CH647742A5 - WASTEWATER TREATMENT PROCESS. - Google Patents

Description

The present invention relates to a wastewater treatment method and an apparatus for carrying out this method.

The object of the present invention is to propose an advantageous process for treating waste water which improves the separation, the concentration and the treatment of colloidal and poorly settable solid materials, by filtration on fine sand, thereby increasing the energy formation potential. of the treatment process and reducing or eliminating subsequent requirements for biological treatment. The present invention aims to reduce the investments and energy costs required.

Solids in wastewater can be suspended or dissolved. They can be filterable or not wire-traceable, volatile or inert, and can be biodegradable or not. These solids, along with the fats and oils typically found in wastewater, generally represent the most significant pollutants, and it is these noxious materials that must be removed or treated during the wastewater treatment process.

The particle size range of suspended solids is 10-8 n at 100 µm and above. In general, solids of 10 n and more are settling and can be removed by gravity separation. Solids between 10-3 dd. and 10 (x do not normally settle and generally require coagulation and flocculation for their removal. Solids of 10 - 3 n and smaller are generally considered to be dissolved solids.

Most biological wastewater treatment devices and methods are designed to allow the separation of large insoluble particles and the treatment of particles that do not settle. A large number of these devices are subjected to random performances due to the lack of flexibility in general of the prior separation process, that is to say the clarification and / or the primary filtering.

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

Suspended and colloidal solids not separated by filtering or clarification must further be processed by one or more biological systems to meet 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 of the activated sludge process, and modifications of fixed microorganisms from the trickle filter process. These systems can range from fairly simple 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 investment and energy costs.

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

This reduction in charge reduces the amount required for biological processes. Physico-chemical processes, which have been recommended for the treatment of wastewater, generally envisage the addition of a coagulant and the flocculation of the particles in suspension. 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 by adsorption on carbon.

However, the addition of a chemical flocculant and / or a coagulant increases the price of chemicals and creates very significant problems, in some cases, far more than the benefits obtained by reducing the suspended solids discharged into the biological system.

The precipitation of the coagulant forms a chemical mud which can be very difficult and very expensive to treat and dehydrate. In addition, chemical sludge generally affects the formation of sludge gases.

Organic materials treated biologically 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 therefore must be carefully separated and treated in a way that does not affect the environment. Therefore, in most biological systems, the activated sludge or the humus from the trickle filters, both consisting mainly of new cellular materials, must be separated from the wastewater. This is usually done by secondary clarifiers. The settled sludge can be returned to a digester for further biological reduction. The digested sludge is finally drawn off and dewatered by various means. Digestion, dehydration and the final processing of new cellular materials are difficult and costly processes.

Granular media filters are commonly used to remove suspended solids from wastewater after other treatment steps. Such a filter effectively used in such applications is described in US patent Reissue No. 28458, issued July 1, 1975. Improvements are described in US Patents No. 3817378, issued June 18, 1974 and No. 3840117, issued October 8, 1974.

An effective method and apparatus for cleaning fats and oils from the media constituting the granular media filters is described in US Patent No. 4032443, issued June 28, 1977.

An apparatus and method for separating and concentrating solids from the filter wash liquid is described in US Patent No. 3,792,773.

Previous attempts to treat wastewater without the addition of coagulants, either before the first clarifier or separator or at the inlet of the granular filtering medium itself, have been negative for various reasons, in particular:

- excessive accumulation of fat in the granular medium obstructing the flow of waste water. According to the state of the art, it was necessary to remove most of the fat before filtration by treatment with chemicals and mechanical action;

- rapid filter blockage due to a high load of solids. The high frequency of back washing required results in an insufficient volume yield of the purification process;

- low solids removal rate. Attempts to avoid clogging of the filters by the use of coarser particle size have resulted in the passage of more solids which are otherwise filterable. In addition, a considerable part of the fats and oils has passed the filter.

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In addition, anaerobic biological activity in the filter medium has sometimes caused its obstruction and / or a higher COD of the filtrate, and bad odors.

The present invention takes necessary measures in order to obtain an economical, efficient and rapid treatment of such waste water. In addition, coagulation chemicals and, in general, the problems resulting from their use are generally avoided completely.

The present invention seeks to eliminate many of the disadvantages of conventional wastewater treatment systems, by removing and collecting organic matter from wastewater containing domestic sewers, without using chemical coagulants. A significant improvement is the additional energy potential of the increased amount of chemical-free primary sludge. Another important advantage is a corresponding reduction in the production of new cellular materials in the factory.

The present invention is a process for treating waste water containing household waste for the removal of suspended and / or colloidal matter, containing fats and oils, comprising the following steps:

- passing said wastewater containing domestic sewers through a clarifier or filtration device to remove some of the materials and clarifying said wastewater, without the addition of coagulating chemicals;

- passing the clarified wastewater through a granular medium filter into a filtration tank to collect a filtrate in a drainage cavity containing less than 40% of the suspended solids present in the untreated wastewater;

- intermittently passing air upwardly through the granular medium to reduce the resistance to flow through the medium and inhibit anaerobic biological activity there, without disturbing the integrity of the filtration medium, and

- intermittently washing back said filter with a portion of said filtrate and a surfactant and / or an oxidizing agent to remove accumulated harmful materials.

