METHOD AND DEVICE FOR TREATING EFFLUENTS COMPRISING SUSPENDED MATTER, NITROGEN AND PHOSPHORUS

Abstract

METHOD AND DEVICE FOR TREATING EFFLUENTS COMPRISING SUSPENDED MATTER, NITROGEN AND PHOSPHORUS The present invention relates to a method and a device for treating effluents comprising suspended matter (SS), nitrogen and phosphorus, preferably said effluents originate from an industrial process, and more preferably from fish farming.

Description

Title of the invention: METHOD AND DEVICE FOR TREATING EFFLUENTS COMPRISING SUSPENDED MATTER, NITROGEN AND PHOSPHORUS FIELD OF THE INVENTION

[0001] The present invention relates to a method and a device for treating effluents comprising suspended matter (SS), nitrogen and phosphorus, preferably said effluents originate from an industrial process, and more preferably from fish farming. STATE OF THE ART

[0002] Effluents must be treated before being released into the environment to reduce the quantity of substances presenting environmental risks. Among these substances, suspended solids (SS) can be a danger to the receiving environment: for example, they can clog fish gills and mobilize oxygen from the receiving environment to eliminate their organic part. Nitrogen and phosphorus must also be taken into account: for example, the ammonium ion NH4+ promotes bacterial proliferation and therefore contributes to lowering the oxygen concentration, while phosphorus contributes to water pollution by promoting excessive algae growth.

[0003] Effluents from fish farming mainly comprise suspended solids, nitrogen and phosphorus. Suspended solids come from fish excrement and uneaten food. Nitrogen is excreted by fish in 80% soluble form and mainly in the form of ammonium ion NH4+. Phosphorus comes mainly from solid fish waste and only 15 to 20% of the phosphorus ingested by fish is released in dissolved form. The legislator imposes discharge thresholds which are defined on average over 24 hours and by difference in concentration of the various parameters between the water at the inlet of the fish farm and the water 100 meters downstream of the discharge point.

[0004] Low tonnage fish farms are generally equipped with a simple decanter used to treat the effluents. Larger fish farms are additionally equipped with one or more rotary filters, usually with a 100 μm mesh, which retains the suspended solids. The effluents pass through the rotary filter(s), the mesh of which is constantly cleaned by a pressurized water system. The water from the backwashing of these filters, whose suspended solids concentration is between 100 and 500 mg / L, is recovered in a decanter. The suspended solids then concentrate at the bottom of the decanter, forming fish sludge.

[0005] This fish sludge, stored in the decanter, can transform and produce greenhouse gases (methane) and nitrogen compounds toxic to the aquatic environment (ammonium ion NH4+ and nitrite ion NO2). They also release a large part of the phosphates they contain in the form of ortho-phosphate ion PO43.

[0006] Furthermore, the preconcentration of suspended solids in the decanter makes it possible to obtain a maximum average dryness rate of around 3 to 4%. As a result, the transport of fish sludge is complicated and the use of spreading surfaces located in or near fish farms is favored. However, few fish farms have spreading surfaces and many surrounding areas already have excess spreading capacity due to the numerous above-ground farms.

[0007] Effluent treatment processes using a constructed wetland have already been reported, especially in the context of wastewater treatment. But despite their advantages, few studies have been carried out under various conditions. In addition, constructed wetlands do not allow for the treatment of a permanent water flow, in particular because of the pause times required for the mineralization / drying of the materials. This makes it even less possible to treat a continuous water flow as high as a fish farm due to the filter surface area, which would have to be extremely large. Constructed wetlands are not intended to capture all livestock effluent either, because clogging of these would make them unusable after a few days, even with low fish production.

[0008] In view of the above, there is therefore a real need to develop a method and an associated device allowing: - better treatment of the solid part of the effluents (i.e. suspended solids (SS)), to obtain sludge with an improved dryness rate, and - better treatment of the liquid part of the effluents which includes the supernatant liquid from the decanter and among other things, in the present invention, the leachates obtained during the treatment of the sludge, for better reduction of the quantity of NH4+, NO2, PO43, and the quantity of remaining MES, before discharge into nature.

[0009] A method for treating effluents comprising suspended solids (SS), nitrogen and phosphorus, and an associated device, has now been discovered, making it possible to achieve the above-mentioned objectives. SUMMARY

[0010] The present invention relates to a method for treating effluents comprising suspended matter, nitrogen and phosphorus, said method comprising the next steps: a. decantation in a decanter from the effluents to obtain a supernatant liquid al and raw sludge a2; b. flocculation by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture bl; c. dehydration on a filter press of the mixture bl to obtain a leachate cl and pressed sludge c2; and d. filtration of the supernatant liquid al and the leachate cl in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices dl.

