ES2315178A1 - Method for the treatment of residual waters and installation to carry out such method. (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Method for the treatment of wastewater, with recovery of energy and nutrients, and installation to carry out said method. It includes the introduction of the waste water to be treated in an anaerobic reactor and its treatment in it, the separation of the treated water from the sludge produced by means of a membrane filter, the selective separation by means of membranes of the different gases produced, and the reintroduction of part of the ch 4 produced in the reactor as a means of stirring the reactor and extracting the various gases dissolved in the water, as well as a set of devices for carrying out said method. (Machine-translation by Google Translate, not legally binding)

Description

Wastewater treatment method e installation to carry out said method.

The present invention aims at a installation and a method for wastewater treatment, in which at least part of the microbiological treatment is anaerobic, understanding the recovery of different gases produced, especially CO 2, H 2 and CH 4, a recirculation of part of the CH4 to the treatment tank, and a membrane filtration of treated water so that produced sludge, which includes microorganisms, remains in the system long enough for the realization of process.

Wastewater treatment plants basically comprise a stage of prior solids separation suspended, organic or not, a stage of biological treatment in mostly aerobic, which requires permanent oxygenation of the body of water, and a stage of sedimentation of solids and Extraction of treated water.

Wastewater has its origin in uses domestic or urban, industrial, agricultural and coming from the rain. These waters are treated by means of stations treatment plants to minimize the impact on their discharge to medium and allow reuse. These treatment plants they are based on fundamentally aerobic processes, and have the need for a great energy contribution due mainly to electric consumption of the motors associated with the blowers, which They pump the air into the biological treatment tanks.

An added problem is the large production of residual sludge These sludges can reach a figure of 1000 Tons of mud for each Hm 3 of treated water. These muds They comprise a large amount of organic matter. While these have been been using in agriculture, the decline in some areas  of the cultivated area reduces the possibility of its use in said medium. In addition, the distance from the point of production to Application can be large, and transportation costs very high. Finally, the legislation establishes certain limits in the use of said sludge. Therefore, the minimization of said residual sludge.

Degradation processes have been carried out anaerobic for the stabilization of sludge produced in the wastewater purification, in the degradation of solid waste and in the treatment of wastewater with very high organic matter concentrations.

Anaerobic degradation of organic matter It is carried out by different groups of microorganisms anaerobes that have a low growth rate, so that high residence times in the reactor are required to achieve adequate degradation of said matter. It implies the need to use large volumes of reaction, which makes unfeasible the purification of large flows. To minimize the necessary reaction volume, input currents to Anaerobic systems are usually heated (35ºC to 55ºC) to favor the growth of the microorganisms involved. The processes known anaerobic digestion are made up of reactors of complete mixing without any recirculation of solids, so the hydraulic retention time and the retention time of the microorganisms match. This fact limits the organic load to treat and the concentrations of microorganisms in the reactor.

Therefore, the use of anaerobic processes in the treatment of wastewater of matter concentration organic low or moderate is not viable, nor economically by the profitability and cost of the process, neither by the investment and size required in the treatment plant.

The volume of reaction needed in the processes anaerobes could be reduced by separating microorganisms from the treated current and reintroducing them back into the reactor. So their concentration is favored and the debug performance. This separation is technically impossible.  through sedimentation or flotation processes.

Thus, the objectives of the present invention are:

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process empowerment anaerobes with membrane separation for the elimination of organic matter present in wastewater;

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obtaining waste gases that enable chemical and energy use;

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reducing sludge of the wastewater treatment process, minimizing the environmental impact associated with its discharge.

In addition, the water obtained after the process Anaerobic can be treated by utilizing processes low energy aerobes to obtain effluents from high quality, allowing the reuse of water in uses Agricultural and industrial.

