A process and system for recycling liquid by-product of a filter press in a biogas purification process

Abstract

This invention discloses a process for recycling liquid by-products from a filter press during biogas purification, comprising the following steps: S1, collecting sulfur-containing wastewater, dust-containing sewage, and condensate generated by the filter press in the biogas purification system into a collection tank, adjusting the pH to weakly alkaline to obtain raw liquid to be treated; S2, after removing large impurities through a bar filter, the raw liquid to be treated is passed into a sedimentation tank, where polyaluminum chloride and polyacrylamide are added to remove suspended solids with a particle size ≥10μm and some colloids to obtain a pretreated liquid; S3, the pretreated liquid is filtered sequentially through a quartz sand filter and an activated carbon filter to obtain a clarified liquid; S4, targeted purification; S5, the liquid treated in S4 is passed into a reverse osmosis membrane system for desalination and purification to obtain recycled water; S6, the recycled water is divided into two streams for reuse: one stream is used as makeup water for the biogas desulfurization tower and dehydrator, and the other stream is disinfected and used as flushing water for the filter press or workshop floor, thus realizing the recycling of water resources.

Description

Technical Field

[0001] This invention relates to the field of biogas resource utilization and environmental protection technology, specifically to a process and system for recovering and utilizing liquid by-products from a filter press during biogas purification. Background Technology

[0002] Biogas, as a clean and renewable energy source, is widely used in power generation, heating, and industrial fuel. In large-scale biogas projects, the biogas produced from anaerobic fermentation of raw materials (livestock manure, straw, organic wastewater, etc.) needs to undergo purification treatments such as desulfurization, dehydration, and dust removal to meet subsequent usage requirements. During the biogas purification process, sulfur-containing sludge from the desulfurization tower, condensate from the dehydrator, and dust-containing wastewater from the dust collector will generate a large amount of by-product liquid after solid-liquid separation by a filter press. This liquid contains pollutants such as sulfides, suspended solids, organic matter, and salts. Direct discharge of these liquids will not only waste water resources but also cause soil and water pollution, failing to meet environmental protection requirements. If traditional wastewater treatment processes (such as biochemical treatment) are used, there are problems such as high treatment costs, sulfide toxicity inhibiting microbial activity, and low treatment efficiency.

[0003] Existing by-product liquid treatment technologies mostly aim for "compliant discharge" and lack resource recovery awareness. For example, some processes simply remove suspended solids through sedimentation and filtration before direct discharge, without recovering valuable components such as sulfides; some processes use dilution followed by biological treatment, resulting in ineffective water reuse and high operating costs. Furthermore, existing technologies do not target the different water quality differences of various by-product liquids (sulfur-containing wastewater, dust-containing wastewater, and condensate), leading to unstable treatment effects and difficulty in meeting the needs of resource utilization. Summary of the Invention

[0004] Therefore, the present invention provides a process and system for recycling liquid by-products from a filter press during biogas purification, in order to solve the above-mentioned problems in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] According to a first aspect of the present invention, a process for recovering and utilizing liquid by-products from a filter press during biogas purification includes the following steps:

[0007] S1. Collect the sulfur-containing waste liquid, dust-containing sewage, and condensate generated by the filter press of the biogas purification system into the collection tank, adjust the pH to weak alkalinity, and control the liquid temperature within the preset constant temperature range to obtain the raw liquid to be treated.

[0008] S2. After removing large impurities through a grid filter, the raw liquid to be treated is introduced into a sedimentation tank, where polyaluminum chloride and polyacrylamide are added. After stirring and mixing, the mixture is allowed to stand for 30-60 minutes to remove suspended solids with a particle size ≥10μm and some colloids, thus obtaining a pretreated liquid.

[0009] S3. The pretreated liquid is filtered sequentially through a quartz sand filter and an activated carbon filter to obtain a clarified liquid; the suspended solids content in the clarified liquid is ≤10mg / L, and the COD is ≤100mg / L.

[0010] S4, Targeted Purification:

[0011] a. If the by-product liquid is sulfur-containing waste liquid, the clarified liquid is passed into the sulfide recovery reactor, ferrous chloride solution is added to generate ferrous sulfide precipitate, and ferrous sulfide by-product is obtained by separation by plate and frame filter press;

[0012] b. If the by-product liquid is dusty wastewater or condensate, the clarified liquid is passed into the ultrafiltration membrane module to remove trace suspended solids and macromolecular organic matter, and ultrafiltration permeate is obtained;

[0013] S5. The liquid treated in S4 is passed into the reverse osmosis membrane system for desalination and purification, with the recovery rate controlled at 70%-85%, to obtain recycled water; the conductivity of the recycled water is ≤100μS / cm, the sulfide content is ≤0.5mg / L, and the suspended solids content is ≤1mg / L.