[0011] Advantageously, the method comprises, before step a), the following step: al) filtration of the effluents on at least one rotary filter to obtain at least one retentate e1 and at least one filtrate e2; and wherein step a) is a decantation in a decanter of at least one retentate el to obtain a supernatant liquid al and raw sludge a2.

[0012] Advantageously, the method comprises, before step a), the following steps: al) filtration of the effluents on a first rotary filter to obtain a first retentate ela and a first filtrate e2a; a2) filtration of the first filtrate e2a on a second rotary filter to obtain a second retentate elb and a second filtrate e2b, the mesh of the second rotary filter being finer than that of the first rotary filter; and wherein step a) is a decantation in a decanter of the first retentate ela and the second retentate elb to obtain a supernatant liquid al and raw sludge a2.

[0013] Advantageously, step d) of filtration of the supernatant liquid al and the leachate cl is carried out in a constructed marsh which comprises at least two separate vertical planted filters which are not connected to each other and at least one horizontal planted filter located downstream of the at least two vertical filters, and preferably the filtration of the supernatant liquid al and the leachate cl is carried out separately from different vertical planted filters.

[0014] The present invention also relates to a device for treating effluents comprising suspended matter, nitrogen and phosphorus, said device comprising: - a decanter 1 making it possible to produce, from the effluents, a supernatant liquid al and raw sludge a2; - at least one tank 2 allowing flocculation by mixing the raw sludge a2 and at least one flocculating agent to obtain a mixture bl; - a filter press 3 for dehydrating the mixture bl to obtain a leachate cl and pressed sludge c2; - a constructed marsh 4 comprising at least one vertical planted filter 5 and at least one horizontal planted filter 6 located downstream of the at least one vertical planted filter 5 and making it possible to filter the supernatant liquid al and the leachate cl to obtain treated juices dl; and - at least one pump allowing the transfer of different solid and / or liquid materials between the different elements of the device.

[0015] Advantageously, the device further comprises at least one rotary filter 7 making it possible to filter the effluents to obtain at least one retentate e1 and at least one filtrate e2; the decanter 1 then making it possible to give, from the at least one retentate e1, the supernatant liquid a1 and the raw sludge a2.

[0016] Advantageously, the device comprises at least two rotary filters 7a-b; the mesh of the second rotary filter 7b being finer than that of the first rotary filter 7a; the first rotary filter 7a making it possible to filter the effluents to obtain a first retentate ela and a first filtrate e2a; the second rotary filter 7b making it possible to filter the first filtrate e2a to obtain a second retentate elb and a second filtrate e2b; the decanter 1 then making it possible to give, from the first retentate ela and the second retentate elb, the supernatant liquid al and the raw sludge a2.

[0017] Advantageously, the constructed marsh 4 comprises at least two vertical planted filters 5a-b which are distinct and not connected to each other and at least one horizontal planted filter 6 located downstream of the at least two vertical planted filters 5a-b.

[0018] Advantageously, the device further comprises at least one tank 8, preferably at least two tanks 8a-b, allowing the homogenization of the raw sludge a2 coming from the decanter 1 before their transfer into the tank 2.

[0019] Advantageously, the device further comprises: - a first submerged pump 9b in the decanter 1 making it possible to draw the raw sludge a2 from the decanter 1 and transfer it into the tank 2 or into at least one tank 8 if the latter is present; and / or - a second submerged pump 9a in the decanter 1 allowing the supernatant liquid al to be pumped from the decanter 1 and transferred into the constructed marsh 4. DEFINITIONS

[0020] In the present invention, the terms below are defined as follows.

[0021] "Flocculating agent" means a substance causing flocculation.

[0022] “Understand” or “includes” should be interpreted in an open and inclusive, but not limited to the characteristics that follow this term.

[0023] “Copolymer” means a molecule formed by the multiple repetition of at least two repeating units, these repeating units being covalently linked to each other. A copolymer results from the polymerization of at least two different monomeric species.

[0024] “Effluent” means a fluid leaving a facility. Effluents may be urban, they then designate all wastewater, runoff water and surface water which are evacuated by the sewers of agglomerations. Effluents can also be industrial, they then designate all fluid discharges from an industry. In the context of the present invention, effluents include suspended solids (SS), nitrogen and phosphorus.

[0025] “Between X and Y” means the interval of values ​​between X and Y, the limits X and Y being included in the said interval.

[0026] “Planted filter” means a filter medium on which plants are planted.

[0027] “Vertical planted filter” means a vertical flow planted filter in which mechanical filtration of particles on the filter media and biological degradation of the pollution by aerobic microorganisms that have developed in the planted filter occur. For example, the ammonium ion NH4+ is transformed into the nitrate ion NO3 by the nitrification reaction in a vertical planted filter according to the following equations: NH3 + O2 => NO2 + 3H+ + 2e NO2 + H2O => NO3 + 2H+ + 2e. In the present invention, the filter medium of the at least one vertical planted filter is preferably limestone gravel.

