FR2913234A1 - Treating urban/industrial used water containing sulfide and ammonium, sewage, condensates and leachate, comprises biologically treating used water in free culture by anoxic treatment to eliminate organic carbon using heterotrophic bacteria - Google Patents

Abstract

The process for treating urban or industrial used water containing sulfide and ammonium, sewage, condensates and leachate, comprises biologically treating the used water in free culture by an anoxic treatment for eliminating organic carbon using heterotrophic bacteria, oxidizing the sulfides and reducing nitrate and nitrite by autotrophic bacteria, subjecting the obtained effluent to an aerobic biological treatment in free culture for transforming ammonium into nitrate, and recirculating the effluent to the anoxic treatment. The process for treating urban or industrial used water containing sulfide and ammonium, sewage, condensates and leachate, comprises biologically treating the used water in free culture by an anoxic treatment for eliminating organic carbon using heterotrophic bacteria, oxidizing the sulfides and reducing nitrate and nitrite by autotrophic bacteria, subjecting the obtained effluent to an aerobic biological treatment in free culture for transforming ammonium into nitrate, and recirculating the effluent to the anoxic treatment. The recirculated effluent is controlled according to a quantity of sulfide to be treated, and is subjected to a quantity of nitrate for oxidizing the sulfides present in water. A mass ratio of sulfur and nitrogen maintained in the anoxic treatment is 0.5-3. The oxidation of sulfide is coupled with nitritation using an aerobic sequencing batch reactor. The anoxic treatment of nitrite obtained from the nitritation is controlled according to the quantity of sulfides to be oxidized with the nitrites. An independent claim is included for an installation for treating urban or industrial used water containing sulfide and ammonium, sewage, condensates and leachate.

Description

METHOD AND SYSTEM FOR TREATING WASTE WATER CONTAINING SULFIDES

AND AMMONIUM.

  The invention relates to a process for treating wastewater loaded with sulphides and ammonia, in particular waste water of urban or industrial origin or digestion returns, condensates, leachates. Wastewater contains in particular carbon, nitrogen and sulfur in various forms of compounds that can be chemically treated by various processes. All physico-chemical treatments consist in separating the compounds of these elements from one liquid phase to concentrate them in another phase. These include the processes of stripping (removal of gas in the water by means of a driving gas), reverse osmosis, distillation, chemical precipitation or catalytic oxidation, the costs of implementation and operating costs are high. The biological elimination of these compounds is an alternative treatment.

  Biological treatments of nitrogen and carbon The carbon and nitrogen pollutants of wastewater are mainly eliminated by biological means. This conventional route is based on the ability of microorganisms to eliminate assimilation or biodegradation pollution. The organic carbonaceous material is oxidized in aerated medium by microorganisms, mainly heterotrophic bacteria. These micro-organisms use organic carbonaceous, colloidal and dissolved matter and convert it into either gas or biomass. As regards the nitrogen treatment, nitrification and denitrification treatments are mainly distinguished, by which ammonium is oxidized in two stages under conditions aerated by autotrophic bacteria (first nitrite then nitrate), and finally reduced to gaseous nitrogen under anoxic conditions by heterotrophic bacteria. The biological reactions are shown in the diagrams below.

  Nitrification: NH4 + - * NO2- -> NO3- Denitrification: NO3- -> NO2 ---> NO -> N20 ---> N2 Limits of nitrogen treatment: - Biological nitrification / denitrification is a efficient process but which requires up to 1/3 of the total oxygen consumed on the treatment plant. - Exploitation is difficult compared to the treatment of carbon with the consequent frequent additions of carbon reagents (methanol, ethanol ..) to complete the denitrification. This treatment requires retention times and large tank volumes, the kinetics of nitrification being very low.

  Disadvantages of the presence of sulfur: Many problems related to the presence of sulfur in influents of purification plants are well identified, namely: - The emission of smelly odors (rotten egg type). These unpleasant odors are detected well before representing a danger for the human being since the olfactory sensors have a threshold of detection at 0.15 ppm. - Health risks related to H2S (hydrogen sulphide). Indeed, this molecule is toxic from 10 ppm, with a worsening of effects depending on the duration of exposure. - Corrosion of concretes and metals due to the oxidation of sulphides to sulfuric acid by certain bacteria like Thiobacillus. - The development of filamentous bacteria. Since water is septic, filamentous bacteria are more competitive than conventional floc bacteria with respect to oxygen. Some are able to accumulate sulfur in the form of granules in their cells. - The need to cover the works to avoid a dispersion of H2S.