[0014] S6. The recycled water is divided into two streams: one stream is used as supplementary water for the biogas desulfurization tower and dehydrator, and the other stream is disinfected and used as flushing water for the filter press or workshop floor, thus realizing the recycling of water resources.

[0015] Further, in S1, the pH of the waste liquid is adjusted to 7.0~8.5, and the temperature of the raw liquid to be treated is controlled at 20~40℃; in S2, the dosage of polyaluminum chloride is 50~150mg / L, and the dosage of polyacrylamide is 5~10mg / L; in S3, the particle size of the quartz sand filter media is 0.5~2.0mm, the specific surface area of ​​the activated carbon filter media is 800~1200m² / g, and the filtration flow rate is controlled at 5~10m / h, removing suspended solids, color, and some organic matter from the water through filtration; in S4a, the mass concentration of the ferrous chloride solution is 10%~20%, the molar ratio of ferrous ions to sulfur ions is controlled at 1.2∶1~1.5∶1, the reaction temperature is 25~35℃, the stirring rate is 100~200r / min, and the reaction time is 30~45min; S4 In section b, the pore size of the ultrafiltration membrane module is 0.01~0.1μm, the filtration operating pressure is 0.1~0.3MPa, and the operating temperature is 25~35℃; in section S5, the desalination and purification operating pressure of the reverse osmosis membrane system is 1.0~2.5MPa, and the operating temperature is 20~35℃.

[0016] In S6, the disinfection is ultraviolet irradiation disinfection, with an irradiation dose ≥30mJ / cm².

[0017] Furthermore, the quartz sand filter and activated carbon filter in S3 adopt a backwashing regeneration mode. The backwash water is the concentrated water generated in S5, the backwash flow rate is 15-20m / h, the backwash time is 10-15min, and the backwash cycle is 8-12h. After regeneration, the quality of the filter effluent meets the requirements of the clarified liquid index.

[0018] Furthermore, the sulfide recovery reactor in S4a is equipped with an online pH monitoring and automatic dosing system. When the pH of the reaction system is less than 7.0, calcium hydroxide solution is automatically added to adjust the pH to 7.5-8.0 to ensure that the ferrous sulfide precipitation reaction is complete.

[0019] Furthermore, the ultrafiltration membrane module in S4b uses hollow fiber membranes. During operation, it is chemically cleaned periodically. The cleaning agents are alternating between sodium hydroxide solution with a mass concentration of 0.5%-1.0% and hydrochloric acid solution with a mass concentration of 0.1%-0.3%. The cleaning cycle is 3-5 days, restoring the membrane flux to more than 85% of the initial flux.

[0020] Furthermore, the reverse osmosis membrane system in S5 uses spiral wound composite membranes. After the concentrate is collected in the concentrate storage tank, part of it is used for filter backwashing, and the remainder is treated by evaporation and crystallization. The crystallized salt can be recovered as an industrial raw material, and there is no wastewater discharge.

[0021] Furthermore, the sedimentation tank in S2 is equipped with inclined tube packing. The sludge at the bottom of the sedimentation tank is pumped to a filter press for dewatering. After dewatering, the sludge has a moisture content of ≤60% and can be used as raw material for organic fertilizer or disposed of safely.

[0022] Furthermore, the inclined angle of the inclined tube packing is 60°, and the tube diameter is 25-50mm.

[0023] According to a second aspect of the present invention, a system for recycling liquid by-products from a filter press during biogas purification includes a liquid collection unit, a pretreatment unit, a staged filtration unit, a targeted purification unit, a deep treatment unit, a recycling unit, and a sludge disposal unit.

[0024] The liquid collection unit includes a liquid collection tank and a pH adjustment device, wherein the pH adjustment device is connected to the liquid collection tank;

[0025] The pretreatment unit includes a bar screen filter, a sedimentation tank, and a sludge conveying device. The bar screen filter is connected to the collection tank, the sedimentation tank is connected to the bar screen filter, and the sludge conveying device is connected to the bottom of the sedimentation tank.

[0026] The graded filtration unit includes a quartz sand filter, an activated carbon filter, and a backwashing system. The quartz sand filter is connected to the sedimentation tank, the activated carbon filter is connected to the quartz sand filter, and the backwashing system is connected to both the quartz sand filter and the activated carbon filter. It is used to rinse and regenerate the filter media of the quartz sand filter and the activated carbon filter. The backwashing wastewater generated by the backwashing system is returned to the sedimentation tank of the pretreatment unit through a pipeline.

[0027] The targeted purification unit includes a targeted purification diversion module, a sulfide recovery reactor, and an ultrafiltration membrane assembly. The activated carbon filter is connected to the targeted purification diversion module, and the targeted purification diversion module is connected to both the sulfide recovery reactor and the ultrafiltration membrane assembly.