[0028] “Horizontal planted filter” means a horizontal flow planted filter in in which anaerobic purification mechanisms occur. For example, the nitrate ion NO3 is converted into non-toxic nitrogen gas N2 by the denitrification reaction in a horizontal planted filter. In the present invention, the horizontal planted filter is preferably vegetated with watercress. In addition, in the present invention, the filter medium of the at least one horizontal planted filter is preferably limestone gravel.

[0029] “Flocculation” means a physicochemical process during which materials suspended in a liquid agglomerate to form larger particles, generally very porous, said particles being called flocs.

[0030] “Constructed wetland” means an artificial filter wetland. It includes at least one planted filter, vertical or horizontal.

[0031] “Filter marsh” means a natural or artificial space which uses plants and bacterial or fungal microflora associated with them to purify water through physical and biological processes.

[0032] “Suspended matter” in a liquid means matter which is not in the form of colloids or dissolved in said liquid.

[0033] “Fish farming” means the breeding of fish.

[0034] “Polyacrylamide” means a polymer resulting from the polymerization of acrylamide.

[0035] “Polymer” means a molecule formed by the multiple repetition of a single repeating unit, with identical repeating units being covalently bonded to each other. A polymer results from the polymerization of a single monomeric species.

[0036] “Aqueous solution” means a mixture of a compound in small quantity (the solute) in water, the latter being in the majority quantity. The water content is greater than or equal to 20% by weight, preferably greater than or equal to 40% by weight, and even more preferably greater than or equal to 80% by weight, relative to the total weight of the solution.

[0037] “Dryness rate”, in reference to a sludge, means the mass percentage of dry matter in the mud. DETAILED DESCRIPTION

[0038] Effluents

[0039] In the context of the present invention, the effluents comprise suspended solids (SS), nitrogen and phosphorus. The effluents preferably come from an industrial process, and more preferably from fish farming.

[0040] In a first embodiment, the total MES content included in the effluents is between 1 and 40 mg per liter of effluents. The measurement of the total MES content included in the effluents is measured on a sample of effluents with a Sartorius filtration bench or using a thermo-balance for the most concentrated samples.

[0041] In a second embodiment, compatible with the first embodiment above, the total nitrogen content included in the effluents is between 1.5 and 2.5 mg per liter of effluents. By total nitrogen content, reference is made to the total content of nitrogen compounds (for example including NH4+). The measurement of the total nitrogen content is carried out using HACH Lange analysis kits.

[0042] In a third embodiment, compatible with the first and second embodiments above, the total phosphorus content included in the effluents is between 0.01 and 0.9 mg per liter of effluents. By total phosphorus content, reference is made to the total content of phosphorus compounds (for example including the ortho-phosphate ion PO43). The measurement of the total phosphorus content is carried out using HACH Lange analysis kits.

[0043] Effluent treatment process

[0044] The present invention relates to a method for treating effluents comprising suspended solids (SS), nitrogen and phosphorus.

[0045] Compared with the processes usually used in fish farms for the treatment of effluents, the process of the present invention allows better treatment of both the solid part of the effluents (to obtain fish sludge with an improved dryness rate, the sludge obtained being therefore more easily transportable and thus more easily recoverable, in particular for spreading and at composting platforms) and the liquid part of the effluents (for discharge into nature in compliance with the standards imposed by the legislator).

[0046] The method of the present invention comprises the following steps: a. decantation in a decanter from the effluents to obtain a supernatant liquid al and raw sludge a2; b. flocculation by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture bl; c. dehydration on a filter press of the mixture bl to obtain a leachate cl and pressed sludge c2; and d. filtration of the supernatant liquid al and the leachate cl in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices dl.

[0047] The method of the present invention therefore comprises a primary treatment of extraction and dewatering of the sludge (steps a) to c)) coupled with a secondary treatment by filtration in a marsh constructed from the supernatant liquid of the decanter and the leachates resulting from the dewatering of the sludge (step d)). The primary treatment makes it possible to obtain pressed sludge whose average dryness rate is improved, which facilitates its transport outside the industrial zone (particularly in the case of fish farming) and therefore its recovery. In addition, the storage of the sludge in the decanter is avoided, which makes it possible to resolve the problems linked to the release of undesirable chemical elements.Secondary treatment allows for a better reduction of the quantity of nitrogen and phosphorus pollutants and the quantity of suspended solids in the supernatant liquid of the decanter and the leachates from the dehydration stage, so that these quantities comply with the standards required by the legislator for discharge into nature.

[0048] The positioning of the at least one horizontal planted filter downstream of the at least one vertical planted filter makes it possible to avoid clogging of the horizontal planted filter(s).

[0049] Advantageously, step b) of flocculation by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture b1 takes place in at least one tank.

