Water treatment system and method coupling enhanced biological heat production with reduced sludge production

Abstract

A water treatment system and method for coupling enhanced biological heat production and reducing sludge production, the system comprising a first biochemical tank, a first sedimentation tank, a second biochemical tank and a second sedimentation tank connected in sequence, and a heat pump system arranged at the front end of the first biochemical tank; the method comprising: taking heat from the heat pump system in the first biochemical tank, then biodegrading under high load and short sludge age conditions, and then separating sludge and water in the first sedimentation tank, the supernatant after separation entering the second biochemical tank for further removal of pollutants under low load and long sludge age conditions, and then being separated from sludge in the second sedimentation tank and discharged; part of the sludge at the bottom of the first sedimentation tank is returned to the front end of the first biochemical tank, and the other part of the sludge is lifted to the second biochemical tank for further biodegradation; part of the sludge in the second sedimentation tank is returned to the second biochemical tank, and part of the remaining sludge is discharged; the method of the present application can improve the heat production capacity of the system and reduce the sludge production by adopting a two-stage process combined with heat taking at the front end.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a water treatment system and method that couples enhanced biological heat generation with reduced sludge production. Background Technology

[0002] Under the vision of carbon neutrality, the utilization of nutrients and energy from wastewater has become an industry consensus, with heat recovery being a crucial pathway for wastewater treatment plants to achieve carbon neutrality. The degradation of pollutants by microorganisms in activated sludge systems generates significant amounts of heat. This heat can be extracted through heat pump systems for building heating and can also raise wastewater temperature, facilitating the degradation of pollutants by microorganisms. Furthermore, the treatment and disposal costs of excess sludge account for 25-40% of the total operating costs of wastewater treatment plants; therefore, reducing sludge production can significantly lower the operating costs of wastewater treatment plants.

[0003] In recent years, with the increasing emphasis placed on sludge treatment by the state, the water treatment industry has developed numerous sludge reduction technologies. For example, patent CN202322450785.X discloses a multi-stage A / O process for enhanced endogenous simultaneous denitrification and phosphorus removal of sludge, achieving sludge reduction through enhanced endogenous respiration. Patent CN200910103737.5 discloses an A / O denitrification wastewater treatment process and device for sludge reduction, achieving sludge reduction by inserting a transition zone between the aeration and sedimentation zones. However, these processes all result in longer system retention times, more complex process structures, and none of them possess the function of enhancing biological heat generation. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to propose a water treatment system and method that couples enhanced biological heat production with reduced sludge production. By optimizing the installation location of the heat pump system, adjusting the system load and sludge age, the biological heat production capacity of sludge is improved, while the sludge production rate is reduced.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A water treatment system that couples enhanced biological heat production with reduced sludge production includes a first biological treatment tank 1, a first sedimentation tank 2, a second biological treatment tank 3, and a second sedimentation tank 4 connected in sequence. A heat pump system 5 is installed at the front end of the first biological treatment tank 1.

[0007] As a further preferred embodiment, the bottom of the first sedimentation tank 2 is connected to the front end of the first biological treatment tank 1 through the first pipe 10, and the bottom of the first sedimentation tank 2 is connected to the front end of the second biological treatment tank 3 through the second pipe 11; the bottom of the second sedimentation tank 4 is connected to the front end of the second biological treatment tank 3 through the third pipe 12, and the bottom of the second sedimentation tank 4 is provided with a sludge discharge pipe 6.

[0008] As a further preferred embodiment, a first reflux pump 7 is configured on the first pipe 10 leading from the bottom of the first sedimentation tank 2 to the front end of the first biochemical tank 1; a booster pump 8 is configured on the second pipe 11 leading from the bottom of the first sedimentation tank 2 to the front end of the second biochemical tank 3; and a second reflux pump 9 is configured on the third pipe 12 leading from the bottom of the second sedimentation tank 4 to the front end of the second biochemical tank 3.

[0009] As a further preferred embodiment, the sludge load of the first biological treatment tank 1 is higher than that of the second biological treatment tank 3.

[0010] As a further preferred option, the sludge age of the first biological treatment tank 1 is shorter than that of the second biological treatment tank 3.