Thus, the wastewater containing domestic sewers from a device such as a filter, a sieve and / or a primary clarifier, passes through a granular medium filter without prior biological, chemical or physico-chemical treatment. Alternatively, the solid matter removal device can also be completely eliminated; the wastewater passes directly to the inlet of the filter and the non-decantable and colloidal solids are trapped by the filtration medium and adsorbed by the surface of the filtration medium.

The efficiency of the removal of these non-settling solids depends on the application rate and the physical characteristics of the medium, typically sand. In general, at least 60% of the suspended matter is removed by a single filter. The solids are allowed to accumulate in the filtration medium until the resistance through the filtration medium causes the water level above the medium to reach a predetermined value, at which time the filter is washed back filter, and harmful materials previously trapped and adsorbed are removed and washed from the medium.

An improvement in the interception and conservation of colloidal and suspended matter is also obtained, by periodic reduction of the resistance of the filtration medium, in the mass and at the surface, by passing air through the medium so ascending and intermittently, to improve porosity and delay anaerobic decomposition. This air is moved upward by the rise of the filtrate in the drainage cavity and the movement of the air. The upward movement of air is sufficient to move the noxious materials inside the filtration bed where these materials are temporarily stored, without destroying the integrity of the filtration medium.

For backwashing, vertical hydraulic jets can be used intermittently with air to provide high speed agitation and medium movement at a variable rate of sub-fluidization to improve the efficiency of the washing system back and use a minimum amount of backwash water.

The washing water in return can be directed to a holding tank where the previously non-decantable particles, now in the washing water, agglomerate and settle. Greases and oils are also allowed to agglomerate for skimming. The settled solids are allowed to generally concentrate without the addition of chemicals. The solids washed back are pumped to a digester for anaerobic stabilization of organic matter, and biological formation of a combustible gas comprising methane and carbon dioxide.

Clarified wash water can be returned to the filter inlet for re-filtration and, under certain conditions, can be directed to a stream or receiving body of water such as a lake, river, ocean , etc.

The pollution characteristics of the filtrate are reduced by the removal of colloidal and non-settling solids present in the clarified wastewater.

Oxygen can be added to the liquid mass by collision, diffusion and impulse through the filter medium, to minimize the normal oxygen deficiency of the clarified waste and the contrary anaerobic conditions in the medium and the liquid filter mass.

An improved medium regeneration cycle can remove fats, oils and biosubstances attached to the medium surface 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 is used, such as hydrogen peroxide, an oxygen-containing gas or liquid, or ozone, with or without detergent or surfactant, thus avoiding the creation of chlorinated hydrocarbons.

By staging the filtration process, the amount of uncanted, colloidal solids removed from the liquid waste can be increased. 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 generally be discharged directly into a watercourse, without any other biological treatment.

By using very small amounts of coagulant between the stages of filtration processes, it is possible to further reduce very fine solids which will neither be trapped nor adsorbed on the surface of the medium. The coagulation chemical is quickly mixed with the primary filtrate and passes to the second filter without a flocculation step. Such a process typically gives a secondary filtrate containing less than 20 mg / 1 of suspended solids and may contain less BOD than that normally attributed to secondary processes. The first stage filter removes the largest portion of the solids, and only very small amounts of coagulant are required in the second stage or stage. Thus, the effect of this chemical on the subsequent treatment of sludge is negligible.

By using a filter, excess flow can be treated, which can harm an existing biological device or one of fixed design, by diverting excess flow outside the biological device via of a fine media filter, and sufficient amounts of suspended solids can be removed from this derived wastewater, as well as biologically treated wastewater. This allows filtration of treated and untreated wastewater to meet the effluent requirements. The efficiency of the biological process is maintained. The biological process is protected against hydraulic overload and the overall characteristics are therefore ensured.

The combination of two-stage filtration in a single container allows varying pressure conditions relative to the flow quantities, the container accepting an extremely high portion of the flows through coarser filtration media.

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The two-stage filter allows the use of more than one dimension of sand and variable application rates for a given filtration load.

The vertical walls of the filtration tank can be cleaned automatically during a backwash. A cleaning agent such as a detergent and oxidizing agent, or a surfactant and an oxidizing agent, can be added to the wash water in return to better clean the walls. The addition of the cleaning agent can be adjusted manually or automatically. A non-halogenated oxidizing agent is preferred.

