FR2490620A1 - METHOD AND APPARATUS FOR TREATING WASTEWATER - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS AND AN APPARATUS FOR REMOVING SUSPENSION AND COLLOIDAL MATERIALS, INCLUDING FATS AND OILS, FROM PRE-TREATED WASTE WATER CONTAINING DOMESTIC WASTE. THE WASTEWATER ARRIVING IN 10 PASS THROUGH A 20 CRUSHING DEVICE THEN IS DIRECTED INTO A 100 CLARIFIER. THE CLARIFIED EFFLUENT IS THEN DIRECTED TO A 200 A GRANULAR MEDIUM FILTER WHICH THE EFFLUENT PASSES TOTALLY TO BE COLLECTED IN A CELLAR. BELOW. EFFLUENT 210 FROM THE FILTER CONTAINING LESS THAN 50 OF THE STARTING SUSPENSION SOLIDS IS DIRECTED TO VARIOUS TREATMENT POSSIBILITIES AS SHOWN IN FIG. 2. THE GRANULAR MEDIUM OF THE FILTER IS RETURN WASHED INTERMITTENTLY WITH PART OF THE FILTRATE AND A LOW OXIDIZING SURFACTANT. AIR PASSES INTERMITTEN AND ASCENDING THROUGH THE ENVIRONMENT TO REDUCE THE RESISTANCE TO FLOW AND TO INHIBIT ANAEROBIC BIOLOGICAL ACTIVITY.

Description

The present invention relates to a method of treating wastewater and

  the apparatus for carrying out this method. More particularly, the present invention relates to an improved wastewater treatment process, which improves the separation, concentration and treatment of colloidal and poorly settling solids, by fine sand filtration, thereby increasing the potential for energy formation. of the treatment process and reducing or eliminating subsequent biological treatment requirements. The present invention reduces the

  investments and the necessary energy costs.

  Solids contained in the wastewater may be suspended or dissolved. They may be filterable or non-filterable, volatile or inert, and may or may not be biodegradable. These solids, as well as the fats and oils typically found in wastewater, generally represent the most significant pollutant constituents, and it is these harmful materials that must be removed or treated during the

  wastewater treatment process.

  The particle size range of suspended solids is 10 8 microns to 100 microns and more. In general, solids of 10 microns and above are degradable and can be removed by gravity separation. Solids between 10-3 microns and microns do not normally decant and generally require coagulation and flocculation for disposal. Solids 10-3 microns and smaller are generally considered

dissolved solids.

  Most biological wastewater treatment devices and processes are designed to allow separation of large insoluble particles and biological treatment of non-settling particles. Many of these devices are subject to random performance because of the general lack of flexibility of the prior separation process, i.e.

and / or primary filtering.

  The primary processes can be subjected to a hydraulic and / or organic load very variable, which gives an effluent of variable quality. The biological systems used thereafter must operate in this range of load variation, which can minimize the effectiveness

of the biological system.

  The suspended and colloidal solids not separated by filtering or clarification must further be processed by one or more biological systems to meet the secondary treatment levels. The energy, investment and maintenance costs due to these

systems are substantial.

  Two of these generally accepted biological systems are modifications by suspended microorganisms

  activated sludge process, and the modifications of micro-

  fixed organisms of the trickle filter process. These systems can range from fairly simple processes to very sophisticated processes, depending on the size of the plant and the equipment used. The need for nitrification of the effluent will further complicate the process by adding

and energy costs.

  Many attempts have been made to modify treatment processes to reduce the energy costs of biological systems. This has generally been tried by process modification and design changes of various mechanical components, to improve the efficiency of solids separation from the clarifier. An accepted and effective solids separation technique is the addition of a chemical coagulant to the influent wastewater that enters the gravity or clarifier settling device. This technique materially increases the amount of solids separated and reduces the organic load to the system

  or subsequent treatment systems.

  This reduction in the load reduces the amount

  necessary for biological processes. Physical processes

  chemicals that have been recommended for the treatment of wastewater, generally consider the addition of a coagulant and the flocculation of suspended particles. This is usually done either in an area in the clarifier or before the clarifier to improve the settling of suspended solids. The clarified wastewater can then be treated in various ways, for example by adsorption on activated carbon or even refiltration followed

adsorption on charcoal.

  However, the addition of a chemical flocculant and / or a coagulant increases the prices of chemicals and creates very significant problems, in some cases far more than the benefits gained from the reduction of materials.

  suspended solids discharged into the biological system.

  Precipitation of the coagulant forms a chemical sludge that can be very difficult and very expensive to process and dehydrate. In addition, chemical sludge generally

formation of sludge gases.

  Organic materials biologically treated in an activated sludge system will form new and additional cellular materials. These highly structured cellular materials ultimately create a potential secondary pollution load and must therefore be carefully separated and treated in a manner that does not affect the environment. Therefore, in most biological systems, activated sludge or humus from runoff filters, both of which are mostly new cellular materials, must be separated from wastewater. This is usually done by secondary clarifiers. Decanted sludge can be returned to a digester for further biological reduction. The digested sludge is finally withdrawn and dehydrated by various means. Digestion, dehydration and the final treatment of new cellular materials are processes

difficult and expensive.

  Granular media filters are commonly used to remove suspended solids particles from wastewater after other processing steps. Such a filter effectively used in such applications is described in U.S. Patent Reissue No. 28,458, issued July 1, 1975. Improvements are described in U.S. Patent Nos. 3,817,378 issued on July 18, 1975. US Pat.

  June 1974 and 3,840,117 issued October 8, 1974.

  An effective method and apparatus for cleaning fats and oils from the media constituting the filters

  Granular media are described in U.S.

  No. 4,032,443 issued June 28, 1977.

  An apparatus and a process for separating and concentrating solids from

  Filter washing is described in U.S.

No. 3,792,773.

  The present invention seeks to overcome many of the disadvantages of conventional wastewater treatment systems by removing and collecting organic matter from wastewater containing domestic sewage without the use of chemical coagulants. A significant improvement is the additional energy potential of the increased amount of primary sludge free of chemicals. Another important benefit is a corresponding reduction in the production of new materials

in the factory.

