AU2008244181B2

AU2008244181B2 - Method and equipment for processing waste water containing sulphides and ammonium

Info

Publication number: AU2008244181B2
Application number: AU2008244181A
Authority: AU
Inventors: Marylene Baron; Adriana Gonzales Ospina
Original assignee: Degremont SA
Current assignee: Suez International SAS
Priority date: 2007-03-02
Filing date: 2008-02-27
Publication date: 2012-02-02
Anticipated expiration: 2028-02-27
Also published as: CN101626983A; MX2009009315A; WO2008132296A2; FR2913234A1; AU2008244181A1; FR2913234B1; WO2008132296A3

Abstract

The invention relates to a method for treating waste water containing sulphides and ammonium, in particular waste water from an urban or industrial origin or digestion feedbacks, condensates and lixiviates. The waste water is first subjected to an anoxic processing (1) in a free-culture biological manner, wherein, in a first step (1a), the organic carbon is essentially removed by heterotrophic bacteria and, during a second step (1b) separate from the first, the sulphides are oxidised in a biological manner by autotrophic bacteria with nitrites or nitrates reduction. The effluent from the second step (1b) is submitted to a free-culture aerobic biological treatment (2) for converting the ammonium into nitrates. The conjunction with a sequential aerobic biological reactor (9) compensates a potential nitrate deficit.

Description

1 PROCESS AND INSTALLATION FOR TREATING WASTE WATER CONTAINING SULPHIDES AND AMMONIUM. The invention relates to a process for treating waste water loaded 5 with sulphides and with ammonium, in particular waste water of urban or industrial origin or materials fed back from digestion, condensates or leachates. Waste water contains in particular carbon, nitrogen and sulphur in various forms of compounds which can be treated chemically by various processes. All the physicochemical treatments consist in separating the 10 compounds of these elements from a liquid phase in order to concentrate them in another phase. They are in particular stripping (removal of gas from water by means of an entrainment gas), reverse osmosis, distillation, chemical precipitation or catalytic oxidation processes, the implementation and running costs of which are high. Removal of these compounds via the biological process 15 presents itself as a treatment alternative. Biological treatments for nitrogen and for carbon Carbonaceous pollution and nitrogenous pollution of waste water are principally eliminated by the biological process. This conventional process is 20 based on the ability of microorganisms to eliminate the pollution by assimilation or by biodegradation. The carbonaceous organic matter is oxidized in an aerated medium by microorganisms, principally heterotrophic bacteria. These microorganisms use the colloidal and dissolved carbonaceous organic matter and convert it 25 either to gas or to biomass. As regards the treatment of nitrogen, the treatments mainly distinguished are treatments by nitrification and denitrification, by which the ammonium is oxidized in two steps under aerated conditions by autotrophic bacteria (first to nitrites then to nitrates) and, finally, reduced to nitrogen gas 30 under anoxic conditions by heterotrophic bacteria. The biological reactions are presented in the schemes below. Nitrification: NH 4 + -+ N0 2 -+ N0 3 Denitrification: NO -- + N0 2 -4 NO -+ N 2 0 -> N 2 2 Limits of the nitrogen treatment: - The nitrification/denitrification by the biological process is an effective process but it demands up to 1/3 of the total oxygen consumed by the purification station. 5 - The treatment is difficult to operate compared with the treatment of carbon, with resulting frequent additions of carbonaceous reactants (methanol, ethanol, etc.) in order to complete the denitrification. - This treatment requires considerable holding times and 10 tank volumes, since the nitrification kinetics are very slow. Drawbacks of the presence of sulphur: Many problems linked to the presence of sulphur in waste water flowing into purification stations have been clearly identified, namely: - The emission of nauseating odours (rotten egg type). 15 These unpleasant odours are detected well before they represent a danger to human beings since the olfactory sensors have a detection threshold at 0.15 ppm. - The health risks related to H 2 S (hydrogen sulphide). In fact, this molecule is toxic starting from 10 ppm, with worsening of the effects 20 according to the duration of exposure. - Corrosion of concrete and metals due to oxidation of sulphides to sulphuric acid by certain bacteria of Thiobacillus type. - The development of filamentous bacteria. Since the water is septic, filamentous bacteria are more competitive than the 25 conventional bacteria of the flock with respect to oxygen. Some are capable of accumulating sulphur in the form of granules in their cells. - The need to cover the works in order to prevent dispersion of H 2 S. 30 Sulphur treatments Sulphates are naturally present in waste water and sulphur enters into the composition of intracellular proteins of microorganisms. The sulphur can be oxidized or reduced according to the conditions of the medium and the populations of bacteria present. In an aerobic medium, sulphides are converted 35 to sulphates by sulphur-oxidizing bacteria, and in an anaerobic medium, sulphates are converted to sulphides by sulphate-reducing bacteria.