By adding an oxidizing or sterilizing liquid to the washing liquid at the end of the washing cycle, the growth of bio-organisms can be reduced. This sterilization or oxidation liquid will also cause oxidation, emulsification or removal of organic substances previously fixed on the surfaces of the medium resulting from the filtration of clarified wastewater on the medium with fine sand. The media surfaces are effectively used to adsorb some of the organic components that make up soluble BOD.

We can minimize the harmful effect of colloidal and suspended particles which clog the pores of activated carbon and coat the surfaces of carbon with organic surfaces, which limits the effective use of activated carbon.

The drainage from below can distribute the oxidation or sterilization liquid in the filtration medium without premature mixing with the washing liquid in return and the detergent or surfactant.

The method according to the invention and the apparatus for its implementation will be described, by way of example, with reference to the attached drawing,

in which:

fig. 1 is a diagram of a conventional wastewater treatment installation, using as main elements a primary clarifier, a biological treatment device, a final clarifier and a sludge digester;

fig. 2 is a diagram of the preferred embodiment of the invention, illustrating the numerous processing possibilities;

fig. 3 is a diagram of the invention combined with a biological treatment;

fig. 4 is a diagram of the invention combined with a device for biological treatment followed by a second filter;

fig. 5 is a diagram of a physico-chemical treatment process placed between two filters;

fig. 6 is a schematic application of the invention to a wastewater treatment device, subject to large variations in the tributary flows, illustrating the treatment solutions for derived flows;

fig. 7 is a sectional view of the apparatus of the invention used to treat derived flows;

fig. 8 is a sectional view of the apparatus of the invention showing the wall washing device and the pulsed bed system;

fig. 9 is a sectional view of the drainage support from below;

fig. 10 is a sectional view of an outlet nozzle of the drainage support from below;

fig. 11 is a sectional view of another possibility of a nozzle detail of the drainage support from below.

The reductions in total biochemical oxygen demand (BOD) of suspended solids and soluble BOD of domestic wastewater clarified by parallel filters with granular media are illustrated in Table I, where the filters used are consistent granular media in quartz having an effective dimension of respectively 0.35 or 0.45 mm, a sand thickness of 25.4 cm and application rates of 80 l / min / m2.

(Table at the top of the next column)

A significant factor generally overlooked in the design and development of wastewater treatment devices is that the bulk of the organic pollution load of wastewater, represented by theoretical oxygen demand (DTO), chemical demand oxygen (COD) or biochemical demand

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Table I

Tributary

Filter No. l,

Filter N ° 2,

of the effluent filter effluent

Sand dimensions (mm)

0.35

0.45

Suspended solids

sion (mg / ml)

81.3

20.8

25.7

Removal efficiency (%)

(74.6)

(68.6)

FTU turbidity

46

23

24

Total DB05 (mg / 1)

131.5

49.0

53.9

Removal efficiency (%)

(62.7)

(59.0)

DB05 soluble (mg / 1)

35.3

23.3

24.9

Removal efficiency (%)

(34.0)

(29.3)

Travel time

mean on filter (h)

3.0

6.0

Wash water /

filtrate (1/1)

0.168

0.088

oxygen (BOD) is contained in suspended solids and colloidal non-decantable. Such solids are present in domestic sewers. For example, the wastewater solids which have been separated by dimensions have the organic impact indicated in Table II. At the start, 66% of the organic pollution load is contained in suspended solids with a particle size of 8 (i and smaller, as measured by COD. It is generally considered that suspended solids of 8 | i and lower are not decantable by themselves.

The significance of the pollutant load of clarified or decanted wastewater can also be illustrated by an analysis of the size and weight of a sample of clarified wastewater. The sample used in Table II comes from the wastewater treatment plant in Lorain, Ohio, USA, and is not atypical of clarified wastewater containing domestic discharges. The wastewater sample was then gradually filtered through increasingly small pore filter membranes. The quantity 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 / 1; COD 182 mg / 1

Dimension of

Solids in

COD crossing filter pores total suspension the filter

retained by the filter

(M)

(mg / 1)

(mg / 1)

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 by filtration on fine sand is very significant and becomes even more substantial at lower hydraulic application rates. For example, tests have shown that the reduction in soluble BOD ranges from a high value of 34% reduction to a low value of 5.6%. Soluble BOD is a definition rather than a true description. It is calculated that the colloidal particles which can pass through a 0.45 µm filter are part of the soluble fraction and are measured as soluble BOD.

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A substantial amount of the colloidal material passing through a 0.45 n filter membrane will settle and be adsorbed on the surface of the grains of a granular medium filter. Some of the organic compounds in the solution are also quickly biologically transformed into biomass when the wastewater passes through a granular bed. The quantity removed depends on the application rate and the size and thickness of the sand. Table III, describing a specific series of tests, shows the efficiency of the removal of soluble BOD according to the present invention.

Therefore, filtration in a single stage or in several stages not only removes the measurable non-settling solids, but materially reduces the soluble fraction of the organic load.