  The present invention is a wastewater treatment process for the removal of suspended and / or colloidal materials, optionally comprising fats and oils, from previously untreated wastewater containing domestic sewage, comprising the steps of: at. passing said sewage water containing domestic sewage into a clarifier or filtration device to remove some of the materials and clarify said sewage, without the essential addition of chemicals; b. passing clarified wastewater without a substantial addition of chemicals through a granular media filter into a filtration vessel to a drainage cavity to produce a filtrate containing less than 40% of the suspended solids present in the untreated wastewater; c. intermittently upwardly passing air through the granular medium to reduce flow resistance through the medium and inhibit anaerobic biological activity therefrom, without destroying the integrity of the filtration medium; and D. intermittently washing back said filter with a portion of said filtrate and a surfactant and / or an oxidizing agent to remove the accumulated harmful materials. For example, wastewater containing domestic sewage from a device such as a filter, sieve and / or primary clarifier is passed through a media filter.

  granular material without biological, chemical or physical

  prior chemical Alternatively, the device

  removal of solids can also be complete-

  eliminated; the wastewater passes directly to the filter inlet and the non-settling and colloidal solids are trapped by the filtration medium and

  adsorbed by the surface of the filtration medium.

  The effectiveness of the removal of these non-settling solids is a function of the rate of application and the

  physical characteristics of the environment, typically sand.

  In general, at least 60% of suspended solids are removed by a single filter. The solids are allowed to accumulate in the filtration medium until resistance through the filtration medium causes the water level above the medium to reach a predetermined value, at which time the solids are washed back into the filter medium. filter, and harmful materials previously trapped and adsorbed

are removed and washed from the middle.

  According to the invention, there is also provided an improvement in the interception and preservation of the colloidal and suspended materials, by periodic reduction of the resistance of the filtration medium, in the mass and on the surface, by passing the air in the medium ascendingly and intermittently, to improve porosity and retard anaerobic decomposition. This air is displaced upwards by the rise of the filtrate in the drainage cavity and the displacement of the air. The upward movement of air is sufficient to move harmful materials into the filter bed where these materials are temporarily stored without destroying the integrity of the filter media. In another aspect of the present invention, there is provided a backwash process, utilizing vertical hydraulic jets intermittently with air to provide high speed agitation and medium motion at a variable speed. sub-fluidization to improve the efficiency of the backwash system and

  use a minimum of wash water in return.

  According to another aspect of the present invention, the backwash water is directed to a holding tank where the previously undecayable particles, found

  now in the wash water, agglomerate and settle.

  Fats and oils are also allowed to agglomerate for skimming. The settled solids are allowed to concentrate generally without the addition of chemicals. In another aspect of the present invention, the washed solids are pumped to a digester for the anaerobic stabilization of organic matter, and biological formation of a combustible gas.

  comprising methane and carbon dioxide.

  According to another aspect of the present invention, the clarified wash water may be returned to the filter inlet for further filtration and, under certain conditions, may be directed to a receiving water body or body of water. like a lake, a river, an ocean, etc. The pollution characteristics of the filtrate are materially reduced by the removal of the colloidal and non-settling solids present in the clarified wastewater. According to another aspect of the present invention, oxygen is added to the liquid mass by collision, diffusion and pulse through the filter medium, to minimize the normal oxygen deficiency of the clarified waste and the anaerobic conditions to the contrary in the medium and the

liquid filtering mass.

  According to another aspect of the invention, there is provided an improved regeneration cycle of the medium which removes fats, oils and biota attached to the surface of the medium by emulsification and hydraulically and pneumatically induced agitation of the medium bed. . In addition, an oxidizing agent such as hypochlorite with or without surfactant is used to regenerate the surfaces of the medium. Preferably, however, a non-halogenated oxidizing agent, such as hydrogen peroxide, a gas or an oxygen-containing liquid, or ozone, with or without a detergent or surfactant, is used.

  thus avoiding the creation of chlorinated hydrocarbons.

  Another important aspect of this invention is the staging of the filtration processes to increase the amount of non-decanted and colloidal solids removed from the liquid waste. Typically, in a two-stage filtration system, the secondary filtrate contains less than 25% of the solids suspended in the untreated water, and the corresponding BOD is low. Such a filtrate can usually be discharged directly into a course

  water, without further biological treatment.

  Another aspect of this invention is the use of very small amounts of coagulant between the staging of the filtration processes to further reduce the very fine solids which will not be trapped or adsorbed on the surface of the medium. The coagulation chemical is rapidly mixed with the primary filtrate and passed to the second filter without a flocculation step. Such a process typically yields a secondary filtrate containing less than 20 mg / l of suspended solids and may contain less than

  BOD than normally assigned to secondary processes.

  The first stage filter removes the largest portion of solids, and only very small amounts of coagulant are needed in the second stage or stage. Thus, the effect of this chemical on the subsequent treatment

sludge is negligible.

  Yet another object of the present invention is the use of a filter to treat excess flow that may adversely affect an existing or fixed biological device by deriving excess flow outside the device. biological media through a fine-media filter, and remove sufficient amounts of suspended solids from these derived wastewater, as well as biologically treated wastewater. This allows filtration of treated and untreated wastewater to meet effluent requirements. In this invention, the effectiveness of the biological process is maintained. The biological process is protected against hydraulic overload and the

  global characteristics are therefore ensured.

  Another aspect of this invention is the combination of a two-stage filtration in a single vessel allowing varying pressure conditions with respect to flow quantities and designed to accept a portion of the extremely high flows through reaction media.

coarser filtration.

  The two-stage filter allows the use of more than one sand dimension and variable application rates for

a given filtration load.

  Another aspect of this invention is the cleaning of the vertical walls of the filter tank automatically during a backwash. A cleaning agent such as a detergent and oxidizing agent, or a surfactant and an oxidizing agent, may be added to the backwash to further clean the walls. The addition of the agent

  cleaning can be set manually or automatically.

