Sulfate reduction-aerobic-precipitation-anaerobic system and process thereof

Abstract

The invention relates to a sewage treatment process by an activated sludge method. The sewage treatment process comprises the following steps: introducing sulfur circulation into a biological reaction for nitrogen and phosphorus removal; a step of adding a sulfur source to the partially concentrated sludge subjected to the secondary precipitation treatment; culturing sulfate reducing bacteria and generating electron donors such as soluble hydrogen sulfide; and returning the treated sludge mixed liquid to the active sludge mainstream reaction tank. The invention also relates to a sewage treatment system which comprises a mainstream activated sludge reaction system and a sidestream-sulfate reduction system. According to the sewage treatment system, the lateral flow-sulfate reduction system is introduced, and the sulfur cycle biological reaction is combined, so that the effects of on-line sludge reduction and main flow denitrification enhancement are realized.

Description

[0001] This patent application is a divisional application of the patent application with the application number 201910307129.X, the application date of April 17, 2019, and the invention title of "Sulfate Reduction-Aerobic-Precipitation-Anaerobic System and Its Process". Technical Field

[0002] The present invention belongs to the field of sewage treatment processes. Specifically, the present application relates to a sulfate reduction-aerobic-precipitation-anaerobic system and a sulfate reduction-aerobic-precipitation-anaerobic process Background Art

[0003] The activated sludge process and its derived improved processes are currently the most widely used technologies in sewage treatment plants and have a high organic matter removal effect. In the traditional activated sludge process, the removal of organic matter and nitrogen elements is achieved through the reactions of autotrophic nitrification and heterotrophic denitrification, thereby completing the transfer of electrons from organic carbon to oxygen. Under different sludge retention times, 50% to 60% of the organic carbon in the sewage will be converted into carbon dioxide, and the remaining 40% to 50% will ultimately be converted into biological sludge. However, the operating cost of the current activated sludge process is relatively high, and the treatment and disposal of excess sludge (including processes such as sludge digestion and stabilization, dehydration, and incineration) account for 30% to 60% of the proportion. At the same time, there are also problems of secondary pollution. In addition, due to the low content of biodegradable organic matter in the sewage (lack of carbon source), the biological nitrogen and phosphorus removal effect of the traditional activated sludge process often fails to meet the national sewage treatment discharge standards. Therefore, reducing sludge while improving the nitrogen and phosphorus removal effect is the main problem that urgently needs to be solved in the current sewage treatment process.

[0004] In the practical application of sludge reduction, physical (heat treatment, ultrasonic fragmentation, etc.) or chemical (acids, alkalis, uncoupling agents, etc.) treatments are usually carried out in the sludge return section of the sewage treatment system. Although the sludge reduction can reach more than 60%, or even complete removal, its required cost is too high, and it will affect the sewage treatment performance in the mainstream activated sludge tank, bringing unnecessary hidden dangers. However, the aerobic-settling-anaerobic (OSA) process is considered to be an ideal reduction approach due to its low energy consumption and good reduction effect. The essence of OSA is to add an anaerobic sludge reaction tank in the sludge return section of the traditional activated sludge process, providing an environment for alternating aerobic and anaerobic operation. However, the sludge reduction effect of the OSA process is only 30%-40%, and at most 50%; the volume of the connected anaerobic reactor is large (accounting for 50% of the mainstream activated sludge reactor); most of the carbon sources are degraded in the anaerobic reactor and cannot be effectively used for denitrification in the mainstream reactor.

[0005] The "SANI process" invented by The Hong Kong University of Science and Technology utilizes the sulfate in the saline sewage caused by the use of seawater for flushing toilets in Hong Kong. By introducing sulfate-reducing bacteria and sulfide-oxidizing bacteria, while achieving efficient simultaneous nitrogen and carbon removal, it can also reduce sludge production by 90%. In the "SANI process", sulfate-reducing bacteria in the first reactor use sulfate to convert the organic matter in the sewage into carbon dioxide, while producing dissolved hydrogen sulfide. Autotrophic nitrifying bacteria convert ammonia nitrogen into nitrate in the third reactor and recycle it to the second reactor, where, under the action of autotrophic denitrifying bacteria, it reacts with hydrogen sulfide to generate nitrogen and sulfate. In the "SANI process", the sulfate-reducing organic matter and autotrophic denitrification reactions greatly reduce the production of sludge volume while achieving the effect of nitrogen removal.