Table III Reduction of soluble BODs (%)

Debit

0.35mm

0.45mm

80 1 / min / m2

34

29.5

2001 / min / m2

18.3

15

3201 / min / m2

7.2

5.6

Let us now consider the drawings which are given by way of illustration of the preferred embodiments of the invention and not by way of limitation.

Consider fig. 1 which represents a conventional biological treatment process for wastewater. The raw sewage inlet pipe 10 is directed to a coarse holding device 20, and via a pipe 11, into the primary settling tank or clarifier 100. The clarified liquid is directed through the pipe 110 to the biological treatment 400, where the wastewater is treated biologically, forming new cellular materials, and is directed via line 410 to the final settling tank 500. A major proportion of the solid matter constituting the sludge is decanted in the clarifier 500 and withdrawn via line 520. Part of the sludge is recycled to biological treatment via line 521. The excess sludge, or rejected sludge, is then mixed with the sludge which has been withdrawn from the primary clarifier 100 via line 120 and the mixture of rejected sludge and primary sludge is directed via line 121 to digester 800 where the sludge is still treated, and part of the organic matter is transformed 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 line 121.

Fig. 2 shows a diagram of the apparatus according to the present invention, where a filtering system 200 is placed after the settling tank or primary clarifier 100. The wastewater treatment system comprises a wastewater inlet pipe 10, where the wastewater is directed to the grinding and / or coarse filtration device 20, then is directed through line 11 to a primary clarifier 100. The clarified effluent leaves the primary clarifier 100 through line 110 and goes to the filter inlet 200.

As shown in fig. 2, the filtrate from line 210 is directed to one or more subsequent treatment elements, such as a biological treatment, which may be of the type with suspended microorganisms or fixed microorganisms. Alternatively, filtration may be followed by second stage filtration and then treated with activated carbon or 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 possible second stage filtration depends on the quality of the wastewater and the distribution of the particle size, as well as the legal requirements for the discharged water. In many cases, the load on the biological system is so reduced that sufficient biological treatment is obtained, for example in a trickle filter without any recycling.

Another embodiment of this invention is a wastewater treatment process for removing suspended and colloidal materials, comprising fats and oils, protein compounds and ammoniacal nitrogen from previously untreated wastewater. containing household waste, consisting of:

a) passing said waste water containing household waste through a clarifying or filtering device to remove part of the materials and clarifying said waste water, without adding chemicals;

b) passing the clarified wastewater, without the addition of chemicals, over a first granular filter in a first filtration tank to a first drainage cavity from below to give a primary filtrate;

c) passing said primary filtrate through a filter with fixed media, such as a trickle filter, where nitrifying microorganisms develop on said fixed media to oxidize said nitrogen contained in the primary filtrate to nitrate and nitrite;

d) passing the primary nitrified filtrate through a second granular medium filter in a second filtration tank to a second drainage cavity from below to produce a secondary filtrate containing less than 20 mg / 1 of suspended solids and less 20 mg / 1 of BODs;

e) intermittently passing air upwardly through each granular medium to reduce resistance to flow through the media and to inhibit anaerobic biological activity therein;

0 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) intermittently washing back said second filter with a portion of said secondary filtrate and a surfactant and / or an oxidizing agent to remove accumulated harmful materials.

This treatment easily produces a secondary filtrate containing less than 20 mg / 1 of suspended solids and less than 20 mg / 1 of BODs, even when the fixed media filter operates at a flow rate equal to or greater than 13.61 / min / m2, without any recycling.

The secondary filtrate will contain less than 1.5 mg / 1 of ammoniacal nitrogen if the temperature of the wastewater exceeds 20 ° C.

The washing water in return from the filter 200 is discharged through line 220 to the clarifier 300, where the solids washed in return settle, and the supernatant liquor from the clarifier is returned to the inlet of the filter 200 through line 310 and the inlet pipe of the filter 110. The quality of the supernatant liquor can be improved by adding coagulation chemicals. The clarified sludge from the clarifier 300 is withdrawn via line 320 and directed to the sludge evacuation pipe 122 which transports the sludge from the primary clarifier 100 through line 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 size of the grains used in the filter 200. The quality of the filtrate can also be improved by a series of possible subsequent treatments, according to the requirements concerning the quality of the final water.

The energy requirements for the further treatment of the clarified wastewater will be materially reduced as a result of the reduction in the organic pollution load of the clarified wastewater which the filter 200 gives.

In addition, the sludge created by the solids concentrated in the washing water of the filter 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 only in the filter 200. The fact that no coagulant is added to the inlet of either the primary settling tank or the filter, ensures that the total sludge withdrawn will contain a minimum of treatment chemicals.

It is known that anaerobic biological production of combustible methane from sludge or wastewater is easier and

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more efficiently when the ratio of primary biological sludge to secondary biological sludge is high. This invention provides increased amounts of primary solids and significantly reduced amounts of secondary solids.

For example, typical household wastewater contains 160 mg / 1 of suspended solids, half of which is removed by simple primary treatment without chemicals.

