RU2305072C1 - Process of biologically removing phosphorus from waste waters - Google Patents

Abstract

FIELD: waste water treatment.

SUBSTANCE: invention relates to processes of biologically treating domestic and compositionally equivalent industrial waste waters. Process comprises consecutive holding of a consortium of microorganisms removing organic and mineral impurities from waste waters under anaerobic, anoxide, and aerobic conditions in container constructions with intensive mass exchange provided by stirrers, pumps, and air bubbling. Recycled active sludge from secondary settlers is mixed with fresh waste water stream having passed grates and sand-catchers. Resulting mixture is subjected to flotation treatment, after which flotation concentrate is held for at least half-hour in anaerobic bioreactors at continuous stirring and clarified fluid with sludge water is loaded to denitrificator along with circulating stream of sludge mix from denitrificator outlet and anaerobically treated flotation concentrate. Further, sludge mix from denitrificator is routed to nitrificator, wherein it is subjected to air bubbling. Biomass of excess active sludge augmented under aerobic conditions of nitrificator is dewatered to cake state and subjected to biocomposting under aerobic conditions in mixture with sawdust without loss of phosphorus so that phosphorus-rich biohumus is obtained.

EFFECT: reduced volume of container constructions and power consumption on removal of phosphorus from waste water and increase of phosphorus in biohumus obtained from active sludge grown on treatment plant.

1 dwg

Description

The invention relates to methods for biological treatment of domestic and similar industrial wastewater composition and can be used in municipal services of cities, towns and industrial enterprises in wastewater treatment from organic and mineral impurities, including nutrients.

It is known to use the biological method for removing biogenic elements, including phosphorus, from wastewater [1] by creating successively anoxic, anaerobic and aerobic zones with intensive mass transfer in aeration tanks with activated sludge in each zone by means of agitators and hydraulic mixing using axial and screw pumps, as well as air sparging.

The disadvantages of this method include: the bulkiness and high energy costs of anaerobic and anoxic zones due to passing through them the entire volume of wastewater to be treated; a large surface of the water mirror in capacitive structures where anaerobic and anoxic conditions are organized, through which oxygen enters the sludge mixture, worsening the conditions for the regeneration of phosphorus-absorbing bacteria; loss of phosphorus during prolonged compaction of adhered activated sludge in gravity sludge compactors.

The objective of the invention is to reduce the volume of capacitive structures and energy costs for wastewater treatment from phosphorus and increase the phosphorus content in vermicompost obtained from activated sludge growing at the treatment plant.

The problem is solved by the fact that in the known method, primary settlers are eliminated and all return activated sludge from the secondary settlers is mixed with a stream of initial wastewater that has been filtered in grates and trapped in sand traps, the mixture is subjected to flotation treatment and then the flotation concentrate is sent for a half-hour anaerobic treatment continuous stirring of the fermenting mass, and clarified water with sludge water is fed into the denitrifier along with the circulation flow of the sludge mixture from the exit of the aerotank-n trifikatora and anaerobnoobrabotannym flotation concentrate. Next, the sludge mixture from the denitrifier is sent to a nitrifier with intensive air bubbling to mix the sludge mixture and introduce oxygen-dissolving air.

The biomass of excess activated sludge that grows under aerobic conditions of the nitrifier is subjected to flotation treatment on flotators released during hours of minimal influx of wastewater to the treatment plant, and the flotation concentrate of the grown biomass of excess activated sludge is sent for mixing with sawdust or other shredded plant waste, and then dehydrated squeezing apparatus, from which sludge water is returned to the denitrificators, and the cake is fed to bio-composters to obtain biohumus.

The technological scheme of the proposed method for the biological removal of phosphorus from wastewater is shown in the drawing. The legend on the diagram is as follows:

A is the flow of source wastewater;

1 - gratings;

2 - sand traps;

3 - wastewater flotators;

4 - anaerobic bioreactor;

5 - denitrifier;

6 - nitrification;

7 - secondary sedimentation tanks;

8 - post-treatment reactor;

9 - contact tank;

10 - flotators of excess activated sludge;

11 - mixer;

12 - spin apparatus;

13 - biocomposter;

14 - a tank with garbage;

15 - sand bunker;

16 - flotation concentrate;

17 - duct;

18 - clarified runoff after flotation;

19 - excess activated sludge;

20 - return activated sludge;

21 - chloragent;

22 - silt water;

23 - sawdust;

24 - flotation concentrate of excess activated sludge;

25 - cake;

26 - vermicompost;

27 - circulation flow of the sludge mixture;

B - purified water.

