RU2296110C1 - Method of biological purification of waste water - Google Patents

Abstract

FIELD: biological purification of waste water.

SUBSTANCE: proposed method includes mechanical purification of waste water in first settler followed by delivery of waste water to bioactivator containing micro-flora where zones at heterogeneous content of oxygen in medium are maintained by controllable introduction of oxygen; then mixture of waste water with activated sludge is directed to secondary settler for separating the mixture into purified waste water and activated sludge which is continuously returned to the beginning of bioactivator. Sediment after first settler is recirculated to primary settler inlet for creating the hydrolysis process and heteroacetogenic process directly in primary settler. Zones of medium at heterogeneous content of oxygen are formed in secondary settler by regulating the rate of recirculation of activated sludge from secondary settler to bioactivator inlet. Zones of medium at heterogeneous content of oxygen in bioactivator are distributed horizontally.

EFFECT: reduction of volume of sediment and excessive activated sludge; low cost of maintenance of purification works; enhanced operational efficiency of purification works.

17 cl, 6 dwg, 3 tbl

Description

The invention relates to the biological treatment of wastewater and can be used in utilities, various industries and agriculture for the treatment of domestic, industrial and similar wastewater containing biodegradable substances, in particular when treating wastewater of settlements, brewing factories, enterprises of food, dairy, meat and dairy industries, and can also be used for the cultivation of aquatic organisms.

Known methods of biological treatment, including two stages - mechanical treatment and biological treatment.

At the first stage, water-insoluble substances in suspension are removed; at the second stage, what remains of the first stage is suspended and plus dissolved in effluents.

The disadvantages of the method include:

- the formation of secondary pollution in the form of crude sludge in the primary sedimentation tanks in the first stage,

- excessively activated sludge formed during biological treatment in the amount of 1-1.5 kg / kg of removed BOD.

Moreover, ammonium salts NH ₄ dissolved in wastewater under the influence of microorganisms of activated sludge are also converted into salts of nitrous NO ₂ and nitric NO ₃ acids dissolved in water. An increase in activated sludge occurs in an amount of 1-1.5 kg / kg of removed BOD (biological oxygen consumption for the complete oxidation of organic oxidation).

In practice, the removal efficiency of the biogenic element (nitrogen) is low and amounts to about 30%.

It is known that nitrogen denitrification is used to increase the efficiency of nitrogen removal, which increases the efficiency of its removal from wastewater, but at the same time secondary pollution remains - excess sludge. This requires additional land resources to accommodate this type of waste, additional costs for disposal and disposal.

A known method of biological treatment of wastewater from nitrogen and phosphorus (US Pat. No. 1346587, c. 06.01.1986, op. 23.10.1987), comprising mixing the source water with activated sludge, sequential treatment of the sludge mixture in anaerobic, oxygen-free and aerobic zones, partial recirculation of the sludge mixture from the aerobic zone to oxygen-free, separation of activated sludge from waste water, its supply to the anaerobic zone and removal of excess activated sludge.

The disadvantage is the low degree of purification from nitrogen (14.8 g / m ³ ) and the presence of excess sludge.

A known method of biological wastewater treatment (US Pat. No. 2220918, z. 20.02.2003, op. 10.01.2004), according to which the wastewater after mechanical treatment is sequentially fed to the anaerobic bioreactor, aerobic bioreactor, sump equipped with airlift with a recirculation pipe activated sludge, bioreactor tertiary treatment with loading for attached microflora and a disinfection chamber. The method provides a reduction in the amount of precipitate formed, which is removed from the anaerobic bioreactor, then it is dehydrated, for example, in filter bags.

The disadvantages include the fact that the method does not solve the problem of minimizing the formation of excess sludge.

The closest analogue adopted for the prototype is a method of biological wastewater treatment (US Pat. RF No. 2170217, z. 30.01.1997, op. 10.07.2001), in which wastewater that has previously undergone mechanical treatment in the primary settler is fed for treatment into a bioactivator with microflora, in which the presence of zones with a heterogeneous oxygen content is maintained by controlled introduction of oxygen. Next, the mixture of wastewater 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 disadvantages of the method include the formation of significant volumes of crude sludge in the primary sump and excess activated sludge removed for disposal.

In addition, the vertical arrangement of zones with a heterogeneous oxygen content in the bioactivator does not make it possible to create conditions for the most complete removal of nutrients (nitrogen and phosphorus) in the form of gaseous products, which leads to the formation of excess activated sludge.

The problem to which this invention is directed, is to minimize the volume of crude sludge and excess activated sludge generated during the treatment of wastewater removed for disposal, reducing the cost of operating treatment facilities, increasing the efficiency of treatment facilities.