Clarified wastewater typically has the following analysis:

Solids in suspension 80 mg / 1

BODs 130 mg / 1

In a conventional treatment, the clarified wastewater is subjected to an activated sludge treatment to meet government requirements on secondary effluents. Approximately 70 mg / 1 of organic sludge solids will be produced. Biological solids thus comprise almost half of the total solids load which is normally anaerobically digested.

In the present invention, the clarified wastewater is filtered through a granular filter to meet secondary standards, which replaces the biological step which has high equipment and operating costs.

In addition, no solid biological treatment material passes through the anaerobic digester; therefore gas production and reduction of solids as well as subsequent dehydration of solids are all improved.

When the biological treatment stage is preceded by filtration on a granular medium, the significantly reduced quantity of new cellular materials gives better operating characteristics of the digester.

Always consider fig. 2; line 151 after the second stage filtration can direct the filtrate to an apparatus for contacting activated carbon. The filtrate can also be treated in a biological device, even better indicated in FIG. 3, or discharged into a stream of water or reused. Alternatively, the second stage filtration can be omitted and the first stage filtrate can be directed to the various processes mentioned.

An important advantage of the invention is the reduction by the filter 200 of the organic pollution charge directed to all the subsequent treatment devices, which reduces the energy and investment requirements.

Now consider fig. 3; there is illustrated the same type of secondary biological process as in FIG. 1, the secondary treatment process now being modified by the use of a filter installed in the pipe 110 of the clarified effluent. The filtrate contained in the outlet pipe 210 requires a markedly reduced biological treatment. The biologically treated wastewater can be directed to a final decanter or clarifier 500, or directed to a subsequent filter 799, as shown in FIG. 4, then to the contact tank with chlorine 600.

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

The organic load brought to the biological process is reduced due to the greater removal of organic solids. Depending on the application and the dimensions of the medium, the residual organic charge brought to the biological process can be reduced to the point that new cell growth can be effectively intercepted by a second filter which is generally of the same type as that used in filter 200, 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 input of the biological process 400 through line 721, as shown in fig. 4. The excess solid matter rejected is then discharged into the return washing separator 300 via line 722.

The growth potential of new cellular material was limited by the reduction of suspended and non-settling matter carried out by filtration on granular medium. The growth of the new cells is proportional to the organic load in the wastewater entering the biological process via line 210.

For example, assuming a rate of new cell growth of 0.4 kg of new cells per kilo of BOD removed, a filtrate residue containing 50 mg / 1 of BODs will give only 20 mg / 1 of new cells. Wastewater containing suspended solids levels below 30 mg / l solids and corresponding values of biochemical oxygen demand can be classified as a secondary effluent. In case suspended solids exceed the requirements for the particular watercourse, a second filter can be added, and the 20 mg / 1 of new cells can easily be separated by filter 700, and the filtrate passing through line 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, further treatment may not be necessary.

Now consider fig. 5; the decanted primary effluent is directed to the first stage filter 200 and the filtrate directed through the line 210 to the mixing chamber 30 where very low concentrations of coagulant coming from the container 40 are pumped into the mixing chamber 30 through the line 50. Coagulant is mixed in mixing chamber 30 with the first stage filtrate from filter 200 and the coagulant / filtrate mixture is discharged onto filter 700 through line 211, without a flocculation step. The coagulant / filtrate mixture is then filtered by the filter 700, and the second stage filtrate is discharged through line 710. The washing liquid returning from the first stage filter 200 is discharged into the holding tank 300 of the washing water via line 220, and the washing water from the filter 700 is also directed to the same device for separating washing solids, via line 720. The decanted sludge in the container 300 is discharged through line 320 and mixed with the sludge removed from the primary container 100 via the line 120, and all of the combined sludge is directed towards the digester 800 via the line 123.

The effluent from line 710 can then optionally be treated in various ways, depending on the requirements of the use or final discharge of the treated wastewater. The water which is re-filtered can be directed as shown in fig. 2 to a full series of other 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 high quality effluent. The limitation will obviously be the soluble constituents which are not removed by filtration. The wastewater effluent, from which the suspended solids and the colloidal solids were removed by filtration, is easily contacted with activated carbon for the absorption of residual organic matter. This type of pretreatment can effectively save significant space and energy 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 giving similar characteristics.

Now consider fig. 6; the primary filtration solution can be most satisfactorily applied to wastewater treatment devices which are subject to extremely high flow variations, such as during heavy rain, where existing biological processes are threatened by hydraulic overload . The inlet pipe 10 represents the wastewater inlet pipe, comprising variable volumes

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rainwater passing through a grinding or filtration device 20, then through an alternate flow bypass chamber and a barrier 60 of the excess flow to go into the primary settling chamber 100. L clarified effluent from line 110 is directed to the hydraulic adjustment chamber 80, where the excess flow from the first stage will be diverted from biological treatment 400 and the final clarifier to arrive in line 510 which is the inlet of filter 200 The washing water in return is directed from the filter 200 to the line 220 and to the settling tank 300. The supernatant liquor from the settling container 300 is returned to the line 510 via the line 310. The sludge the settled water is returned via line 320 and mixed with the decanted sludge from the clarifier 100 via line 120 and directed for further treatment via line 124 to a digester or u n other sludge treatment device.

