RU2753657C1 - Method for biological purification of waste water from phosphates - Google Patents

Abstract

FIELD: water purification.

SUBSTANCE: invention can be used for purification of waste water. Waste water is purified from phosphates in an SBR-type sequencing batch bioreactor under cyclic conditions. 1. The stage of creating anaerobic conditions by blowing the reactor with nitrogen for 5 minutes. 2. The stage of anaerobic growth of phosphate-accumulating organisms (PAO) acetate as a source of carbon, executed while stirring, at a pH of the medium of 8.5 to 8.7 and a temperature of 18 to 20°C. 3. The stage of growth of the PAO under conditions of air aeration at an intensity providing an oxygen concentration in the medium of 2 to 3 mg/l for 3 hours, forming a microbial community characterised by the presence of aggregates with a size not exceeding 25 mcm, containing PAO of the Rhodocyclaceae family belonging to the Dechloromonas and Zoogloea genera. 4. The stage of removing a part of the culture with the purified water in the absence of the stage of settling and deposition of silt. Stages 1 to 3 are executed in each cycle. Stage 4 can be executed after completing several cycles consisting of stages 1 to 3.

EFFECT: invention provides an increase in the specific efficiency of purification of waste water and provides a possibility of cultivating new phosphate-accumulating microorganisms.

3 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of wastewater treatment from phosphorus compounds. The invention can be used to obtain microbial communities enriched with phosphate-accumulating microorganisms with their further use as an inoculum at industrial treatment facilities using the technology of biological phosphorus removal. The invention can also be used to obtain enrichment cultures of phosphate-accumulating organisms for research purposes.

Phosphorus is a nutrient that plays a key role in many natural and artificial ecosystems. The intensification of its extraction and use has led to the emergence of two large-scale problems: massive eutrophication of water bodies caused by the ingress of phosphorus with wastewater and the danger of a global phosphorus deficit in the coming decades due to the limited and non-renewable nature of its mineral reserves.

The most rational way to solve these problems is to develop and implement technologies for removing phosphorus from wastewater to an environmentally friendly level and converting the extracted phosphorus into a commercial product for reuse (Cordell D., White S. Sustainable Phosphorus Measures: Strategies and Technologies for Achieving Phosphorus Security // Agronomy 2013. V. 3. P. 86-116. Cornel P., Schaum C. Phosphorus recovery from wastewater: needs, technologies and costs // Water Science & Technology. 2009. V. 59. No 6. P. 1069- 1076.).

Effective methods for removing phosphorus compounds from wastewater include stages of biological phosphorus removal (Hirota R., Kuroda A., Kato J., Ohtake H. Bacterial phosphate metabolism and its application to phosphorus recovery and industrial bioprocesses // J. Biosci. Bioeng. 2010 V. 109. P. 423-432), based on cyclic biochemical processes characteristic of microorganisms belonging to the poorly studied group of phosphate-accumulating organisms (FAO).

Known technologies for biological phosphorus removal refer either to continuous processes or to the so-called SBR-processes organized in reactors of the SBR type (Sequencing Batch Reactor) (Wastewater Engineering. Treatment and Resource Recovery, fifth ed., Metcalf & Eddy / AECOM. Revised by G. Tchobanoglous, HD Stensel, R. Tsuchihashi, F. Burton, M. Abu-Orf, G. Bowden, W. Pfrang. Mc Graw Hill Education, New York, NY, 2014; Sequencing Batch Reactor Technology. Scientific & Technical Reports No. 10 / Eds. Wilderer PA, Irvine RL, Goronszy MC IWA Publishing. 2001, 76). For example, there is a known method for biological removal of phosphorus in a continuous process, which consists in mixing return activated sludge with incoming waste water under anaerobic conditions, and then transferring the sludge mixture to the aeration zone, where "greedy" absorption of phosphates occurs (US 3236766.1966).

