FR2729381A1 - Treatment of effluents containing organic matter of animal origin - Google Patents

Abstract

A process for the treatment of effluents containing organic wastes comprises passing the effluent (b) through a decanting centrifuge (3) which separates liquid and solid, producing a supernatant (e) containing less than 1 g/l suspended solids and a solids stream (c) containing at least 20% dry matter. These solids can be used directly for silaging or pelleting. The supernatant is filtered in an ultrafiltration unit (7), followed by reverse osmosis (14) to produce a filtrate (m) clear enough to discharge into the environment. The flow rate of liquid (g) overflowing from the ultrafilter feed vessel (5) is equal to the flow of liquid leaving the filter (i), and that overflowing (j) from the reverse osmosis feed vessel (12) is equal to the flow rate of liquid leaving the unit (m). Also claimed is appts for carrying out the process.

Description

PROCESS AND PLANT FOR PURIFYING AN EFFUJEW
CONTAINING ORGANIC WASTE
The present invention relates to a method and an installation for purifying an effluent containing organic waste. It also relates to the application of said method to the treatment of organic animal excrement.

 The known methods of the genus in question combine physical, chemical or physicochemical purification treatments which generally consist of - a first step of liquid / solid separation of the tanning type; - a second physicchemical stage of the coagulation-flocculation type; - a third physical stage of the membrane ultra-filtration type followed by a reverse osmosis phase.

The first step is always a liquid / solid separation phase.

The second stage, which uses large quantities of chemical additives, does not allow to drop below 2 g / l of solid matter suspended in the effluent and to go over a dryness rate of the extracted solid matter 10%.

The first figure (2 g / l) leads to a high filter clogging rate in the ultrafiltration stage, therefore to more frequent cleaning and latent filter changes.

The second (1or) leads to the obligation of an additional operation of dewatering the solids extracted so as to bring this figure to a value at least equal to 20% which corresponds to the limit for good silage and shoveling of said materials.

The third step, of a conventional type, which operates on the basis of a concentration principle, also leads to a high filter clogging rate, therefore to more frequent cleaning and filter changes.

 The invention therefore aims to achieve a method, which combines only physical treatments, and an installation - eliminating the step of coarse liquid / solid separation; - replacing the physico-chemical stage (coagulation-loculation) by a stage of liquid / solid separation entirely physical, of the centrifugal decantation type, so as to save chemical additives, to reduce the rate of suspended solids (savings in the next step) and increasing the dryness rate to remove the dehydration step; - now the stage of ultra-filtration and reverse osmosis but by making it work according to a principle of non-concentration to also save on filters (cleaning and changes) in the stage in q qoe tion.

The overall economy generated with the process and the installation according to the invention compared with the known process mentioned above, is of the order of 50X per m 3 of treated effluent.

With such a process - all the solid waste extracted is recovered and can be used directly, for example as an agricultural amendment; - the permeate obtained in the final phase can be discharged directly into the natural environment or recycled (low BOD / COD content)
The subject of the invention is therefore a method for purifying an effluent containing organic waste, characterized in that it consists in implementing the following successive physical purification operations: - the effluent is subjected to an operation centrifugal decantation which allows liquid / solid separation so as to obtain, on the one hand, a filtrate which has a maximum rate of 1 g / l of suspended solids and, on the other hand, extracted solids which a dryness rate of 20% or more so as to make them directly and directly usable for silage and shoveling; - The filtrate (or centrate) thus obtained is subjected to an ultra filtration operation followed by a reverse osmosis operation so as to obtain a permeate directly and immediately disposable in the state in nature; and in that the ultra-filtration and reverse osmosis operations are carried out without the slightest concentration, in other words by automatically maintaining, on the one hand, the flow rate of the overflow of the ultra-filtration tank equal to that of the permeate leaving the corresponding filter and, on the other hand, the flow rate of the overflow of the reverse osmosis tank equal to that of the per eat leaving the corresponding filter.

The ultra-filtration operation is part of the membrane separation techniques whose transfer force is a pressure gradient.

Reverse osmosis is also part of membrane separation techniques.

The separation efficiency can be adjusted by the choice of membranes or pressures.

The method according to the invention is also characterized in that - in the ultra-filtration operation, the volume of the retentate obtained is equal to 8 times that of the permeate (or ultra-filtrate) obtained at the outlet of the corresponding filter; - in the reverse osmosis operation, the volume of the retentate obtained is equal to 8 times that of the permeate obtained at the outlet of the corresponding filter; - The volume of the permeate obtained in the reverse osmosis phase is equal to half the volume of the permeate obtained in the ultra-fitration phase.

 The subject of the invention is also an installation for purifying an effluent containing organic waste which is characterized in that it comprises in series - a liquid / solid separation means of the centrifuge type by decantation capable of providing, on the one hand, a filtrate (or centrate) which has a maximum rate of 1 g / l of suspended solids and, on the other hand, extracted solids which have a dryness rate of 20% or more so as to make them directly and immediately usable for silage and shoveling; - Ultra-filtration and reverse osmosis means capable of providing a permeate directly and immediately disposable in the state in nature.