To solve the problem in a method of biological wastewater treatment, in which the wastewater is subjected to mechanical treatment in the primary sump, then, after separation of the raw sludge, the wastewater is fed into a bioactivator with microflora, in which the presence of zones with a heterogeneous oxygen content is maintained by controlled oxygen input , and then the mixture of wastewater with activated sludge enters the secondary sump for separation into treated wastewater and activated sludge, which is constantly returned to the beginning of bioactive According to the invention, the raw sludge after the primary sump is returned to the inlet of the primary sump and recycled to create conditions for the hydrolysis and heteroacetogenic process directly in the primary sump, and zones with a different oxygen content in the secondary sump are created for biological treatment, by regulating the rate of recirculation of activated sludge returned from the secondary sump to the input of the bioactivator, while in the bioactivator s with heterogeneous medium oxygen content distributed in the horizontal direction.

The return of crude sludge to the entrance of the primary sump is carried out once every 24 hours.

Raw sludge is recycled to the input of the primary sump until the content of easily oxidized organic matter in the wastewater at the outlet of the primary sump is increased compared to its content at the inlet by 15%. The recirculation ratio is 10-20, preferably 15.

In this case, the raw sludge is recycled with a rupture of the jet at the entrance to the primary settler of 500-800 mm.

The volume of crude sludge undergoing recycling in the primary sump is 1 / 5-1 / 10 of the volume of the primary sump.

The number of zones with a heterogeneous oxygen content in the bioactivator is at least three.

In the oxygen-depleted zone (anaerobic), the content of dissolved free oxygen is maintained at 0.6-0.8 g / m ³ .

In the zone with a high oxygen content (aerobic), the content of dissolved free oxygen is maintained at 2.2-4.4 g / m ³ .

Between the aerobic and anaerobic zones of the bioactivator there is a transition zone, the content of dissolved free oxygen in which is supported by 1.2-1.8 g / m ³ .

Preferably, 1/3 of the useful volume of the bioactivator works as aerobic, 1/3 of the useful volume of the bioactivator works as a transition, 1/3 of the useful volume of the bioactivator works as anaerobic.

Preferably, 2/3 of the useful volume of the secondary sump works as an aerobic zone, 1/3 of the useful volume of the secondary sump works as an anaerobic zone.

The content of dissolved free oxygen of 0.4-0.8 g / m ^{3 is} maintained in the bottom of the secondary sump, due to the rate of active sludge recirculation from the secondary sump to the beginning of the biological activation zone (at the input of the bioactivator).

Recycling the raw sludge after mechanical treatment in the primary sump creates the conditions for the hydrolysis and heteroacetogenic process directly in the primary sump, which leads to a decrease in the volume of sludge removed for processing.

The creation in the secondary sump of zones with a heterogeneous oxygen content by controlling the rate of active sludge recirculation allows nitrification and denitrification processes to be carried out in it, which reduces the amount of activated sludge formation directly in the secondary sludge, removing biogenic elements from the effluents in the form of gaseous products rather than in as an increase in sludge biomass.

Biological wastewater treatment in a bioactivator with a horizontal distribution of zones with heterogeneous oxygen content creates conditions for the most complete removal of nutrients (nitrogen and phosphorus) in the form of gaseous products.

The method is illustrated in the drawing (figure 1), which shows a diagram of the proposed biological wastewater treatment, where

1 - sewage supply pipe,

2 - primary clarifier mechanical cleaning,

3 - pipeline supplying raw sludge to the input of the primary sump,

4 - drain pipe from the primary sump,

5 - bioactivator - a tank of any shape, equipped with aerators, for example pneumatic or mechanical,

6 - secondary sump

7 - recirculated activated sludge from the secondary sump 6,

8, 9, 10, respectively, aerobic, transitional, anaerobic zones into which the bioactivator 5 is conditionally divided,

11 - pipeline mixture of wastewater and activated sludge coming from the bioactivator 5 into the secondary sump 6,

12, 13 - respectively, the aerobic and anaerobic zones into which the secondary sump 6 is conventionally divided,

14 - pipeline purified sewage from the secondary sump.

The method is as follows.