[0011] This invention also provides a water treatment method that couples enhanced biological heat production with reduced sludge production, comprising the following steps:

[0012] Step 1: After the sewage enters from the front end of the first biological treatment tank 1, it is first heated by the heat pump system 5 located at the front end of the first biological treatment tank 1. Then, under the conditions of high load and short sludge age, the pollutants are removed in the first biological treatment tank 1. Subsequently, the sludge-water mixture flows into the first sedimentation tank 2 for sludge-water separation. The supernatant of the first sedimentation tank 2 enters the second biological treatment tank 3. Under the conditions of low load and long sludge age, the pollutants are further removed in the second biological treatment tank 3. After sludge-water separation in the second sedimentation tank 4, the supernatant is discharged.

[0013] Step 2: Part of the sludge at the bottom of the first sedimentation tank 2 is returned to the front end of the first biological treatment tank 1 to maintain its sludge concentration, and the other part of the sludge is lifted to the second biological treatment tank 3 by the lift pump 8 for further biodegradation.

[0014] Step 3: Part of the sludge from the second sedimentation tank 4 is returned to the second biological treatment tank 3 via the second return pump 9 to maintain its high sludge concentration, while part of it is discharged as excess sludge.

[0015] As a further preferred embodiment, in step 1, the load of the first biochemical tank 1 is 0.2-0.4 g COD / gVSS / day, and the load of the second biochemical tank 3 is 0.05-0.20 g COD / gVSS / day.

[0016] As a further preferred embodiment, in step 1, the sludge age in the first biological treatment tank 1 is 8-12 days, and the sludge age in the second biological treatment tank 3 is 12-25 days.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1) Improve the heat generation capacity of sludge:

[0019] This invention utilizes a heat pump system 5 built into the front end of the biochemical system for thermal extraction, which lowers the sludge temperature. This lower temperature stimulates microorganisms to generate more metabolic heat. Simultaneously, the microorganisms operating in the first biochemical tank 1 under high load and short sludge age conditions can also generate more heat. The extracted heat can be used for building heating, and the increased heat production can raise the wastewater temperature, ensuring efficient metabolism of pollutants by the microorganisms.

[0020] 2) Reduce excess sludge production:

[0021] Meanwhile, under the conditions of lower temperature, higher load, and shorter sludge age in the first biological treatment tank 1, the sludge yield coefficient is significantly reduced, which greatly reduces the amount of biological sludge and can reduce the operating cost of the wastewater treatment plant.

[0022] 3) Ensure that the discharged water meets the standards:

[0023] This invention ensures the complete removal of pollutants and achieves compliant effluent discharge by connecting a low-load, long-sludge-age second biological treatment tank 3 at the end of the biological system.

[0024] In summary, this invention combines the technical solution of separating the load and sludge age of the activated sludge system with a front-end heat extraction method, which has the advantages of improving heat production capacity and reducing sludge production. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of the system of the present invention.

[0027] Figure 2 This is a process flow diagram of the present invention.

[0028] Wherein: 1-First biological treatment tank, 2-First sedimentation tank, 3-Second biological treatment tank, 4-Second sedimentation tank, 5-Heat pump system, 6-Sludge discharge pipe, 7-First reflux pump, 8-Lift pump, 9-Second reflux pump, 10-First pipeline, 11-Second pipeline, 12-Third pipeline. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0030] like Figure 1As shown, a water treatment system that couples enhanced biological heat generation with reduced sludge production includes a first biological treatment tank 1, a first sedimentation tank 2, a second biological treatment tank 3, and a second sedimentation tank 4 connected in sequence. A heat pump system 5 is installed at the front end of the first biological treatment tank 1. The heat extracted by the heat pump system 5 is used for building heating or other industrial applications, reducing dependence on fossil fuels and playing a positive role in promoting energy structure transformation and achieving sustainable development.

[0031] As a further preferred embodiment, the bottom of the first sedimentation tank 2 is connected to the front end of the first biological treatment tank 1 through the first pipe 10, and the bottom of the first sedimentation tank 2 is connected to the front end of the second biological treatment tank 3 through the second pipe 11; the bottom of the second sedimentation tank 4 is connected to the front end of the second biological treatment tank 3 through the third pipe 12, and the bottom of the second sedimentation tank 4 is provided with a sludge discharge pipe 6.

[0032] As a further preferred embodiment, a first reflux pump 7 is configured on the first pipe 10 leading from the bottom of the first sedimentation tank 2 to the front end of the first biochemical tank 1; a booster pump 8 is configured on the second pipe 11 leading from the bottom of the first sedimentation tank 2 to the front end of the second biochemical tank 3; and a second reflux pump 9 is configured on the third pipe 12 leading from the bottom of the second sedimentation tank 4 to the front end of the second biochemical tank 3.