  Sulfur Treatments Sulfates are naturally present in wastewater and sulfur is included in the intracellular protein composition of microorganisms. Sulfur can be oxidized or reduced depending on the environmental conditions and the populations of bacteria present. In an aerobic environment, sulphides are

  converted into sulphates by sulphooxidizing bacteria and in anaerobic medium, the sulphates are converted into sulphides by sulphate-reducing bacteria.

  Aerobic: S2- -3 SO42- Anaerobic: SO42- -3 S2- + H2S

  The treatment of wastewater by autotrophic denitrification with sulphide oxidation has been described in FR 2841548-A1. This process uses three biomass series biological reactors fixed on a mobile support: anaerobic, anoxic and aerobic. The first reactor makes it possible to reduce sulphates to sulphides and to treat the carbon charge. In the second reactor, the sulphides are oxidized to sulphates by reducing the nitrates from the recirculation of the aerobic basin to the anoxic basin. In the aerobic reactor, ammonium is converted into nitrates. This method has a constraint on the investment cost since it requires a large volume of expensive support materials. The limit of this treatment scheme is based on the quantity of sulphides to be oxidized by autotrophic denitrification, which consumes alkalinity. The proposed operating mode, being a consumer of alkalinity (autotrophic nitrification in the aerated pool + autotrophic denitrification in the anoxic basin), in case of excess of sulphides to be treated, the anoxic environment would be limiting in alkalinity, or even in nitrates. The oxidation of sulphides would not be total.

  In addition, the production of volatile fatty acids in the first anaerobic reactor also consumes alkalinity, which is all the more unfavorable to the oxidation reactions of the sulfides in the second anoxic reactor. The object of the invention is, above all, to provide a process which makes it possible to eliminate the sulphides and the different forms of nitrogen in an economical and efficient manner. The process according to the invention for the treatment of sulphide and ammonium-laden wastewater, in particular waste water of urban or industrial origin or digestion returns, condensates, leachates is characterized in that: the waste water first undergoes an anoxic treatment by biological free-culture means according to which, in a first step, the organic carbon is essentially eliminated by heterotrophic bacteria, and in

  a second step, separated from the first, the sulphides are oxidized biologically by autotrophic bacteria with reduction of nitrates and / or nitrites, the effluent leaving the second stage is subjected to an aerobic biological treatment in free cultures for the transformation of ammonium into nitrates. Preferably, a fraction of the effluent which has undergone the aerobic biological treatment in free cultures, and which contains nitrates, is recirculated to the second stage and the first stage of the anoxic treatment. The fraction of the effluent recirculated to the anoxic treatment is advantageously regulated as a function of the amount of sulphides to be treated. In the second stage of the anoxic treatment, the mass ratio S, N (sulfur / nitrogen) is preferably maintained between 0.5 and 3. The recirculated fraction may be slaved to the amount of nitrates / nitrites necessary to oxidize all the elements. sulphides present in the water in the second stage of anoxic treatment. Advantageously, the recirculated fraction is slaved to ensure, in the second step of the anoxic treatment, the mass ratio S / N (sulfur / nitrogen) of between 0.5 and 3. The oxidation of the sulphides by biological means can be coupled to a sequential aerobic biological reactor (SBR) nitritation with a feed of the second stage of anoxic nitrite treatment from nitrite. Feeding the second stage of the anoxic nitrite treatment from the nitritation can be regulated depending on the amount of sulfide to be oxidized with the nitrites. The invention also relates to an installation for carrying out the process defined above, characterized in that it comprises two free-culture series biological reactors, the first reactor being a two-stage anoxic biological reactor comprising a heterotrophic basin. and a separate autotrophic basin, while the second reactor is an aerated basin in free cultures. Preferably, a recirculation of nitrates is carried out from the aerated pool to the anoxic basins as a function of the concentration of sulphides to be oxidized. The nitrate recirculation can be carried out by stepped feeding or step feed from the aerated basin to the anoxic basins according to the sulphide concentration to be oxidized. The installation includes measurement probes in the anoxic basins and in the aerated basin for several parameters including the

  carbon content of the incoming effluent, and the sulphide content in the autotrophic anoxic basin, these measurement probes being connected to a controller which controls the recirculation flow rates according to the parameters measured. In the case of an installation for a treatment plant comprising a sludge die with an anaerobic digester and a sequential aerobic biological reactor providing partial nitrification and denitrification of ammonium concentrated effluents, the sequential aerobic biological reactor can be coupled to the pond. anoxic autotrophic for a supply of nitrites from this basin.