[0028] The advanced treatment unit includes a reverse osmosis membrane system and a concentrate storage tank. The sulfide recovery reactor and the ultrafiltration membrane module are both connected to the reverse osmosis membrane system. The concentrate storage tank is connected to the reverse osmosis membrane system and is used to store the concentrate produced by the reverse osmosis membrane system. The concentrate storage tank is also connected to the sedimentation tank through a pipeline to realize concentrate reflux and reprocessing.

[0029] The recycling unit includes a recycled water storage tank, a disinfection device, and a delivery pump. The recycled water storage tank is connected to the reverse osmosis membrane system and is used to store purified water after deep purification. The disinfection device is connected to the recycled water storage tank and is used to pressurize and send the disinfected purified water out for recycling.

[0030] The sludge treatment unit includes a sludge filter press and a sludge storage area. The sludge filter press is connected to the sludge conveying equipment and the ultrafiltration membrane module, respectively, and is used to dewater and compress the sludge generated throughout the process. The sludge storage area is connected to the sludge filter press and is used to centrally store the dewatered dry sludge. The filtrate produced by the sludge filter press is returned to the collection tank of the liquid collection unit through a pipeline.

[0031] Furthermore, the pH adjustment device includes a reagent storage tank, a metering pump, and a mixing agitator. The reagent storage tank stores an alkaline adjusting agent. One end of the metering pump is connected to the reagent storage tank, and the other end is connected to a collection tank. It is used to meter and deliver the adjusting agent. The mixing agitator is installed inside the collection tank to fully mix the adjusting agent with the by-product liquid.

[0032] The present invention has the following advantages:

[0033] 1. This invention employs targeted purification technology, achieving a sulfide recovery rate of ≥95% in sulfur-containing wastewater and a recovered ferrous sulfide purity of ≥90%, thus realizing the resource utilization of pollutants and increasing the added value of by-products compared to traditional treatment processes.

[0034] 2. The integrated treatment process enables closed-loop water reuse, and the quality of the reused water meets the water standards of the biogas purification system and workshop. The water reuse rate is ≥85%, and each ton of treated water can save more than 0.85 tons of fresh water consumption, reducing operating costs by 30%-40%.

[0035] 3. The synergistic effect of graded treatment and deep purification ensures that the suspended solids content in the treated water is ≤1mg / L, the sulfide content is ≤0.5mg / L, and the COD is ≤50mg / L, meeting the industrial water standards, avoiding environmental pollution caused by wastewater discharge, and complying with environmental protection requirements.

[0036] 4. The system adopts automated control, with real-time monitoring and adjustment of parameters of each unit. It is easy to operate, runs stably, and is suitable for biogas projects of different scales (daily biogas production of 1000-10000 m³). It can also flexibly switch the processing mode according to the type of by-product liquid, making it highly adaptable.

[0037] 5. The sludge treatment unit achieves dewatering and volume reduction of settled sludge. After dewatering, the sludge moisture content is ≤60%, which can be used as raw material for organic fertilizer or safely disposed of without secondary pollution, achieving environmental protection throughout the entire process. Attached Figure Description

[0038] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0039] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0040] Figure 1 This is a flowchart illustrating a process for recovering and utilizing liquid byproducts from a filter press during biogas purification, provided in some embodiments of the present invention.

[0041] Figure 2 A schematic diagram of a system for recovering and utilizing by-product liquid from a filter press during biogas purification, provided in some embodiments of the present invention. Figure 1 .

[0042] Figure 3 A schematic diagram of a system for recovering and utilizing by-product liquid from a filter press during biogas purification, provided in some embodiments of the present invention. Figure 2 .

[0043] Figure 4 A schematic diagram of a system for recovering and utilizing by-product liquid from a filter press during biogas purification, provided in some embodiments of the present invention. Figure 3 .

[0044] Figure 5 A schematic diagram of a system for recovering and utilizing by-product liquid from a filter press during biogas purification, provided in some embodiments of the present invention. Figure 4 .

[0045] Figure 6 A schematic diagram of a system for recovering and utilizing by-product liquid from a filter press during biogas purification, provided in some embodiments of the present invention. Figure 5 .

[0046] Figure 7 A schematic diagram of a system for recovering and utilizing by-product liquid from a filter press during biogas purification, provided in some embodiments of the present invention. Figure 6 .