  A non-halogenated oxidizing agent is preferred.

  Another aspect of this invention is the addition of an oxidizing or sterilizing liquid to the wash liquid at the end of the wash cycle to reduce the growth of biota. This sterilization or oxidation liquid will also cause the oxidation, emulsification or removal of the organic substances previously fixed on the surfaces of the medium resulting from the filtration of clarified wastewater on the fine sand medium. Medium surfaces are actually used to adsorb some of the organic components

which constitute the soluble BOD.

  Another aspect of this invention is the possibility of minimizing the deleterious effect of colloidal and suspended particles which clog the pores of activated charcoal and coat coal surfaces with organic surfaces,

  which limits the effective use of activated charcoal.

  Another aspect of this invention is an improved underwater drainage system that effectively dispenses the oxidation or sterilization liquid into the filtration medium without premature mixing with the wash liquid.

  back and the detergent or surfactant.

  Figure 1 is a schematic diagram of a conventional wastewater treatment system, using as primary elements a primary clarifier, a treatment device

  biological, a final clarifier and a sludge digester.

  FIG. 2 is a diagram of the preferred embodiment of the invention, illustrating the numerous systems of

  possible treatment that can be used.

  Figure 3 is a diagram of the invention combined with

biological treatment.

  Figure 4 is a diagram of the invention combined with

  a biological treatment device followed by a second filter.

  Figure 5 is a diagram of a treatment method

  physico-chemical placed between two filters.

  Figure 6 is a schematic application of the invention to a wastewater treatment device subject to large variations in tributary flows, illustrating

  treatment solutions for derived flows.

  Figure 7 is a sectional view of the device of

  the invention used to treat derivative flows.

  Figure 8 is a sectional view of the device of the invention showing the wall washing system and the

pulsed bed system.

  Figure 9 is a sectional view of the system of

  Underground drainage support described in this invention.

  Figure 10 is a sectional view of an outlet nozzle of the drainage support system from below

described in this invention.

  Figure 11 is a sectional view of another possibility of a nozzle detail of the support system of

  drainage from below described in this invention.

  The reductions in total oxygen demand (BOD) of suspended solids and soluble BOD of domestic wastewater clarified by parallel filters with granular media are shown in Table I, where the filters used are granular media consisting of made of quartz having an effective dimension of 0.35 mm or 0.45 mm respectively, a sand thickness of 25.4 cm and application rates of 80 liters

per minute per square meter.

TABLE I

  Tributary Filter N0 1, FilterN0 2, effluent effluent filter Dimensions of sand, mm. 0.35 0.45 Suspended solids, mg / ml 81.3 20.8 25.7 Effectiveness of removal,% (74.6) (68.6) Turbidity FTU 46 23 24 total BOD5, mg / i 131.5 49.0 53.9 Effectiveness of removal,% (62.7) (59.0) soluble BOD5, mg / l 35.3 23.3 24.9 Effectiveness of removal,% ( 34.0) (29.3) Mean filter travel time, h 3.0 6.0 Washing water / filtrate ratio,

1/1 0.168 0.088

  A significant neglected factor in the design and development of wastewater treatment devices is that the bulk of the organic pollution load of wastewater, represented by the theoretical oxygen demand (DTO), the chemical demand oxygen (COD) or biochemical oxygen demand (BOD), is contained in suspended solids and non-settling colloidal solids. Such solids are present in domestic sewers. For example, sewage solids that have been separated by

  dimension have the organic impact shown in Table II.

  Basically, 66% of the organic pollution load is contained in suspended solids with a particle size of 8 microns and smaller, as measured by COD. It is generally considered that suspended solids of 8 microns and

not decantable by themselves.

  The significance of the pollutant load of clarified or decanted wastewater can be further illustrated by a size and weight analysis of a sample of clarified wastewater. The sample used in Table II is from the Lorain, Ohio, U.S.A. wastewater treatment plant, and is not atypical of clarified wastewater containing domestic waste. The wastewater sample was then progressively filtered through filter membranes of increasingly smaller pores. The amount of solids retained on each filter was determined,

  as well as the COD of the solids retained.

TABLE II

  Primary effluent from Lorain, Ohio Total suspended solids in decanted wastewater 84.5 mg / l; COD 182 mg / l Size of solids COD through filter pores, filter suspensions, total mg / l retained by filter, mg / l

8.00 38.4 121.0

3.00 14.7 80.9

1.20 10.7 62.7

0.80 11.5 62.7

0.45 7.6 65.9

0.22 1.6 48.9

  The reduction of soluble BOD is another aspect of

  this invention. The reduction of soluble BOD by

  sand is very significant and becomes even more substantial at lower hydraulic application rates. For example, tests have shown that the reduction of soluble BOD is between a value

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  high of 34% reduction up to a low value of .6%. Soluble BOD is a definition rather than a

  true description. It is calculated that the colloidal particles that

  can pass through a 0.45 micron filter are part of the soluble fraction and are measured as soluble BOD. A substantial amount of the colloidal material passing through a 0.45 micron filter membrane will bind and adsorb to the grain surface of a granular media filter. Some of the organic compounds in the solution are also rapidly converted biologically into

  biomass when wastewater passes through a granular bed.

  The quantity removed is a function of the application rate and the size and thickness of the sand. Table III, describing a specific series of tests, shows the effectiveness

  removal of the soluble BOD according to the present invention.

  Thus, single or multi-stage filtration not only removes measurable non-settling solids, but materially reduces the soluble fraction of the solids.

organic load.

TABLE III

  Reduction of soluble BOD (%) -5 Flow 0.35 mm 0.45 mm 80 l / min.m2 34 29, 5 1 / min.m2 18.3 15 320 1 / min.m 7.2 5.6 Now consider the drawings that are given by way of illustration of the preferred embodiments of

  the invention and not as a limitation.

  Consider Figure 1 which represents a conventional biological wastewater treatment process. The inlet pipe 10 of the raw wastewater is directed to the mill or filter device 20, and via a

  pipe 11, in the decanter or primary clarifier 100.

