RU2587181C1 - Method for biological treatment of waste water from phosphorus compounds - Google Patents

Abstract

FIELD: processing and recycling wastes; ecology.

SUBSTANCE: invention relates to waste water treatment, in particular, to methods for biological treatment of waste water from biogenic elements such as phosphorous compounds, and may be used for treatment of domestic waste water or industrial waste water contaminated with biodegradable organic compounds, as well as for mixtures thereof. Waste water after mechanical clearing is treated in aeration tank in presence of active sludge, followed with further separation of sludge mixture into purified water, return sludge, and excess active sludge. Return sludge is fed back into aeration tank, and excess active sludge is divided into two flows. One of flows of excessive active sludge undergoes autolysis in anaerobic conditions while stirring in presence of reagent, followed with further return for treatment into aeration tank, and second flow is directed for processing sewage sludge.

EFFECT: purification of waste water from phosphorous compounds to maximum allowable concentration (MAC) specified for water bodies for fish farming, reduction of formed excessive active sludge volumes, directed to further processing, at simultaneous reduction of capital and operating costs.

4 cl, 1 dwg

Description

The invention relates to the field of wastewater treatment, in particular to methods for biological treatment of wastewater from nutrients, and can be used for treatment of domestic wastewater, industrial wastewater contaminated with biodegradable organic compounds, as well as mixtures thereof.

Under conditions of increased quality requirements for treated domestic and industrial wastewater, including nitrogen and phosphorus compounds, requirements are also being made to reduce the amount of wastewater sludge generated, including excess activated sludge, which must be further processed and / or disposal, which leads to significant capital and operating costs.

A known method of biological wastewater treatment, according to which the wastewater is subjected to mechanical treatment in the primary sump, from which the wastewater is fed into a bioactivator (aeration tank) with microflora, in which the presence of zones with a heterogeneous oxygen content by maintaining oxygen, and then the mixture of wastewater water with activated sludge enters the secondary sump for separation into treated wastewater and activated sludge, which is constantly returned to the beginning of the bioactivator. The crude sludge after the primary sump is recycled to the input of the primary sump to create the conditions for the hydrolysis process and the heteroacetogenic process directly in the primary sump. In the secondary sump, zones with a heterogeneous oxygen content are created by adjusting the rate of recirculation of activated sludge from the secondary sump to the bioactivator inlet / RF Patent No. 2296110, C02F 3/30, 2007 /.

The disadvantages of this method are the high operating costs, since the entire volume of activated sludge is constantly returned to the beginning of the bioactivator, and the sediment from the primary sump is recycled, as well as an insufficient degree of wastewater treatment from phosphorus compounds.

A known method of biological treatment of wastewater from phosphates, according to which biological treatment is carried out using an inert loading material, fouling biofilm, in direct contact with which a metal is introduced, creating conditions for biological corrosion. As a result of electrochemical reactions and biological corrosion occurring in the local zone at the interface between the wastewater and the biofilm and the dissolved metal, intensive biological oxidation of organic contaminants and the formation of insoluble salts that precipitate are carried out. The precipitate is sorbed on the surface of the biofilm and free-floating activated sludge. Part of the activated sludge and spent biofilm is taken out together with purified water into the sump, and the other part that has precipitated is periodically removed directly from the aeration zone / RF Patent No. 2197436, C02F 3/02, 2003 /.

The disadvantages of this method are the high operating costs due to the large air consumption for aeration, as well as the fact that the technology used does not reduce the amount of precipitation formed, including excess activated sludge.

The closest in technical essence and the achieved result to the proposed one is a method for removing phosphorus from wastewater, which includes mechanical, biological, physico-chemical treatment with the return of compacted activated sludge depleted in phosphorus, from the sludge compactor to the aeration tank, with sludge enriched water enriched in the compactor volatile fatty acids produced in the acidifier, operating on crude sludge from primary sedimentation tanks in the mode of the first stage of anaerobic digestion, and the excess asset th yl, freed from PO ₄ ^3- in ilouplotnitele added in atsidofikator. Due to the introduction of excess activated sludge into the acidifier, the deficiency of organic substances is compensated for at low values of the BOD of the initial wastewater and the required amount of volatile fatty acids is supplied to the sludge compactor for the dephosphatization process / RF Patent No. 2276108, C02F 3/30, 2006/. of this method are high operating costs due to the large number of reagents used in the wastewater treatment process, as well as insufficient reduction in the volume of excess of activated sludge.