Wastewater 1 (any) or close in composition is supplied to the primary sump 2, where the separation of undissolved solids occurs. Crude sludge 3 from primary sump 2 once a day (24 hours) in a volume of 1 / 5-1 / 10 of its static volume is recycled - returned again to the beginning of primary sump 2. During recycling, sludge 3 is saturated with oxygen at the moment it reaches the beginning (distribution cup) of the primary clarifier 2 up to 100% due to the rupture of the jet at the entrance to the primary clarifier 2, which is 500-800 mm Conditions are created directly in the sump 2 to ensure the processes of hydrolysis and heteroacetogenic process. In this case, the gases contained in the sediment are degassed: CO ₂ ↑, N ₂ ↑, N ₂ O ↑, which are replaced by oxygen. Dissolved oxygen interferes with the decay process with the further presence of this sediment in the primary sump and stimulates the processes of hydrolysis, nitrification, denitrification, heteroacetogenic (oxidation of organic matter to CO ₂ ) in a mixture of wastewater with raw sludge. The sludge digestion process in the primary settler itself is stimulated.

Due to the degassing of the raw sludge, its volume decreases, this allows to increase the time of its stay in the sump 1 until discharge up to 10-20 days, which reduces the operating costs for the disposal and placement of raw sludge.

The rate of recirculation of crude sludge is determined by the presence of a 15% increase in the amount of easily oxidizable organic acids at the outlet of the primary sump compared to their inlet content and is 10-20, preferably 15.

The amount of sludge removed for further disposal is reduced in proportion to the recycling rate. Thus, in the primary sump, the processes of mechanical sedimentation and the processes of biological treatment of sludge are combined.

The runoff 4 from the primary settler enters bioactivator 5 with microflora, the concentration of which is 2.5-10.0 kg / m ³ . Recycling activated sludge 7 is fed into the same bioactivator 5 from the secondary clarifier 6. The bioactivator 5 is conditionally divided into zones with a heterogeneous oxygen content: 8 - aerobic with an O ₂ content _of 2.2-4.4 g / m ³ , 9 - transitional with an oxygen content of 1.2-1.8 g / m ³ , 10 - anaerobic with an O ₂ content _of 0.6-0.8 g / m ³ . Zones of dissimilar oxygen concentration in bioactivator 5 can be at least 2 or more. The transition zone as a separate zone may be absent in the bioactivator 5. The zones are not spatially separated from each other, but are conditionally distributed horizontally of the bioactivator 5.

In the bioactivator, the process of simultaneous (simultaneously occurring in time) nitrification is carried out - denitrification. When the number of zones is at least three or more, the cleaning efficiency increases due to the stimulation of the metabolism (metabolism) of microorganisms when they get into adverse conditions for them - from a zone with O _{2 of} 0.6-0.8 g / m ³ to a zone with O ₂ 2 , 2-4.4 g / m ³ and from the zone with O ₂ 2.2-4.4 g / m ³ to the zone with O ₂ 0.6-0.8 g / m ³ through the transition zone, etc. . In this case, bypassing the nitrification stage, nitrogen is removed from the effluent in the form of gaseous products N ₂ O ↑, N ₂ ↑. Organics are also excreted in the form of a gaseous product CO ₂ ↑ (up to 80%). At the same time, the amount of excess activated sludge formed, which is subject to further disposal, is 0.0-0.1 kg / kg of removed BOD.

Measurement of oxygen concentration is carried out by the electrochemical method (oximeters) or by the chemical method (Winkler method).

In the aerobic zone 8, the nitrification process is ongoing, in the anaerobic zone 10 the denitrification process is underway. In the transition zone 9 there is an increase in the efficiency of microorganisms that carry out different types of metabolism (anaerobic and aerobic). The oxygen content in this zone of 1.2-1.8 g / m ³ is unfavorable for both groups of microorganisms, which increases the efficiency of oxidation of nutrients (nitrogen and phosphorus).

In zone 10, where the denitrification process takes place, microorganisms performing aerobic metabolism, once again falling into adverse conditions, increase the efficiency of oxidation.

In each zone 8, 9, 10 of bioactivator 5, the oxidative power of both anaerobic and aerobic microorganisms is constantly optimized by zoning according to oxygen concentration. The actual oxygen content is adjusted in accordance with the set value by adjusting its input.

With this sequence of placement of zones in the bioactivator, the volume of formation of excess activated sludge is 0.0-0.1 kg / kg of removed BOD. In this case, the products of the metabolism of microorganisms are removed from the treated wastewater in the form of gases (СО ₂ , N ₂ O, N ₂ , N ₂ O ₃ , etc.). In known methods, the volume of excess activated sludge is 1-1.5 kg / kg removed BOD.

A mixture of 11 wastewater with activated sludge comes out of bioactivator 5 and enters a secondary clarifier 6, which is also conditionally divided into zones — 12 — aerobic and 13 — anaerobic, in which the oxidative power of both anaerobic and aerobic microorganisms is constantly optimized by zoning by oxygen concentration.