  The clarified liquid is directed through line 110 to logic process 400, where the wastewater is biologically treated, forming new cellular materials, and is directed through line 410 to final settling tank 500. A major proportion of solids constituting the sludge is decanted in the clarifier 500 and removed by the pipe 520. A portion of the sludge is recycled to the biological process via the pipe 521. The excess sludge, or rejected sludge, is then mixed with the sludge were removed from the primary clarifier 100 through line 120 and the mixture of sludge rejected and primary sludge is directed by line 121 to the digester 800 where the sludge is further treated and some of the organic material is converted into methane and carbon dioxide. The excess of sludge discharged from the clarifier 500 can pass directly into the digester 800 and not undergo the mixing process in the pipe

  121, according to the preferences of the engineer.

  FIG. 2 represents a diagram of the present invention, where a filter system 200 is placed after the settling tank or primary clarifier 100. The wastewater treatment system comprises a wastewater inlet pipe 10, where the water waste are directed to the grinding device and / or coarse filtration, then are directed by line 11 to a primary clarifier 100. The clarified effluent leaves the primary clarifier 100 through line 110 and directs

to the filter inlet 200.

  As shown in Figure 2, the filtrate of line 210 is directed to one or more subsequent treatment elements, such as a biological treatment, which may be of the suspended microorganism or fixed microorganism type. Alternatively, the filtration may be followed by a second stage filtration, then treated with activated charcoal or by a biological treatment to remove organic matter and / or nitrogen, or discharged into a receiving stream, or to any other means of treatment or reuse. The need for the possible second stage filtration is a function of the quality of the wastewater and the distribution of the grain size, as well as the legal requirements for the discharged water. In many cases, the burden on the biological system is so small that sufficient biological treatment is obtained, for example in a trickle filter without

no recycling.

  Another embodiment of this invention is a wastewater treatment process for the removal of suspended and colloidal materials, including fats and oils, protein compounds and ammoniacal nitrogen from previously untreated wastewaters. containing domestic refuse, consisting of: passing said wastewater containing domestic waste into a clarifier or defiltration device to remove some of the materials and to clarify said wastewater, without the addition of chemicals; b. passing the clarified wastewater, without addition of chemicals, to a first granular filter in a first filter tank to a first drainage cavity from below, to provide a primary filtrate; c. passing said primary filtrate through a fixed media filter, such as a trickle filter, where nitrifying microorganisms develop on said fixed media, for oxidizing said nitrogen contained in the primary filtrate to nitrate and nitrite; d. passing the primary nitrified filtrate to a second granular media filter in a second filtration vessel to a second subterranean drainage cavity to produce a secondary filtrate containing less than 1 mg / l of suspended solids and less de 20 mg / l of BOD5; e. intermittently passing air upward through each granular medium to reduce flow resistance through the media and inhibit anaerobic biological activity therein; f. intermittently washing back said first filter with a portion of said primary filtrate and a surfactant and / or an oxidizing agent to remove accumulated harmful materials; g. washing back intermittently said

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  second filter with a portion of said secondary filtrate and a surfactant and / or an oxidizing agent to remove the

harmful materials accumulated.

  This treatment easily produces a secondary filtrate containing less than 20 mg / l of suspended solids and less than 20 mg / l of BOD5 even when the fixed media filter operates at a flow rate equal to or greater than 13.6 l / min. m,

without any recycling.

  The secondary filtrate will contain less than 1.5 mg / l of ammonia nitrogen if the temperature of the wastewater exceeds C. The backwash water of the filter 200 is discharged through line 220 to the clarifier 300, where the solids decanted backwash, and the supernatant liquor of the clarifier is returned to the inlet of the filter 200 through the conduit 310 and the inlet conduit of the filter 110. The quality of the supernatant liquor can be improved by addition of coagulation chemicals . The clarifier 300 clarified sludge is withdrawn via line 320 and directed to sludge discharge line 122 which carries sludge from primary clarifier 100 through

driving 120.

  The quality of the filtrate will depend on the flow rate of the wastewater application, the pollutant concentrations of the wastewater, the thickness of the bed and the average grain size used in the filter 200. The quality of the filtrate may furthermore be improved by a series of possible subsequent treatments, depending on the requirements

  concerning the quality of the final water.

  Energy requirements for the further treatment of clarified wastewater will be materially reduced as a result of the reduction in the organic pollution load of

  clarified wastewater from the filter 200.

  In addition, the sludge created by the solids concentrated in the filter wash water 200 is added to the sludge removed in the settling tank or primary clarifier 100. The total amount of primary sludge is the sum of the primary sludge obtained both in the gravity clarifier 100 than in the filter 200. The

  that no coagulant is added to the inlet or the reservoir.

  see primary settling or filter, ensures that the total sludge withdrawn will contain a minimum of treatment chemicals. It is known that anaerobic biological generation of methane fuel from sludge or wastewater is more easily and efficiently done when the ratio of primary biological sludge to secondary biological sludge is high. This invention provides materially increased amounts of primary solids and amounts of

  secondary solids significantly reduced.

  For example, typical domestic wastewater contains mg / l of suspended solids, half of which is

  removed by simple primary treatment without chemicals.

  The clarified wastewater typically has the following analysis. Suspended solids 80 mg / l BOD5 130 mg / l In conventional treatment, clarified wastewater is subjected to activated sludge treatment to meet government requirements for secondary effluents. Approximately 70 mg / l of biological sludge solids will be produced. Thus biological solids comprise almost half of the total solids load that is normally

digested anaerobically.

  In the present invention, the clarified wastewater is filtered on a granular filter to meet secondary standards, which replaces the biological step which has

  high equipment and operating costs.

  In addition, no biological treatment solids pass into the anaerobic digester; therefore the production of gas and the reduction of solids as well as the subsequent dehydration of solids are

all improved.

  When the biological treatment step is preceded by granular media filtration, the significantly reduced amount of new cellular material

  better operating characteristics of the digester.