[0050] Advantageously, the dryness rate of the pressed sludge c2 at the end of the step of dehydration on a filter press of the mixture bl (step c)) is greater than 4%, preferably between 5 and 35% and more preferably between 10 and 30%. This dryness rate allows easier transport and therefore recovery of sludge, and in particular fish farming sludge.

[0051] In one embodiment, the method comprises the following steps: al) filtration of the effluents on at least one rotary filter to obtain at least one retentate el and at least one filtrate e2; a) decantation in a decanter of at least one retentate el to obtain a supernatant liquid al and raw sludge a2; b) flocculation by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture bl; c) dehydration on a filter press of the mixture bl to obtain a leachate cl and pressed sludge c2; and d) filtration of the supernatant liquid al and the leachate cl in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices dl.

[0052] Thus, in this embodiment, the effluents are previously filtered on the at least one rotary filter to capture the suspended solids. Preferably, in this embodiment, the mesh of the at least one rotary filter is between 50 and 500 μm.

[0053] In a preferred embodiment, the method comprises the following steps: a1) filtration of the effluents on a first rotary filter to obtain a first retentate ela and a first filtrate e2a; a2) filtration of the first filtrate e2a on a second rotary filter to obtain a second retentate elb and a second filtrate e2b, the mesh of the second rotary filter being finer than that of the first rotary filter; a) decantation in the decanter of the first retentate ela and the second retentate elb to obtain a supernatant liquid al and raw sludge a2; b) flocculation by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture bl; c) dehydration on a filter press of the mixture bl to obtain a leachate cl and pressed sludge c2; and d) filtration of the supernatant liquid al and the leachate cl in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices dl. In this preferred embodiment, the second filtrate e2b can be directly released into nature without further treatment. Preferably, in this preferred embodiment, the mesh of the first rotary filter is between 200 and 500 pm and the mesh of the second rotary filter is between 50 and 150 pm.

[0054] Advantageously, when the method further comprises steps a1) and a2), the method further comprises a step a3), which follows step a2) and which precedes step a), consisting of a backwash of the mesh of the second rotary filter to recover the second retentate elb.

[0055] Advantageously, the method further comprises an additional step, after the settling step in a decanter (step a)) and before the flocculation step by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture b1 (step b)), of homogenizing the raw sludge a2. Preferably, this step of homogenizing the raw sludge a2 takes place in at least one tank, preferably at least two tanks.

[0056] Step d) consists of filtering the supernatant liquid al and the leachate cl in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices dl. In other words, the supernatant liquid al and the leachate cl are first filtered on the at least one vertical planted filter and then on the at least one horizontal planted filter. The treated juices dl are therefore obtained at the outlet of the at least one horizontal planted filter.

[0057] In an embodiment compatible with the preceding embodiments, step d) of filtration of the supernatant liquid al and the leachate cl is carried out in a constructed marsh which comprises at least two separate vertical planted filters not connected to each other and at least one horizontal planted filter located downstream of the at least two vertical planted filters. Thus, in this embodiment, the at least two vertical planted filters each open onto the at least one horizontal planted filter. Furthermore, preferably, the filtration of the supernatant liquid al and the leachate cl are carried out separately from different vertical planted filters. In other words, the filtration of the supernatant liquid al is carried out from at least one of the vertical planted filters while the filtration of the leachate cl is carried out from at least one other of the vertical planted filters.

[0058] Advantageously, the at least one flocculating agent of step b) is chosen from non-ionic polymers and their mixtures, preferably chosen from polyacrylamide, acrylamide copolymers and their mixtures, and more preferably the at least one flocculating agent is polyacrylamide.

[0059] Advantageously, the at least one flocculating agent of step b) is in the form of an aqueous solution. Thus, the method may further comprise an additional step of diluting the at least one flocculating agent to obtain at least one flocculating agent in the form of an aqueous solution.

[0060] In an embodiment compatible with the preceding embodiments, the method comprises the following steps: a. decantation in a decanter from the effluents to obtain a supernatant liquid al and raw sludge a2; b. flocculation by mixing the raw sludge a2 with at least one flocculating agent to obtain a mixture bl; c. dehydration on a filter press of the mixture bl to obtain a leachate cl and pressed sludge c2; d. filtration of the supernatant liquid al and the leachate cl in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices dl; e. transfer of treated juices dl into the decanter; f. at least one repetition of steps a) to e), the repeated step a) being a decantation in the decanter from the treated juices dl to obtain a supernatant liquid al and raw sludge a2.

[0061] Advantageously, the method further comprises at least one additional step of transferring the various solid and / or liquid materials obtained.

[0062] In a preferred embodiment, the method further comprises a step of withdrawing the raw sludge a2 from the decanter and transferring this raw sludge a2 into the tank(s) where the homogenization step takes place, when it is included in the method, or into the tank(s) where the flocculation step b) takes place, via a submerged pump.

[0063] In a second preferred embodiment compatible with the previous one, the method further comprises a step of pumping the supernatant liquid al from the decanter and transferring this supernatant liquid al into the constructed marsh via a submerged pump.