The installation according to the invention is also characterized in that: - the booster and circulation pumps and the valve, associated with the ultra-filtration means, are sized and adjusted to give, on the one hand, the flow rate of the permeate (or ultra-filtrate) equal to that of the overflow and, on the other hand, the flow rate of the retentate equal to 8 times that of said permeate; - the booster and circulation pumps and the valve, associated with the oyons of reverse osmosis are sized and adjusted to make, on the one hand, the permeate flow rate equal to that of the overflow and, on the other hand, the flow rate of the retentate equal to 8 times that of said permeate; ; - the circulation and booster pumps and the valves, respectively associated with the ultra-filtration and reverse osmosis means, are adjusted to make the flow rate of the permeate leaving the reverse osmosis filter equal to half the flow rate of the permeate leaving the ultrafiltration filter.

 The subject of the invention is also an application of the method and of the installation for the treatment of effluents containing organic waste and more particularly for the treatment of organic animal excrement.

 The characteristics and advantages of the invention will appear more clearly on reading the detailed description which follows of a preferred embodiment of the invention given by way of non-limiting example and shown in the appended drawing (single figure) which is a basic view of the process and the associated installation.

 The effluent to be purified (a), contained in the drainage pit (1), is pumped by a pump (2), at a flow rate (b), to a centrifuge (3) which performs an operation (A) of liquid / solid separation, of the centrifugal decantation type, so as to obtain a filtrate, or centrate, (e), capable of undergoing subsequent stages of filtration, and extracted solid matter (c) capable of being evacuated, via a conveyor belt (4), to be used directly for silage and shoveling.

Operation (A) is carried out continuously and the experiment, the data and results of which are given below, was carried out using a commercial decanter centrifuge of the GUINARD D-18 type on the basis of a rotation speed of 7000 rpm, for a number of g (9.81) equal to 4930 and for an absorbed power of 7 KW.

Whereas a conventional coagulation-flocculation operation leads to the following results - content of solid matter in suspension in the effluent (MES): 2 g / l minimum; - dryness of the solids extracted: at most equal to 10Z; the liquid / solid separation operation according to decantation by centrifugal gation leads to the following new results - MES content: 1 g / l maximum; - corresponding dryness: 20% or more.

A MES rate at most equal to 1 g / l leads, in the following filtration stages, to savings in terms of the surfaces of the membranes used, their frequency of cleaning and their replacement (lifetime over a longer period).

A dryness equal to or greater than 20% leads to the elimination of the stage of dehydration of solid materials which is expensive (investment and labor) since the product in question is directly usable in the state.

In addition, the elimination of the coagulation-flocculation step leads to a significant saving directly linked to the elimination of chiai adjuvants; ques.

By way of example, for the only step (A), compared with a physicochemical step of the coagulation-flocculation type, life preceded by a step of liquid / solid physical separation of the sieving type, the saving is about - 40% per m of treated effluent (pig manure for example) taking into account the economics of chemical additives and labor. To this economy is added that linked to the following stages (ultra-filtration and reverse osmosis), which we are going to analyze now, which brings to approximately 50X the saving achieved on the whole process (15 to 18 F / i ' effluent treated by the process according to the invention against 30 to 35 F / m ′ by a physicochemical process followed by a stage of ultrafiltration and reverse osmosis).

Step (A) follows the formula: b = c + e
The effluent (e) from operation (A) is transmitted to a tank (5), comprising an overflow (g) which returns to the pit (1), to be conveyed, via a booster pump (6), with a membrane filter (7), of known type, for undergoing a micro and ultra-filtration operation (B) capable of using any type of membrane (organic, carbon, mineral).

The filter (7) is associated with - a circulation pump (8); - a circulation loop (h); - two pressure gauges (9) and (10) indicating the pressure on both sides of the filter
UF so as to determine the fouling rate of the latter as well as the cleaning frequency; - a return loop (f) to the tank (5); - a valve (11) regulating the pressure in the UF circuit; - an outlet (i) of the UF permeate (or ultra-filtrate).

Step (B) obeys the formulas - g = i which means that the overflow (g) returned to the tank (1) is equal to the flow rate of the permeate (i); - f = 8i which means, with the previous one, that operation (B) does not carry out any concentration unlike known processes, in particular physico-chemical processes, which carry out a concentration (of the order of 2 to 2.5 ).

The principle of non-concentration in step (B) has the following advantages - the reduction in the frequency of washing filters (once a month instead of once a day generally) with a saving of manpower. wash and wash products; - increasing the lifespan of the membranes; - the possibility of using cheaper organic membranes because their lifespan is limited to approximately 100 washes.

 The effluent (i) from operation (B) is transmitted to a tank (12), comprising an overflow (j) which returns to the pit (1), to be conveyed, through a booster pump (13), to a filter (14) with a reverse osmosis membrane, of known type, for undergoing a reverse osmosis operation (C) capable of also using any type of membrane.