From the biochemical point of view, the process of anaerobic degradation of organic matter can be divided into four phases (hydrolysis, acidogenesis, acetogenesis and methanogenesis) in which different groups of coexist microorganisms Some of these groups relate to each other in synophic form, being its activity dependent on that of the other group. One of the most relevant cases of sytrophy is that It exists among the H 2 consuming methanogenic bacteria (hydrogenotrophic methanogens) and the bacteria responsible for the anaerobic degradation of fatty acids of more than two atoms of carbon. Also, when the influent contains quantities important sulfates may become important competition because of the H2 that exists between the hydrogenotrophic methanogens and another group of bacteria called sulfatoreductors. This group of bacteria is responsible for the appearance of H2S in the biogas stream, decreasing the yield of CH4 obtained per unit of organic matter eliminated according to the amount of sulfate in the food. The reduction of sulfate is more thermodynamically favorable than the production of CH_ {4}. The presence of H2S in biogas worsens its quality for later use and will require separation to avoid corrosion problems in pipes and equipment energy use.

The acetogenic reactions are thermodynamically unfavorable at high concentrations of H2. Various studies have shown that in conditions anaerobes a low hydrogen partial pressure is necessary, of order of 10-4 -10-5 atm for the process to take place in favorable conditions. The high production of H2 during these reactions therefore require that it be consumed by the bacteria that live in symphony with the producers of H2 to avoid inhibition of the acetogenic process.

The use of membranes will generate large constant efforts in the filtration process and high turbulence in the reactor that can alter the biochemistry of process, and may lead to the acidification of the reactor by the accumulation of volatile fatty acids associated with the inhibition of methanogenic hydrogenotrophic bacteria by disappearance of synergy between different groups of microorganisms participants in the process. Therefore, in a process of anaerobic degradation with membranes, if the synergy between Hydrogenotrophic and acetogenic bacteria is affected, it will not be possible to ensure low concentrations of H2, causing acidification of the medium. As indicated, for the application of membrane technologies to anaerobic processes it is necessary to give solution to the acidification problems caused, either by the lack of alkalinity in the influent water, either because of the disappearance of the synergy between acetogenic and methanogenic bacteria hydrogenotrophic

To compensate for the lack of alkalinity in the influent water, given the high flow to be treated, you cannot consider the addition of reagents as a viable alternative. For the Therefore, the process requires maintenance of the pH by other means. It is proposed in this invention the favor of desorption of the CO2 dissolved in the reaction medium. This desorption is a physical process that depends on the transfer coefficient of matter and saturation of CO2 in the liquid, related with the partial pressure of CO2 in the gas phase. Therefore, the extraction of the CO2 contained in the gas will favor its desorption of the reaction medium. The recirculation of part of the biogas current produced after the separation of CO2 contained in said stream, will maximize both the desorption as the decrease in the partial pressure of CO2 in the gas phase recirculated to the reactor. Also, recirculation of the biogas stream solves the accumulation of H2 by the possible disappearance of the syndrome between the bacteria acetogenic and hydrogenotrophic methanogenic provided separate the H2 from said stream. In addition, the desorption of the H2 will reduce the growth of sulfatoreductive bacteria, allowing greater energy use of matter organic and minimizing the problem of H2S in the streams of biogas. The separate gas stream rich in H2 will allow its use as a high quality biofuel, which results an additional advantage of the proposed treatment method.

The first stage of water treatment residual, based on an anaerobic membrane process, will allow remove practically all organic matter from water present in the water, letting the water pass to a later stage. In this later stage will be treated biologically the content in Ammoniacal phosphorus and nitrogen. In said later stage the treatment is carried out in a discontinuous sequential reactor that requires little energy consumption for aeration, every time that almost all organic matter has already been separated and degraded in the previous anaerobic stage.

The use of sequential reactors industrial-scale discontinuous offers versus systems traditional lower cost and more control and operation efficient, especially in biological elimination processes of nutrients, since in a single reactor the anaerobic, anoxic and aerobic stages necessary for elimination of organic matter, nitrogen and phosphorus, eliminating the currents of recirculation of the activated sludge existing in the processes in continuous.

