In-situ resourceful treatment method of a bacteria-algae system and application thereof

Abstract

This invention relates to the field of waste sludge treatment technology, specifically to an in-situ resource utilization method for a microbial-algae system and its application. The in-situ resource utilization method for the microbial-algae system includes: placing waste sludge, microalgae, and sodium sulfite in an anaerobic fermentation reactor, then adjusting the pH of the mixture and fermenting under anaerobic conditions; wherein the microalgae include at least one of the phyla of green algae, cyanobacteria, and diatoms; and no anaerobic sludge is added to the anaerobic fermentation reactor. This method can effectively utilize the microbial-algae system to increase the yield of volatile fatty acids during anaerobic fermentation in situ, and can also reduce the yield of waste sludge in situ, thereby lowering the subsequent disposal costs of sludge and microalgae in the secondary sedimentation tank.

Description

Technical Field

[0001] This invention relates to the field of bacterial and algal system treatment technology, and more specifically, to an in-situ resource utilization method for bacterial and algal systems and its application. Background Technology

[0002] Currently, the activated sludge process remains the mainstream technology in biological wastewater treatment. This technology generates a large amount of excess sludge, which requires further treatment. Anaerobic digestion is a commonly used method for treating excess sludge, reducing sludge volume while producing methane. However, the low biomass content of the excess sludge leads to insufficient substrate for microorganisms, thus reducing biomass energy production. Furthermore, excessive algae growth is common in secondary sedimentation tanks of wastewater treatment plants. Algae growth increases the concentration of suspended solids in the effluent, not only reducing effluent quality but also causing secondary pollution. Combining excess sludge with algae to form a microbial-algae system can not only increase the biomass content of the excess sludge but also reduce algae disposal costs.

[0003] Patent CN109942159A discloses an in-situ treatment method for excess sludge. The method involves pretreating the excess sludge by mixing it with sulfite. The sulfite decomposes the sludge, increasing the dissolved chemical oxygen demand (COD). (After pretreatment, the sulfite decomposes; if it doesn't, it alters the redox potential of the system, inhibiting the activity of methanogenic bacteria and reducing methane production.) The sludge is then mixed with anaerobic sludge (anaerobic digesting bacteria) for anaerobic digestion, utilizing the increased dissolved COD to boost methane production. While this method can improve methane yield, the economic benefits are low. Furthermore, the sludge treatment in this patent is an ex-situ treatment, resulting in lower efficiency.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide an in-situ resource utilization method for a bacterial-algae system. This method can not only increase the yield of volatile fatty acids during anaerobic fermentation in situ, but also increase the consumption of excess sludge and the utilization rate of algae in the secondary sedimentation tank.

[0006] The second objective of this invention is to provide the application of the in-situ resource utilization method of the aforementioned bacterial and algal system in wastewater treatment.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] This invention provides an in-situ resource utilization method for a bacterial-algae system, comprising the following steps:

[0009] The remaining sludge, microalgae, and sodium sulfite were placed in an anaerobic fermentation reactor, and the pH of the mixture was adjusted to carry out fermentation under anaerobic conditions.

[0010] The microalgae include at least one of the following phyla: green algae, cyanobacteria, and diatoms;

[0011] There is no anaerobic sludge in the anaerobic fermentation reactor.

[0012] Preferably, the algal density of the microalgae in the anaerobic fermentation reactor is 1×10⁻⁶. 9 Cells / L ~ 1×10 10 Cells / L.

[0013] Preferably, the microalgae include at least one of Chlorella, Anabaena, Nostoc, and Rhomboidella.

[0014] Preferably, the concentration of sodium sulfite dissolved in the anaerobic fermentation reactor is ≤500 mg S / L.

[0015] Preferably, the concentration of sodium sulfite dissolved in the anaerobic fermentation reactor is 100 mg S / L to 500 mg S / L.

[0016] Preferably, the pH of the mixture is adjusted to 4-10, and more preferably to 5-7.

[0017] Preferably, the temperature inside the anaerobic fermentation reactor is 20℃~45℃, and more preferably 25℃~40℃.

[0018] Preferably, the fermentation time is ≤14 days.

[0019] Preferably, the fermentation time is 7 to 13 days.

[0020] Preferably, the anaerobic fermentation reactor comprises a fully mixed reactor and / or an anaerobic baffle reactor.