The technical result obtained from the use of the proposed method consists in the treatment of wastewater from phosphorus compounds to the maximum permissible concentration (MPC) established for fisheries for water use, as well as to reduce the volume of generated excess activated sludge sent for further processing, while reducing capital and operating costs.

The technical result is achieved due to the fact that in the method of biological treatment of wastewater from phosphorus compounds, the wastewater after mechanical treatment is treated in an aeration tank in the presence of activated sludge, followed by separation of the sludge mixture into purified water, return sludge, which is fed into the aeration tank, and excess active sludge, which is divided into two streams, one of which is subjected to autolysis under anaerobic conditions with stirring in the presence of a reagent, followed by return to the aeration tank for processing, and the second flow accurate activated sludge is sent to the treatment of sewage sludge, while up to 99% of excess activated sludge is sent to autolysis, aluminum or iron salts are used as a reagent, and the autolysis time is at least 3 hours.

The drawing shows a diagram of the biological treatment of wastewater from phosphorus compounds, where 1 is the feed wastewater for treatment, 2 is a mechanical treatment unit, 3 is wastewater after mechanical treatment, 4 is aeration tank, 5 is a sludge mixture, 6 is a secondary sump, 7 - treated wastewater, 8 - return sludge, 9 - excess activated sludge, 10 - excess activated sludge fed to autolysis, 11 - excess activated sludge sent to treat sewage sludge, 12 - anaerobic autolysis reactor, 13 - mixing device, 14 - introduction of the reagent, 15 - f sforosoderzhaschy autolysate.

The method is as follows.

The source wastewater 1 is treated in a mechanical treatment unit 2 (sand traps, grease traps, primary sump, etc.), from which the treated wastewater 3 is sent to aeration tank 4, in which it is treated together with activated sludge. The sludge mixture 5 from the aeration tank 4 is sent to the secondary sump 6, where it is separated into purified water 7, return activated sludge 8, which is sent to the aeration tank 4, and excess activated sludge 9, which is divided into two streams: excess activated sludge, which is fed to autolysis 10, and excess activated sludge, which is sent to the treatment of sewage sludge 11. Excess activated sludge 10 is fed to the anaerobic reactor 12 with a stirring device 13, which also contains reagent 14 and where autolysis takes place. Autolysate 15, containing phosphorus compounds, is fed into aeration tank 4.

In the process of autolysis of excess activated sludge 10 under the conditions of an anaerobic reactor 12 with a mixing device 13, activated sludge is aged, cells are damaged, and the structure of molecules is destroyed with the release of enzymes and phosphates. In the presence of introduced reagents, preferably aluminum and iron salts, the phosphates released from the cells of activated sludge are bound into insoluble compounds. The resulting mixture - autolysate 15 is sent to aeration tank 4. To destroy the cells and release phosphate from them, a residence time of at least 3 hours is required, while up to 99% of excess activated sludge is fed to the autolysis. Excess activated sludge, which is sent to the treatment of sewage sludge 11, removes phosphorus compounds from the process.

As a result of the passage of mechanically treated wastewater 3 through aeration tank 4 in the presence of autolysate 15 and return activated sludge 8, autolysate 15 is oxidized as an additional organic substrate and, accordingly, activated sludge consumes additional phosphorus (P).

An example of the method

When the flow rate of the initial wastewater Q = 100,000 m ³ / day, the volume of aeration tanks with an aeration period of 12 hours V = 50,000 m ³ , the dose of activated sludge in the aeration tank a _i = 3 g / l (with an ash content of 30%, in ash units 0, 3 - and the phosphorus content of 2% in terms of P) and the dose of compacted sludge discharged from the secondary sumps a _{i upl} = 7 g / l, the amount of excess activated sludge discharged from biological treatment plants (secondary sump) is Q _i = 2350 m ³ / day

Purified wastewater after secondary sedimentation tanks contains 2 mg / l P - PO ₄ .

The maximum permissible concentration for phosphorus (P) established for fishery water bodies is 0.2 mg / l.

Thus, the excess of MPC for phosphorus compounds in purified water without autolysis will be:

P _huts = P _{purification-} MPC = 2-0.2 = 1.8 mg P / l = 1.8 g P / m ³ ,

where P _huts - excess phosphorus (P) in purified water;

P _purification - the amount of phosphorus (P) in purified water;

MAC - the maximum permissible concentration of phosphorus (P).

The following amount of phosphorus must be removed per day:

P _total = P _log × Q = 1.8 × 100000 = 180,000 g / day = 180 kg / day,

where P _total - the total amount of phosphorus that must be removed per day, kg / day;

R _huts - excess phosphorus in purified water, kg / m ³ ;

Q is the flow rate of the source wastewater, m ³ / day.