Excess flows are directed away from the treatment to protect the integrity of this biological treatment and prevent its disturbance by hydraulic shock, and to further reduce the biochemical oxygen demand of the bypass flow passing through line 90 by the action of filter 200, so as to reduce the content of suspended solids.

Excess flows can also be derived away from the primary clarifier 100, in the event that the design indicates that the maximum hydraulic conditions of the clarifier 100 would be exceeded. We can therefore provide a bypass chamber 60 upstream of the primary clarifier 100, and flows beyond the design values can be directed through line 70 in a bypass line 91 to line 510 leading to the filter 200 to improve still their quality due to 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 when the tributary volumes change due to the impact of heavy rain water flows and dry weather flows. During dry periods, when the wastewater flows are weak, the residence times of the solid materials in the sewer pipes are relatively long, resulting in considerable solubilization of the polluting materials. The BOD of wastewater is high.

In addition, high water levels during wet periods quickly sweep the sewer lines. The wastewater is not only diluted with additional water, but is cooler: for example, there has been less solubilization.

While high flows interfere with the operation of conventional biological treatment devices, pollutants in such high-flow wastewater are more subject to removal by filtration through granular media than are pollutants in low-flow wastewater . As a result, diverting excessive wastewater flows away from the biological treatment devices and to a granular media filter will maintain a high level of biological treatment while providing a high level of filtration treatment to the excessive flows. The result is a very acceptable effluent at a time when the quality of the effluent is normally deteriorated.

In another embodiment, the filter with a granular medium completely passed through in FIG. 7 allows effective and efficient treatment of wastewater at highly variable flow rates. The treated and derived tributary flows are directed to the filtration container 200 through line 510, as previously described in FIG. 6. A flow indicator 530 placed in line 510 signals the amount of flow going to the filter. Within predetermined limits and at lower values of the interval, 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 200 with a low hydraulic load on the filter media 250. When the flows increase, the flow meter 530 then signals to the valve 512 to be close and at valve 514

to open, and will allow the water level to enter the filter 200 at a higher point.

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

Let us still consider fig. 7; the return wash trough 260 is located above the filter sand 250 and before the return wash, the water level 240 is lowered at the weir 262 of the return wash trough. In the prior art, this volume of water above the weir 262 is added to the volume of washing water in return, which increases the amount of washing water to be treated.

When the water level in operation is modified as determined by the flow indicator up to level 242 or 244 or up to intermediate levels, the volume of water discharged is obviously increased.

The arrangement of the filtration cell 200A completely inside the filter 200 reduces the volume of water above the filtration bed 150 without reducing the efficiency of the filtration system. The volume of wasted water is thus reduced.

The discharge of the volume of water passing over the weir 262 into a separate discharge chamber 270 before the start-up of the return washing pump 222 significantly reduces the volume of washing water to be treated. The sequence of the washing back operation is initiated by a washing request signal from the level detector 352, 354 and 356 according to the appropriate water level 240, 242 or 244, this level being determined by the signal coming from the flow indicator 530. Under the action of the signal, the valve 277 opens and lets the mass of liquid above the overflow 262 drain through the line 266 to the discharge chamber of the waste water 270 where the total volume of the liquid located above the weir 262 is now retained. After draining the liquid mass located above the weir 262, as shown by a signal from a timer device, the valve 277 is closed and the valve 278 is open, the return wash pump 222 is started , the valve 226 is open, 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. The washing liquid is then directed to the reservoir for retaining the washing liquids 290 and can then be treated as described in US Patent No. 3792773. The volume of liquid now retained in the reservoir 270 is pumped into the filter 200 by the pump 272 after stopping of the pump 222, closing of the valve 226 and opening of the valve 225, and the filtrate of the filter 200 is again directed towards the clean well 280 for retaining the filtrate.

The volume of liquid above weir 262 contains less solids than the backwash liquid. Mixing these volumes increases the total liquid volume and increases the cost of processing this liquid volume by diluting the backwash mixture. This dilution reduces the ability of the mixture to reach the autoflocculation point without the addition of chemicals. Self-flocculation or self-agglomeration is much easier with an increased concentration of solids. The discharge of water located at the head of the filtration chamber, as shown forming part of the filtration system of FIG. 7, can be used independently. This aspect of the reduced volume of the overhead water gives an improvement in operating costs and operating efficiency5

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in any filtration system where volumes of water are kept above the level of the backwashing weir.

By modifying the pipes, this filter can also be used to treat wastewater 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 granules thinner.