[0021] This invention also provides the application of the in-situ resource utilization method of the bacterial and algal system described above in wastewater treatment.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention uses sodium sulfite to treat a microalgae and residual sludge system, which not only improves the yield and total amount of volatile fatty acids during anaerobic fermentation in situ, but also reduces the production of residual sludge and lowers the subsequent disposal costs of sludge and algae. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 The results of the comparison of dissolved chemical oxygen demand of the residual sludge obtained after fermentation in each group provided by the present invention;

[0026] Figure 2 The results show the comparison of the degradation rate of volatile suspended solids of the residual sludge obtained after fermentation in each group provided by the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0028] In a first aspect, the present invention provides an in-situ resource utilization method for a microbial-algae system, wherein the microbial-algae system refers to a system containing residual sludge and microalgae, specifically a method for treating microalgae and residual sludge with sodium sulfite for co-fermentation (co-digestion), which includes the following steps:

[0029] The remaining sludge, microalgae, and sodium sulfite were placed in an anaerobic fermentation reactor, and the pH of the mixture was adjusted for fermentation under anaerobic conditions.

[0030] The microalgae include at least one of the following phyla: green algae, cyanobacteria, and diatoms.

[0031] The anaerobic fermentation reactor does not contain anaerobic sludge. This means the mixed materials can undergo in-situ anaerobic fermentation. Traditional reactions generally require the addition of anaerobic sludge, and the fermentation products need to be controlled with chemicals. However, this invention does not require anaerobic sludge or additional chemicals; it can be directly treated with sodium sulfite and microalgae.

[0032] This invention directly mixes sodium sulfite with excess sludge and microalgae and places it in an anaerobic fermentation reactor. Without adding anaerobic sludge, the residual microorganisms in the excess sludge are directly used for anaerobic fermentation. Sodium sulfite increases the redox potential in the anaerobic fermentation reactor, which inhibits the activity of methanogens (because methanogens are suitable for low redox potential environments), but promotes the yield of short-chain fatty acids (volatile fatty acids).

[0033] Volatile fatty acids refer to organic acids with carbon chains of 1 to 6 carbon atoms, including acetic acid, propionic acid, isobutyric acid, valeric acid, isovaleric acid, n-butyric acid, etc., but not limited to these.

[0034] Meanwhile, microalgae are rich in protein, polysaccharides, and trace elements, which can effectively increase the dissolved organic carbon content in waste sludge. However, the cell walls of microalgae can hinder the anaerobic digestion and hydrolysis process, reducing the release of soluble organic matter. This invention utilizes sodium sulfite to disrupt the cell structure (cell wall) of microalgae, causing the cell wall to lyse into polysaccharides and other nutrients, providing abundant substrate for the proliferation and growth of anaerobic bacteria (co-digesting microalgae with waste sludge effectively increases the yield of biomass energy). This promotes the production of volatile fatty acids by anaerobic bacteria and increases the consumption of waste sludge, thereby effectively reducing the amount of sludge.

[0035] It is evident that by using sodium sulfite to co-treat the microalgae and residual sludge system, this invention not only improves the yield and total amount of volatile fatty acids during anaerobic fermentation (while inhibiting the yield and total amount of methane), thus enhancing the resource utilization rate and economic added value of sludge, but also increases the consumption of residual sludge, thereby improving sludge treatment efficiency.

[0036] Furthermore, this method also has the advantages of being simple to operate, low in cost, and environmentally friendly.

[0037] Compared with the existing technology that first mixes the residual sludge with sulfite for pretreatment and then mixes it with anaerobic sludge for anaerobic digestion, the in-situ resource utilization method of the bacterial-algae system provided by the present invention is simpler. It can mix residual sludge, microalgae and sodium sulfite at the same time without the need to add additional anaerobic digesting bacteria (anaerobic sludge), and can increase the production of short-chain fatty acids, i.e., in-situ bacterial-algae system treatment.

[0038] Preferably, the algal density of the microalgae in the anaerobic fermentation reactor is 1×10⁻⁶. 9 Cells / L ~ 1×10 10 Cells / L, including but not limited to 2×10 9 Cells / L, 3×10 9 Cells / L, 4×109 Cells / L, 5×10 9 Cells / L, 6×10 9 Cells / L, 7×10 9 Cells / L, 8×10 9 Cells / L, 9×10 9 The point value of either Cells / L or the range value between either of them.

[0039] The algal density refers to the number of algal cells per unit volume of water.

[0040] Preferably, the microalgae include at least one of Chlorella, Anabaena, Nostoc, and Rhomboidella.