[0006] The existing OSA process still has great room for improvement. By combining sulfate-reducing bacteria and sulfide-reducing bacteria, it can enhance the effects of sludge reduction and nitrogen and phosphorus removal, which is of extremely important significance in the practical application of new sewage treatment processes. Summary of the Invention

[0007] In view of the deficiencies of the existing OSA system, the present invention realizes the effects of on-line sludge reduction and enhanced mainstream denitrification by introducing a sidestream-sulfate reduction system and combining sulfur cycle biological reactions (sulfate reduction, sulfide oxidation-autotrophic denitrification reaction).

[0008] Specifically, the above object is achieved through the following technical solutions:

[0009] (1) An activated sludge process for sewage treatment, comprising the following steps:

[0010] Introducing a sulfur cycle step in the biological reaction for nitrogen and phosphorus removal;

[0011] Adding a sulfur source to a part of the concentrated sludge after secondary sedimentation treatment;

[0012] Cultivating sulfate-reducing bacteria and generating electron donors such as dissolved hydrogen sulfide;

[0013] Returning the treated sludge mixture to the activated sludge mainstream reaction tank.

[0014] (2) According to the process described in (1), it further includes a step of promoting the growth of low-sludge-producing bacteria.

[0015] (3) According to the process described in (1), the sewage treatment process further includes a step of recovering phosphorus by struvite precipitation.

[0016] (4) According to the process described in (1), the sulfur source is a substance that can provide an electron acceptor for sulfate-reducing bacteria.

[0017] (5) According to the process described in (3), the sulfur source includes sulfate, elemental sulfur, thiosulfate, and sulfite.

[0018] (6) According to the process described in claim (1), the activated sludge process includes aerobic process, anoxic-aerobic process, and anaerobic-anoxic-aerobic process.

[0019] (7) A sewage treatment system includes a mainstream activated sludge reaction system and a sidestream-sulfate reduction system,

[0020] wherein the mainstream activated sludge reaction system includes:

[0021] An influent device for providing sewage;

[0022] An activated sludge mainstream reaction tank into which the sewage enters via the influent device;

[0023] A secondary sedimentation tank;

[0024] An effluent device; and

[0025] A sludge return device for returning a part of the concentrated sludge treated by the secondary sedimentation tank to the activated sludge mainstream reaction tank;

[0026] The sidestream-sulfate reduction system includes:

[0027] A sulfate addition device for adding sulfate to another part of the concentrated sludge treated by the secondary sedimentation tank; and

[0028] A sulfate reduction sidestream sludge digestion device.

[0029] (8) According to the sewage treatment system described in (7), it further includes a struvite recovery device for recovering phosphorus through struvite reaction.

[0030] (9) According to the sewage treatment system described in (7), the activated sludge mainstream reaction tank includes a sequencing batch reactor, a membrane reactor, a granular sludge bed reactor, or a moving bed biofilm reactor.

[0031] (10) According to the sewage treatment system described in (7), the sulfate reduction sidestream sludge digestion device includes a continuous stirred reactor, a semi-batch stirred reactor, or an upflow anaerobic sludge bed reactor.

[0032] Through the sulfate reduction-aerobic-precipitation-anaerobic (SOSA) process of the present invention, by coupling the combined sulfur cycle bioreaction with the activated sludge process, carbon sources are saved, and while strengthening sewage denitrification and phosphorus removal, sludge production is reduced. In addition, the SOSA system according to the present invention also has the advantages of simple equipment, flexible operation, low renovation cost, etc., and is applicable to sludge reduction in newly built sewage treatment plants and is also suitable for upgrading and improving existing sewage treatment plants. Description of the Drawings

[0033] Figure 1 Shows the process of removing organic matter and denitrifying and dephosphorizing in the traditional activated sludge process;