  Still consider Figure 2, line 151 after the second stage filtration can direct the filtrate to an activated carbon contacting apparatus. The filtrate may also be processed in a biological device as best shown in Figure 3, or discharged into a stream of water or reused. Or, the second stage filtration can be omitted and the filtrate of the first stage

  be directed to the different processes mentioned.

  An important advantage of the invention is the reduction by filter 200 of the organic pollution load directed to all subsequent treatment devices, which

  Reduces energy and investment needs

  Now consider Figure 3; it illustrates the same type of secondary biological process as in Figure 1, the secondary treatment process is now modified by using a filter installed in the line 110 of the clarified effluent. The filtrate contained in the outlet pipe 210 requires a substantially reduced biological treatment. The biologically treated wastewater may be directed to a decanter or final clarifier 500, or directed to a subsequent filter 700 as shown in Figure 4, and then to the reservoir

contact with chlorine 600.

  In addition, according to this invention, the primary sludge is withdrawn from the primary settling tank 100 via the pipe 120. The colloidal and generally non-settling solids contained in the clarified wastewater are then intercepted by the filter 200, the filtrate of the filter 200 being then directed by the pipe 210 to the biological process 400. The washing water back from the pipe 220 is directed to the inlet of the washing liquid separator 300, where the washed solids are allowed to settle, and are discharged and mixed with the solids of the primary settling tank 100, thereby increasing the total primary solids removed from the process.

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  The organic feed to the biological process is materially reduced due to the greater removal of organic solids. According to the application and the dimensions of the medium, the residual organic load brought to the biological process can be reduced to the point that the new cell growth can be efficiently intercepted by a second filter which is generally of the same type as that used in the filter, and a final decanter is not necessary. The filter 700 will intercept the mixture of solids and new cells and return these solids to the entry of biological process 400 through line 721 as shown in Figure 4. The excess solids discarded is then discharged into the separator. backwash 300

by driving 722.

  According to this invention, the growth potential of new cellular material has been limited by the reduction of suspended and non-settling solids effected by filtration on granular media. The growth of the new cells is proportional to the organic load in the wastewater entering the biological process by the

driving 210.

  For example, assuming a new cell growth rate of 0.4 kg of new cells per kg of BOD removed, a filtrate residue containing 50 mg / l

  of DB05 will give only 20 mg / l of new cells.

  Wastewater containing suspended solids content of less than 30 mg / l solids and corresponding biochemical oxygen demand values may be classified as a secondary effluent. In the case where the suspended solids exceed the permitted requirements for the particular watercourse, a second filter may be added, and the 20 mg / l of new cells can easily be separated by the filter 700, and the filtrate passing through Conduit 710 meets a low solids requirement. If the requirements of the watercourse are such that the solids to be discharged do not exceed the standard, additional treatment may not be necessary. Now consider Fiaure 5; the decanted primary effluent is directed to the first stage filter and the filtrate directed through the line 210 to the mixing chamber 30 o very low concentrations of coagulant from the container 40 are pumped into the mixing chamber 30 by the pipe 50. Coagulant is mixed in the mixing chamber 50 with the filtrate of the first stage from the filter 200 and the coagulant-filtrate mixture is discharged onto the filter 700 through the pipe 211, without flocculation step. The coagulant-filtrate mixture is then filtered by the filter 700, and the second stage filtrate is discharged through line 710. The backwash liquid of the first stage filter 200 is discharged into the holding tank 300 of the effluent water. washing by the pipe 220, and the washing water of the filter 700 is also directed to the same washing solids separation device, via the pipe 720. The sludge decanted in the container 300 is discharged via the pipe 320 and mixed with the sludge removed from the primary container 100 via the pipe 120, and all the sludge together is directed

  to the digester 800 through line 123.

  The effluent from the line 710 can then be optionally treated in various ways, depending on the requirements of the final use or discharge of the treated wastewater. The water that is refiltered can be directed as shown in Figure 2 to a complete series of further processing steps depending on use and final requirements. This type of system significantly reduces or completely eliminates the biological cell growth material normally associated with biological treatment plants, and simultaneously provides a high quality effluent. The limitation will obviously be the soluble constituents which are not removed by filtration. The wastewater effluent, from which suspended solids and colloidal solids have been removed by filtration, is readily contacted with activated charcoal for adsorption of residual organic matter. This type of pretreatment can effectively save space and energy important and gives an effluent of determined quality. This is particularly true in the many areas of water reuse. The filtration process will reduce the energy requirements normally associated with conventional wastewater treatment.

similar characteristics.

  Now consider Figure 6; the primary filtration solution can be applied most satisfactorily to wastewater treatment devices that are subject to extremely

  flows, such as during heavy rains, where

  existing biocedures are threatened by hydraulic overload. Now consider particularly Figure 6; the inlet pipe 10 represents the wastewater inlet pipe, comprising variable volumes of water of violent rain passing through a grinding or filtration device 20, then by an alternating flow diversion chamber and a dam 60 of the excess flow to go into the primary settling chamber 100. The clarified effluent of the pipe 110 is directed to the hydraulic control chamber 80, where the excess flow of the first scale will be deviated from the process 400 and the final clarifier to arrive in the conduit 510 which is the inlet of the filter 200. The return wash water is directed from the filter 200 to the pipe 220 and to the settling tank 300. The supernatant liquor of the container decant 300 is returned to line 510 via line 310. The settled sludge is returned via line 320 and mixed with decanted sludge from 100 through the conduit 120 and directed for further processing by the conduit 124 to a digester or other device

sludge treatment.

  According to this invention, the excess flows are directed away from the biological process to protect the integrity of the biological process and to prevent its disturbance by the hydraulic shock, and to further reduce the biochemical oxygen demand of the passing derivative flow. by the pipe 90, by the action of the filter 200 so as to reduce the

  solids content in suspension.

