the effluent from said zone ranges between about 6.5 and about 9.5, destabilizing colloidal particles suspended in the water, and filtering the effluent water from the equalization zone so that said filtered water includes no more than about twenty parts of oil and grease per million parts of water and no more than about twenty parts of suspended solids per million parts of water.
20. The process according to claim 19 wherein the differ-ence in temperature between the influent water entering the equalization zone and the effluent water exiting the equaliza-tion zone is less than about 20°F and the total retention time in the equalization zone ranges from about 2 to 15 hours.
21. The process according to claim 19 wherein any solid material floating in the water surface in the equalization zone is removed by skimming.
22. The process according to claim 19, 20 or 21 wherein a coagulant or flocculant is added to the water to destablize the colloidal particles in the water.
23. The process according to claim 19, 20 or 21 wherein the water in the first compartment is monitored to detect any rapid change in contaminant concentration.
24. The process according to claim 19, 20 or 21 wherein gallic acid or hydroquinone is added to the water in the aerated compartment to accelerate the rate of immediate oxygen demand removal.
25. A continuous process for purifying contaminated water including solids, oil and grease, comprising (a) passing the water through an equalization zone wherein the pH of the water is adjusted to a range from about 6.5 to about 9.5 and the contaminated water is distributed in a larger body of water so that the changes in concentration of contaminants in the effluent water to the equalization zone will produce gradual changes in concentration of contaminants in effluent water from said zone, (b) aerating the water in the equalization zone so that the dissolved oxygen in the water is at least about three parts of dissolved oxygen per million parts of water, (c) adding a destabilizing agent to the water so that colloidal particles in the water aggregate, (d) passing the water from the equalization zone through a filter so that particles and hydrocarbons will be removed therefrom and the effluent from the filter will have less than about ten parts of suspended solids per million parts of water and less than about ten parts of oil and grease per million parts of water, (e) passing effluent from the filter through a multi-stage biological treating zone having a first stage where the water flows into a contact zone and contacts activated sludge which decontaminates the water by biodegradation of contaminants, a second stage where the water from the first stage is clari-fied to separate suspended sludge particles from decontaminated water, a portion of said separated sludge particles being recycled to the first stage and the bulk of the clarified decontaminated water being withdrawn from the second stage, a third stage where that portion of the separated sludge particles not recycled are concentrated by removing the bulk of the residual water therefrom, and a fourth stage where said con-centrated sludge particles are digested, (f) aspirating air into the water and sludge mix as it flows between the first and second stages, so that the sludge in the second stage is maintained in an acrobic state and clarified water from said second stage contains at least about five parts of dissolved oxygen per million parts of water, and (g) filtering separated water withdrawn from the second stage to remove minute suspended sludge particles not separated from this water in said second stage.
26. The process according to claim 25 including the additional steps of aerating the water entering the first stage and aerating the sludge particle mix as it flows between the second, third and fourth stages.
27. The process according to claim 25 wherein the filtered water from step (g) is contacted with activated carbon.
28. The process according to claim 25, 26 or 27 wherein a portion of the sludge from the second stage is mixed with the water and sludge flowing between the first and second stages.
29. The process according to claim 25, 26 or 27 wherein a portion of the sludge from the third stage is mixed with the water and sludge flowing between the first and second stages.
30. The process according to claim 25, 26 or 27 wherein a portion of sludge from the fourth stage is mixed with the water and sludge flowing between the first and second stages.
31. The process according to claim 25, 26 or 27 wherein the average age of the activated sludge in the first stage is greater than ten days.
32. The process according to claim 25, 26 or 27 wherein the dissolved oxygen concentration in the water flowing to the biological treating zone is at least about three parts of dissolved oxygen per million parts of water.
33. The process according to claim 25, 26 or 27 wherein the air, water, and sludge mix entering the second stage of the biological treating zone is confined in a zone of high turbulence.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA234,524A CA1062820A (en) | 1975-09-02 | 1975-09-02 | Process for the purification of waste water |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA234,524A CA1062820A (en) | 1975-09-02 | 1975-09-02 | Process for the purification of waste water |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1062820A true CA1062820A (en) | 1979-09-18 |
Family
ID=4103944
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA234,524A Expired CA1062820A (en) | 1975-09-02 | 1975-09-02 | Process for the purification of waste water |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1062820A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102826724A (en) * | 2012-09-20 | 2012-12-19 | 江苏艾特克环境工程有限公司 | Acidic coal mine wastewater treatment device and method |
| CN114804366A (en) * | 2022-04-28 | 2022-07-29 | 湖北省水利水电科学研究院 | Freshwater aquaculture tail water ecological treatment method |
| CN115571979A (en) * | 2022-11-21 | 2023-01-06 | 菲立化学工程(遂昌)有限公司 | Municipal sewage purification method based on biological treatment |
-
1975
- 1975-09-02 CA CA234,524A patent/CA1062820A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102826724A (en) * | 2012-09-20 | 2012-12-19 | 江苏艾特克环境工程有限公司 | Acidic coal mine wastewater treatment device and method |
| CN114804366A (en) * | 2022-04-28 | 2022-07-29 | 湖北省水利水电科学研究院 | Freshwater aquaculture tail water ecological treatment method |
| CN114804366B (en) * | 2022-04-28 | 2024-03-26 | 湖北省水利水电科学研究院 | Ecological treatment method for freshwater aquaculture tail water |
| CN115571979A (en) * | 2022-11-21 | 2023-01-06 | 菲立化学工程(遂昌)有限公司 | Municipal sewage purification method based on biological treatment |
| CN115571979B (en) * | 2022-11-21 | 2023-03-10 | 菲立化学工程(遂昌)有限公司 | Municipal sewage purification method based on biological treatment |
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