  The invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed hereinafter with regard to exemplary embodiments described with reference to the appended drawings, but which are not in no way limiting. In these drawings: 1 is a diagram of an installation according to the invention, and FIG. 2 is a diagram of an alternative embodiment of the installation. Referring to Fig.1 of the drawings, there can be seen an installation according to the invention for the treatment, in a continuous flow, of wastewater loaded with sulphides and ammonium. This installation includes an anoxic reactor 1 compartmentalized in a heterotrophic basin followed by an autotrophic basin 1 b. The two basins 1a and 1b are separated and the effluent exiting the basin is taken up by pumping means and sent into the basin lb. The basin receives the flow Q of wastewater containing carbon, sulphides and ammonium. Aa, Ab agitation means are provided in each basin 1a, 1b. There is no insufflation of air or oxygen in these basins. Heterotrophic and autotrophic bacteria are naturally present in wastewater and in pools 1a, 1b, in the form of free cultures.

  Since the anoxic basin receives a flow Q loaded with organic carbon, the heterotrophic bacteria grow rapidly in this basin, while the autotrophic bacteria grow much less rapidly under such conditions. The anoxic basin is thus heterotrophic and makes it possible to treat the incoming carbon, and to denitrify a surplus of nitrates coming from an aerated basin 2 and which are not used for the oxidation of the sulphides in the anoxic basin autotrophic lb. The aerated pond 2 is located downstream of the pool lb

  The pond 1b receives the effluent leaving the basin 1a, effluent in which the organic carbon has been essentially eliminated. The action of autotrophic bacteria in pond 1b is favored by the low organic carbon load of water from compartment 1a. Thus, by separating the anoxic basins 1a, 1b, conditions have been created which favor the action of heterotrophic bacteria in the basin, and in the basin the action of autotrophic bacteria. The autotrophic anoxic basin 1b makes it possible to treat the sulphides present in the raw water by virtue of the nitrates originating from the aerated pool 2 and / or the nitrites resulting from the nitritation stage of the sequential aerobic biological reactor (3BR). Sulphides are oxidized by autotrophic denitrification which consumes alkalinity. The heterotrophic denitrification that takes place in the basin allows it to produce alkalinity. Thanks to this alkalinity production in the basin 1a, the process is not slowed down or stopped by a decrease in alkalinity due to consumption in the basin 1b. The effluent from basin 1b is sent, for an aerobic biological treatment in free cultures, into the aerated pond 2 which comprises agitation means Ac and aeration means B located in the bottom of the basin 2 for injecting air or oxygen bubbles in the pool fluid. The aeration means B can be formed by perforated air blowing tubes or by nozzles installed in the floor or by any other conventional means. The biological treatment of water in reactor 2 results in nitrification and the conversion of ammonium NH4 + to nitrate NO3-. The effluent leaving basin 2 contains SO42-sulphates originating from the oxidation of sulphides from nitrates and / or nitrites. A recirculation duct 3 is provided between the ventilated basin 2 and the anoxic basin 1a, a pump 3p being mounted on the duct 3. Similarly a duct 4 is provided for the recirculation of the ventilated basin 2 to the anoxic basin 1b, a 4p pump being inserted in this conduit. The recirculation of the aerated tank 2 to the anoxic zones 1a, 1b to provide them with nitrates is therefore carried out in step feed or step-feed. The recirculation flow rate is slaved to the amount of nitrates necessary to oxidize all the sulphides present in the water in a S / N mass ratio (sulfur / nitrogen) of between 0.5 and 3. To adjust the recirculation flow, an automated controller 5 controls the operating speed, and therefore the flow rate, of the pumps 3p and 4.p. To make the proposed treatment more reliable, the installation can include a series of