  Consider again Figure 6; the excess flows can also be derived away from the primary clarifier 100, in the case where the design indicates that the maximum hydraulic conditions of the clarifier 100 would be exceeded. Thus, a bypass chamber 60 can be provided upstream of the primary clarifier 100, and flows beyond the design values can be directed through line 70 in bypass line 91 to line 510 leading to filter 200 to further improve their quality because of the elimination by

  filtration of suspended solids.

  Another aspect of this invention is the ability of the filtration device to meet various variable filtration standards as tributary volumes change due to the impact of violent rainwater flow and dry weather flow. During dry periods, when the wastewater flows are low, the durations of residence of the solids in the earpipes are relatively long, resulting in considerable solubilization of the polluting materials. BOD5

wastewater is high.

  In addition, high water levels during

  wet periods quickly sweep the sewer pipes.

  The wastewater is not only diluted with additional water but is more "fresh", for example there is

had less solubilization.

  While high flows impede the operation of conventional biological treatment devices, pollutant materials in such high-flow wastewater are more susceptible to granular media removal than pollutants in low-flow wastewaters. . As a result, bypassing excess wastewater out of the biological treatment devices and into a granular media filter will maintain a high level of biological treatment while providing a high level of overflow filtration treatment. The result is a very acceptable effluent at a time when the

  quality of the effluent is normally deteriorated.

  In another embodiment, the fully traversed granular medium filter of FIG. 7 allows efficient and effective treatment of the wastewater at highly variable flow rates. Consider Figure 7; the treated and derived tributary flows are directed to the filtration vessel 200 through line 510 as previously described in Figure 6. Returning to Figure 7; a flow indicator 530 placed in line 510

  indicates the amount of flow going to the filter.

  Within predetermined limits and at the lower values of the gap, the valve 512 remains open and the valve 514 remains closed. The flow in dry weather at low water levels from the conduit 510 enters the filter 100 with

  a low hydraulic load on the filter media 250.

  When the flows increase, the flow meter 530 then signals the valve 512 to close and the valve 514 to open, and allow the water level to enter the

filter 200 at a higher point.

  Simultaneously, the flow indicator 530 will change the operating level from the previous operating water level indicated at level 240 to level 242 and possibly to level 244, thereby increasing the capacity of the filter. As the flow further increases, a signal from the flow indicator 530 will then restrict the flow through the flow diversion chamber 516 to the filter 200 and cause a proportional flow to pass through line 518 into the Filtration container 200A placed entirely within the limits of the filter container 200. The filtrates of the filter 200 and the filter 200A passing through the lines 223 and 223A are then mixed in a single line for the effluent from the plant. The operating levels in the filter 200 are themselves modified in proportion to the flow demand as determined by the indicator

flow 530.

  Consider again Figure 7; the backwash trough 260 is located above the filter sand 250 and before backwashing, the water level 240 is lowered at the weir 262 of the backwash trough. In the prior art, this volume of water above spillway 262 is added to the volume of backwash water, which

  increases the amount of wash water to be treated.

  When the operating water level is changed as determined by the flow indicator to 242 or 244 or intermediate levels, the

  The volume of water discharged is obviously increased.

  One aspect of this invention is the arrangement of the filter cell 200A completely inside the filter, which reduces the volume of water above the filter bed 150 without reducing the efficiency of the filter system.

  filtration. The amount of water wasted is reduced.

  Another aspect of this invention is the rejection of the volume of water passing over weir 262 into a separate discharge chamber 270 prior to start-up of the backwash pump 222, significantly reducing the volume of washing water to be treated. The sequence of the return wash operation is initiated by a wash request signal from the level detector 352, 354 and 356 as a function of the appropriate water level 240, 242 or 244, this level being determined by the signal from the flow indicator 530. Under the action of the signal, the valve 277 opens and allows the mass of liquid above the weir 262 to escape through line 266 to the discharge chamber of the wastewater 270 o the total volume of the liquid located above the spillway 262 is now retained. After draining the liquid mass above the weir 262, as shown by a signal from a timer device, the valve 277 is closed and the valve 278 is opened, the return wash pump 222 is started , the valve 226 is opened, the valve 225 is closed, and the washing liquid is then directed from the drainage cavity from below 208 and through the sand bed 250 to the overflow weir 262. washing is then directed to

2'490620

  the wash liquids holding tank 290 and can

  then be treated as described in U.S.

  No. 3,792,773. The volume of liquid now retained in the tank 270 is pumped into the filter 200 by the pump 272 after stopping the pump 222, closing the valve 226 and opening the valve 225, and filter filtrate 200. is again directed to the "clean well" 280 filtrate retainer. The volume of liquid above the weir 262 contains substantially less solids than the backwash liquid. The mixing of these volumes increases the total liquid volume and increases the cost of treating this liquid volume by dilution of the lavaae mixture back. This dilution reduces the ability of the mixture to reach the point of self-flocculation without the addition of chemicals. Self-flocculation or self-agglomeration is much easier with an increased concentration of solids. The discharge of water at the top of the filtration chamber as shown in the filtration system of Figure 7 with other aspects of this invention can be used independently. This reduced volume of head water provides improved operating costs and operating efficiency in any filtration system where volumes of water are kept above the level of the washing weir. return. By modifying the pipes, this filter can also be used to treat sewage in two consecutive stages. In this case, the wastewater is first passed through the upper filtration bed 250A and then through the filtration bed 250. The granular medium of the first bed 250A will be relatively coarse while the bed

  250 will be composed of finer granules.

  Now consider Figure 8; it illustrates another feature of the filter 200. A perimeter wash ring 226 is located at the top wall of the filter 200, with the nozzles 228 positioned to clean the walls of the filter 200. A feed pipe 224 the wash ring communicates with the return wash pump 222 and the chemical feed pump 262 via line 266. One aspect of this invention is the use of a special cleaning solution for washing the walls of the filter at predetermined times. Filtration of primary wastewater involves the introduction of highly contaminated biological waste into the filtration cell. Biological waste can be deposited on the walls where biota can develop. Then, the absence of oxygen will cause unpleasant growths and odors. Effective cleaning and disinfection of the walls is necessary to improve the overall functioning of the

filtration device.