In the secondary clarifier 6, the mixture is separated - the clarified part is removed to discharge 14, and the settled activated sludge 7 is constantly removed to the beginning of the activation zone — to the “head” of the bioreactor 5.

The rate of recirculation of activated sludge is chosen taking into account the creation of anaerobic conditions with an oxygen concentration of 0.4-0.8 g / m ³ .

As confirmation of the effectiveness of the method, the test results of the proposed method for biological wastewater treatment at the treatment facilities of BFB HBK MUP "Vodokanal" in Revda are given.

The test results are presented in tables 1, 2, 3.

Table 1 presents the performance indicators of treatment facilities.

Table 2 shows the data on the performance of the installation for months when using the proposed method.

Table 3 shows the data on the performance of the installation for months when using the known method.

Figure 2, 3, 4, 5, 6 presents graphs of comparative indicators of the quality of wastewater treatment by the present method:

figure 2 - the content of ammonium nitrogen in the treated wastewater,

figure 3 - nitrogen content of nitrates in the treated wastewater,

figure 4 - phosphorus phosphate content in the treated wastewater,

figure 5 - the content of suspended solids in the treated wastewater,

6 is the number of drains.

Table 1 Parameter Results before implementation Results after implementation per day per month per day per month Excess activated sludge discharged to sludge ponds 60 m ³ 1800 m ³ 0 0 Crude sediment from the primary: 1 time per - radial sedimentation tanks, m ³ 40 1200 10 days Total amount, m ³ 3000 40 120 Steam treatment of crude sludge in digesters - natural gas, m ³ 200 6000 0 0 Boiler operation E 1/9 g, h four 120 0 0 Work of the pumping unit in the building of digesters (22 kW), h 13 390 0.5 fifteen Turbocharger electric motor load, A / h 340 275 The amount of electricity, kW / h 6300 189000 5900 177000 Natural gas savings amounted to 6000 m ³ / month Energy savings amounted to 12,000 kW / h / month

table 2 Month Number of drains m ³ / day Phosphates PO ₄ -P (mg / dm ³ ) Ammonium nitrogen NH ₄ -N (mg / dm ³ ) Nitrogen nitrite NO ₂ -N (mg / DM ³ ) Nitrate nitrates NO ₃ -N (mg / dm ³ ) entrance Exit entrance Exit entrance Exit entrance Exit January 25-160000 11.3 1,1 32.6 0.24 0,03 0.02 1,2 2,5 February 10.8 0.7 29.4 0.38 0.10 0.017 0.8 3,1 March 12.6 0.9 33.5 0.32 0.12 0,025 2.1 2,8 April 13.8 1,2 42.6 0.36 0.08 0,031 1.3 2,4 May 14.2 0.9 25.1 0.33 0.02 0,023 1.4 3.2 June 16,4 1,2 38.1 0.41 0.12 0,026 1.8 1,2 July 13,2 0.9 41.6 0.38 0.15 0,031 2,4 3,1 August 11.8 1.3 28.5 0.33 0.24 0,026 1.8 2.6 September 12.8 1,1 32.9 0.29 0.23 0,032 1,6 2.1 October 12.6 0.9 29.3 0.42 0.18 0,021 2,4 2,8 November 13,2 1,2 31,2 0.38 0.21 0.018 1.9 3.2 December 10.8 0.7 28.6 0.39 0.18 0.017 2.1 3,1 Minimum total mineral nitrogen removal efficiency: 69.78% - by a known method; 86.57% - by the present method. Maximum removal efficiency of total mineral nitrogen: 88.44% - by a known method; 93.65% - by the present method.

Table 3 At the entrance At the exit At the entrance At the exit At the entrance At the exit At the entrance At the exit At the entrance At the exit At the entrance At the exit date of Kolich. BOD ₅ BOD ₅ COD COD PO ₄ -P PO ₄ -P NH ₄ -N NH ₄ -N NO ₂ -N NO ₂ -N NO ₃ -N NO ₃ -N Average value Dry weather mg / l mg / l mg / l mg / l mg / l mg / l mg / l mg / l mg / l mg / l mg / l mg / l 4-500 m ³ / day January 225 3 470 34 16.5 1,1 33,4 5.3 0.02 0.017 1,5 4.3 February 190 3 430 38 12.1 1,0 28,4 3.6 0.02 0.01 0.9 4.0 March 190 3 370 32 15.4 0.9 41.3 3.8 0.017 0.02 1,1 4.3 April 220 3 410 32 18.9 1,2 27.4 5.8 0.18 0.017 1,6 3.0 May 200 3 420 32 16.8 0.9 31,4 4.0 0.17 0.04 4.0 2,4 June 210 3 320 29th 12,4 0.9 43,4 2,4 0.21 0.17 3.3 2,5 July 220 3 420 28 11.8 0.7 41.3 3.2 0.17 0.16 3.2 1.8 August 190 3 340 thirty 14.3 1,0 36,4 3.0 0.46 0.21 4.1 1.4 September 190 3 420 32 11.8 1,2 38,0 4.3 0.34 0.28 2.2 1.4 October 180 3 420 31 13,4 0.9 38,4 3,1 0.23 0.17 2,8 2,3 November 190 3 410 thirty 13,4 1,0 39,4 4.0 0.43 0.23 3.4 4,5 December 180 3 410 28 11.9 0.9 34.3 4,5 0.43 0.36 3.4 4.4