[0033] As a further preferred embodiment, the sludge load of the first biological treatment tank 1 is higher than that of the second biological treatment tank 3, and the sludge age of the first biological treatment tank 1 is shorter than the sludge age of the sludge load in the second biological treatment tank 3. The first biological treatment tank 1 is used to enrich bacteria with high heat production and low sludge production, and the third biological treatment tank is used to further reduce the residual pollutants in the water to below the discharge standard.

[0034] like Figure 2 As shown, in order to enhance biological heat production and reduce sludge yield, this invention also provides a water treatment method that couples enhanced biological heat production with reduced sludge yield, comprising the following steps:

[0035] Step 1: Pretreated wastewater enters the system from the front end of the first biological treatment tank 1. It first passes through a heat pump system 5 located at the front end of the first biological treatment tank 1 for heat extraction, and then operates in the first biological treatment tank 1 under high load and short sludge age conditions. Under these conditions, microorganisms with strong heat-generating capacity and low sludge yield can be enriched, and a large amount of pollutants are degraded. Therefore, the wastewater temperature rises significantly, which is beneficial to improving microbial activity and extracting more heat. Subsequently, the sludge-water mixture flows into the first sedimentation tank 2 for sludge-water separation. The supernatant from the first sedimentation tank 2 enters the second biological treatment tank 3, where pollutants are further removed under low load and long sludge age conditions. After sludge-water separation in the second sedimentation tank 4, the supernatant meets the standards and is discharged.

[0036] Step 2: Part of the sludge at the bottom of the first sedimentation tank 2 is returned to the front end of the first biological treatment tank 1 to maintain its sludge concentration, and the other part of the sludge is pumped into the second biological treatment tank 3, which operates under low load and long sludge age conditions. Due to the low load, the sludge in the second biological treatment tank 3 is further promoted to reduce the sludge volume under the endogenous respiration.

[0037] Step 3: Part of the sludge from the second sedimentation tank 4 is returned to the second biological treatment tank 3 to maintain a high sludge concentration in the second biological treatment tank 3, so as to achieve low load and long sludge age operation. A small amount of sludge is discharged as surplus sludge.

[0038] After the heat is recovered by the heat pump system 5 at the front end of the first biological treatment tank 1, the sludge temperature is reduced, which can stimulate microorganisms to produce more metabolic heat and less residual sludge.

[0039] The first biological treatment tank 1 has a load of 0.20-0.40 g COD / g VSS / day and a sludge age of 8-12 days. Its main function is to enhance biological heat generation, reduce sludge production, and remove most of the organic matter.

[0040] The second biological treatment tank has a load of 0.05-0.20 g COD / g VSS / day and a sludge age of 12-25 days. Its main function is to ensure further degradation of ammonia nitrogen and that the effluent COD meets the standards.

[0041] The first biological treatment tank 1 and the second biological treatment tank 3 are square or circular, and both are equipped with aeration equipment at the bottom to provide oxygen to the activated sludge and maintain the dissolved oxygen concentration at 0.5-6 mg / L.

[0042] Both the first sedimentation tank 2 and the second sedimentation tank 4 have an inverted conical structure with a cross-section that gradually increases from bottom to top. Their main function is to separate mud and water.

[0043] The heat pump system 5 includes a heat pump unit, a wastewater heat exchanger, and a control system, used to extract heat from wastewater.

[0044] The effects of the present invention will be further illustrated below through specific embodiments.

[0045] Using sludge from the end of the aerobic tank at a municipal wastewater treatment plant in Xi'an as inoculum, three reactors were cultured in the laboratory under different conditions. The first group consisted of reactors R1, R2, and R3, operated at different temperatures (10℃, 20℃, and 30℃) to evaluate the effect of temperature on heat production and sludge yield. The second group consisted of reactors R4 and R5, used to evaluate the effect of the loading ratio (F / M) on the heat-producing sludge yield. The loading ratios for the two reactors were 0.2 and 0.4 g COD / gVSS / day, respectively. The third group consisted of reactors R6 and R7, used to evaluate the effect of the sludge duration ratio (SRT) on the heat-producing sludge yield. The sludge durations for the two reactors were 12 and 20 days, respectively. After each reactor stabilized, the biothermal capacity and sludge yield of the sludge in each reactor were measured.