The phosphorus content (C _P ) in activated sludge with an ash content of 30% is 2% in terms of R. That is, 100 g of activated sludge contains 2 g of phosphorus or 70 g (100-30) of ashless activated sludge substance contains the same 2 g P (C _{P ashless} ).

To determine the percentage of phosphorus per ashless activated sludge substance, use the formula:

where C _{P ashless} - phosphorus content calculated on the ashless substance of activated sludge,%;

С _Р - phosphorus content in activated sludge,%;

Ash - ash content of activated sludge in units.

The amount of activated sludge as an organic substrate based on an ashless substance for binding the required amount of phosphorus will be:

where a _{i without days} is the amount of activated sludge calculated as ashless substance necessary for binding the total amount of phosphorus, kg / day;

P _total - the total amount of phosphorus, which must be removed per day, kg / day;

C _{P ashless} - phosphorus content calculated on the ashless substance of activated sludge,%.

Organics for binding excess phosphorus during the growth of activated sludge comes from the construction (anaerobic reactor), where autolysis of activated sludge occurs. A part of the excess sludge compacted in the secondary settling tanks at a concentration a _{i usl} = 7 g / l enters the autolysis tank.

Based on the ashless substance of activated sludge, the concentration of compacted activated sludge will be:

$$a_{i\text{away}}=a_{i\mathrm{at}Pl}\times (\mathrm{one}-3\mathrm{about}lbn)=7\times 0.7=4.9\text{g / l}=\text{four}{\text{9 kg / m}}^{\text{3}}\text{, (2)}$$

where a _{i upl ashless} - the concentration of compacted activated sludge in terms of ashless substance, kg / m ³ ;

a _{i upl} - the concentration of compacted activated sludge, kg / m ³ ;

Ash - ash content of activated sludge in units.

The required amount of autolysed mixture is:

where Q _aut - the amount of autolysate, m ³ / day;

a _{i without days} - the amount of activated sludge calculated on the ashless substance of activated sludge to bind the total amount of phosphorus per day, kg / day;

a _{i upl ashless} - the amount of excess activated sludge calculated on the ashless substance of activated sludge, kg / m ³ .

Thus, part of the excess activated sludge from biological treatment facilities, in this example from secondary settling tanks, in the amount of 1284 m ³ / day is fed to autolysis in an anaerobic reactor with a capacity of 5000 m ³ . In the anaerobic reactor, excess activated sludge is kept under stirring with the coagulant for four days, after which the resulting autolysed mixture — autolysate — is returned directly to the aeration tanks. The remainder of the excess activated sludge is sent to wastewater sludge treatment facilities in the amount of:

Q _ost = Q _i -Q _aut = 2350-1284 = 1066 m ³ / day,

where Q _ost - the amount of excess activated sludge for the treatment of sewage sludge, m ³ / day;

Q _i - the amount of excess activated sludge, m ³ / day;

Q _aut - the amount of autolysate, m ³ / day.

The general formula for calculating the required amount of autolysate for binding excess phosphorus is:

where Q _aut - the amount of autolysate, m ³ / day;

R _huts - an excess of phosphorus compounds, kg / m ³ ;

Q is the flow rate of the source wastewater, m ³ / day;

With _{P ashless} - the percentage of phosphorus calculated on the ashless part of activated sludge, calculated by the formula (1),%;

a _{i off ashless} - the concentration of compacted activated sludge calculated on an ashless substance, calculated by the formula (2), kg / m ³ .

Thus, the proposed method of biological wastewater treatment allows to reduce the content of phosphorus compounds in purified water to the MPC established for reservoirs of fishery use, and to reduce the amount of generated excess activated sludge sent for further processing, while reducing capital and operating costs.

Claims (4)

1. The method of biological treatment of wastewater from phosphorus compounds, characterized in that the wastewater after mechanical treatment is treated in an aeration tank in the presence of activated sludge, followed by separation of the sludge mixture into purified water, return sludge that is fed into the aeration tank, and excess activated sludge, which is divided into two streams, one of which is subjected to autolysis under anaerobic conditions with stirring in the presence of a reagent, followed by return to the aeration tank for processing, and the second excess activated sludge stream is attributed to the treatment of sewage sludge. 2. The method according to p. 1, characterized in that up to 99% of excess activated sludge is sent to autolysis. 3. The method according to p. 1 or 2, characterized in that the reagent is aluminum or iron salts. 4. The method according to p. 1, characterized in that the autolysis time is at least 3 hours.

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