[0041] Preferably, the sodium sulfite concentration in the anaerobic fermentation reactor is ≤500 mg S / L, including but not limited to any one of 450 mg S / L, 400 mg S / L, 350 mg S / L, 300 mg S / L, 250 mg S / L, 200 mg S / L, 150 mg S / L, 100 mg S / L, 80 mg S / L, 50 mg S / L, 30 mg S / L, and 10 mg S / L, or a range between any two.

[0042] The unit mg S / L refers to the number of milligrams of sulfur element contained in each liter of solution.

[0043] Studies have found that excessively high sulfite concentrations can inhibit the cell activity of acid-producing bacteria, thereby reducing the yield and total amount of volatile fatty acids.

[0044] Preferably, the sodium sulfite concentration in the anaerobic fermentation reactor is 100 mg S / L to 500 mg S / L, including but not limited to any one of 130 mg S / L, 150 mg S / L, 180 mg S / L, 200 mg S / L, 230 mg S / L, 250 mg S / L, 280 mg S / L, 300 mg S / L, 330 mg S / L, 350 mg S / L, 380 mg S / L, 400 mg S / L, 420 mg S / L, 450 mg S / L, and 480 mg S / L, or a range between any two.

[0045] Preferably, adjusting the pH of the mixture to 4-10 includes, but is not limited to, any one of the following values ​​or a range between any two: 5, 5.2, 5.4, 5.5, 5.7, 5.9, 6.0, 6.2, 6.4, 6.5, 6.7, 6.9, 7, 8, and 9; more preferably, adjusting the pH of the mixture to 5-7.

[0046] In some specific embodiments of the present invention, the pH of the system during the fermentation process is 5 to 7, including but not limited to any one of 5.2, 5.4, 5.5, 5.7, 5.9, 6.0, 6.2, 6.4, 6.5, 6.7, and 6.9, or any range between two of them.

[0047] By controlling the pH of the mixture to 5-7 or the pH of the system during fermentation to 5-7, the production of methane can be suppressed while ensuring the survival of acid-producing bacteria.

[0048] In some specific embodiments of the present invention, the pH of the mixture is adjusted using a dilute hydrochloric acid solution and / or a sodium hydroxide solution; preferably, the molar concentration of the dilute hydrochloric acid is 0.01 to 0.1 mol / L, including but not limited to any one of 0.03 mol / L, 0.05 mol / L, 0.07 mol / L, or 0.09 mol / L, or a range between any two; the molar concentration of the sodium hydroxide solution is 0.01 to 0.1 mol / L, including but not limited to any one of 0.03 mol / L, 0.05 mol / L, 0.07 mol / L, or 0.09 mol / L, or a range between any two.

[0049] Preferably, the temperature inside the anaerobic fermentation reactor is 20℃~45℃, including but not limited to any one of 25℃, 27℃, 29℃, 30℃, 32℃, 34℃, 35℃, 37℃, 39℃, and 40℃, or a range between any two; more preferably, it is 25℃~40℃.

[0050] That is, the fermentation temperature is 20℃~45℃, preferably 25℃~40℃.

[0051] Preferably, the fermentation time is ≤14 days, including but not limited to any one of 13 days, 12 days, 11 days, 10 days, 9 days, 8 days, 7 days, 6 days, 5 days, 4 days, 3 days, 2 days, and 1 day, or any range between two of them.

[0052] The in-situ resource utilization method of the microbial-algae system provided by the present invention shortens the digestion time by introducing microalgae and residual sludge for co-fermentation.

[0053] Preferably, the fermentation time is 7 to 13 days, including but not limited to any one of 8 days, 9 days, 10 days, 11 days, and 12 days, or any range between two of them.

[0054] Preferably, the anaerobic fermentation reactor comprises a fully mixed reactor and / or an anaerobic baffle reactor.

[0055] In some specific embodiments of the present invention, stirring is also performed during the fermentation process under anaerobic conditions.

[0056] In some specific embodiments of the present invention, the anaerobic conditions are achieved by introducing nitrogen gas.

[0057] In some specific embodiments of the present invention, the source of the excess sludge includes the aerobic, anaerobic and anoxic sections of the activated sludge process, or it can be sludge from the secondary sedimentation tank.

[0058] In some specific embodiments of the present invention, the total solids concentration of the residual sludge in the anaerobic fermentation reactor is 4 to 15 g / L, including but not limited to any one of 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, and 14 g / L, or a range between any two.