[0046] Table 1. Heat generation and sludge yield of sludge cultivated under different conditions.

[0047]

[0048] Table 1 shows that under different temperature conditions, as the temperature decreases, the sludge heat production increases while the sludge yield decreases. Under different load conditions, as the load increases, the sludge heat production increases while the sludge yield decreases. Under different sludge ages, as the sludge age decreases, the sludge heat production increases while the sludge yield decreases. This indicates that under conditions such as low temperature, high load, and short sludge age, the sludge's metabolism of pollutants tends to be more decompositional than anabolic. Therefore, controlling the process under these conditions can, on the one hand, increase the heat of biological metabolism, and on the other hand, reduce sludge production.

[0049] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A water treatment method that couples enhanced biological heat production with reduced sludge production, characterized in that: Includes the following steps: Step 1: After the sewage enters from the front end of the first biological treatment tank (1), it first takes heat from the heat pump system (5) located at the front end of the first biological treatment tank (1), and then removes pollutants in the first biological treatment tank (1) under high load and short sludge age conditions. Then the sludge-water mixture flows into the first sedimentation tank (2) for sludge-water separation. The supernatant of the first sedimentation tank (2) enters the second biological treatment tank (3), where pollutants are further removed under low load and long sludge age conditions. Then the supernatant is discharged after sludge-water separation in the second sedimentation tank (4). After heat extraction by the heat pump system (5) built into the front end of the first biological tank (1), the sludge temperature decreases and the lower temperature stimulates the microorganisms to generate more metabolic heat. At the same time, the microorganisms generate more heat in the first biological tank (1) under high load and short sludge age conditions, and the sludge yield coefficient is significantly reduced, resulting in a significant reduction in the amount of biological sludge. Step 2: Part of the sludge at the bottom of the first sedimentation tank (2) is returned to the front end of the first biological treatment tank (1) to maintain its sludge concentration, and the other part of the sludge is lifted to the second biological treatment tank (3) by the lift pump (8) for further biodegradation. Step 3: Part of the sludge from the second sedimentation tank (4) is returned to the second biochemical tank (3) via the second return pump (9) to maintain its high sludge concentration, and part of it is discharged as excess sludge.

2. The water treatment method according to claim 1, which couples enhanced biological heat production with reduced sludge production, is characterized in that: In step 1, the load of the first biochemical tank (1) is 0.2-0.4 g COD / g VSS / day, and the load of the second biochemical tank (3) is 0.05-0.20 g COD / g VSS / day.

3. The water treatment method according to claim 1, which couples enhanced biological heat production with reduced sludge production, is characterized in that: In step 1, the sludge age in the first biochemical tank (1) is 8-12 days, and the sludge age in the second biochemical tank (3) is 12-25 days.

4. The water treatment method according to claim 1, which couples enhanced biological heat production with reduced sludge production, is characterized in that: The water treatment method is implemented based on a water treatment system, which includes a first biochemical tank (1), a first sedimentation tank (2), a second biochemical tank (3), and a second sedimentation tank (4) connected in sequence. A heat pump system (5) is installed at the front end of the first biochemical tank (1).

5. The water treatment method according to claim 4, characterized in that: The bottom of the first sedimentation tank (2) is connected to the front end of the first biological tank (1) through the first pipe (10), and the bottom of the first sedimentation tank (2) is connected to the front end of the second biological tank (3) through the second pipe (11); the bottom of the second sedimentation tank (4) is connected to the front end of the second biological tank (3) through the third pipe (12), and the bottom of the second sedimentation tank (4) is provided with a sludge discharge pipe (6).

6. The water treatment method according to claim 4, which couples enhanced biological heat production with reduced sludge production, is characterized in that: A first reflux pump (7) is installed on the first pipe (10) leading from the bottom of the first sedimentation tank (2) to the front end of the first biochemical tank (1); a booster pump (8) is installed on the second pipe (11) leading from the bottom of the first sedimentation tank (2) to the front end of the second biochemical tank (3); and a second reflux pump (9) is installed on the third pipe (12) leading from the bottom of the second sedimentation tank (4) to the front end of the second biochemical tank (3).

7. The water treatment method according to claim 4, characterized in that: The sludge load of the first biological treatment tank (1) is higher than that of the second biological treatment tank (3).

8. The water treatment method according to claim 4, characterized in that: The sludge age of the first biological treatment tank (1) is shorter than that of the second biological treatment tank (3).

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