Now consider fig. 8; it illustrates another characteristic of the filter 200. A perimeter washing ring 226 is placed at the level of the upper wall of the filter 200, nozzles 228 being placed so as to clean the walls of the filter 200. A line 224 for supplying the wash ring communicates with the return wash pump 222 and the chemical supply pump 262 via line 266. A special cleaning solution is used to wash 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 microorganisms can develop. Then, the lack of oxygen will cause unpleasant growths and odors. Effective wall cleaning and disinfection is necessary to improve the overall functioning of the filtration device.

Let us still consider fig. 8 and in particular the backwashing technique: air under high pressure is supplied by the pump 280, which directs it via line 282 to the static mixer 284 where it is mixed with washing water in return. This mixture is injected into the drainage cavity from below 108.

The air intermittently introduced into the static mixer 284 causes additional agitation of the medium 250, due to the vertical rinsing jets drawn 292 from the drainage system from below. Thus, backwashing more thoroughly cleans the medium 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 sufficiently disinfect the filtration media, delaying the accumulation of biosubstances in the environment , or on the surface of the filter.

The most important problem associated with the wastewater filtration process is the adsorption and accumulation of fat films and / or colloidal oils on the surface of the middle grains. This particular problem is amplified by the high percentage of fats and colloidal oils present in the primary flows and the primary flows and rainwater combined. Contact and washing with a detergent solution or an oxidant and a surfactant effectively remove greases and colloidal oils from the surface of the grains of the medium.

We therefore seek to obtain an improvement of the drainage system from below described in US Patent No. 3,840,117, as well as an improvement of the chemical cleaning device described in US Patent No. 4032443. Cleaning cycles by products Frequent or excessive chemicals using halogenated compounds can be harmful to the functioning of a system

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the quality of the filtrate from the wastewater treatment device. Halogenated compounds such as those containing bromine or chlorine can combine with the hydrocarbons present in wastewater to form trihalomethanes which are considered to be carcinogenic. Bromoforms and chloroforms are examples of halogenated hydrocarbons which can result from the use of halogenated compounds.

Now consider figs. 9 to 11; they represent a preferred embodiment of the drainage device from below described in US Pat. No. 3,840,117, comprising a modification by adding an oxidant chamber 1000, an inlet pipe 1100 and sleeves 1200. The chamber 1000 is formed of an upper plate and a lower plate, carrying a network of horizontal bars and generally of the same dimension as these bars. The bars in turn carry the screen, and the screen carries the bed of granular medium. The plates are held in parallel by non-limiting spacers.

The uniformly spaced sleeves 1200 pass vertically through the upper and lower plates to allow an upward or downward flow of liquid or gas.

Uniformly spaced air distribution chambers 208 are open at the bottom end and closed at the top end by the bottom plate of the oxidant chamber.

A detergent, usually a linear alkylsulfonate, is introduced into the drain cavity. After introducing a predetermined quantity of the detergent into the drainage cavity, an oxidizing solution, such as hydrogen peroxide, or a gaseous oxidizing agent such as ozone, is introduced into the line 1100, into the chamber 1000, in the nozzle 1400 through the orifice 1420, and it is mixed with the detergent and filtrate solution introduced by force into the air distribution chamber 208 and through the orifice 1450. Another possible structure of the sleeves 1200 and a another possible arrangement of the orifices 1450 are shown in FIGS. 10 and 11.

Detergents or surfactants like linear alkyl 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 oxidant by mixing them just before, at the time of or just after the passage of the filtrate in the medium, still providing a uniform distribution in the middle of the mixture. This process reduces the cost of chemical cleaning by eliminating the formation of all trihalomethanes and eliminating the problems of rejecting non-biodegradable or phosphate-type detergents. The chemical cleaning device will quickly emulsify any greasy coating remaining on the grains of medium and will wash the surfaces of the grains, removing any residue of grease or oil.

Shown in fig. 9 is the final passage of air into the drainage system from below via the line 1500 and the valve 1510 operating intermittently towards the line 1100 which causes a pulsation of jets. This pulsation of jets makes it more effective to remove grease and oil films from the medium formed by the sand.

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4 sheets of drawings

Claims (10)