[0064] Effluent treatment device

[0065] The present invention also relates to a device for treating effluents comprising suspended solids (SS), nitrogen and phosphorus.

[0066] The device according to the present invention comprises: - a decanter 1 making it possible to produce, from the effluents, a supernatant liquid al and raw sludge a2; - at least one tank 2 allowing flocculation by mixing the raw sludge a2 and at least one flocculating agent to obtain a mixture bl; - a filter press 3 for dehydrating the mixture bl to obtain a leachate cl and pressed sludge c2; - a constructed marsh 4 comprising at least one vertical planted filter 5 and at least at least one horizontal planted filter 6 located downstream of the at least one vertical planted filter 5 and making it possible to filter the supernatant liquid al and the leachate cl to obtain treated juices dl; and - at least one pump allowing the transfer of different solid and / or liquid materials between the different elements of the device.

[0067] Advantageously, the decanter 1 is a cylindro-conical decanter. This type of decanter makes it possible to centralize the sludge at a central low point, facilitating its collection using just a pump or a discharge pipe below. Cylindro-conical decanters also make it possible to accelerate the decantation speed.

[0068] Advantageously, the filter press 3 is a disc press.

[0069] Advantageously, the constructed marsh 4 comprises at least two vertical planted filters 5a-b which are distinct and not connected to each other and at least one horizontal planted filter 6 located downstream of the at least two vertical planted filters 5a-b.

[0070] In one embodiment, the device further comprises at least one rotary filter 7 for filtering the effluents to obtain at least one retentate e1 and at least one filtrate e2; the decanter 1 then making it possible to give, from the at least one retentate e1, the supernatant liquid a1 and the raw sludge a2. Preferably, the at least one rotary filter 7 is conical. Preferably, in this embodiment, the mesh of the at least one rotary filter is between 50 and 500 μm.

[0071] In a preferred embodiment, the device further comprises at least two rotary filters 7a-b; the mesh of the second rotary filter 7b being finer than that of the first rotary filter 7a; the first rotary filter 7a making it possible to filter the effluents to obtain a first retentate ela and a first filtrate e2a; the second rotary filter 7b making it possible to filter the first filtrate e2a to obtain a second retentate elb and a second filtrate e2b; the decanter 1 then making it possible to give, from the first retentate ela and the second retentate elb, the supernatant liquid al and the raw sludge a2. Preferably, in this preferred embodiment, the mesh of the first rotary filter is between 200 and 500 μm and the mesh of the second rotary filter is between 50 and 150 μm.

[0072] Advantageously, the device further comprises a waste pump 10 making it possible to withdraw the first retentate 1a from the first rotary filter 7a and transfer it into the decanter 1.

[0073] Advantageously, the device further comprises at least one tank 8, preferably at least two tanks 8a-b, allowing the homogenization of the raw sludge a2 coming from the decanter 1 before their transfer into the tank 2. Preferably, the tank(s) 8 are located at the same level as the filter press 3.

[0074] Advantageously, when the device further comprises at least one tank 8, said device further comprises a screw pump 11 for withdrawing the sludge. raw materials a2 from at least one tank 8, after homogenization, and transferring them into tank 2. The use of the screw pump 11 allows a constant and little variable flow rate.

[0075] In a preferred embodiment, the device further comprises a first submerged pump 9b in the decanter 1 for withdrawing the raw sludge a2 from the decanter 1 and transferring it to the tank 2 or to the at least one tank 8 if the latter is present. The first submerged pump 9b makes it possible to withdraw the raw sludge a2 from the decanter 1 without creating a sedimentation cone in the decanter 1. In addition, the evacuation of the raw sludge a2 from the decanter 1 is more regular and the dry matter content more constant. Advantageously, the first submerged pump 9b is positioned in the center of the decanter 1.

[0076] In another preferred embodiment compatible with the previous one, the device further comprises a second submerged pump 9a in the decanter 1 making it possible to pump the supernatant liquid al from the decanter 1 and transfer it into the constructed marsh 4.

[0077] Advantageously, the decanter 1 comprises a scraper. The scraper makes it possible to more efficiently recover the raw sludge a2 which may remain stuck along the walls of the decanter 1.

[0078] Advantageously, the device further comprises a tank 13 allowing the storage of at least one flocculating agent.

[0079] Advantageously, the device further comprises a tank 14 allowing the dilution of the at least one flocculating agent, to obtain the at least one flocculating agent in the form of an aqueous solution.

[0080] Advantageously, the device further comprises a tank 15 allowing the storage of the pressed sludge c2. DESCRIPTION OF FIGURES

[0081] [Fig.l] shows an effluent treatment device of the present invention in one embodiment.