C NRPonbl\DCC\DYB\4051934_ .DOC. 6ATE * 12ERGEFOR12AT -3 Aerobic: S 2 - - 804 Anaerobic: SO ~-> S2- + H 2 S The treatment of waste water by autotrophic denitrification with 5 oxidation of sulphides has been described in FR 2841548-Al. This process uses three biological reactors in series with biomass fixed on a mobile support: anaerobic, anoxic and aerobic. The first reactor makes it possible to reduce the sulphates to sulphides and to treat the carbonaceous load. In the second reactor, the sulphides are 10 oxidized to sulphates by reduction of the nitrates originating from the recirculation from the aerobic tank to the anoxic tank. Finally, in the aerobic reactor, ammonium is converted to nitrates. This process puts a constraint on expenditure since it requires a large volume of expensive support materials. 15 The limit of this treatment scheme is based on the amount of sulphides to be oxidized by autotrophic denitrification which consumes alkalinity. Since the proposed operating method consumes alkalinity (autotrophic nitrification in the aerated tank + autotrophic denitrification in the anoxic tank), in the event of an excess of sulphides to be treated, the anoxic medium would be limiting in terms of 20 alkalinity, or even in terms of nitrates. The oxidation of the sulphides would not therefore be complete. Moreover, the production of volatile fatty acids in the first anaerobic reactor also consumes alkalinity, which is all the more unfavourable to the sulphide-oxidation reactions in the anoxic second reactor. 25 The present invention especially seeks to provide a process which makes it possible to remove the sulphides and the various forms of nitrogen economically and effectively. The process according to the invention for the treatment of waste water loaded with sulphides and with ammonium, in particular of waste water of urban or 30 industrial origin or materials fed back from digestion, condensates or leachates, is characterized in that: - the waste water first undergoes a free-culture anoxic treatment via the biological process, according to which, in a first step, organic carbon is essentially eliminated by heterotrophic bacteria, and in a second step, separate from the first, 35 the sulphides are oxidized via the biological process by autotrophic bacteria with reduction of nitrates and/or of nitrites, C:4WRPorblDCC\WAMU9441921. DOC-2511W2011 -4 - the waste water leaving the second step is subjected to a free-culture aerobic biological treatment for conversion of the ammonium to nitrates. Preferably, a fraction of the effluent which has undergone the free culture aerobic biological treatment, and which contains nitrates, is recirculated to 5 the second step and the first step of the anoxic treatment. The fraction of the effluent recirculated to the anoxic treatment is advantageously adjusted according to the amount of sulphides to be treated. In the second step of the anoxic treatment, the S/N (sulphur/nitrogen) ratio by mass is preferably maintained between 0.5 and 3. 10 The recirculated fraction may be adjusted according to the amount of nitrates/nitrites required to oxidize all the sulphides present in the water in the second step of the anoxic treatment. Advantageously, the recirculated fraction is adjusted so as to ensure, in the second step of the anoxic treatment, the S/N (sulphur/nitrogen) ratio by mass of between 0.5 and 3. 15 The oxidation of the sulphides via the biological process can be coupled to nitrite formation by means of an aerobic sequential biological reactor (SBR), with the second step of the anoxic treatment being fed with nitrites originating from the nitrite formation. The feeding of the second step of the anoxic treatment with nitrites 20 originating from the nitrite formation can be adjusted according to the amount of sulphides to be oxidized with the nitrites. The invention also relates to an installation for implementing the process defined above, characterized in that it comprises two free-culture biological reactors in series, the first reactor being a two-stage anoxic biological 25 reactor comprising a heterotrophic tank and an autotrophic tank which are separate, while the second reactor is an aerated free-culture tank. Preferably, recirculation of the nitrates is carried out from the aerated tank to the anoxic tanks according to the concentration of sulphides to be oxidized. The nitrate recirculation can be carried out by step-feed from the aerated tank to 30 the anoxic tanks according to the concentration of