State of the art

Aerobic treatment techniques of sewage, which comprises primarily aerobic tanks and decanters, which are usually used in stations sewage treatment plants

Membrane separation means are known with high permeate flows. The biological membrane reactors Aerobes include the confinement of microorganisms in the inside the system, allowing precise control of your time of permanence in said reactor. However the reactors aerobic biological membranes have high costs of acquisition and operation, fouling of membranes, and the high concentration of microorganisms presents problems of aeration. In addition, the viscosity of the mixed liquor becomes significant when the concentration of microorganisms is very high, making reactor agitation and filtration difficult across the membrane

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Water treatment studies have been done residuals by applying membranes for treatment anaerobe. In this case it has been operated at temperatures higher than 35 ° C and to compensate for acidification it has been necessary to add bland.

WO 0136340 A1 discloses a purification plant Biological wastewater with two anaerobic digesters and the corresponding debugging process, which requires heat the influents for the biological process, and has a alkaline dispenser for pH regulation.

EP 0 751 913 consists of a device and procedure for simultaneous biological elimination of phosphorus and nitrogen from wastewater in aerobic, anoxic areas and anaerobic, containing floating substrate material, with a Secondary secondary treatment plant and collection line sludge, the nitrification stage (2) being connected with integrated simultaneous denitrification.

The proposed invention comprises a method for wastewater treatment comprising fundamentally:

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a previous screening; saying sieving allows removing non-organic solid elements from water received;

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a regulation of influents; the regulation of the influents allows to regulate the process cycle in the anaerobic reactor to which it drains that the organic load variations are not made abruptly;

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water separation from sludge by filtering, such as filtering by means of membrane;

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obtaining a biogas composed primarily of CH4, but containing hydrogen (H2) and other compounds such as hydrogen sulfide (H2S) and carbonic anhydride (CO2);

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gas extraction produced in the anaerobic reactor; gas production supposes a decrease in the mass of organic matter present in the reactor;

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selective separation by membrane of the different gases produced, to obtain a CH4 current, free of other gases, and optionally the separation of H2 from the rejection current;

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reintegration after selective separation of part of the biogas, constituted mainly by CH 4, in the reactor tank, favoring the gas extraction from sludge mass;

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the extraction of sludge from sludge reactor tank for final evacuation;

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evacuation of filtered water, including depressurization and gas separation; Y optionally

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aerobic biological treatment of effluent waters for the elimination of compounds of nitrogen and phosphorus

Brief description of the drawings

In order to illustrate the explanation that will follow, attached to this specification a sheet of drawings, which in a single figure represents the essence of the present invention, and in which:

Figure 1 shows a schematic of a installation that also carries out the process object of the present invention

Detailed description of the invention

As indicated above so In summary, a method for water treatment is proposed residuals that after a pre-processing and before a post treatment, It comprises the following phases:

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Introduction of sifted water a an anaerobic reactor;

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Separation of treated water from sludge through a membrane;

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Extraction of biogas produced in the anaerobic reactor;

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Separation of the different gases produced, and particularly CH 4, H 2, CO 2 and H2S;

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Reintroduction of part of the CH4 produced in the reactor by reincorporation into same; the reintroduction will normally take place through the pumping through multiple nozzles arranged in the base Anaerobic reactor bottom.

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Since the sludges are permanently recirculated, these will have part of dissolved CH4, and to a lesser extent measure other gases, since they are extracted but not reintroduced into The anaerobic reactor. Therefore, preferably, the method it also includes the extraction of CH4 at the stage of depressurization after separation of treated water by membranes.