[0082] [Fig.2] represents a balance of MES concentration at the inlet and outlet of the vertical planted filters of the constructed marsh and at the inlet and outlet of the horizontal planted filter of the constructed marsh. DIGITAL REFERENCES

[0083] al - supernatant liquid

[0084] a2 - raw sludge

[0085] bl - mixture

[0086] cl-leachate

[0087] c2 - pressed sludge

[0088] dl-processed juices

[0089] el, ela, elb - retentate

[0090] e2, e2a, e2b - filtrate

[0091] 1 - decanter

[0092] 2, 8, 8a, 8b, 13-15 - tank

[0093] 3 - filter press

[0094] 4 - constructed marsh

[0095] 5, 5a, 5b, 5c - vertical planted filter

[0096] 6 - horizontal planted filter

[0097] 7, 7a, 7b - rotating filter

[0098] 9, 9a, 9b - submersible pump

[0099] 10 - waste pump

[0100] 11 - screw pump EXAMPLE

[0101] The present invention will be better understood by reading the following example which illustrates the invention in a non-limiting manner.

[0102] Materials and methods

[0103] The device and method according to the present invention were used on the site of the Inrae Experimental Fish Farm of the Monts d'Arrée (PEIMA), Drennec dam, 29450, Sizun.

[0104] The effluent treatment device used, shown [Fig.l], comprises: - a first conical rotary filter 7a for filtering the effluents to obtain a first retentate ela and a first filtrate e2a; - a second conical rotary filter 7b, the mesh of which is finer than that of the first rotary filter 7a, making it possible to filter the first filtrate e2a to obtain a second retentate elb and a second filtrate e2b; - a cylindrical-conical decanter 1 allowing to give, from the first retentate ela and the second retentate elb, the supernatant liquid al and the raw sludge a2; - a waste pump 10 for withdrawing the first retentate ela from the first rotary filter 7a and transferring it into the decanter 1; - a tank 13 allowing the storage of the flocculating agent; - a tank 14 allowing the dilution of the flocculating agent to obtain an agent flocculant in the form of an aqueous solution; - a tank 2 allowing flocculation by mixing the raw sludge a2 and the flocculating agent in the form of an aqueous solution to obtain a mixture bl; - two tanks 8a-b allowing the homogenization of raw sludge a2 coming from decanter 1 before their transfer into tank 2; - a first submerged pump 9b in the decanter 1 allowing extraction the raw sludge a2 from decanter 1 and transfer it into the two tanks 8a-b; - a second submerged pump 9a in the decanter 1 making it possible to pump the supernatant liquid al from the decanter 1 and transfer it into the constructed marsh 4; - a screw pump 11 for withdrawing the raw sludge a2 from the two tanks 8a-b, after homogenization, and transferring it into tank 2; - a disc press 3 for dehydrating the mixture bl to obtain a leachate cl and pressed sludge c2; - a tank 15 allowing the storage of pressed sludge c2; - a constructed marsh 4 comprising three separate and unconnected vertical planted filters 5a-c (in limestone gravel) and a horizontal planted filter 6 (in limestone gravel) located downstream of the three vertical planted filters 5a-c and allowing the supernatant liquid al and the leachate cl to be filtered to obtain treated juices dl.

[0105] The method used comprises the following steps: a. filtration of the effluents on the first conical rotary filter 7a to obtain a first retentate ela and a first filtrate e2a; b. filtration of the first filtrate e2a on the second conical rotary filter 7b to obtain a second retentate elb and a second filtrate e2b which can be directly discharged into nature without additional treatment; c. withdrawal and transfer of the first retentate ela into the decanter 1 via the waste pump 10; d. backwashing of the mesh of the second conical rotary filter 7b to recover the second retentate elb and transfer of the latter into the decanter 1; e. decantation in decanter 1 of the first retentate ela and the second retentate elb to obtain a supernatant liquid al and raw sludge a2; f. withdrawal and transfer of raw sludge a2 into tanks 8a-b via submersible pump 9b; g. homogenization of raw sludge a2 in tanks 8a-b; h. transfer of the flocculating agent from tank 13 to tank 14; i. diluting the flocculating agent in tank 14 to obtain a flocculating agent in the form of an aqueous solution; j. transfer of the flocculating agent in the form of an aqueous solution from tank 14 to tank 2; k. withdrawal and transfer of raw sludge a2, after homogenization, from tanks 8a-b to tank 2 via screw pump 11; 1. flocculation, in tank 2, by mixing the raw sludge a2 with the agent flocculant to obtain a bl mixture; m. transfer of the bl mixture into the disc press 3; n. dehydration on the disc press 3 of the mixture bl to obtain a leachate cl and pressed mud c2; o. transfer of leachate cl into the first vertical planted filter 5a of the constructed marsh; p. transfer of the supernatant liquid al into the second and third vertical planted filters 5b-c of the constructed marsh; q. filtration of the supernatant liquid al from the second and third vertical planted filters 5b-c of the constructed marsh and filtration of the leachate cl from the first vertical planted filter 5a of the constructed marsh, to obtain treated juices dl.