In accordance with the technological scheme, the initial wastewater A is sent for filtering to the grates 1, for the allocation of sand in the sand traps 2, and then after mixing with the return activated sludge stream, it is fed to flotators 3, where using an air-water mixture obtained at a pressure of at least 15 MPa provide for the removal into the flotation concentrate 16 of biomass of return activated sludge 20 suspended solids and dissolved organic substances sorbed by activated sludge from the source waste water stream. The clarified initial wastewater and sludge water of the return activated sludge is sent to the denitrifier 5 by the clarified effluent stream after flotation 5. The circulation stream of the sludge mixture 27 from the outlet of the nitrifier 6, as well as the flotation concentrate anaerobically treated in anaerobic bioreactors 4, are also fed to the denitrifier 5. Mixing of the sludge mixture in both denitrifiers 5 and nitrifiers 6 is carried out by bubbling with air supplied through air ducts 17.

From the nitrifying agents 6, the sludge mixture is fed to the secondary clarifiers 7. Return activated sludge is returned to the flotators 3, and the biologically purified clarified wastewater is sent to the post-treatment reactor 8. Air is supplied to the post-treatment reactors 8 through air ducts 17. The treated stock is sent for disinfection to the contact tank 9 where the wastewater comes in contact with a chlorine agent or is exposed to ultraviolet radiation.

Disinfected wastewater is discharged by a stream of purified water into a water intake.

Wastewater waste is discharged in the form of garbage into a garbage bin 14, into a sand bunker15.

The grown biomass of excess activated sludge is discharged to flotators 10, from which the sludge water is returned to the nitrifier 5, and the flotation concentrate of excess sludge is sent to the mixer 11 for mixing with sawdust and then to the squeezer 12. From the squeezing machine 12 cakes are fed into the bio-composter 13 to produce biohumus and sludge water is pumped into a nitrification 6.

The process of biological wastewater treatment from phosphorus is as follows.

The initial runoff, freed from large mechanical impurities (rags, fruit seeds, pockets, and other plastic products) in the gratings 1, as well as from sand in the sand traps 2, enters the flotator 3. At the same time, return active sludge 20 and a water-air mixture are fed to the flotator 3 obtained from potable water and air under a pressure of at least 15 MPa. In flotator 3, microbubbles of air released from a water-air mixture due to a decrease in pressure to atmospheric and the presence of hydrophobic and surface-active substances in the wastewater - centers for the allocation of microbubbles, raise particles of activated sludge 3, suspended solids of wastewater, its organic impurities to the surface of the flotator water. including fatty, surfactant and hydrophobic substances such as, for example, petroleum products. Impurities that have surfaced on the surface form a flotation concentrate 16 having a moisture content of 95 ... 96%. The chemical oxygen demand in the liquid phase of the flotation concentrate reaches 40 ... 50 kgO / m ³ . At the same time, most of the mass of suspended substances of the flotation concentrate is represented by activated sludge microorganisms, which need oxygen for their life.

The flotation concentrate is collected from the surface of the flotator 3 and sent to anaerobic bioreactors 4, where with continuous stirring for at least half an hour the suspension of activated sludge and wastewater impurities, the organic impurities present therein are transformed into compounds more absorbed by aerobic microorganisms, such as acetate, propionate, butyrate and lactate . Phosphorus-absorbing bacteria in the anaerobic zone consume the above compounds and turn them into polyhydroxyalkonates (PHA), mainly poly-β-hydroxybutyrate and poly-β-hydroxyvalerate. The transport of organic acids into the cell and the biosynthesis of RIA require energy, which polyphosphate accumulating organisms (PAO _S ) obtain by hydrolytic cleavage of polyphosphate. They synthesize polyphosphate under aerobic conditions, taking phosphorus from waste water and accumulating it in cells in much larger quantities than is required for cell synthesis and physiological needs. For the biosynthesis of polyphosphate under conditions of limited availability of nutrients in the aerobic zone, PAO _S use PHA accumulated under anaerobic conditions as energy. Under anaerobic conditions, phosphorus leaves the cell and saturates the waste water. Under aerobic conditions, phosphorus enters the cell, removing it from waste water. Therefore, an excess of activated sludge should be removed from the treatment plant only under aerobic conditions and anaerobic conditions should not be allowed to occur both during compaction of excess activated sludge and during its dehydration.

From the anaerobic bioreactors 4, the flotation concentrate is fed, mixing again with the wastewater clarified in flotators 3, as well as with the sludge mixture circulation stream from nitrifier 6, to the denitrifier 5. And the wastewater clarified in flotators 3 and the sludge circulation stream, contain sludge 5 denitrifiers are reduced to molecular nitrogen, absorbing electrons in oxidative processes carried out by denitrifying microorganisms. Given the need to create intensive mass transfer in the volume of denitrification tanks, to remove the released molecular nitrogen from the surface of the cells, mixing the sludge mixture in denitrifiers 5 is organized in several ways.

At the bottom of the sludge mixture is stirred up with stirrers or axial or propeller pumps, and closer to the surface of the water mirror in the denitrification tanks, where the cassettes with the nozzle for holding attached microorganisms are located, aeration bubblers under the nozzle are located. Sparging is carried out periodically to update the surface of the nozzle and loosen the formed clumps of suspended solids and biomass of denitrifying microorganisms.