In the anaerobic reactor, the highest part of the organic matter present in the wastewater transforming it into biogas through biological processes anaerobes The content of the reactor is passed through the membrane ultrafiltration in which two streams are obtained: one with low concentration in organic matter and practically free of suspended solids (permeate) and a concentrated sludge stream (rejection) that is mostly reintroduced into the reactor anaerobic, allowing work at high retention times mobile. These high times allow a sludge production very low, in addition to said residual sludge being stabilized

To improve the quality of the water stream obtained in the permeate, it is subjected at a later stage to a aerobic biological treatment in which the amount of soluble organic matter, ammonium and phosphorus, remaining after anaerobic process In said reactor the nitrification of the ammonium present, denitrification of nitrate formed in the Ammonium oxidation and biological phosphorus removal. The organic matter necessary for denitrification processes and phosphorus removal will be contained in the stream of permeate and its concentration can be controlled with the operation of the biological anaerobic membrane reactor.

On the other hand, as a result of degradation anaerobic organic matter in the biological reactor of membranes, a compound biogas stream will be obtained mainly by CH 4, CO 2, H 2, and small amounts of N 2 and H 2 S. In order to separate the CH 4 of the remaining gases produced, membranes will be used selective. In a first separation a current is obtained enriched in CH_ {4} and a rejection current with the rest of the gases. Optionally, the rejection of this first membrane it can be introduced in a second membrane where you will get a permeate stream enriched with H2 for its use separately. As a result of this separation selective, three differentiated gas streams are obtained:

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A stream enriched in CH 4 free of H 2 S, H 2 and CO 2.

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A stream enriched in H2.

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A stream of rejection composed of CH 4, CO 2 and with traces of H 2 S.

A part of the stream enriched in CH4 is recirculated to the anaerobic reactor to favor the desorption and entrainment of all dissolved gases. So by how much CO2 is extracted and the H2 of the reactor formed by the anaerobic degradation of organic matter, the reactor acidification.

The installation object of the invention is formed by a pretreatment zone, a treatment zone anaerobic, a gas separation zone, and a zone of biological elimination of nutrients.

The pretreatment zone comprises a sieve 2 at the water inlet 1, which passes to a regulation raft 3. In said regulating raft 3 will deposit the water until it is Start the further process. When the system requires new supply, either continuously or discontinuously, the pump is activated of supply 4 that will provide flow to the treatment system anaerobe.

Said anaerobic treatment system comprises a pumping means 5 that drives towards a membrane filter 6 the sludge from at least one anaerobic reactor 7. The filter of membrane 6 receives a current, said composite current being sludge received from anaerobic reactor 7 and from water coming from of the regulation tank 3, together with the water to be recycled. The filter membrane 6 will allow filtered water to pass to a third post-treatment zone or zone, leaving the sludge resulting in said membrane, which are redirected back to reactor. Only some materials will remain in the filtered water soluble, such as phosphorus or nitrogen compounds. Because that anaerobic reactions are relatively slow, allows keep said sludge in the reactor for as long as it is estimated convenient. When deemed convenient, the device has a purge means 16 in which the sludge will be removed when it is no longer are likely to participate significantly in the reaction.

Due to the digestion processes of microorganisms, gases 8 resulting from said reaction. Said gases 8 are extracted by means of a device pumping 9, and will be passed through separators 10, 12, in the that H_ {2} will be obtained, which will be treated and stored in at least one deposit 11 or will be conducted for direct use; CO 2, CH4 and H2S, which will be stored separately in the corresponding reservoir 13, and practically pure CH4, which it will also be stored in its corresponding deposit 15. The device includes the corresponding gas analyzers 14. In the embodiment shown, a CH4 separator is provided of the rest of the gases 10, and a second membrane 12 separating the H 2 of CO 2, CH 4 and H 2 S.

To favor the desorption of gases dispersed in sludge as a result of digestion of the different microorganisms, CH4 is pumped as a means of sludge agitation and entrainment of the gases produced. Due to the drag along the CH_ {4} of CO2_ and H2_, it is possible to keep pH without the need to provide reagents for pH control.