sulphides to be oxidized. The installation can comprise measuring probes in the anoxic tanks and in the aerated tank, for several parameters including the carbon content of the effluent flowing in, and the sulphide content in the autotrophic anoxic tank, these measuring probes being connected to a controlling device which controls the 35 recirculation flow rates according to the parameters measured. In the case of an installation for a purification station comprising a C:NRPortbrDCCWAM944192.IDOC-25/10/W2011 -5 sludge system with an anaerobic digester and an aerobic sequential biological reactor providing partial nitrification and partial denitrification of effluents with a high concentration of ammonium, the aerobic sequential biological reactor can be coupled to the autotrophic anoxic tank so as to feed this tank with nitrites. 5 Apart from the arrangements disclosed above, the invention comprises a certain number of other arrangements which will be described more explicitly hereinafter in terms of exemplary embodiments described with reference to the attached drawings, but which are in no way limiting. On these drawings: Fig. 1 is a scheme of an installation according to an embodiment of the 10 invention, and Fig. 2 is a scheme of a variant of an embodiment of the installation. Referring to Fig. 1 of the drawings, an installation according to an embodiment of the invention for the treatment, according to a continuous flow, of waste water loaded with sulphides and with ammonium can be seen. This 15 installation comprises an anoxic reactor 1 compartmentalized into a heterotrophic tank 1a followed by an autotrophic tank 1b. The two tanks 1a and 1b are separate and the effluent leaving the tank 1a is taken up by pumping means and sent to the tank 1b. The tank la receives the flow Q of waste water containing carbon, 20 sulphides and ammonium. Stirring means Aa, Ab are provided in each of the tanks 1a, 1b. There is no blowing of air or oxygen into these tanks. Heterotrophic and autotrophic bacteria are naturally present in the waste water and in the tanks 1a, 1b, in the form of free cultures. Due to the fact that the anoxic tank 1a receives a flow Q loaded with 25 organic carbon, the heterotrophic bacteria develop rapidly in this tank 1a, while the autotrophic bacteria develop much less rapidly under such conditions. The anoxic tank la is thus heterotrophic and makes it possible to treat the entering carbon, and to denitrify a surplus of nitrates originating from an aerated tank 2 and which are not used in the oxidation of the sulphides in the autotrophic anoxic tank 1b. 30 The aerated tank 2 is downstream of the tank 1b. The tank lb receives the waste water leaving the tank 1a, the organic carbon having been for the most part removed from said waste water. The action of the autotrophic bacteria in the tank lb is promoted by the low organic carbon load of the water originating from the compartment la. Thus, by separating the 35 anoxic tanks la, 1b, conditions have been created which promote, in the tank la, the action of the heterotrophic bacteria and, in the tank 1b, the action of the C:WRPonb\DCCWAM'944192_I.DOC-25/110/2011 -6 autotrophic bacteria. The autotrophic anoxic tank lb makes it possible to treat the sulphides present in the raw water by virtue of the nitrites derived from the aerated tank 2 and/or of the nitrites derived from the nitrite formation step in the aerobic 5 sequential biological reactor (SBR). The sulphides are oxidized by autotrophic denitrification which consumes alkalinity. The heterotrophic denitrification which takes place in the tank 1a makes it possible to produce alkalinity. By virtue of this production of alkalinity in the tank 1a, the process is not slowed down or stopped by a decrease in alkalinity due to the consumption in the tank 1b. 10 The effluent or waste water originating from the tank lb is sent, for aerobic free-culture biological treatment, to the aerated tank 2 which comprises stirring means Ac and aeration means B located at the bottom of the tank 2 for injecting bubbles of air or oxygen into the liquid of the tank. The aeration means B may be formed by perforated tubes for blowing air or by nozzles installed in the 15 floor or by any other conventional means. The biological treatment of the water in the reactor 2 leads to nitrification and the conversion of ammonium NH 4 * to nitrate N0 3 . The effluent leaving the tank 2 contains sulphates SO42 originating from the oxidation of the sulphides using the nitrates and/or nitrites. 