From the denitrifiers 5, the sludge mixture flows by gravity to nitrifier 6, where it is continuously mixed due to intensive bubbling with air entering the air ducts 17. In nitrifiers 6, activated sludge is saturated with phosphorus to form polyphosphates, ammonium nitrogen is oxidized to nitrates, and the total concentration of organic substances dissolved in water is reduced. therefore, when the sludge mixture flows into the secondary sedimentation tanks 7 or thin-layer sludge separators, after separation of the return activated sludge from the biomass, it has the quality parameters Twa, close to the quality standards of water fishery ponds. To bring the quality of the treated wastewater to the level of discharge requirements, it is sent to the after-treatment reactor unit 8. To the after-treatment units 8, along with the biological processes of filtering sediment filters for activated sludge particles removed from the secondary settling tanks 7, they organize the wastewater treatment with reagents to bind residual amounts of phosphorus dissolved in water into insoluble compounds and filtering wastewater through a granular or other charge to separate water-insoluble impurities from one hundred -water. From the after-treatment unit 8, the treated wastewater flows into the contact tank 9 for contact with the chlorine agent, disinfection and adjusting the quality of the purified water B by bacterial contamination to the standards for release into the reservoir of fishery value.

Sewage sludge is discharged from three construction sites. Coarse mechanical impurities isolated in the grates 1 are stored in garbage bins 14 and periodically, as they accumulate, they are taken to solid domestic waste landfills for disposal in fuel or construction materials. The sand released in the sand traps 2 is discharged into the sand bunker 15, where it, as it accumulates through the drainage system, is freed from excess moisture and then taken out for the restoration of disturbed lands or for construction purposes. And finally, the excess activated sludge is removed from the secondary settling tanks 7 into the flotators of the excess activated sludge 10, where it is thickened, divided into two streams. One stream - a stream of sludge water 22, is returned to the nitrifying agent 6, and the second stream - a stream of flotation concentrate of excess activated sludge is fed to a mixer 11, where the sludge mixture, interacting with sawdust, is conditioned and prepared for dehydration. From the mixer 11, the flotation concentrate mixture of excess activated sludge and sawdust is sent to an extraction apparatus 12, where it is partially freed from excess sludge water 22 returned to the nitrification device 6 and discharged in the form of cake 25 into bio composter 13. After processing by microorganisms and vermiculture, the cake is converted into biohumus, which can be used as organomineral fertilizer in agriculture and urban greenery.

The implementation of the objectives of the invention can be demonstrated by example. As an example, we used the experience of reconstructing the aeration tanks sections of the Kuryanovskaya and Lyubertsy aeration stations of the Mosvodokanal MGP. So, during the reconstruction of the four-corridor section of the aeration tank of the Lyubertsy aeration station under the processes of the anaerobic and anoxide stages of wastewater treatment and return activated sludge, two corridors of four in the section were used. If we go over to the proposed method for removing phosphorus from wastewater biologically, then using primary sedimentation tanks that were shut down during the experiment at the Lyubertsy aeration station, they can organize not only the flotation process, but also the process of anaerobic processing of flotation concentrate in 2 hours . As a result, one and a half corridors of the aeration tank previously occupied by anaerobic-anoxide processes can be freed up for aerobic biological treatment or the flow of wastewater can be increased by 30% from the existing one. If you build a new treatment plant, then the amount of capital investment in the construction of biological wastewater treatment facilities is reduced by 30%. Reducing the volume of anaerobic bioreactors by more than 5 times can reduce the energy consumption for mixing the fermenting mass in them.

Since biohumus is obtained from excess activated sludge, dehydrated without being under anaerobic conditions, phosphorus losses are excluded from it, and this guarantees the solution of another set problem - increasing the phosphorus content in biohumus.

Claims (1)

A method for the biological removal of phosphorus from wastewater, including sequentially maintaining a community of microorganisms that purify wastewater from organic and mineral impurities, under anaerobic, anoxic and aerobic conditions in capacitive facilities with intensive mass transfer, created by means of stirrers, pumps and sparging air, characterized in that the return activated sludge from the secondary settling tanks is mixed with the flow of the initial waste water passing through the grates and sand traps, the mixture is subjected to flotation processing, after which the flotation concentrate is kept for at least half an hour in anaerobic bioreactors with continuous stirring, and the clarified liquid with sludge water is fed into the denitrifier along with the circulation flow of the sludge mixture from the outlet of the nitrifier and the anaerobically treated flotation concentrate, then the sludge mixture is sent from the denitrifier, subjected to mixing by air bubbling, while the biomass of excess activated sludge growing under aerobic conditions of the nitrifier is subjected to flotation After treatment on flotators, the flotation concentrate of excess activated sludge is dehydrated to cake and subjected to bio-composting under aerobic conditions without loss of phosphorus in the mixture with sawdust to obtain biohumus enriched in phosphorus.