The advantages of the proposed technical solution compared to the known are as follows:

- reduction in the volume of crude sludge and excess or almost up to 0.0-0.1 kg / kg of removed BOD,

- reduction of capital and operating costs for biological treatment facilities,

- the removal of dissolved nutrient contaminated substances occurs at the stage of mechanical cleaning,

- improving the efficiency of wastewater treatment plants through the fermentation of raw sludge directly in the primary sump,

- in the activation zone, biological compounds with high efficiency remove nitrogen and phosphorus compounds (up to 95%) with minimal formation of excess activated sludge,

- the treated wastewater that has undergone such processing is suitable for reuse, and there is no need to use equipment for sludge treatment,

- the proposed method does not require the construction of special facilities and can be used in existing biological treatment plants.

Claims (17)

1. A method of biological wastewater treatment, in which the wastewater is subjected to mechanical treatment in a primary sump, then fed to a bioactivator with microflora, in which the presence of zones with a heterogeneous oxygen content is maintained by controlled oxygen supply, then a mixture of wastewater with activated sludge is supplied in the secondary sump for separation into purified wastewater and activated sludge, which is returned to the inlet of the bioactivator, characterized in that the crude sludge after the primary sump is recycled and at the entrance of the primary sump to create conditions for the hydrolysis and heteroacetogenic process directly in the primary sump, and in the secondary sump, create zones with a heterogeneous oxygen content environment for biological treatment in it by controlling the rate of recirculation of activated sludge returned from the secondary sump bioactivator, while in the bioactivator zones with heterogeneous oxygen content are distributed in the horizontal direction. 2. The method according to claim 1, characterized in that the raw sludge is returned to the input of the primary sump once every 24 hours. 3. The method according to claim 1, characterized in that the recirculation of the raw sludge at the inlet of the primary sump is carried out to increase the content of easily oxidized organic matter in the wastewater at the outlet of the primary sump compared to its content at the inlet by 15%. 4. The method according to claim 1, characterized in that the ratio of the recirculation of crude sludge in the primary sump is 10-20, preferably 15. 5. The method according to claim 1, characterized in that the recycling of the crude sludge is carried out with a rupture of the jet at the entrance to the primary sump. 6. The method according to claim 1, characterized in that the rupture of the jet of crude sediment at the entrance to the primary sump is 500-800 mm 7. The method according to claim 1, characterized in that the volume of crude sludge undergoing recycling in the primary sump is 1 / 5-1 / 10 of the volume of the primary sump. 8. The method according to claim 1, characterized in that the number of zones with a heterogeneous oxygen content in the bioactivator is at least three. 9. The method according to claim 1, characterized in that in the oxygen-depleted zone (anaerobic) of the bioactivator, the content of dissolved free oxygen is maintained at 0.6-0.8 g / m. 10. The method according to claim 1, characterized in that in the zone with a high oxygen content (aerobic) of the bioactivator, the content of dissolved free oxygen is maintained at 2.2-4.4 g / m ³ . 11. The method according to claim 1, characterized in that between the aerobic and anaerobic zones of the bioactivator there is a transition zone, the content of dissolved free oxygen in which support 1.2-1.8 g / m ³ . 12. The method according to claim 1, characterized in that preferably 1/3 of the useful volume of the bioreactor works as aerobic. 13. The method according to claim 1, characterized in that preferably 1/3 of the useful volume of the bioactivator works as a transition. 14. The method according to claim 1, characterized in that preferably 1/3 of the useful volume of the bioactivator works as anaerobic. 15. The method according to claim 1, characterized in that in the bottom of the secondary sump create an anaerobic zone in which the content of dissolved free oxygen is maintained at 0.4-0.8 g / m ³ . 16. The method according to claim 1, characterized in that preferably 2/3 of the useful volume of the secondary sedimentation tank works as an aerobic zone. 17. The method according to claim 1, characterized in that preferably 1/3 of the useful volume of the secondary sump works as an anaerobic zone.

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