  Another aspect of this invention is the improved backwash device for removing particles that are stubbornly attached to the grains of the medium and introducing a cleaning and disinfecting solution into the medium at times predetermined to delay the

growth of biota.

  Referring now to Figure 8 and in particular the backwashing technique, a high pressure air device is alternatively provided by the pump under air pressure 280, directing air through line 282 to the static mixer. 284 by mixing the air and wash water back and directing this mixture into the cavity

drainage from below 208.

  The air introduced intermittently into the static mixer 284 causes further agitation of the medium 250, due to the pulsed vertical rinse streams 292 in the underflow drainage system. Thus, the backwash cleans the medium more thoroughly than was previously possible and minimizes the need for frequent chemical cleaning. However, the same device is designed so that the chemical can be introduced into the drainage system from the chemical tank 260 to adequately disinfect the filter media, delaying the accumulation of biota either in

the middle is on the surface of the filter.

  The most important problem associated with the wastewater filtration process is the adsorption and accumulation of grease and / or colloidal oil films on the surface of the grains of the medium. This particular problem is magnified by the high percentage of colloidal fats and oils present in primary flows

  and primary flow and rainwater combined. The-

  contact and washing with a detergent solution or an oxidant and a surfactant effectively remove fats and colloidal oils from the surface of the grains of the medium. Another aspect of this invention is therefore an improvement of the underfloor drainage system disclosed in U.S. No. 3,840,117 as well as an improvement of the chemical cleaning device described in U.S. Pat. No. 4,032,443. Frequent or excessive chemical cleaning cycles using halogenated compounds may be detrimental to the operation of a biological system or the quality of the filtrate of the wastewater treatment device. Halogenated compounds such as those containing bromine or chlorine can combine with the hydrocarbons in the wastewater to form trihalomethanes which are considered to be carcinogens. Bromoforms and chloroforms are examples of the halogenated hydrocarbons that can result from

  the use of halogenated compounds.

  Now consider Figure 9; it represents

  a preferred embodiment of this aspect of the invention.

  There is illustrated an improvement of the drainage device below that described in US Pat. No. 3,840,117, comprising a modification by addition of an oxidant chamber 1000, an inlet conduit 1100 and sleeves 1200. The chamber 1000 is formed of an upper plate and a lower plate, bearing a network of horizontal bars and generally of the same size as these bars. The bars in turn carry the sieve and the sieve carries the bed of granular medium. The plates are maintained

  in parallelism by non-limiting spacers.

  The uniformly spaced sleeves 1200 vertically cross the upper and lower plates to allow upward or downward flow of liquid or gas. Air distribution chambers 208 uniformly spaced are open at the lower end and closed at the upper end by the bottom plate of the

oxidizing chamber.

  A detergent, usually a linear alkylsulfonate, is introduced into the drain cavity. After introduction of a predetermined quantity of the detergent into the emptying cavity, an oxidizing solution, such as hydrogen peroxide, or a gaseous oxidant such as ozone, is introduced into line 1100 in chamber 1000. in the nozzle 1400 through the orifice 1420, and is mixed with the detergent and filtrate solution forcibly introduced into the air distribution chamber 208 and through the orifice 1450. Another possible structure of the sleeves 1200 and a other possible arrangement of the orifices 1450 are shown in the FIGS.

and 11.

  Detergents or surfactants such as alkyl-

  Linear sulfonates are biodegradable, and oxidizing solutions as strong as hydrogen peroxide or ozone for example will reduce the strength of the mixture if they are mixed before entering the granular medium, and if allowed to remain in the Mixed state before use in the medium. This device protects the strength of the chemicals and allows the use of a biodegradable detergent with a strong oxidizer by mixing them just before, at or just after passing the filtrate into the medium, providing

  still a uniform distribution in the middle of the melanae.

  This process reduces the cost of chemical cleaning by eliminating the formation of all trihalomethanes and eliminating the problems of non-biodegradable detergent release or

  phosphate type. The chemical cleaning device emulsified

  will quickly sift any residual greasy coating on the middle grains and wash the surfaces of the grains into

  ridding you of any residue of grease or oil.

  Another aspect of this invention as shown in FIG. 9 is the final passage of air through the drain system from below via line 1500 and valve 1510 operating intermittently to line 1100. which causes a pulsation of jets. This pulsation of jets makes the elimination of dandruff of grease and oil from

of the middle constituted by the sand.

Claims (10)