[0047] In the picture:

[0048] 1. Liquid collection unit; 2. Pretreatment unit; 3. Staged filtration unit; 4. Targeted purification unit; 5. Advanced treatment unit; 6. Recycling unit; 7. Sludge disposal unit;

[0049] 101. Liquid collection tank; 102. pH adjustment device;

[0050] 201. Bar screen filter; 202. Sedimentation tank; 203. Sludge pump;

[0051] 301. Quartz sand filter; 302. Activated carbon filter; 303. Backwashing system;

[0052] 401. Targeted purification and diversion module; 402. Sulfide recovery reactor; 403. Ultrafiltration membrane module;

[0053] 501. Reverse osmosis membrane system; 502. Concentrate storage tank;

[0054] 601. Reclaimed water storage tank; 602. Disinfection device; 603. Transfer pump;

[0055] 701. Sludge filter press; 702. Sludge storage yard. Detailed Implementation

[0056] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments 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.

[0057] like Figures 1 to 7 As shown in the first aspect embodiment of the present invention, a process for recovering and utilizing the by-product liquid of a filter press during biogas purification is described:

[0058] (1) By-product liquid collection: The sulfur-containing waste liquid, dust-containing sewage and condensate generated by the filter press of the biogas purification system (desulfurization tower, dehydrator, dust collector) are collected into the collection tank, the pH value is adjusted to 7.0-8.5, and the liquid temperature is controlled at 20-40℃ (preset constant temperature range) to obtain the raw liquid to be treated;

[0059] (2) Pretreatment: After the raw liquid to be treated is filtered through a grid (pore size 5-10mm) to remove large impurities, it is introduced into a high-efficiency sedimentation tank, and PAC (polyaluminum chloride) and PAM (polyacrylamide) are added. The dosage of PAC is 50-150mg / L and the dosage of PAM is 5-10mg / L. After stirring and mixing, it is allowed to stand for 30-60min to remove suspended solids with a particle size ≥10μm and some colloids to obtain the pretreated liquid;

[0060] (3) Staged filtration: The pretreated liquid is filtered sequentially through a quartz sand filter (filter media particle size 0.5-2.0 mm) and an activated carbon filter (specific surface area 800-1200 m² / g), with the filtration flow rate controlled at 5-10 m / h, to remove suspended solids, color and some organic matter, and obtain a clear liquid; the suspended solids content in the clear liquid is ≤10 mg / L, and the COD is ≤100 mg / L;

[0061] (4) Targeted purification:

[0062] a. If the by-product liquid is sulfur-containing waste liquid, the clarified liquid is passed into a sulfide recovery reactor, and ferrous chloride solution (mass concentration 10%-20%) is added. The Fe²⁺ to S²⁻ molar ratio is controlled at 1.2:1-1.5:1, the reaction temperature is 25-35℃, the stirring rate is 100-200 r / min, and after reacting for 30-45 min, ferrous sulfide precipitate is generated. The ferrous sulfide by-product is obtained by separating it through a plate and frame filter press.

[0063] b. If the by-product liquid is dusty wastewater or condensate, pass the clarified liquid into an ultrafiltration membrane module (membrane pore size 0.01-0.1μm) and filter it under the conditions of pressure 0.1-0.3MPa and temperature 25-35℃ to remove trace suspended solids and macromolecular organic matter, and obtain ultrafiltration permeate;

[0064] (5) Deep treatment: The liquid treated in step (4) is passed into a reverse osmosis (RO) membrane system and desalinated and deeply purified under the conditions of pressure 1.0-2.5MPa and temperature 20-35℃. The recovery rate is controlled at 70%-85% to obtain recycled water. The conductivity of the recycled water is ≤100μS / cm, the sulfide content is ≤0.5mg / L, and the suspended solids content is ≤1mg / L.

[0065] (6) Recycling: The recycled water is divided into two streams. One stream is used as supplementary water for biogas desulfurization tower and dehydrator, and the other stream is disinfected (ultraviolet disinfection, dosage ≥30mJ / cm²) and used as flushing water for filter press or workshop floor, so as to realize the recycling of water resources.

[0066] In step (2), the high-efficiency sedimentation tank is equipped with inclined tube packing (inclination angle 60°, tube diameter 25-50mm). The sludge at the bottom of the sedimentation tank is transported to the filter press for dewatering by sludge pump 203. After dewatering, the sludge moisture content is ≤60%, which can be used as raw material for organic fertilizer or safely disposed of.

[0067] In step (3), the quartz sand filter and the activated carbon filter adopt the backwash regeneration mode. The backwash water is the concentrated water generated in step (5). The backwash flow rate is 15-20 m / h, the backwash time is 10-15 min, and the backwash cycle is 8-12 h. After regeneration, the quality of the filter effluent meets the requirements of the clarified liquid index.

[0068] In step (4)a, the sulfide recovery reactor is equipped with an online pH monitoring and automatic dosing system. When the pH of the reaction system is less than 7.0, calcium hydroxide solution is automatically added to adjust the pH to 7.5-8.0 to ensure that the ferrous sulfide precipitation reaction is complete.