20 A recirculation pipe 3 is provided between the aerated tank 2 and the anoxic tank la, a pump 3p being mounted on the pipe 3. Similarly, a pipe 4 is provided for recirculation from the aerated tank 2 to the anoxic tank 1 b, a pump 4p being inserted in this pipe. The recirculation from the aerated tank 2 to the anoxic zones 1 a, 1 b in order to provide them with nitrates is therefore carried out by step 25 feed. The recirculation flow rate is adjusted according to the amount of nitrates required to oxidize all the sulphides present in the water according to an S/N (sulphur/nitrogen) ratio by mass of between 0.5 and 3. To adjust the recirculation flow rate, an automated controlling device 5 controls the operating speed, and therefore the flow rate, of the pumps 3p and 4p. 30 In order to make the proposed treatment reliable, the installation may comprise a series of flowmeters installed on the various pipes, and various sensors or measuring probes. The control instructions are established, in particular, according to parameters such as the organic carbon content in the in-flow Q and in the heterotrophic anoxic tank 1a, the sulphide content in the in-flow Q and in the 35 autotrophic anoxic tank lb and the nitrate content in the aerated tank 2. These parameters are obtained by measuring probes such as 6, 7 and 8 provided in the C NRPonbl\DCCWAM\3944192_l.DOC.25/lOII -7 tanks 1a, 1b, 2 and connected to the controlling device 5. Other parameters such as pH, oxidoreduction potential, temperature or dissolved oxygen can be measured by appropriate probes. This information serves to optimize the operating parameters of the tanks Ia, lb and 2. The probes and sensors connected to the 5 controlling device 5 allow the evolution of the treatment to be continuously monitored and corrective actions to be controlled. Fig. 2 is a scheme of a variant of an installation according to the invention in the case of a purification station where there is a sludge system comprising an anaerobic digester (not represented) which provides dewatering 10 supernatants loaded with nitrogen. These supernatants can be treated separately by the biological process in an aerobic sequential biological reactor SBR 9. The flow U of effluents with a very high concentration of N-NH 4 +, of the centrate, filtrate, condensate or leachate type, is transferred into the reactor 9 which is a free-culture aerated tank reactor with stirring means and means for blowing in air 15 or oxygen at the bottom, as for the aerated tank 2. In the reactor 9, the treatment of effluents with a high concentration of ammonium is carried out by partial nitrification and partial denitrification. The ammonium is oxidized to nitrites which are reduced to nitrogen gas, without it being necessary to go through nitrite conversion to nitrates. This process, also 20 called "nitrate shunt", described for example in EP-A-0826639, is theoretically capable of reducing the supply of oxygen for nitrification by 25% and the supply of biodegradable carbonaceous reactants for denitrification by 40%, and also the production of associated heterotrophic sludge. The elimination of effluents with a high concentration of nitrogen in the 25 reactor 9 comprises several fractionated feed, aeration and anoxia phases, respectively, the number and the duration of these phases and also the addition of carbonaceous reactants being adjusted by virtue of a series of real-time measurements in the effluent to be treated, in the waste, and in the biological reactor 9. 30 Nitrite feed for the autotrophic anoxic reactor 1b is provided by a pipe 10 which leaves the reactor 9 and opens out into the reactor 1b. A pump 11, controlled by the controlling device 5, is placed on the pipe 10. The feeding of the reactor lb is carried out using a fraction of the volume of water treated by the reactor 9 during the aerated phase, during the course of which there is production 35 of nitrites. A part of these nitrites is therefore sent to the tank 1b. The flow rate in the pipe 10 is adjusted according to the nitrite needs for oxidizing the sulphides in C:WR Potbl\DCC\WAM\944192_.LDOC-25/1020I I -7A the autotrophic anoxic reactor 1b. Treatment examples are given hereinafter. These examples of embodiments of the invention are non-limiting. 5 In general, the concentration ranges for the various physicochemical parameters during the treatment described in the scheme of Fig. 1 are: 8 Parameter Unit Raw water Tank 1a Tank lb Tank 2 COD mg/ 200-750 0-50 0-50 0-20