The filter (14) is also associated with - a circulation pump (15); - a recirculation loop (1); - two manometers (16) and (17) indicating the pressure on both sides of the OI filter so as to determine the rate of fouling of the latter and the frequency of cleaning; - a return loop (k) to the tank (12); - a valve (18) regulating the pressure in the OI circuit; - an outlet (m) of the permeate OI which can be rejected as it is in nature.

Step (C) follows the following formulas - j = m which means that the overflow (j) returned to the tank (1) is equal to the permeate flow (m); - k = 8 i which means, with the previous one, that operation (C) does not effect any concentration unlike the known methods.

The principle of non-concentration in step (C) induces the same advantages as those analyzed for the previous step (B).

The overflows (g) and (j) use the same return line (d).

The system thus described also obeys the following formulas: -d = g + j = i + m - i = j + m = 2m - e = i + g = 2i = 4 - b = e + c = 2i + c = 4m + c
Without limitation, the experiment was carried out with the following pressures - pressure gauge (9): 2.5 to 4.5 bars - pressure gauge (10): 4 to 6 bars - pressure gauge (16): 23 to 48 bars - pressure gauge (17): 25 to 50 bars
The tanks (5) and (12) include drain valves (19) and (20).

 The method and the installation according to the invention can be used to purify all the effluents containing organic waste such as for example organic animal excrement (pig manure for example).

The assembly operates continuously and can be adapted to any effluent capacity to be treated.

Claims (9)

 1- Purification process of an effluent (b) containing organic waste, characterized in that it consists in implementing the following successive physical purification operations: - the effluent (b) is subjected to an operation decantation-centrifuge (A) which allows the liquid / solid separation so as to obtain, on the one hand, a filtrate (e) which has a maximum rate of 1 g / l of suspended solids and, on the other hand , extracted solids (c) which have a dryness rate of 20X or more so as to make them directly and immediately usable for silage and shoveling; - the filtrate thus obtained (e) is subjected to an ultra-filtration operation (B) followed by a reverse osmosis operation (C) so as to obtain a permeate (m) directly and i immediately disposable therein state in nature; and in that the ultra-filtration (B) and reverse osmosis (C) operations are carried out without any concentration, in other words by automatically maintaining, on the one hand, the flow rate (g) of the overflow of the ultrafiltration tank (5) equal to that (i) of the permeate leaving the corresponding filter (7) and, on the other hand, the flow rate (j) of the overflow of the reverse osmosis tank ( 12) equal to that (m) of the permeate leaving the corresponding filter (14).  2- Method according to claim 1, characterized in that, in the ultra-filtration operation (B), the volume of the retentate (f) obtained is equal to 8 times that of the permeate (i) obtained at the outlet of the corresponding filter (7).  3 Method according to claim 1, characterized in that, in the reverse osmosis operation (C), the volume of the retentate (k) obtained is equal to 8 times that of the permeate (m) obtained at the outlet of the filter (14) correspondent.  4- Method according to claim 1, characterized in that the volume of the permeate (m) obtained in the reverse osmosis phase (C) is equal to half the volume of the permeate (i) obtained in the ultra phase -filtration (B).  5 Installation for purifying an effluent (b) containing organic waste, characterized in that it comprises in series - a liquid / solid separation means (3) of the centrifuge type by decanting capable of supplying, on the one hand , a filtrate (e) which has a maximum level of 1 g / l of suspended solids and, on the other hand, extracted solids (c) which have a dryness rate equal to or greater than 20X so as to make it directly and immediately usable for silage and shoveling; - Ultra-filtration (5,7) and reverse osmosis (12,14) means capable of providing a permeate (1) directly and immediately disposable in the natural state.  6- Installation according to claim 5, characterized in that the booster pumps (6) and circulation (8) and the valve (11), associated with the ultra-filtration means (5,7), are adjusted for make, on the one hand, the flow rate of the permeate (i) equal to that of the overflow (g) and, on the other hand, the flow rate of the retentate (f) equal to 8 times that of the permeate (i).  7- Installation according to claim 5, characterized in that the booster pumps (13) and circulation (15) and the valve (18), associated with the reverse osmosis means (12,14), are adjusted to make on the one hand, the flow rate of the permeate (m) equal to that of the overflow (j) and, on the other hand, the flow rate of the retentate (k) equal to 8 times that of the permeate (I).  8- Installation according to claim 5, characterized in that the booster pumps (6) and (13), the circulation pumps (8) and (15), the valves (11) and (18), respectively associated with ultrafiltration (5,7) and reverse osmosis (12,14) means are adjusted to make the flow rate of the permeate (m) leaving the reverse osmosis filter (14) equal to half the flow rate of the permeate (i) leaving the ultrafiltration filter (7).  9; Application of the method according to any one of claims 1 to 5 and of the installation according to any one of claims 6 to 8, to the treatment of effluents containing organic waste and more particularly to the treatment of animal organic excrement.