[0034] Figure 2 Shows the flow chart of the traditional aerobic-precipitation-anaerobic (OSA) process;

[0035] Figure 3 Shows the schematic diagram of the "sludge killing" process;

[0036] Figure 4 Shows the flow chart of the sulfate reduction-aerobic-precipitation-anaerobic (SOSA) process according to the present invention;

[0037] Figure 5 Shows (a) the relationship between the sludge retention time (SRT) and the volatile sludge reduction percentage (VSR); (b) the relationship between the sludge retention time (SRT) and the sludge degradation rate (SSR);

[0038] Figure 6 Shows (a) the illustration of the use of dissolved hydrogen sulfide in the sulfate reduction side-stream reactor for mainstream activated sludge denitrification; (b) the degree of improvement in sludge dewaterability. Detailed Embodiments

[0039] The following further elaborates the present invention in conjunction with the drawings and specific embodiments, but the embodiments do not limit the present invention in any form.

[0040] The present invention provides an activated sludge process for sewage treatment, including the following steps: the step of introducing the sulfur cycle into the biological reaction for denitrification and dephosphorization; the step of adding a sulfur source to a part of the concentrated sludge after secondary sedimentation treatment; the step of culturing sulfate-reducing bacteria in the sulfate reduction sludge digestion tank to produce electron donors such as dissolved hydrogen sulfide; the step of returning the treated sludge mixture to the mainstream activated sludge reaction tank.

[0041] Herein, the "concentrated sludge" refers to concentrated sludge with a concentration of 1 g TSS / L to 2 g TSS / L. The proportion of a part of the concentrated sludge is 10 - 100% / d.

[0042] In this article, the activated sludge process for sewage treatment is also known as the sulfate reduction-aerobic-precipitation-anaerobic (SOSA) process.

[0043] In the SOSA process of the present invention, a sulfate reduction sidestream sludge digester is introduced, making the sludge reduction effect superior to that of the anaerobic digester in the traditional OSA process. Moreover, the generated soluble hydrogen sulfide can accelerate the decay rate of activated sludge, which is beneficial to shortening the sludge retention time in the sidestream reactor, thereby reducing the volume of the sidestream reactor and lowering the process investment and operating costs.

[0044] By returning the generated soluble hydrogen sulfide to the activated sludge mainstream reaction tank, it can be used to cultivate autotrophic denitrifying bacteria-sulfide-oxidizing bacteria, redirect the electron flow, and strengthen the mainstream denitrification nitrogen removal effect.

[0045] In addition, in the SOSA process of the present invention, there is also a step of promoting the growth of low-sludge-yield bacteria. The low-sludge-yield bacteria are sulfate-reducing bacteria and sulfide-oxidizing bacteria. The sulfate-reducing bacteria include, but are not limited to, Desulfococcus, Desulfobacteraceae, etc. The sulfide-oxidizing bacteria include, but are not limited to, Paracoccus, Thiobacillus, etc. The sulfate-reducing bacteria achieve sludge reduction by acting together with fermentative bacteria and hydrolytic bacteria in the sulfate reduction sidestream reactor. The sulfide-oxidizing bacteria carry out autotrophic denitrification reactions in the activated sludge mainstream reaction tank using the hydrogen sulfide generated by the sulfate reduction sidestream reactor, thereby strengthening the mainstream nitrogen removal effect.

[0046] In a specific embodiment, the sulfate-reducing bacteria cultured in the sidestream reactor can survive even at 20°C - 60°C or pH 5 - 10.

[0047] In a preferred embodiment, the SOSA process of the present invention further includes a step of recovering phosphorus by struvite precipitation. As described above, soluble hydrogen sulfide is generated in the sulfate reduction sludge digester. Since hydrogen sulfide can stimulate the release of soluble phosphorus, excellent phosphorus recovery effects can be achieved by periodically recovering phosphorus in the form of struvite in its supernatant or filtrate.

[0048] In the SOSA process of the present invention, the added sulfur source is a substance that can provide an electron acceptor for sulfate-reducing bacteria, and the form of electron transfer is shown in Equation 1.