[0106] First, the effectiveness of the primary treatment of extraction and dewatering of fish sludge was evaluated.

[0107] Then, a quantification and qualification campaign of the incoming and outgoing flows of the constructed marsh was carried out to be able to evaluate the effectiveness of the secondary treatment. Concentration assessments of the main polluting elements (nitrogen, phosphorus and suspended solids) were carried out.

[0108] The campaign began with sample collections at different locations in the system: - at the entrance to the second and third vertical planted filters 5b-c (FT1); - at the input of the first vertical planted filter 5a (FT2); - at the outlet of the vertical planted filters 5a-c (FT3); and - at the output of horizontal filter 6 (FT4).

[0109] For each sampling point, the parameters analyzed are as follows: ammonium ion NH4+ content, nitrite ion NO2, nitrate ion NO3, total nitrogen content, total phosphorus content, and MES content.

[0110] Analyses of the different forms of nitrogen and phosphorus were carried out in the laboratory using HACH Lange analysis kits. Measurement of the MES content in the samples was carried out using a Sartorius filtration bench or using a thermo-balance for the most concentrated samples. [YES] Results

[0112] Primary treatment for extraction and dehydration of fish sludge

[0113] [Tables 1] Quantity of feed distributed at 93% dry matter (kg) 4114.08 Raw sludge (a2) collected (litres) 25,608 Average dryness rate of raw sludge (a2) (%) 1.3 Pressed sludge (c2) collected (kg) 1496 Average dryness rate of pressed sludge (c2) (%) 15.4 Performance of primary treatment for extraction and dewatering of fish sludge

[0114] The average dryness rate of the pressed sludge (c2) obtained is equal to 15.4%, which is significantly higher than the average dryness rate obtained after treatment of effluents in fish farms equipped only with one or more rotary filters and a decanter.

[0115] Secondary treatment

[0116] Reduction of MES

[0117] As shown [Fig.2], the MES content contained in the supernatant liquid al of decanter 1 is of the order of 14.7 mg / L (FT1). The vertical planted filters 5a-c have a very low efficiency in reducing MES due to the very type of support used, which explains why the average MES content at the outlet of these filters (FT3) is not significantly different from that observed at the inlet (FT1). The majority of MES is retained by the horizontal planted filter 6, with a reduction of more than 60%, which brings the MES content at the outlet (FT4) to 6 mg / L, which is very close to the content of the new water and very much lower than the threshold authorized for discharge into nature (15 mg / L).

[0118] Nitrogen reduction

[0119] [T ableaux2] Concentration FT1 FT3 FT4 Total N Abatement (mg / L) 8.37 7.60 7.05 -15.8% NH4+ (mg / L) 0.24 0.13 0.13 -47.0% NO2 (mg / L) 0.06 0.06 0.04 -38.4% NO3 (mg / L) 2.53 2.94 2.88 13.7% Organic N (mg / L) 5.53 4.47 4.00 -Z1J% Nitrogen concentration balance at the inlet and outlet of the vertical planted filters of the constructed marsh and at the inlet and outlet of the horizontal planted filter of the marsh built.

[0120] A clear decrease in the concentration of ammonium ion NH4+ is observed at the outlet of the vertical planted filters with a reduction of 47%. A clear decrease in the concentration of nitrite ion NO2 is observed at the outlet of the horizontal planted filter with a reduction of 38%. The concentrations of ammonium ion NH4+ (0.13 mg / L) and nitrite ion NO2 (0.04 mg / L) obtained at the outlet of the constructed marsh are lower than the thresholds authorized for discharge into nature. The reduction of total nitrogen (15.8%) obtained at the outlet of the constructed marsh is significant.

[0121] Phosphorus reduction

[0122] [Tables3] Water quality parameters FT1 FT3 FT4 Total P reduction (mg / L) 0.95 0.88 0.57 - 40.6% Phosphorus concentration balance at the inlet and outlet of the vertical planted filters of the constructed marsh and at the inlet and outlet of the horizontal planted filter of the constructed marsh.

[0123] Most of the phosphorus in the effluent is extracted by the rotary filters 7a-b and is found in the raw sludge (a2). However, some of the phosphorus is still solubilized in the supernatant liquid al of the decanter 1 (FT1 0.95 mg / L) which is treated by the vertical planted filters 5b-c (FT3 0.88 mg / L) and the horizontal planted filter 6 (FT4 0.57 mg / L). The reduction resulting from this treatment (40.6%) is due to an adsorption and precipitation phenomenon linked to the support used.

[0124] Conclusion

[0125] The method and the effluent treatment device of the present invention make it possible to obtain pressed sludge c2 whose dryness rate is greater than 4%. They also make it possible to treat the supernatant liquid al of the decanter 1 and the leachates cl obtained during the dehydration of the fish sludge for a better reduction of the quantity of nitrogen and phosphorus pollutants and the quantity of remaining suspended solids, before discharge into nature.