[0069] In step (4)b, the ultrafiltration membrane module uses a hollow fiber membrane. During operation, chemical cleaning is performed regularly. The cleaning agents are sodium hydroxide solution with a mass concentration of 0.5%-1.0% and hydrochloric acid solution with a mass concentration of 0.1%-0.3% alternately. The cleaning cycle is 3-5 days, and the membrane flux is restored to more than 85% of the initial flux.

[0070] In step (5), the RO membrane system uses a spiral wound composite membrane. After the concentrate is collected in the concentrate storage tank, part of it is used for filter backwashing, and the remaining part is treated by evaporation and crystallization. The crystallized salt can be recycled as an industrial raw material, and there is no wastewater discharge.

[0071] 1. Byproduct liquid collection: The sulfur-containing waste liquid, dust-containing sewage and condensate generated by the filter press in each stage of biogas purification are collected in the collection tank and the pH value is adjusted to the neutral range (7.0-8.5) to avoid corrosion of subsequent treatment equipment by acidic or alkaline conditions, and at the same time to create a suitable environment for subsequent chemical reactions.

[0072] 2. Pretreatment: A combined process of "grid filtration + high-efficiency sedimentation" is adopted to first remove large impurities, and then PAC and PAM are added to form flocs, which quickly settle suspended solids and colloids. Inclined tube packing is installed in the high-efficiency sedimentation tank to improve sedimentation efficiency and shorten the settling time. The suspended solids removal rate after pretreatment can reach more than 90%, effectively reducing the load on subsequent filtration units.

[0073] 3. Staged Filtration: The quartz sand filter removes residual suspended solids and particulate matter, while the activated carbon filter adsorbs color, odor, and some organic matter (such as volatile organic compounds and some COD). The two-stage filtration works synergistically to ensure stable clarified water quality, laying the foundation for targeted purification. The filter adopts a backwash regeneration mode, using the concentrated water generated from subsequent deep treatment to reduce water consumption.

[0074] 4. Targeted Purification: Differentiated treatment schemes are adopted for different types of by-product liquids: sulfur-containing wastewater is treated by adding ferrous chloride to generate ferrous sulfide precipitate, and high-purity ferrous sulfide is recovered (which can be used as a chemical raw material or soil conditioner); dust-containing wastewater and condensate are treated by ultrafiltration membranes to remove trace suspended solids and macromolecular organic matter, ensuring the lifespan of the membrane elements in the subsequent reverse osmosis treatment. This design realizes the resource utilization of pollutants and improves the economics of the process.

[0075] 5. Advanced Treatment: The RO membrane system desalinates and deeply purifies the targeted purified liquid, removing salts, residual sulfides, trace organic matter, etc., to obtain high-purity reclaimed water. The concentrate from the RO membrane is used for filter backwashing, and the remaining portion is evaporated and crystallized to recover salts, achieving zero wastewater discharge.

[0076] 6. Recycling: The recycled water is divided into two streams according to water quality requirements, which meets the water needs of different scenarios such as replenishing water for biogas purification systems and rinsing water for filter presses. The water resource recycling rate is over 85%, which significantly reduces the fresh water consumption of biogas projects.

[0077] Beneficial effects

[0078] 1. This invention employs targeted purification technology, achieving a sulfide recovery rate of ≥95% in sulfur-containing wastewater and a recovered ferrous sulfide purity of ≥90%, thus realizing the resource utilization of pollutants and increasing the added value of by-products compared to traditional treatment processes.

[0079] 2. The integrated treatment process enables closed-loop water reuse, and the quality of the reused water meets the water standards of the biogas purification system and workshop. The water reuse rate is ≥85%, and each ton of treated water can save more than 0.85 tons of fresh water consumption, reducing operating costs by 30%-40%.

[0080] 3. The synergistic effect of graded treatment and deep purification ensures that the suspended solids content in the treated water is ≤1mg / L, the sulfide content is ≤0.5mg / L, and the COD is ≤50mg / L, meeting the industrial water standards, avoiding environmental pollution caused by wastewater discharge, and complying with environmental protection requirements.

[0081] 4. The system adopts automated control, with real-time monitoring and adjustment of parameters of each unit. It is easy to operate, runs stably, and is suitable for biogas projects of different scales (daily biogas production of 1000-10000 m³). It can also flexibly switch the processing mode according to the type of by-product liquid, making it highly adaptable.

[0082] 5. The sludge treatment unit achieves dewatering and volume reduction of settled sludge. After dewatering, the sludge moisture content is ≤60%, which can be used as raw material for organic fertilizer or safely disposed of without secondary pollution, achieving environmental protection throughout the entire process.