The disadvantages of continuous processes are the large areas occupied by structures, the need to pump significant volumes of liquid to create technological zones (the so-called "recycle"), which significantly increases the cost and complicates water purification.

Methods using batch-type reactors - SBR-reactors, characterized by a higher volumetric power due to combining the functions of a bioreactor and a settler (sludge separator) in one vessel - are devoid of this drawback. In one cycle in SBR, the culture goes through a series of phases with a given duration and sequence: filling the reactor, phase with anoxic conditions, phase with anaerobic conditions, phase with aerobic conditions, settling phase and disposal of the spent medium.

For example, there is a known method for purifying wastewater from biogenic elements, including phosphorus, in an SBR bioreactor with the formation of a fluidized bed, according to which, in the first stage, wastewater is supplied to a reactor with granular activated sludge, then mixing under anaerobic conditions occurs, in the next stage, the reactor aerated, at the fourth stage, the sludge mixture settles, at the fifth stage, the purified water is drained (US 2014/0224729, 2014). The main condition for the implementation of the SBR wastewater treatment process is the ability of the grown biomass to settle (in a broad sense, to sufficiently quickly separate from the liquid phase), and therefore the biomass is grown in the form of floccules or granules of rapidly settling activated sludge or on the surface of loading elements.

A known method for biological removal of phosphorus in an SBR-type reactor, using granular activated sludge, and provides for the need for a stage of settling the sludge in the bioreactor (RU 2334685, 2008).

However, activated sludge floccules have a complex multicomponent structure, contain ballast substances, therefore, it is extremely difficult to obtain an artificial microbial community with controlled microbial components dominated by FAO in this case. Another disadvantage of using granular biomass is the slowdown of biochemical reactions due to slow mass transfer caused by the presence of a diffusion barrier between the outer and inner layers of activated sludge granules, which has millimeter dimensions. In addition, the use of floccules or granules can lead to clogging of the diffusers of aeration systems, as well as to the accumulation of sludge at the bottom of the bioreactor in case of emergency shutdown of mixing systems.

The closest technical solution, which we have chosen as a prototype, is a method for biological purification of waste water from phosphates, carried out in a bioreactor of sequential-periodic action. The method includes the stage of feeding wastewater and activated sludge containing microbial cultures enriched with phosphate-accumulating organisms (FAO) into the bioreactor, the stage of anaerobic growth of FAO using acetate ions as a carbon source, the stage of FAO growth under conditions of aeration with air, the stage of precipitation of activated sludge and a step for withdrawing the purified aqueous medium. Activated sludge in the well-known solution removes 75-80% of phosphorus from the environment to be purified (Kotlyarov R.Yu. et al., New phosphate-accumulating bacteria found in a plant for purifying wastewater from phosphates, Microbiology, vol. 88, 6, 2019, p. 710-714).

However, the known method is not effective enough. Achieving a high degree of purification from phosphates requires a significant time for the process due to the low specific activity of the biomass of activated sludge containing those specified in the known FAO solution.

The task of the proposed technical solution is to develop a new effective method for purifying wastewater from phosphates using microbial associations enriched with FAO.

The technical result of the invention is to increase the rate of removal of phosphates from waste water and stabilize the process due to the development of microorganisms in the bioreactor with increased specific activity, as well as expanding the range of biological methods for purifying waste water from phosphates.

The problem is solved by the described method of purification of waste water from phosphates in a bioreactor of sequential-periodic action (reactor of the SBR type), which includes the stage of feeding waste water and activated sludge containing microbial cultures enriched in cultured phosphate-accumulating organisms (FAO) into the bioreactor, the stage of creating anaerobic conditions, the stage of anaerobic growth of FAO using acetate ions as a carbon source, the stage of growth of FAO under conditions of aeration with air at an intensity that provides an oxygen concentration in the medium of 2-3 mg / L, with the formation of a microbial community characterized by the presence of aggregates not exceeding 25 µm, containing FAO of the family Rhodocyclaceae belonging to the genera Dechloromonas and Zoogloea, and the stage after aeration of the withdrawal of the purified homogeneous aqueous medium, carried out in the absence of sedimentation and concentration of activated sludge in the bioreactor.