N-NH

4 * mg/I 20-70 20-70 20-70 0-10 N-NOx mg/I 0-5 0-5 0-5 20-70 s2- mg/I 5-100 5-100 0-0.5 0-0.5 S-S0 4 2 - mg/I 20-100 20-100 25-200 25-200 Temperature 0 C 15-45 15-45 15-45 15-45 The above table reveals the drop in COD (chemical oxygen demand) produced by the treatment in the tank la, which corresponds to the elimination of most of the organic carbon, which elimination is completed in the aerated 5 tank 2. The conversion of the ammonium nitrogen N-NH 4 * to nitrate nitrogen N-NOx takes place in the aerated tank 2. The oxidation of the sulphides S 2 - to sulphates takes place in the tank 1b. 10 In the following two examples, the following operating conditions are, in general, found: The anoxic reactors Ia and 1b have a mechanical stirring system and 15 the aerated tank 2 has a system for blowing in air in addition to a mechanical stirrer. The concentration of material in suspension in the tanks 1a, 1b and 2 is maintained between 1 and 5 g/l. The degree of step-feed recirculation depends on the concentration of 20 nitrates and of sulphides and oscillates between 50 and 400%. In all the tanks, the pH is between 6.5 and 8.5. The age of sludge in the tanks is between 6 and 20 days, depending on the temperature. The hydraulic residence time or HRT in each of the reactors 1a and 25 1b is from 2 to 3 h, and in the reactor 2 is from 4 to 6 h. 1st Example: Two tanks 1a and lb each with a HRT of 2 h, and a tank 2 with a HRT of 4 h.

9 Characterization of the raw and treated water: Parameter Unit Raw water Treated water Recirculation COD mg/I 450 30 N-NH4* mg/I 45 1 N-NOx mg/I 3 1-3 45 s2- mg/I 30 0.1 S-SO42- mg/I 35 75 Temperature 0 C 20 20 It is noted that the chosen ratio of sulphides to be eliminated/nitrates 5 consumed is 1.5. Under these conditions, to oxidize 30 mg/I of sulphides, 20 mg/ of N-N0 3 ~ are necessary. The recirculation of the nitrates from the tank 2 to the tank 1 b should make it possible to provide this concentration. The excess nitrates, i.e. 25 mg/l, are denitrified by recirculation to the tank 1 a. 10 The proposed system is capable of eliminating 100% of the sulphides present in the raw water, and of completely nitrifying and denitrifying. 2 nd Example: According to the same initial operating conditions (pH, T*, 02, age of sludge, 15 etc.), but with raw water having a different typology: Parameter Unit Raw water Treated water Recirculation COD mg/I 450 30