[0083] Example 1: Process for recycling sulfur-containing waste liquid (byproduct of biogas desulfurization tower pressure filtration)

[0084] 1. Properties of by-product liquid: sulfur-containing waste liquid, pH=6.8, temperature 32℃, sulfide content 850mg / L, suspended solids content 1200mg / L, COD=350mg / L;

[0085] 2. Collection and Adjustment: The solution is collected in a collection tank, and 5% sodium hydroxide solution is added to adjust the pH to 7.8. The temperature is maintained at 30℃.

[0086] 3. Pretreatment: After filtration by bar screen (8mm aperture), the water is introduced into a high-efficiency sedimentation tank. PAC (100mg / L) and PAM (8mg / L) are added, stirred and mixed, and then allowed to stand for 45 minutes. The suspended solids content of the effluent from the inclined tube sedimentation tank is 85mg / L, and COD is 220mg / L.

[0087] 4. Graded filtration: Quartz sand filter (filter media particle size 0.8-1.5mm, flow rate 8m / h) produces a suspended solids content of 25mg / L; activated carbon filter (specific surface area 1000m² / g, flow rate 6m / h) produces a suspended solids content of 8mg / L and COD=95mg / L.

[0088] 5. Targeted purification: The solution is introduced into a sulfide recovery reactor, and a 15% ferrous chloride solution is added. The Fe²⁺ to S²⁻ molar ratio is 1.3:1. The reaction temperature is 30℃, the stirring rate is 150 r / min, and ferrous sulfide precipitate is formed after 40 min of reaction. The ferrous sulfide product is then separated by a plate and frame filter press with a purity of 92%.

[0089] 6. Advanced treatment: The clarified liquid after reaction is passed into the RO membrane system at a pressure of 1.8 MPa and a temperature of 30℃. The recovery rate is 80%, the conductivity of the recycled water is 85 μS / cm, the sulfide content is 0.3 mg / L, and the suspended solids content is 0.8 mg / L.

[0090] 7. Recycling: 60% of the recycled water is used as makeup water for the desulfurization tower, and 40% is disinfected with ultraviolet light (dosage 35mJ / cm²) and then used as flushing water for the filter press, with a water resource recycling rate of 80%.

[0091] Example 2: Process for recycling dusty wastewater (byproducts of biogas dust collector filter press)

[0092] 1. Properties of by-product liquid: Dust-containing wastewater, pH=7.5, temperature 28℃, suspended solids content 950mg / L, COD=280mg / L, sulfide content 35mg / L;

[0093] 2. Collection and Adjustment: The solution is collected in a collection tank. No pH adjustment is required, and the temperature is maintained at 28℃.

[0094] 3. Pretreatment: After filtration by bar screen (6mm aperture), the water is introduced into a high-efficiency sedimentation tank. PAC (80mg / L) and PAM (6mg / L) are added, and the water is allowed to stand for 35 minutes. The suspended solids content of the effluent from the inclined tube sedimentation tank is 65mg / L, and the COD is 180mg / L.

[0095] 4. Staged filtration: Quartz sand filter (flow rate 7m / h) results in a suspended solids content of 20mg / L; activated carbon filter (flow rate 5m / h) results in a suspended solids content of 6mg / L and COD=85mg / L.

[0096] 5. Targeted purification: The ultrafiltration membrane module (hollow fiber membrane, pore size 0.05μm) is introduced, the pressure is 0.2MPa, the temperature is 30℃, the suspended solids content of the ultrafiltration permeate is 0.5mg / L, and the COD is 70mg / L;

[0097] 6. Advanced treatment: Ultrafiltration permeate is fed into the RO membrane system at a pressure of 1.5 MPa and a temperature of 28℃, with a recovery rate of 85%. The conductivity of the recycled water is 72 μS / cm, the sulfide content is 0.2 mg / L, and the suspended solids content is 0.6 mg / L.

[0098] 7. Recycling: 70% of the recycled water is used as makeup water for the dewatering machine, and 30% is used as water for washing the workshop floor, with a water resource recycling rate of 85%.

[0099] Example 3: This example discloses a system for recycling liquid by-products from a filter press during biogas purification, including a liquid collection unit 1, a pretreatment unit 2, a graded filtration unit 3, a targeted purification unit 4, a deep treatment unit 5, a recycling unit 6, and a sludge disposal unit 7. Each unit is connected in sequence through corrosion-resistant pipes to form a closed-loop treatment system.

[0100] The liquid collection unit 1 includes a pH adjustment device 102 and a collection tank 101. The pH adjustment device 102 is connected to the collection tank 101. Specifically, one end of the metering pump of the pH adjustment device 102 is connected to the outlet of the reagent storage tank through a pipeline, and the other end of the metering pump is directly connected to the internal chamber of the collection tank 101 through a delivery pipeline. The mixing agitator is fixedly installed inside the collection tank 101 and does not require additional pipeline connection, directly mixing the liquid and reagent in the tank.