647742 2 1. A method of treating waste water containing household waste for the elimination of materials in suspension and / or in colloidal distribution, comprising fats and oils, characterized in that the waste water is passed without the addition of products coagulating chemicals in a coarse clarifier or filter to remove some of the said materials and clarify the waste water, the clarified waste water is passed through a granular medium filter located in a filtration tank to collect a filtrate containing in a drainage cavity less than 40% of the suspended solids present in the untreated wastewater, air is intermittently passed from bottom to top through the granular medium to reduce the resistance to flow through the medium and inhibit anaerobic biological activity without disturbing the integrity of the filter medium and the filter is washed intermittently using a p part of the filtrate and a surfactant and / or oxidizing agent to remove accumulated harmful materials. 2. Method according to claim 1, characterized in that the clarified waste water is passed without the addition of coagulating chemicals through a first granular medium filter in a first filtration tank to obtain a primary filtrate, this is passed primary filtrate through a second granular medium filter in a second filtration tank to obtain a secondary filtrate containing less than 25% of the solids in suspension compared to those present in untreated wastewater, air is passed intermittently from bottom to top through the granular medium of each filter to reduce resistance to flow through the medium and inhibit anaerobic biological activity there, without disturbing the integrity of the filtration medium, washed back intermittently the first filter with a portion of the primary filtrate and a surfactant and / or oxidizing agent to remove harmful materials, and washed back intermittently the second filter with a portion of the secondary filtrate and a surfactant and / or oxidizing agent to remove harmful materials. 3. Method according to claim 2, characterized in that a coagulation chemical is mixed with the primary filtrate and this filtrate is passed without coagulation step through a second filter with granular medium in a second filtration tank to a second drainage cavity to obtain a secondary filtrate containing less than 10% of the solids in suspension compared to the solids present in the untreated wastewater. 4. Method according to claim 2, the wastewater comprising in addition reduced forms of nitrogen, characterized in that the primary filtrate is passed through a fixed medium filter where nitrifying microorganisms develop on the fixed medium , to oxidize the nitrogen contained in the primary filtrate to nitrate and nitrite, and the primary nitrified filtrate is passed through a second granular medium filter in a second filtration tank to a second drainage cavity to obtain a filtrate secondary containing less than 20 mg / 1 of suspended solids and a BOD less than 20 mg / 1. 5. Method according to one 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 the drainage cavity, which moves the air upwards . 6. Method according to one of claims 1 to 5, characterized in that it comprises passing the filtrate having a reduced potential for the production of new cellular materials, to a step of aerobic biological treatment where biological solid materials are brought into contact with the filtrate. 7. Method according to claim 6, characterized in that the aerobic biological treatment comprises passing over a trickling filter without recycling the effluent from the trickling filter. 8. Method according to one of claims 1 to 7, characterized in that the surfactant is added to the portion of the filtrate with which the filter is washed back, and the oxidizing agent is injected into a stream of the filtrate just before, at the time or just after the passage of the filtrate through the granular medium. 9. Apparatus for implementing the method according to one of claims 1 to 4, characterized in that it comprises: - a first filtration container (200) comprising a bottom wall and side walls; - a first filtration bed (250) of particulate materials close to the bottom wall of the first filtration container and having an upper surface; - a means for entering wastewater (510); - A drainage cavity (208) located below and having the same area as the first filtration bed (250); - a means of evacuation (233) from the drainage cavity of the filtered waste water after the filtered waste water has passed through the first bed; - a second filtration container (200A) smaller than the first filtration container, comprising a bottom wall and side walls, located in the first filtration container above the first filtration bed; - a second filtration bed (250A) of particulate materials near the bottom wall of the second filtration container (200A) and having an upper surface; - a second drainage cavity (208A) below the second filtration bed and of the same area as this bed; - Means (223A) for evacuating the filtered waste water from the second drainage cavity after the waste water has passed through the second bed; - a filtrate tank (280) intended to receive and store part of the filtered waste water discharged from the first and second drainage cavities; - a pump (222) intended to wash back the two filtration beds (250; 250A), separately or simultaneously, with the filtered waste water coming from the filtrate tank (280), to clean the filtration beds and put the materials pests suspended in filtered sewage washing back over the two beds; - lines intended to remove the filtered washing waste water back from above the filtration beds to bring them to a container of washing liquid (290); - pipes (266) intended to remove the excess of unfiltered waste water from above the filtration beds to a discharge chamber (270) of waste water before starting the return washing , and - Pumps (272) intended to return excess unfiltered wastewater from the wastewater discharge chamber to the inlet means (51 OB) of the wastewater so that it is filtered. 10. Apparatus according to claim 9, with a drainage device from below carrying a sieve for supporting a filtration bed with a granular medium and situated above a drainage cavity at the bottom of a filtration, characterized in that the device comprises: - a network of horizontally spaced transverse bars which carry the screen; - An oxidant chamber (1000) formed of an upper plate and a lower plate of the same area as the network of bars and carrying this network of bars, the plates being separated in parallel by several non-limiting spacers; - uniformly spaced sleeves (1200) extending vertically through the upper and lower plates to allow an upward or downward flow of liquid or gas, - uniformly spaced air distribution chambers (208) having open lower ends and upper ends generally closed by the lower plate; - inlet means (1100) intended to inject one or more oxidants comprising air, oxygen, ozone or another gaseous oxidant or a solution of hydrogen peroxide or of a halogenated compound, into the oxidant chamber, and 5 10 15 20 25 30 35 40 45 50 55 60 65 3 647,742 - Means (1420) for passing the oxidant from the oxidant chamber into the upward flow of liquid immediately before its passage through said screen and into the filtration bed (250).