[0049]

[0050] Preferably, the substances that can provide an electron acceptor for sulfate-reducing bacteria include, but are not limited to, sulfate (SO4), elemental sulfur (S0 ) Thiosulfate (S2O3) and sulfite (SO3).

[0051] Preferably, the activated sludge process used in the main stream activated sludge reaction tank is not limited to a specific activated sludge process, and may include aerobic processes, anoxic-aerobic processes, anaerobic-anoxic-aerobic processes, etc.

[0052] The present invention also provides a sewage treatment system, including a main stream activated sludge reaction system and a side stream-sulfate reduction system. The main stream activated sludge reaction system includes: a water inlet device for providing sewage; a main stream activated sludge reaction tank into which the sewage enters via the water inlet device; a secondary sedimentation tank; an effluent device; and a sludge return device for returning a part of the concentrated sludge treated by the secondary sedimentation tank to the main stream activated sludge reaction tank. The side stream-sulfate reduction system includes: a sulfate addition device for adding sulfate to another part of the concentrated sludge treated by the secondary sedimentation tank; and a sulfate reduction side stream sludge digestion device.

[0053] Preferably, the sewage treatment system further includes a struvite recovery device for recovering phosphorus through struvite reaction.

[0054] The sewage treatment system of the present invention is also called a sulfate reduction-aerobic-sedimentation-anaerobic (SOSA) system. In a specific embodiment, sewage enters the main stream activated sludge reaction tank through the water inlet system. After organic matter removal and nitrogen and phosphorus removal reactions, the effluent sludge mixture is introduced into the secondary sedimentation tank for sedimentation separation, and the treated sewage is discharged through the effluent system. A part of the concentrated sludge at the bottom of the secondary sedimentation tank is refluxed to the main stream activated sludge reaction tank through the sludge reflux system; another part of the concentrated sludge is added with sufficient sulfate through the sulfate addition system and then flows into the sulfate reduction side stream sludge digestion tank. At the same time, an equal amount of sludge from the sulfate reduction side stream sludge digestion tank is pumped into the main stream activated sludge reaction tank. When the concentrated sludge enters the sulfate reduction side stream sludge digestion tank, the sludge is in a completely starved state and hydrolyzes under anaerobic conditions, releasing organic matter. Sulfate-reducing bacteria use sulfate to degrade the organic matter, achieving sludge reduction and simultaneously generating dissolved hydrogen sulfide. When the sludge mixture in the sulfate reduction side stream sludge digestion tank enters the main stream activated sludge reaction tank, a part of the dissolved organic matter and hydrogen sulfide it carries can be used to enhance mainstream nitrogen and phosphorus removal.

[0055] The supernatant or filtrate of the sulfate reduction side stream sludge digestion tank is periodically extracted, and struvite precipitation is generated by adding alkali and magnesium salts in the struvite recovery system to recover phosphorus. The supernatant or filtrate after being treated by the struvite recovery system is refluxed to the main stream activated sludge reaction tank.

[0056] In a specific embodiment, the design of the mainstream activated sludge reaction tank is not limited to a specific type of reactor, and may include a sequencing batch reactor, a membrane reactor, a granular sludge bed reactor, a moving bed biofilm reactor, etc.

[0057] In other specific embodiments, the sulfate-reducing sidestream sludge digestion device includes a continuously stirred reactor, a semi-batch stirred reactor, or an upflow anaerobic sludge bed reactor.

[0058] The SOSA process according to the present invention can improve sludge properties, enhance the dewaterability and sedimentation of activated sludge, and reduce the input cost of subsequent sludge treatment and other processes. In addition, the SOSA process can achieve online sludge reduction and simultaneous efficient nitrogen and phosphorus removal, with low input and operation costs, strong reliability, and long-term economic and environmental benefits, and has broad development prospects in the actual application in sewage treatment plants.