[0101] The liquid collection tank 101 of liquid collection unit 1 is connected to the bar screen filter 201 of pretreatment unit 2 via a closed pipeline. The pipeline connects the outlet of liquid collection tank 101 to the inlet of bar screen filter 201, and is used to transport the pH-adjusted by-product liquid to bar screen filter 201 for preliminary filtration. The outlet of bar screen filter 201 is connected to the inlet of sedimentation tank 202 via a pipeline. The liquid after filtering out large particulate impurities flows into sedimentation tank 202 through this pipeline. The inlet of sludge conveying equipment (sludge pump 203) is connected to the sludge outlet at the bottom of sedimentation tank 202 via a pipeline, and is used to extract the settled sludge in sedimentation tank 202.

[0102] The sedimentation tank 202 of the pretreatment unit 2 is connected to the quartz sand filter 301 of the graded filtration unit 3 through a pipeline. The pipeline connects the supernatant outlet of the sedimentation tank 202 to the feed inlet of the quartz sand filter 301, so that the supernatant after sedimentation in the sedimentation tank 202 is transported to the quartz sand filter 301 for deep filtration.

[0103] Quartz sand filter 301 and activated carbon filter 302: The outlet of quartz sand filter 301 is connected to the inlet of activated carbon filter 302 through a pipe. The liquid after being filtered by quartz sand flows into activated carbon filter 302 to remove odors, pigments and some small molecule impurities.

[0104] Backwashing system 303 and quartz sand and activated carbon filters 302: Backwashing system 303 is connected to the backwash port of quartz sand filter 301 and the backwash port of activated carbon filter 302 through two branch pipes, respectively, to introduce backwashing medium (water) into the two filters to realize filter media rinsing and regeneration; at the same time, the backwashing wastewater outlet of backwashing system 303 is connected to the inlet of sedimentation tank 202 of pretreatment unit 2 through a pipe, so that the backwashing wastewater flows back to sedimentation tank 202 for re-pretreatment.

[0105] The activated carbon filter 302 of the graded filtration unit 3 is connected to the sulfide recovery reactor 402 of the targeted purification unit 4 through a pipeline. The pipeline connects the outlet of the activated carbon filter 302 to the inlet of the sulfide recovery reactor 402, and the liquid after two-stage filtration is transported to the targeted purification diversion module 401 for diversion processing.

[0106] The sulfide recovery reactor 402 is connected to the inlet of the sulfide recovery reactor and the inlet of the ultrafiltration membrane module 403, respectively, and the liquid flow direction is controlled by valves:

[0107] a. If the by-product liquid is sulfur-containing waste liquid, the clarified liquid is passed into the sulfide recovery reactor 402, ferrous chloride solution is added to generate ferrous sulfide precipitate, and ferrous sulfide by-product is obtained by separation by plate and frame filter press;

[0108] b. If the by-product liquid is dusty wastewater or condensate, the clarified liquid is passed into the ultrafiltration membrane module 403 to remove trace suspended solids and macromolecular organic matter, and ultrafiltration permeate is obtained;

[0109] The targeted purification unit 4 includes a targeted purification diversion module 401, a sulfide recovery reactor 402, and an ultrafiltration membrane assembly 403. The outlet of the activated carbon filter 302 is connected to the inlet of the targeted purification diversion module 401 via a delivery pipeline. The targeted purification diversion module 401 is a diversion control system, the core of which is a three-way diversion valve or two parallel controlled electric valves, which can switch the liquid to different branches according to the inlet water quality signal (e.g., the detection value from an online sulfide analyzer installed on the pipeline) or manual command.

[0110] Branch A (Sulfur Recovery): When the influent is high-concentration sulfur-containing wastewater, the diversion module 401 directs the liquid to the sulfide recovery reactor 402. This reactor 402 is equipped with a stirrer, an online pH probe, and an automatic dosing pump connected to the ferrous chloride and calcium hydroxide dosing tanks. The sludge discharge port at the bottom of reactor 402 is connected to a plate and frame filter press (not shown separately in the diagram, but can be considered an external system device or integrated into the sludge treatment unit 7) for separating ferrous sulfide precipitate. The supernatant after the reaction is discharged from the outlet at the top of reactor 402.

[0111] Branch B (Ultrafiltration): When the influent is dusty wastewater or condensate, the diversion module 401 directs the liquid to the ultrafiltration membrane module 403. This module uses a hollow fiber membrane and is equipped with an influent pump. The product water outlet of the ultrafiltration membrane module 403 discharges the filtrate, while the concentrated sludge produced is discharged from the sludge outlet.