Preferably, the withdrawal of the purified aqueous medium from the bioreactor is carried out after n cycles, consisting of the stages of anaerobic and aerobic growth of FAO, while the volume of the withdrawn aqueous medium is equal to the total volume of the medium to be purified supplied in n cycles, where n = 4.

Mainly, when the bioreactor is started, activated sludge is supplied from the biological wastewater treatment plant to remove phosphorus, containing the well-known FAO of the Rhodocyclaceae family - Ca. Accumulibacter.

The step of creating anaerobic conditions is preferably, but not exclusively, carried out by purging the reactor with nitrogen for 5 minutes.

The stage of anaerobic growth of FAO is preferably carried out at a pH of the medium of 8.5-8.7 and a temperature of 18-20 ° C for 2 hours 50 minutes.

The stage of aerobic growth is preferably carried out at a pH of the medium of 8.5-8.7 and a temperature of 18-20 ° C for 3 hours.

The technical result of the invention is achieved in the scope of an independent claim, since when carrying out the method in the amount of the totality of features included in the independent claim, conditions are created for the cultivation of a new microbial community of FAO, which has a higher specific activity compared to the specific activity of the microbial community cultivated in the method prototype.

The proposed method, after feeding into the reactor the initial purified medium containing activated sludge, in fact, consists of the following sequentially proceeding stages:

1. Stage of creation of anaerobic conditions;

2. Anaerobic stage with addition of readily available carbon and energy source in the form of acetate;

3. Aerobic stage, carried out under stated conditions after consumption of acetate;

4. The stage of removing the purified aqueous medium and part of the culture without carrying out the stage of settling the sludge;

In this case, stages 1-3 are necessarily included in each cycle, and stage 4 (removal) can be repeated after several stages 1-3.

Figure 1 shows one of the possible installation schemes for implementing the claimed method, where the corresponding position numbers indicate the following units:

1 - bioreactor;

2 - pump for waste water supply;

3 - pump for removing the purified medium and culture;

4 - air compressor;

5 - a source of gaseous nitrogen;

6 - gas supply control system;

7 - oxygen meter.

FIG. 2 shows a graph of the content of soluble phosphates in the bioreactor during the cultivation process: curve 1 is the concentration of P-PO ₄ in the waste water entering the reactor, curve 2 is the concentration of P-PO4 at the outlet of the bioreactor.

The effectiveness of the method developed by us is confirmed below.

Example.

The laboratory setup for the cyclic cultivation of the microbial community is made on the basis of the BIOSTAT B bioreactor (SARTOPJUS) with a working volume of 2 liters, equipped with a stirring device and an external jacket for thermostating.

The cyclical nature of cultivation consisted of alternating anaerobic conditions with the presence of acetate (a readily available source of carbon and energy) and aerobic conditions without acetate (after its consumption in the anaerobic stage). The supply of the purified medium to the bioreactor and the withdrawal of the purified medium and culture were carried out using two peristaltic pumps. Aerobic and anaerobic conditions are created by supplying air or nitrogen to the bioreactor, purified from traces of oxygen, using a gas supply control system (LLC ELTOCHPRIBOR, RF). Gas flows and peristaltic pumps are controlled automatically using a universal logic module LOGO (SIEMENS).

Each cycle of cultivation of the microbial community in the bioreactor lasted 6 hours and consisted of several successive stages:

(1) creating anaerobic conditions by purging the reactor with nitrogen for 5 minutes (during this time, the concentration of O ₂ in the culture fell below 0.05 mg / l), after which 0.125 l of waste water is fed into the bioreactor. The total duration of this stage was 10 minutes.

(2) an anaerobic stage, during which the medium is stirred with a stirrer at a speed of 200 rpm. The duration of the anaerobic period was 2 hours 50 minutes.