[0059] Compared with the SANI process, the SOSA process has a low retrofit cost. Only a sidestream reactor needs to be added to the activated sludge process treatment system of the original sewage treatment plant. After the microorganisms in the sludge are domesticated for a certain period of time, online sludge reduction can be achieved, and the effect of nitrogen and phosphorus removal can be improved. Secondly, the sulfur source added in the SOSA process is mainly targeted at the sidestream. When treating sewage without sulfate, the sulfur source addition cost of SOSA is lower. In addition, the phosphorus removal effect of the SANI process is limited, while the SOSA process can not only improve the phosphorus removal effect, but also recover phosphorus simultaneously (in the form of struvite).

[0060] Examples

[0061] Example 1

[0062] System construction: To determine the possibility of sulfate reduction reaction using activated sludge as a carbon source in a sulfate-reducing sidestream sludge digester, a semi-continuous flow experiment was carried out in an anaerobic reactor with an effective volume of 4.0 L. The concentrated activated sludge used in the experiment mainly came from the Shatin Sewage Treatment Plant in Hong Kong. The sludge-water mixture contained 300 mg S / L of sulfate, and the basic parameters were 17 - 23 g TSS / L and 13 - 16 g TSS / L. In this experiment, the sulfate reduction reaction was carried out at different sludge retention times (5, 10, 20, 40 days) and different temperatures (25°C and 35°C).

[0063] Results: Table 1 lists the experimental results of the sulfate-reducing sidestream reactor, including the organic loading rate (OLR, kg VS / m 3 / d), the sludge degradation rate (SSR, kg VS / m 3 / d), Volatile Sludge Reduction Percentage (VSR, %), and Sulfate Reduction (ΔSO4, mg S / L). As can be seen from Table 1, at a temperature of 35°C, when the SRT is 20 and 40 days, the volatile sludge reduction and sulfate reduction effects are good. However, when the SRT is shortened to 10 and 5 days (at 35°C), their performance (VSR and ΔSO4) is halved. When the temperature drops to 25°C, although the sludge reduction effect deteriorates, the sulfate reduction effect is still good. When the SRT is 5 days (when the temperature drops to 25°C), ΔSO4 can still reach 105 mg S / L. According to the measured data of T1, T2, T3, and T4 (Table 2), the relationships between the Sludge Retention Time (SRT), Volatile Sludge Reduction Percentage (VSR), and Specific Sludge Reduction Rate (SSR) are respectively shown in Figure 5 (a) and (b). Combining Table 1 and Figure 5 It is concluded that the sulfate reduction reaction can still rapidly degrade sludge and carry out the sulfate reduction reaction when the sludge retention time is 5 - 10 days; at the same time, shortening the sludge retention time greatly improves the specific sludge reduction rate.

[0064] Table 1 Experimental Results of Sulfate Reduction Side-Flow Reactor

[0065]

[0066] Table 2 Relationships between Sludge Retention Time (SRT), Sludge Reduction Rate (SSR), and Volatile Sludge Reduction Percentage (VSR).

[0067]

[0068] Example 2

[0069] Experiment: Verification of the Possibility of Using Dissolved Hydrogen Sulfide in the Sulfate Reduction Side-Flow Reactor for Mainstream Activated Sludge Denitrification; Improvement Degree of Dewaterability of Treated Sludge.

[0070] The activated sludge used in Experiment a was taken from the Shatin Sewage Treatment Plant in Hong Kong. Autotrophic denitrification reaction (25°C) was carried out in a 2.0 L glass anaerobic reactor, with an initial sulfide concentration of 75 mg S / L and an initial nitrate concentration of 50 mg N / L. Samples were taken every 30 minutes until the nitrate or sulfide concentration was 0.

[0071] In Experiment b, the dewatering performance of three kinds of sludge was compared simultaneously. The sludge from the anaerobic digester of the Shatin Sewage Treatment Plant in Hong Kong was used for the sludge digested by the methane production method. The sludge digested by the sulfate reduction method was taken from the sludge of T5 in Example 1. The activated sludge was taken from the activated sludge tank of the Shatin Sewage Treatment Plant. The dewatering performance was expressed by the sludge specific resistance, and its physical meaning is the resistance per unit filtration area when a unit mass of sludge is filtered under a certain pressure. The larger the sludge specific resistance, the worse the dewatering performance.