The installation includes an area of post-treatment, in which filtered water from the membrane filter 6 are led to a depressurizer 17. Because these waters still have dissolved gases from digestion, in said depressurizer gases are redirected to a reservoir 18 or redirect to the anaerobic reactor outlet line.

The extracted waters are conducted to a tank of regulation 19 that by means of the corresponding pumping means 20 they are redirected to a reactor 22, in which by biological means extract the nitrogen and phosphorus compounds, among others, Remnants in the water. To facilitate the reaction is introduced by means of one or more air blowers 21 in the tank by means of a plurality of aeration nozzles arranged at the bottom, leaving a purge and extraction zone at the bottom sludge 23, and at the top an outlet 24 of purified water. 22 mixing means are also arranged in said aerobic reactor. 25.

It must be understood within the scope of this invention any variation in number and arrangement of the means employees, as long as the essence of what is here is maintained described

Application in water treatment residual

Claims (18)

1. Method for water treatment residuals that after a pre-processing and before a post treatment, It comprises the following phases:

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Water supply influences to an anaerobic tank;

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Separation of treated water from sludge through a membrane filter;

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Extraction of biogas produced in the anaerobic reactor;

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Selective separation of different gases produced by membranes;

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Anaerobic tank agitation and entrainment of the gases produced with part of the CH4 produced in the reactor by pumping and reincorporating the same.

2. Method for the treatment of wastewater, according to claim 1, characterized in that the reintroduction of CH4 takes place by pumping through nozzles arranged in the lower part of the anaerobic reactor. 3. Method for the treatment of wastewater, according to claim 1, characterized in that it comprises depressurization of the water resulting from the separation of water and sludge, and extraction in said phase of the resulting gases. 4. Method for the treatment of wastewater, according to claim 1, characterized in that it comprises the selective separation of the extracted gases. 5. Method for the treatment of wastewater, according to claim 1, characterized by comprising the analysis of the extracted gases. 6. Method for the treatment of wastewater, according to claim 1, characterized in that the purging of the sludge from the tank is understood when the organic matter present in these is already scarce. 7. Installation for carrying out the method of claim 1, characterized by comprising at least:

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An area of pretreatment;

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A treatment area anaerobic, said anaerobic treatment zone understanding

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At least one anaerobic reactor (7);

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At least one membrane filter (6) sludge separation, permeable to water and retaining these sludge;

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A separator set of gases

8. Installation according to claim 7, characterized in that the pretreatment zone includes at least one sieve (2) and a regulating raft (3). 9. Installation according to claim 7, characterized in that the anaerobic reactor (7) has a biogas extraction zone (8), said compression and / or pumping means (9) comprising said compressed and / or pumped biogas being conducted to a gas separation zone. 10. Installation according to any of claims 7 and 9, characterized in that the gas separation zone comprises at least one membrane separator (10) permeable to CH4 and impermeable to the rest of the gases. 11. Installation according to any of claims 7, 9 and 10, characterized in that the gas separation zone comprises at least one selective membrane separator for H2 (12). 12. Installation according to claim 10, characterized in that it comprises a pumping and reintroduction line of CH4 in the anaerobic reactor. 13. Installation according to claim 7, characterized by comprising storage devices for the extracted gases. 14. Installation according to claim 7, characterized in that it comprises conduction lines of the extracted gases for direct use. 15. Installation according to claim 7, characterized in that it comprises a device for purging sludge in excess of the anaerobic tank (16). 16. Installation according to claim 7, characterized by comprising downstream of the membrane filter (6) a depressurizing device (17), and extracting means of the residual gases carried by the filtered water. 17. Installation according to claims 9 and 16, characterized in that the gases obtained from the depressurizer (17) are stored or taken to the gas separation zone. 18. Installation according to claim 7, characterized in that it further comprises an aerobic reaction zone, including regulating means such as a regulating tank, pumping means (20) to the reactor, aeration means (21), mixing means ( 25) and purge means (23).