(3) the aerobic stage, during which the microbial community contained in the aquatic environment is aerated with air at an intensity that provides an oxygen concentration of 2-3 mg / l. The duration of the aerobic stage was 3 hours.

Every four cycles, consisting of anaerobic and aerobic stages (total duration 24 hours), at the end of the aerobic period (5 minutes before its end), the air supply is stopped and 0.5 liters of a homogeneous aqueous medium containing the formed microbial community is drained from the bioreactor.

At stage (1), the rector was inoculated with sludge from the aerotanks of the Lyubertsy treatment facilities (Moscow). The waste water supplied to the reactor corresponded in composition to the waste water of municipal treatment facilities. The aqueous medium supplied for purification had the following composition (in g / l): CH ₃ COONa × 3H ₂ O - 0.708; (NH ₄ ) ₂ SO ₄ - 0.046; KH ₂ PO ₄ -0.109; yeast extract - 0.009; MgSO ₄ × 7H ₂ O - 0.135. pH - 8.5-8.7, temperature - 18-20 ° С.

Chemical analyzes were performed according to standard methods. The dissolved oxygen concentration was measured electrochemically using an Oxi 197 oxygen meter (WTW, Germany).

The morphology of cells and their aggregates was examined on an Olympus CX41 microscope with phase contrast (Olympus, Japan). Phosphate-accumulating bacteria in the microbial community were determined by the presence of phosphorus-containing granules in the cells. The number of cells (% of the cell composition of the entire community) containing various inclusions was determined based on the average value obtained by counting cells in 80 fields of view.

Four samples of activated sludge were examined:

(1) from an industrial bioreactor for the removal of organic matter, ammonium and phosphorus (Lyubertsy Wastewater Treatment Plant, Moscow). This sample was used to download a lab setup.

(2) sludge sampled from the laboratory bioreactor on the 8th day from the moment of its start-up.

(3) sludge sampled from the laboratory bioreactor on the 15th day from the moment of its start-up.

(4) sludge taken from the laboratory bioreactor on the 22nd day from the moment of its start-up.

During the process, the phosphorus content in the water purified in the bioreactor was determined, as well as the composition of the microbial community using metagenomic methods of molecular biology (Mardanov AV et al. Metagenome of the microbial community of anammox granules in a nitritation / anammox wastewater treatment system // Genome Announcements. 2017. V5. Iss. 42. e01115-17).

The content of suspended matter in the bioreactor after its inoculation with activated sludge was 3.4 g / L, pH 8.5. During the first 15 days, the suspension weight decreased to 0.2 g / l. After 15 and up to 22 days of operation, the concentration of microbial biomass and the pH value of the aqueous phase in the reactor were at a constant level, which indicated the stabilization of its operation. At the same time, there was a gradual decrease in the content of phosphates in the aqueous phase of the reactor. On the 5th day of cultivation, the difference between the amount of phosphates in the original medium and the bioreactor drain water was 4.9 mg / l. By the 8th day, this figure increased 1.5 times (up to 7.2 mg / L), and by the 22nd day it was 11-12 mg P-PO ₄ / L, which corresponded to 50% of phosphorus removal from the incoming medium (see. Fig. 2 and Table 1).

At the same time, the specific activity of the activated sludge biomass increased 17 times, which indicates the efficiency of the increase in the activity of FAO and an increase in their share in the microbial community of the activated sludge.

This example illustrates the technical feasibility and efficiency of wastewater treatment using the developed technology - using a modified SBR-type reactor. As can be seen from table 1, carrying out the process under the conditions of the prototype is much less effective than under the conditions of the claimed method.

It is important that the phosphate-accumulating microbial community cultivated under the stated conditions turned out to be 2 times more active than in the prototype, and it was obtained in just 2 weeks, whereas usually the commissioning period takes up to several months.