[0072] The experimental results are as Figure 6 shown in a. While enhancing anaerobic sludge reduction, the sulfate-reducing sidestream reactor can produce dissolved hydrogen sulfide, which can be used for denitrification in the mainstream to improve nitrogen removal efficiency; Figure 6 The results in b show the improvement of sludge dewaterability. The dewaterability of the activated sludge by sulfate-reducing digestion is improved by 45%, which is comparable to that of the sludge digested by methanogens.

[0073] Therefore, adding a small amount of sulfate to the sidestream reactor to cultivate sulfate-reducing bacteria to achieve on-line sludge reduction and enhance the mainstream denitrification efficiency is a new technology with low cost and low energy consumption, which is applicable to sulfur-containing wastewater or ordinary wastewater (by adding sulfate).

Claims

1. An activated sludge process for sewage treatment, comprising the following steps: A step of introducing sewage into the main-stream activated sludge reaction tank to carry out organic matter removal and nitrogen and phosphorus removal reactions, wherein the main-stream activated sludge reaction tank adopts an anaerobic-anoxic-aerobic process; A step of introducing the effluent sludge mixture of the main-stream activated sludge reaction tank into a secondary sedimentation tank for sludge-water separation; A step of returning a part of the concentrated sludge at the bottom of the secondary sedimentation tank to the main-stream activated sludge reaction tank through a sludge return system; A step of adding a sufficient amount of sulfate to another part of the concentrated sludge at the bottom of the secondary sedimentation tank and flowing it into a sulfate-reducing side-stream sludge digestion tank, wherein the concentrated sludge flowing into the sulfate-reducing side-stream sludge digestion tank is in a completely starved state and hydrolyzes and releases organic matter under anaerobic conditions, and sulfate-reducing bacteria utilize sulfate radicals to degrade organic matter and simultaneously produce dissolved hydrogen sulfide; A step of introducing the sludge mixture of the sulfate-reducing side-stream sludge digestion tank into the main-stream activated sludge reaction tank, wherein a part of the dissolved organic matter and hydrogen sulfide carried by the sludge mixture enhance mainstream nitrogen and phosphorus removal, and sulfide-oxidizing bacteria carry out autotrophic denitrification reactions in the main-stream activated sludge reaction tank using the hydrogen sulfide in the sludge mixture.

2. The process according to claim 1, further comprising a step of promoting the growth of low-sludge-yield bacteria.

3. The sewage treatment process according to claim 1, further comprising a step of recovering phosphorus by struvite precipitation method.

4. The process according to claim 1, wherein the sulfur source is a substance capable of providing an electron acceptor for sulfate-reducing bacteria.

5. The process according to claim 3, wherein the sulfur source includes sulfate, elemental sulfur, thiosulfate and sulfite.

6. A sewage treatment system, comprising a main-stream activated sludge reaction system and a side-stream-sulfate reduction system, wherein the main-stream activated sludge reaction system includes: An inlet device for providing sewage; A main-stream activated sludge reaction tank, the sewage enters the main-stream activated sludge reaction tank through the inlet device, and the main-stream activated sludge reaction tank adopts an anaerobic-anoxic-aerobic process; A secondary sedimentation tank; An outlet device; And A sludge return device for returning a part of the concentrated sludge treated by the secondary sedimentation tank to the main-stream activated sludge reaction tank; The side-stream-sulfate reduction system includes: A sulfate addition device for adding sulfate to another part of the concentrated sludge treated by the secondary sedimentation tank; And A sulfate-reducing side-stream sludge digestion device.

7. The sewage treatment system according to claim 6, further comprising a struvite recovery device for recovering phosphorus by struvite reaction.

8. The sewage treatment system according to claim 6, wherein the main-stream activated sludge reaction tank includes a sequencing batch reactor, a membrane reactor, a granular sludge bed reactor or a moving bed biofilm reactor.

9. The sewage treatment system according to claim 6, wherein the sulfate-reducing side-stream sludge digestion device includes a continuous stirred reactor, a semi-batch stirred reactor or an upflow anaerobic sludge bed reactor.

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