  flowmeters installed on the different ducts, and different sensors or measuring probes. The control instructions are established, in particular, according to parameters such as the organic carbon content in the incoming flow Q and in the heterotrophic anoxic basin 1a, the sulphide content in the incoming flow Q and in the autotrophic anoxic basin 1b. and the nitrate content in the aerated pool 2. These parameters are obtained by measurement probes such as 6, 7 and 8 provided in the pools 1a, 1b, 2 and connected to the controller 5. Other parameters such as the pH, oxidation-reduction potential, temperature, dissolved oxygen can be captured by appropriate probes. This information is used to optimize the operating parameters of the basins 1a, 1b and 2. The probes and sensors connected to the controller 5 allow continuous monitoring of the evolution of the treatment and the control of corrective actions. Fig.2 is a diagram of an installation variant according to the invention in the case of a purification plant where there is a sludge die comprising an anaerobic cligester (not shown) giving the supernatants of hydration, loaded nitrogen. These supernatants can be separately treated biologically in a SBR sequential aerobic biological reactor. The U flow of effluents that are highly concentrated in N-NH 4 + of the centrates, filtrates, condensates and lixiviatsa type is discharged into the reactor 9, which is a free culture aerated pond reactor with stirring means and means for blowing air. or oxygen in the bottom, as for the aerated pond 2. In the reactor 9 the treatment of concentrated ammonium effluents is achieved by partial nitrification and denitrification. Ammonium is oxidized to nitrites which are reduced to gaseous nitrogen, without the need for nitrite to nitrates. This process, also known as the nitrate shunt, described for example in EP-A-0826639, is theoretically capable of reducing by 25% the oxygen inputs for nitrification and by 40% the contributions of biodegradable carbonaceous reactants for denitrification, as well as the production of associated heterotrophic sludge. The elimination of effluents concentrated in nitrogen in the reactor 9 comprises several fractionated phases respectively feeding, aeration and anoxia, the number and the duration of these phases as well as the addition of carbon reactants being adjusted thanks to a series of real-time measurements in the effluent to be treated, in the discharge, and in the biological reactor 9. A supply of nitrites from the autotrophic anoxic reactor 1b is provided by a pipe 10 leaving the reactor 9 and opening into the reactor 1b. A pump 11, controlled by the controller 5, is arranged on

  The pipe 10. The reactor 1b feed is made from a fraction of the volume of water treated by the reactor 9 during the aerated phase during which there is production of nitrites. Part of these nitrites is sent to the basin 1b. The flow in line 10 is controlled according to the need for nitrites to oxidize the sulfides in the autotrophic anoxic reactor 1b. Examples of treatment are given below.

  Generally, the concentration ranges of the various physicochemical parameters during the treatment described in the scheme of FIG. 1 are: Parameter Unit Raw water Basin 1 to Basin 1b Basin 2 COD mg / I 200-750 0-50 0 -50 0-20 N-NH4 + mg / I 20-70 20-70 20-70 0-10 N-NOx mg / I 0-5 0-5 0-5 20-70> 2 mg / I 5-100 5 -100 0-0.5 0-0.5 S-SO42- mg / I 20-100 20-100 25-200 25-200 Temperature C 15-45 15-45 15-45 15-45 The table above shows the fall of COD (Chemical Oxygen Demand) produced by the treatment in the pool 1a, which corresponds to the removal of most of the organic carbon, which is completed in the aerated pool 2. The transformation of the nitrogen ammonium N-NH4 + in Nitrogen Nitrogen NNOx takes place in aerated pond 2. Oxidation of sulphides S2- into sulphates takes place in pond lb.

  In the following two examples, in general, we find the following operating conditions:

  The anoxie reactors 1a and 1b have a mechanical stirring system and the aerated pool 2 of an air blowing system in addition to mechanical agitation. The concentration of suspended solids in tanks 1a, 1b and 2 is maintained between 1 and 5 g / l.

  The step-feed recirculation rate is a function of the concentration of nitrates and sulphides and varies between 50 and 400%. In all basins, the pH is between 6.5 and 8.5.

  The sludge age in pools is between 6 and 20 days, depending on the temperature. The hydraulic residence time or TSH in each of the reactors 1a and 1b is 2 to 3h and in the reactor 2 from 4 to 6h. Example: Two basins la and lb each with a TSH of 2h and a pool 2 with a TSH of 4h.

  Characterization of raw and treated water: Parameter Unit Raw water Treated water Recirculation DCO mg / I 450 30 - N-NH4 + mg / I 45 1 - N-NOx mg / I 3 1-3 45: ~ 2- mg / I 0.1 - S-SO42- mg / I 35 75 - Temperature C 20 20 _ It is noted that the ratio of sulphides to be eliminated / nitrates consumed chosen is 1.5. Under these conditions, to oxidize 30 mg / l of sulphides, 20 mg / l of N-NO3 is required. The recirculation of nitrates from basin 2 to basin lb must make it possible to bring this concentration. Excess nitrates, ie 25 mg / l, are denitrified by recirculation in the basin 1a.