[0059] The total solids concentration, also known as total evaporation residue, refers to the substances remaining after a water sample is evaporated and dried to constant weight under specified conditions.

[0060] In some specific embodiments of the present invention, the microalgae can be obtained in any conventional way, such as by purchasing, or by using microalgae from lakes, reservoirs and secondary sedimentation tanks of sewage treatment plants, in order to alleviate the harm caused by algae to water bodies.

[0061] Secondly, the present invention also provides the application of the in-situ resource utilization method of the bacterial and algal system described above in wastewater treatment.

[0062] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0063] Example 1

[0064] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment includes the following steps: Residual sludge removed from the secondary sedimentation tank of a wastewater treatment plant, Chlorella vulgaris, and sodium sulfite are placed in an anaerobic fermentation reactor (completely mixed reactor) that does not contain anaerobic sludge. The residual sludge has a total solids concentration of 24.98 g / L and a volatile solids content of 14.19 g / L; the sodium sulfite concentration is 100 mg S / L; and the Chlorella vulgaris density is 1 × 10⁻⁶. 9Cells / L. The pH of the mixture was then adjusted to 6.5 using a 0.1 mol / L dilute hydrochloric acid solution. Nitrogen gas was then introduced to achieve complete anaerobic digestion, and the mixture was stirred and fermented under anaerobic conditions for 14 days (during which the pH was stabilized at 6.5 using a 0.1 mol / L sodium hydroxide solution). The temperature inside the anaerobic fermentation reactor was maintained at 25°C throughout the fermentation process.

[0065] Example 2

[0066] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment includes the following steps: Residual sludge removed from the secondary sedimentation tank of a wastewater treatment plant, *Anabaena spp.*, and sodium sulfite are placed in an anaerobic fermentation reactor (completely mixed reactor) that does not contain anaerobic sludge. The residual sludge has a total solids concentration of 20.44 g / L and a volatile solids content of 9.18 g / L; the sodium sulfite concentration is 300 mg S / L; and the *Anabaena spp.* algal density is 1 × 10⁻⁶. 10 Cells / L. The pH of the mixture was then adjusted to 6.5 using a 0.1 mol / L dilute hydrochloric acid solution. Nitrogen gas was then introduced to achieve complete anaerobic digestion, and the mixture was stirred and fermented under anaerobic conditions for 7 days (during which the pH was stabilized at 6.5 using a 0.1 mol / L sodium hydroxide solution). The temperature inside the anaerobic fermentation reactor was maintained at 33°C during the fermentation process.

[0067] Example 3

[0068] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment includes the following steps: Excess sludge removed from the secondary sedimentation tank of a wastewater treatment plant, nigrum algae, and sodium sulfite are placed in an anaerobic fermentation reactor (anaerobic baffled reactor) that does not contain anaerobic sludge. The total solids concentration of the excess sludge is 30.87 g / L, and the volatile solids content is 18.48 g / L; the dissolved concentration of sodium sulfite is 300 mg S / L; and the algal density of nigrum algae is 5 × 10⁻⁶. 9 Cells / L. The pH of the mixture was then adjusted to 6.3 using a 0.1 mol / L dilute hydrochloric acid solution. Nitrogen gas was then introduced to achieve complete anaerobic digestion in the reactor, and the mixture was stirred and fermented under anaerobic conditions for 10 days (during which the pH was stabilized at 6.3 using a 0.1 mol / L sodium hydroxide solution). The temperature inside the anaerobic fermentation reactor was maintained at 30°C during the fermentation process.

[0069] Example 4

[0070] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment is basically the same as that in Example 1, except that the concentration of sodium sulfite dissolved in the anaerobic fermentation reactor is 300 mg S / L.

[0071] Example 5

[0072] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment is basically the same as that in Example 1, except that the concentration of sodium sulfite dissolved in the anaerobic fermentation reactor is 500 mg S / L.

[0073] Example 6

[0074] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment is basically the same as that in Example 1, except that the concentration of sodium sulfite dissolved in the anaerobic fermentation reactor is 700 mg S / L.

[0075] Example 7

[0076] The in-situ resource utilization method of the bacterial-algae system provided in this embodiment is basically the same as that in Example 5, except that the fermentation time is 30 days.

[0077] Comparative Example 1

[0078] The in-situ resource utilization method of the bacterial-algae system provided in this comparative example is basically the same as that in Example 1, except that sodium sulfite is not added to the anaerobic fermentation reactor.