  A method of treating wastewater for the removal of suspended and / or colloidal materials, optionally comprising fats and oils, from previously untreated wastewater containing domestic waste, characterized in that: at. passing said wastewater containing domestic waste through a clarifier or a coarse filtration device to remove some of the materials and clarify said wastewater, without the essential addition of chemicals; b. said clarified wastewater is passed without an essential addition of chemicals into a granular media filter in a filtration vessel to a drainage cavity from below to obtain a filtrate containing less than 40% of the suspended solids present in said untreated wastewater; c. intermittently air is passed upwardly through the granular medium to reduce flow resistance through the medium and inhibit anaerobic biological activity therein, without destroying the integrity of the filtration medium; and D. intermittently washing said filter with a portion of said filtrate and a surfactant   and / or oxidizing agent to remove accumulated harmful materials.   A method of treating wastewater for the removal of suspended and / or colloidal materials, optionally comprising fats and oils, from previously untreated wastewater containing domestic waste, characterized in that: at. passing said wastewater containing domestic waste through a clarifier or a coarse filtration device to remove some of the materials and clarify said wastewater, without the essential addition of chemicals; b. said clarified wastewater is passed without an essential addition of chemicals, through a first granular medium filter into a first filter tank to obtain a primary filtrate c. passing said primary filtrate without substantially adding chemicals through a second granular medium filter into a second filter tank to obtain a secondary filtrate containing less than 25% of the suspended solids present in said untreated wastewater; d. intermittent air is passed upward through the granular medium of each filter to reduce flow resistance through the medium and inhibit anaerobic biological activity therein, without destroying the integrity of the medium of the medium. filtration; e. intermittently washing said first filter with a portion of the primary filtrate and a surfactant and / or oxidizing agent to remove the harmful materials; and F. we wash back. intermittently said second filter with a portion of the secondary filtrate and a surfactant and / or oxidant to remove the materials harmful.   A method of treating wastewater for the removal of suspended and / or colloidal materials, optionally comprising fats and oils, from previously untreated wastewater containing domestic waste, characterized in that: a . passing said wastewater containing domestic waste through a clarifier or a coarse filtration device to remove some of the materials and clarify said wastewater, without the essential addition of chemicals; b. passing said clarified wastewater without substantially adding chemicals through a first granular medium filter into a first filtration vessel to a first drainage cavity to obtain a primary filtrate; c. a coagulation chemical is rapidly mixed with said primary filtrate and the filtrate is passed without a coagulation step through a second granular medium filter in a second filtration vessel to a second drainage cavity to obtain a secondary filtrate containing less than 10% of suspended solids present in said untreated wastewater d. intermittent air is passed upward through the granular medium of each filter to reduce flow resistance through the medium and inhibit anaerobic biological activity therein, without destroying the integrity of the medium of the medium. filtration; e. intermittently washing said first filter with a portion of said primary filtrate and a surfactant and / or oxidizing agent to remove accumulated harmful materials; and F. said second filter is intermittently backwashed with a portion of said secondary filtrate and a surfactant and / or oxidant to remove the materials harmful accumulated.   4. Sewage treatment process for the removal of suspended and / or colloidal materials, possibly including fats and oils, and reduced forms of nitrogen from previously untreated sewage containing waste domestic, characterized in that a. said waste water containing domestic waste is passed through a clarifier or a coarse filtration device to remove some of the materials and to clarify said wastewater without the essential addition of chemicals; b. clarified wastewater is passed without a substantial addition of chemicals, through a first granular medium filter into a first filtration vessel to a first drainage cavity to obtain a primary filtrate; c. said primary filtrate is passed through a fixed medium filter where nitrifying microorganisms develop on said fixed media, to oxidize the nitrogen contained in the primary filtrate to nitrate and nitrite; d. the primary nitrified filtrate is passed through a second granular medium filter into a second filtration vessel to a second drainage cavity to obtain a secondary filtrate containing less than 20 mg / l of suspended solids and a lower BOD5 at 20 mg / l; e. intermittent and ascending air is passed through each granular medium to reduce flow resistance through the media and inhibit the biological activity therein. f. intermittently washing said first filter with a portion of said primary filtrate and a surfactant and / or oxidizing agent to remove the accumulated harmful materials; g. said second filter is intermittently back-washed with a portion of said secondary filtrate and a surfactant and / or oxidant to remove the materials harmful accumulated.   5. Wastewater treatment process according to one   any of claims 1 to 4, characterized in that   the upward circulation of air through the granular medium is caused by the rise of the filtrate in said   drainage cavity, which moves the air upward.   6. Wastewater treatment process according to one   any of claims 1 to 5, which includes the passage   said filtrate of step (b) having a markedly reduced potential for producing new cellular materials, at an aerobic biological treatment step o materials   Biological solids are contacted with said filtrate.   7. A method of treating wastewater according to claim 6, characterized in that said aerobic biological treatment step comprises a passage on a trickle filter without recycling the filter effluent. runoff.   8. Process according to any one of the claims   1 to 7, characterized in that said surfactant is added to said portion of the filtrate with which the filter is backwashed, and said oxidizing agent is injected into a stream of said filtrate just before, at or just after the   passage of said filtrate in the granular medium.   9. A granular medium filtration apparatus for removing suspended and / or colloidal materials, including fats and oils, from wastewater, characterized in that it comprises: a first filtration vessel having a bottom wall and side walls; a first particulate material filtration bed proximate said bottom wall of said first filtration vessel and having a top surface; wastewater inlet means; a drainage cavity located below and generally having the same area as said first filtration bed; means for discharging said filtered wastewater drainage cavity after said filtered wastewater has passed through said first bed; a second filter vessel smaller than said first filter vessel, having a bottom wall and side walls, located in said first filter vessel above said first filter bed; a second particulate material filtration bed near said bottom wall of the second filtration vessel and having an upper surface; a second drainage cavity below said second filtration bed and generally of the same area as this bed; means for evacuating said filtered wastewater from said second drainage cavity after said wastewater has passed through said second bed; a filtrate tank for receiving and retaining a portion of filtered wastewater discharged from said first and second drainage cavities; a pump for back-washing the two filter beds, separately or simultaneously, with the filtered wastewater from said filtrate tank, to clean said filter beds and to put the harmful materials in suspension in the filtered backwash waste water above the two beds;   pipes intended to remove said water -   filtered backwash from above the filter beds to a separate treatment step; pipes for removing excess unfiltered wastewater from above the filter beds to a wastewater discharge chamber prior to initiation of said backwashing; and pumps for returning said unfiltered wastewater in excess of said wastewater discharge chamber to said wastewater inlet means for are filtered.   Underground drainage structure for carrying a filter screen of a granular medium filter bed, said structure being located above a drainage cavity at the bottom of a filter chamber, characterized in that it comprises: an array of transversely extending and horizontally spaced bars for carrying said screen, an oxidizer chamber formed of an upper plate and a lower plate, generally of the same area as said array of bars and carrying said array of bars, said plates being separated in parallel by a plurality of non-limiting spacers, uniformly spaced sleeves extending vertically through said upper and lower plates to allow upward or downward flow of liquid or gas , uniformly spaced air distribution chambers having open bottom ends and ex upper trenches generally closed by said lower plate, means for injecting one or more oxidants comprising air, oxygen, ozone or another gaseous oxidant or a solution of hydrogen peroxide or a halogenated compound, in said oxidant chamber, and means for passing said oxidant from the oxidant chamber into said upward flow of liquid immediately prior to its passage through   said sieve and in the filter bed.