N-NH

4 * mg/I 10 1 N-NOx mg/ 3 1-3 10 s2- mg/I 30 _

S-SO

4 2 - mg/I 35 Temperature *C 20 20 The S/N ratio of 1.5 is no longer adhered to since there is a nitrate deficiency due to a low concentration of ammonium entering the station. It is still 20 necessary to have 20 mg/I of N-NOx in order to oxidize the 30 mg/ of sulphides. In the present case, it was chosen to recirculate 50% of the flow leaving the aerated tank 2 to the heterotrophic anoxic tank 1a, i.e. 5 mg/I of N-NOx, since it C:\NRPorbDCOWAMG944192_ DOC-2$/10/20l1 - 10 is essential to recover the TA (total alkalinity) for the autotrophic denitrification. 15 mg/ of N-NOx are lacking, but can be compensated for by the fraction of the volume of treated water provided by the reactor 9. The invention allows treatment of waste water virtually without consuming 5 expensive chemical reactants, and with reduced sludge production due to the low growth of autotrophic bacteria in the autotrophic anoxic tank. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior 10 publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as 15 "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. Process for the treatment of waste water loaded with sulphides and with ammonium, characterized in that: 5 - the waste water first undergoes a free-culture anoxic treatment via a biological process, according to which in a first step, organic carbon is essentially eliminated by heterotrophic bacteria, and in a second step, separate from the first step, the sulphides are oxidized via the biological process by autotrophic bacteria with reduction of nitrates and/or nitrites, and 10 - the waste water leaving the second step is subjected to a free-culture aerobic biological treatment for conversion of the ammonium to nitrates.

2. Process according to Claim 1, characterized in that the waste water is of urban or industrial origin or effluent from digestion, or is a condensate or a leachate. 15

3. Process according to Claim 1 or 2, characterized in that a fraction of the waste water which has undergone the free-culture aerobic biological treatment, and which contains nitrates, is recirculated to the second step and the first step of the anoxic treatment. 20

4. Process according to Claim 3, characterized in that the fraction of the waste water recirculated to the first and second steps of anoxic treatment is adjusted according to the amount of sulphides to be treated. 25

5. Process according to any one of Claims 1 to 4, characterized in that, in the second step of the anoxic treatment, the S/N (sulphur/nitrogen) ratio by mass is maintained between 0.5 and 3.

6. Process according to Claim 3 or 4, characterized in that the recirculated fraction 30 is adjusted according to the amount of nitrates required to oxidize all the sulphides present in the water in the second step of the anoxic treatment.

7. Process according to Claim 3 or 4, characterized in that the recirculated fraction is adjusted so as to ensure, in the second step of the anoxic treatment, a S/N 35 (sulphur/nitrogen) ratio by mass of between 0.5 and 3. C:V4"o1bDCCUDYBW05j934_ I DOC. I O t/I2012 - 12

8. Process according to any one of the preceding claims, characterized in that the oxidation of the sulphides via the biological process is coupled to nitrite formation by means of an aerobic sequential biological reactor (SBR), with the second step of the anoxic treatment being fed with nitrites originating from the nitrite formation. 5

9. Process according to Claim 8, characterized in that the feeding of the second step of the anoxic treatment with nitrites originating from the nitrite formation is adjusted according to the amount of sulphides to be oxidized with the nitrites.

10 10. Process for the treatment of waste water loaded with sulphides and with ammonium substantially as hereinbefore described with reference to the accompanying figures and/or examples.

11. Installation for implementing a process according to any one of the preceding 15 claims, characterized in that it comprises two free-culture biological reactors in series, the first reactor being a two-stage anoxic biological reactor comprising a heterotrophic anoxic tank and an autotrophic anoxic tank which are separate, while the second reactor is an aerated free-culture tank. 20

12. Installation according to Claim 11, characterized in that recirculation of nitrates is carried out from the aerated tank to the anoxic tanks according to the concentration of sulphides to be oxidized.

13. Installation according to Claim 11, characterized in that it comprises measuring 25 probes in the anoxic tanks and in the aerated tank, for several parameters including the carbon content of the effluent flowing in, the sulphide content in the autotrophic anoxic tank and the nitrate content in the aerated tank, these measuring probes being connected to a controlling device which controls the recirculation flow rates according to the parameters measured. 30

14. Installation according to any one of Claims 11 to 13, for a purification station comprising a sludge system with an anaerobic digester and an aerobic sequential biological reactor providing partial nitrification and partial denitrification of effluents with a high concentration of ammonium, characterized in that the aerobic 35 sequential biological reactor is coupled to the autotrophic anoxic tank so as to feed C:NRPotbl\DCCDYB\4051934 l.DOC-9/I12/20I I - 13 this tank with nitrites.

15. Installation according to claim 11 substantially as hereinbefore described with reference to the drawings and/or examples. 5