[0079] Comparative Example 2

[0080] The in-situ resource utilization method of the bacterial-algae system provided in this comparative example is basically the same as that in Example 1, except that Chlorella is not added to the anaerobic fermentation reactor.

[0081] Experimental Example 1

[0082] The yields of volatile fatty acids and methane produced after fermentation in each of the above examples and comparative examples were measured, and the results are shown in Table 1 below.

[0083] The method for testing the yield of volatile fatty acids is as follows: Take 7 mL of fermentation broth from each group, add 2 drops of 6 mol / L dilute sulfuric acid solution to lower the pH to 3.5, centrifuge for 25 min, take 3 mL of the clear supernatant, add 0.15 mL of concentrated formic acid, and the final pH is 2.0. Then, add 3.15 mL of the mixture to a gas chromatograph (GC-2014C, Shimadzu) for analysis. The gas chromatograph injection temperature is 250℃, and the detection temperature is 300℃. The gas chromatograph is set to an initial temperature of 80℃, held for 2 min, and then heated to 180℃ at a rate of 20℃ / min and held for 1 min.

[0084] The method for testing methane production is as follows: The volume of residual gas in the anaerobic fermentation reactor is measured to be V. 剩 The generated biogas was collected using a SAMCO glass syringe and the volume was recorded as V. 收The collected gas was then monitored using a gas chromatograph (Thermo Fisher Scientific, GC-Trace1300), and the methane content was determined to be P. 甲烷 Then methane production = (V 剩 +V 收 )×P 甲烷 .

[0085] Table 1. Production of volatile fatty acids and methane in each group.

[0086] Group Production of volatile fatty acids methane production Example 1 124.21mg COD / g VS <![CDATA[13.52mL CH4 / g VS]]> Example 2 247.74mg COD / g VS <![CDATA[7.42mL CH4 / g VS]]> Example 3 251.94mg COD / g VS <![CDATA[6.31mL CH4 / g VS]]> Example 4 247.74mg COD / g VS <![CDATA[7.42mL CH4 / g VS]]> Example 5 317.88mg COD / g VS <![CDATA[2.76mL CH4 / g VS]]> Example 6 268.42mg COD / g VS <![CDATA[6.96mL CH4 / g VS]]> Example 7 311.12mg COD / g VS <![CDATA[2.91mL CH4 / g VS]]> Comparative Example 1 112.45mg COD / g VS <![CDATA[10.63mL CH4 / g VS]]> Comparative Example 2 103.52mg COD / g VS <![CDATA[14.67mL CH4 / g VS]]>

[0087] Comparing the experimental results of Examples 1, 4, 5 and 6, it can be seen that appropriately increasing the concentration of sodium sulfite can increase the production of volatile fatty acids. However, in Example 6, the concentration of sodium sulfite was too high, which would inhibit the cell activity of acid-producing bacteria and thus inhibit the production of volatile fatty acids.

[0088] Comparing the experimental results of Example 7 and Example 5, it can be seen that in Example 7, extending the fermentation time actually reduced the yield of volatile fatty acids. This is because after the substrate of the anaerobic bacteria was consumed, a small number of methanogenic bacteria synthesized methane from the volatile fatty acids. Therefore, Example 5, by controlling the appropriate fermentation time, can obtain a higher yield of volatile fatty acids and significantly shorten the processing cycle.

[0089] Comparing the experimental results of Example 1 and Comparative Example 1, it can be seen that the amount of volatile fatty acids produced in Comparative Example 1 is significantly lower than that in Example 1 because sodium sulfite was not added. This results in insufficient substrate for methanogenic bacteria, and therefore, the methane yield in Comparative Example 1 is also lower than that in Example 1.

[0090] Comparing the experimental results of Example 1 and Comparative Example 2, it can be seen that the addition of Chlorella significantly increases the production of volatile fatty acids.

[0091] Traditional anaerobic fermentation of waste sludge yields short-chain fatty acids (SCFAs) at a rate of 104 kg / ton of volatile solids (VLS). In contrast, the in-situ anaerobic fermentation of SCFAs using a microbial-algae system after sulfite treatment, as described in this application, yields 317 kg / ton of VLS. This method produces 3.05 times the VLS yield of traditional anaerobic fermentation of waste sludge. Based on the market prices of SCFAs—acetic acid (5440 RMB / ton), propionic acid (7480 RMB / ton), butyric acid (6800 RMB / ton), and valeric acid (19040 RMB / ton)—the profit from this method is 1724.48 RMB / ton of VLS, higher than the 565.76 RMB / ton of VLS produced by traditional anaerobic fermentation of waste sludge.