Comparison of the results of water purification, obtained by the technology developed by us, with the results of water purification by the known technology, showed an increased efficiency of phosphorus removal by the proposed method. In particular, the concentration of phosphorus in wastewater is usually 4-8 mg / L and decreases to concentrations below 1 mg / L. At the same time, the concentration of activated sludge in industrial aeration tanks, as a rule, is in the range of 3-4 g / l, which, taking into account the residence time of 12 hours, gives the value of the specific activity of biomass for removing phosphorus not more than 0.2 mg P / g sludge * h. Under the conditions of the implementation of the proposed method, the specific activity was 0.85 mg P / g sludge * h (4 times higher than in industrial aeration tanks).

The calculated specific activity of the activated sludge biomass in the prototype method after 3 weeks is 0.38 mg R / g sludge * h (Table 2), that is, 2 times lower than the proposed method.

The obtained technical result is directly related to the fact that we have identified the conditions for the implementation of the proposed purification method: the sequence of stages and their parameters, indicated above, in which the microbial community is cultivated, containing new dominant representatives of FAO with increased activity.

Molecular biological methods made it possible to trace the dynamics of the development of the microbial community and determine the dominant representatives of FAO. In the activated sludge of the treatment plant, which we used as an inoculant, the well-known FAO of the family Rhodocyclaceae - Ca were identified. Accumulibacter, which are considered representative of this physiological group, typical of sewage treatment plants.

However, during the implementation of the method, the proportion of the original microorganisms decreased. By the time of the most effective phosphorus removal by the microbial community (22 days), the original Candidatus "Accumulibacter phosphatis" bacteria were not identified in the composition. After the aeration stage in the absence of the precipitation stage, representatives of the Rhodocyclaceae family, belonging to the genera Dechloromonas and Zoogloea, were formed as the dominant group in the community, the proportion of which increased during the operation of the reactor as much as possible in comparison with other bacteria and reached 22% of the number of all bacteria. It is these bacteria that are included in the aggregates, the size of which, when excluding the precipitation stage, does not exceed 25 microns, provide a higher rate of phosphorus removal from waste water, i.e. increased process efficiency.

The proposed method with a modified cyclic sequential-periodic carrying out of the stages of cultivation of the microbial community makes it possible to cultivate new FAOs with increased activity and are a promising tool for the further development of biotechnologies for the removal of phosphorus from aqueous media. In addition, the method developed by us can be used for the cultivation of new FAO representatives in significant quantities.

The invention expands the range of effective methods for biological purification of aqueous media from contamination with phosphorus compounds.

Claims (3)

1. A method for biological purification of waste water from phosphates in a bioreactor of sequential-periodic action of the SBR type, including the stage of feeding waste water and activated sludge enriched in phosphate-accumulating organisms (FAO) into the bioreactor, the stage of creating anaerobic conditions by blowing the reactor with nitrogen for 5 minutes, the stage of anaerobic growth of FAO using acetate as a carbon source, which is carried out with stirring, the pH of the medium is 8.5-8.7 and a temperature of 18-20 ° C, the stage of growth of FAO under conditions of aeration with air at an intensity that ensures the concentration of oxygen in medium 2 -3 mg / L for 3 h, with the formation of a microbial community characterized by the presence of aggregates not exceeding 25 μm, containing FAO of the family Rhodocyclaceae belonging to the genera Dechloronomas and lack of sedimentation and concentration of activated sludge in the bioreactor. 2. The method according to claim 1, characterized in that the withdrawal of the purified aqueous medium from the bioreactor is performed after n cycles, consisting of the stages of anaerobic and aerobic growth of FAO, while the volume of the withdrawn aqueous medium is equal to the total volume of the medium to be purified supplied for n cycles, where preferably n = 4. 3. The method according to claim 1, characterized in that when the bioreactor is started, activated sludge is supplied from biological wastewater treatment plants for phosphorus removal, containing the known FAO of the Rhodocyclaceae family - Ca. Accumulibacter.

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