  The proposed system is capable of removing 100% of the sulphides present in the raw water, completely nitrifying and denitrifying.25

  2nd example: According to the same initial operating conditions (pH, T, 02, sludge age) but with raw water having a different typology: Parameter Unit Raw water Treated water Recirculation DCO mg / I 450 30 - N-NH4 + mg / I 10 1 - N-NOx mg / l 3 1-3 10 S2- mg / I 30 - S-SO42- mg / l 35 - the temperature C 20 20 - The ratio SIN of 1.5 is no longer respected as it There is a deficit of nitrates due to a low concentration of ammonium at the entrance station. It is still necessary to have 20 mg / l of N-NOx to oxidize the 30 mg / l of sulphides. In the present case, it has been chosen to recirculate 50% of the outflow from the aerated tank 2 to the anoxic hetérotrophe basin 1a, ie 5 mg / l of N-NOx, since it is essential to recover TAC (complete alkalimetric titre). for autotrophic denitrification. 15 mg / l of N-NOx are missing which can be compensated for by the fraction of the volume of treated water supplied by the reactor 9.

  The invention allows treatment of wastewater virtually without consuming expensive chemical reagents, and with reduced sludge production due to the low growth of autotrophic bacteria in the autotrophic anoxic basin.

Claims (4)

  1. Process for the treatment of sulphide and ammonium-laden wastewater, in particular waste water of urban or industrial origin or digestion returns, condensates, leachates, characterized in that: - sewage first undergo anoxic treatment (1) biologically in free cultures according to which, in a first step (la), the organic carbon is essentially removed by heterotrophic bacteria, and in a second step (1b), separated from the first, the sulphides are biologically oxidized by autotrophic bacteria with reduction of nitrates and / or nitrites, - the effluent leaving the second stage (1b) is subjected to an aerobic biological treatment in free cultures (2) for the transformation of ammonium into nitrates.   2. Method according to claim 1, characterized in that a fraction of the effluent which has undergone the aerobic biological treatment in free cultures (2), and which contains nitrates, is recirculated to the second step (1 b) and the first step (la) of the anoxic treatment.   3. Method according to claim 2, characterized in that the fraction of the effluent recirculated to the anoxic treatment (1 a, 1 b) is regulated according to the amount of sulphides to be treated. 25   4. Method according to one of claims 1 to 3, characterized in that, in the second step (1b) of the anoxic treatment the mass ratio S / N (sulfur / nitrogen) is maintained between 0.5 and 3. Process according to claim 2 or 3, characterized in that the recirculated fraction is slaved to the amount of nitrates necessary to oxidize all the sulphides present in the water in the second stage (1b) of the anoxic treatment. 6. Process according to claim 2 or 3, characterized in that the recirculated fraction is slaved to ensure, in the second stage (lb) of the anoxic treatment, the mass ratio S / N (sulfur / nitrogen) of between 0, 5 and 3.207. Process according to any one of the preceding claims, characterized in that the oxidation of the sulfides by biological means is coupled to a sequential aerobic biological reactor (SBR) nitritation with a feed of the second stage (1b) of the treatment anoxic to nitrites from nitritation. 8. The method of claim 7, characterized in that the supply of the second step (lb) of the anoxic treatment of nitrites from the nitritation (9) is controlled according to the amount of sulfide to be oxidized with the nitrites. 9. Installation for carrying out a process according to any one of the preceding claims, characterized in that it comprises two biological reactors (1,2) in series with free cultures, the first reactor (1) being a two-stage anoxic biological reactor comprising a heterotrophic basin (1a) and a separate autotrophic basin (1b), while the second reactor (2) is an aerated pool in free cultures. 10. Installation according to claim 9, characterized in that a recirculation of nitrates is carried out from the aerated pool (2) to basins (1a, 1b) of anoxia as a function of the concentration of sulphides to be oxidized. 11. Installation according to claim 9, characterized in that it comprises measurement probes (6,7,8) in the anoxic basins (1a, 1b) and in the aerated basin (2) for several parameters including the carbon of the incoming effluent, the sulphide content in the autotrophic anoxic basin (lb) and the nitrate content in the aerated basin, these measurement probes being connected to a controller (5) which controls the recirculation flow rates as a function of measured parameters 12. Installation according to one of claims 9 to 11, for a purification plant comprising a sludge die with an anaerobic digester and a sequential aerobic biological reactor (9) providing partial nitrification and denitrification of e concentrated in ammonium, characterized in that the sequential aerobic biological reactor (9) is coupled (10,11) to the autotrophic anoxic tank (1b) for a supply of nitrite from this basin (1b).