[0092] Currently, the price of natural gas is 3400 yuan / thousand cubic meters. The methane produced using this method has a volatile solids content of 11.61 cubic meters per ton, resulting in a methane revenue of 34.578 yuan per ton of volatile solids. Traditional anaerobic fermentation of waste sludge produces an average methane yield of 350 mL / g VS, or 350 cubic meters per ton of volatile solids, with a revenue of 1190 yuan per ton of volatile solids.

[0093] Therefore, from an economic perspective, the method provided by this invention yields a benefit of 1724.48 yuan / ton of volatile solids from short-chain fatty acid production, while the traditional anaerobic fermentation method for methane production yields a benefit of 1190 yuan / ton of volatile solids. It is evident that the method provided by this invention is superior to the traditional anaerobic fermentation method for waste sludge.

[0094] Experiment Example 2

[0095] The dissolved chemical oxygen demand (COD) of the bacterial-algae systems obtained after fermentation in Examples 1, 4, 5, and Comparative Example 1 was determined using the dichromate method according to the national standard GB11914-89. The results are as follows: Figure 1 As shown.

[0096] from Figure 1 It can be seen that the dissolved chemical oxygen demand (COD) increases with the increase of sodium sulfite content. Increased COD is beneficial to acid-producing bacteria, providing them with a richer substrate and leading to the production of more short-chain fatty acids.

[0097] Furthermore, the degradation rate of volatile suspended solids in the residual sludge obtained after fermentation in Examples 1, 4, 5, and Comparative Example 1 was determined, and the results are as follows: Figure 2 As shown.

[0098] The determination of the total volatile solids was performed according to the following standard method published by the American Public Health Association in 2005: First, a crucible was washed and ignited to constant weight (approximately 60 minutes at 550°C); 10 ml of sludge was measured using a pipette and placed in the crucible; the crucible was placed in an oven at 105°C for 24 hours, then removed and cooled to room temperature in a desiccator, and then weighed (M1); the crucible was then ignited in a muffle furnace at 550°C for 2 hours, removed and cooled to room temperature in a desiccator, and then weighed (M2); the volatile solids content (VS) of the sludge was obtained by dividing M1-M2 by the volume of the sludge.

[0099] from Figure 2 It can be seen that the degradation rate of volatile suspended solids gradually increases with the increase of sodium sulfite content. This indicates that the treatment method provided by this invention has excellent in-situ sludge reduction characteristics, requires no additional anaerobic sludge, and is more economical.

[0100] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for in-situ resource utilization of a bacteria-algae system, characterized in that, The method comprises the following steps: putting residual sludge, microalgae and sodium sulfite into an anaerobic fermentation reactor, then adjusting pH of the mixture, and carrying out fermentation under anaerobic condition; wherein the phylum of the microalgae comprises at least one of Chlorophyta, Cyanophyta and Bacillariophyta; there is no anaerobic sludge in the anaerobic fermentation reactor; The algal density of the microalgae in the anaerobic fermentation reactor is 1 x 10 9 Cells / L~1 x 10 10 Cells / L; the fermentation time is 7-13 days.

2. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, characterized in that, the microalgae comprise at least one of Chlorella, Anabaena, Nostoc and Nitzschia.

3. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, characterized in that, the dissolved concentration of the sodium sulfite in the anaerobic fermentation reactor is ≤500mg S / L.

4. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, characterized in that, the dissolved concentration of the sodium sulfite in the anaerobic fermentation reactor is 100-500mg S / L.

5. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, characterized in that, the pH of the mixture is adjusted to 4-10.

6. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, wherein, the pH of the mixture is adjusted to 5-7.

7. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, wherein, the temperature in the anaerobic fermentation reactor is 20-45℃.

8. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, characterized in that, the temperature in the anaerobic fermentation reactor is 25-40℃.

9. The method of in-situ resourceful treatment of a bacteria-algae system according to claim 1, characterized in that, the anaerobic fermentation reactor comprises a complete-mixing reactor and / or an anaerobic baffled reactor.

10. Application of the method for in-situ resourceful treatment of the bacteria-algae system according to any one of claims 1-9 in sewage treatment.

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