[0126] Thus, the present invention describes a method and a device which allow better treatment of both the solid part of the effluents (to obtain fish sludge with an improved dryness rate, the sludge obtained being therefore more easily transportable and thus recoverable, in particular for spreading and at composting platforms) and the liquid part of the effluents (for discharge into nature in compliance with the standards imposed by the legislator).

Claims

Claims

1. A method for treating effluents comprising suspended matter, nitrogen and phosphorus, said method comprising the following steps: a. decanting in a decanter from the effluents to obtain a supernatant liquid (al) and raw sludge (a2); b. flocculation by mixing the raw sludge (a2) with at least one flocculating agent to obtain a mixture (bl); c. dewatering on a filter press of the mixture (bl) to obtain a leachate (cl) and pressed sludge (c2); and d. filtration of the supernatant liquid (al) and the leachate (cl) in a constructed marsh comprising at least one vertical planted filter and at least one horizontal planted filter located downstream of the at least one vertical planted filter, to obtain treated juices (dl).

2. Method according to claim 1, comprising, before step a), the following step: a1) filtration of the effluents on at least one rotary filter to obtain at least one retentate (e1) and at least one filtrate (e2); and wherein step a) is a decantation in a decanter of the at least one retentate (e1) to obtain a supernatant liquid (a1) and raw sludge (a2).

3. A method according to claim 2, comprising, before step a), the following steps: a1) filtration of the effluents on a first rotary filter to obtain a first retentate (ela) and a first filtrate (e2a); a2) filtration of the first filtrate (e2a) on a second rotary filter to obtain a second retentate (elb) and a second filtrate (e2b), the mesh of the second rotary filter being finer than that of the first rotary filter; and wherein step a) is decantation in a decanter of the first retentate (ela) and the second retentate (elb) to obtain a supernatant liquid (al) and raw sludge (a2).

4. A method according to any one of claims 1 to 3, wherein step d) of filtering the supernatant liquid (al) and the leachate (cl) is carried out in a constructed marsh which comprises at least two filters separate vertical planted filters not connected to each other and at least one horizontal planted filter located downstream of the at least two vertical filters, and preferably the filtration of the supernatant liquid (al) and the leachate (cl) are carried out separately from different vertical planted filters.

5. Device for treating effluents comprising suspended matter, nitrogen and phosphorus, said device comprising: - a decanter (1) for producing, from the effluents, a supernatant liquid (al) and raw sludge (a2); - at least one tank (2) for flocculation by mixing the raw sludge (a2) and at least one flocculating agent to obtain a mixture (bl); - a filter press (3) for dehydrating the mixture (bl) to obtain a leachate (cl) and pressed sludge (c2); - a constructed marsh (4) comprising at least one vertical planted filter (5) and at least one horizontal planted filter (6) located downstream of the at least one vertical planted filter (5) and for filtering the supernatant liquid (al) and the leachate (cl) to obtain treated juices (dl); and - at least one pump allowing the transfer of different solid and / or liquid materials between the different elements of the device.

6. Device according to claim 5, further comprising at least one rotary filter (7) making it possible to filter the effluents to obtain at least one retentate (el) and at least one filtrate (e2); the decanter (1) then making it possible to give, from the at least one retentate (el), the supernatant liquid (al) and the raw sludge (a2).

7. Device according to claim 6, comprising at least two rotary filters (7a-b); the mesh of the second rotary filter (7b) being finer than that of the first rotary filter (7a); the first rotary filter (7a) making it possible to filter the effluents to obtain a first retentate (ela) and a first filtrate (e2a); the second rotary filter (7b) making it possible to filter the first filtrate (e2a) to obtain a second retentate (elb) and a second filtrate (e2b); the decanter (1) then making it possible to give, from the first retentate (ela) and the second retentate (elb), the supernatant liquid (al) and the raw sludge (a2).

8. A device according to any one of claims 5 to 7, wherein the constructed marsh (4) comprises at least two vertical planted filters (5a-b) which are distinct and not connected to each other and at least one horizontal planted filter (6) located downstream of the at least two vertical planted filters (5a-b).

9. Device according to any one of claims 5 to 8, further comprising at least one tank (8), preferably at least two tanks (8a-b), allowing the homogenization of the raw sludge (a2) coming from the decanter (1) before their transfer into the tank (2).

10. A device according to any one of claims 5 to 9, further comprising: - a first submerged pump (9b) in the decanter (1) making it possible to draw off the raw sludge (a2) from the decanter (1) and transfer it into the tank (2) or into at least one tank (8) if the latter is present; and / or - a second submerged pump (9a) in the decanter (1) for pumping the supernatant liquid (al) from the decanter (1) and transferring it into the constructed marsh (4).

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