[0112] The outlet of the sulfide recovery reactor 402 is connected to the inlet of the reverse osmosis membrane system 501 through a pipeline, and the liquid after sulfide recovery is transported to the reverse osmosis membrane system 501.

[0113] The outlet of the ultrafiltration membrane module 403 is connected to the inlet of the reverse osmosis membrane system 501 through a pipeline, and the clarified liquid after ultrafiltration is transported to the reverse osmosis membrane system 501.

[0114] The concentrate outlet of the reverse osmosis membrane system 501 is connected to the feed inlet of the concentrate storage tank 502 via a pipeline, which is used to transport the concentrate produced by the reverse osmosis membrane system 501 to the concentrate storage tank 502 for storage.

[0115] The outlet of the concentrated water storage tank 502 is connected to the inlet of the sedimentation tank 202 of the pretreatment unit 2 through a pipeline, so that the concentrated water can be returned to the sedimentation tank 202 for re-pretreatment and subsequent filtration process.

[0116] The purified water outlet of the reverse osmosis membrane system 501 is connected to the feed inlet of the recycled water storage tank 601 of the recycling unit 6 through a pipeline, and the purified water after deep purification is transported to the recycled water storage tank 601; the discharge outlet of the recycled water storage tank 601 is connected to the feed inlet of the disinfection device 602 through a pipeline, and the stored purified water is transported to the ultraviolet disinfection device 602 for sterilization and disinfection.

[0117] The outlet of the ultraviolet disinfection device 602 is connected to the inlet of the conveying pump 603 through a pipeline. The outlet of the conveying pump 603 is connected to external recycling equipment (such as water replenishment for biogas purification systems, workshop flushing, etc.) through a pipeline to pressurize and send the disinfected water out for recycling.

[0118] The feed end of the sludge filter press 701 is connected to the discharge end of the sludge conveying equipment of the pretreatment unit 2 through a pipeline to receive the sludge settled in the sedimentation tank 202.

[0119] The feed end of the sludge filter press 701 is connected to the sludge outlet of the ultrafiltration membrane module 403 of the targeted purification unit 4 through another branch pipe, and receives the sludge generated by the ultrafiltration membrane module 403.

[0120] The dry sludge outlet of the sludge filter press 701 is connected to the sludge storage yard 702 via a conveying device, which is used to transport the dewatered and compressed dry sludge to the storage yard for centralized storage.

[0121] The filtrate outlet of the sludge filter press 701 is connected to the feed inlet of the liquid collection tank 101 of the liquid collection unit 1 through a pipeline, so that the filtrate produced by the filter press is returned to the liquid collection tank 101 for pH adjustment and subsequent treatment.

[0122] All pipelines are closed-loop process pipelines to ensure no leakage during the transport of liquids and sludge. Each unit connection point corresponds to the inlet, outlet or dedicated interface of each piece of equipment to achieve closed-loop operation of the entire process.

[0123] This system constructs a closed-loop treatment system by sequentially connecting the liquid collection unit 1, pretreatment unit 2, staged filtration unit 3, targeted purification unit 4, deep treatment unit 5, recycling unit 6, and sludge disposal unit 7. This achieves a virtuous cycle of "collection-treatment-recovery-reuse" for the by-product liquid of the filter press. On the one hand, the purified water after deep treatment can be directly used for reusing scenarios such as replenishing water for the biogas purification system and cleaning the workshop through the recycling unit 6, replacing fresh water sources, effectively saving water resources and reducing the company's water costs. On the other hand, the targeted purification unit 4 can specifically recover useful components such as sulfides from the by-product liquid, realizing the secondary utilization of resources, avoiding the waste of useful substances, and improving the comprehensive utilization level of resources in the biogas purification industry chain. Meanwhile, the filtrate generated by the sludge treatment unit 7 is returned to the liquid collection unit 1 for reprocessing, the backwash wastewater from the backwash system 303 is returned to the sedimentation tank 202 for further processing, and the concentrated water in the concentrated water storage tank 502 is returned to the pretreatment unit 2 for recycling, truly achieving zero wastewater and zero waste liquid discharge and maximizing the resource recycling rate.

[0124] This system adopts a step-by-step treatment process of "pretreatment - graded filtration - targeted purification - deep treatment". Each unit has a clear division of labor and works together efficiently, which effectively solves the problems of incomplete impurity removal and large fluctuations in water quality in traditional treatment processes. Liquid collection unit 1, through the cooperation of pH adjustment device 102 and mixing agitator, can precisely adjust the pH value of the by-product liquid, laying a stable foundation for subsequent treatment processes; the bar screen filter 201 and sedimentation tank 202 of pretreatment unit 2 work together to quickly remove large particulate impurities and suspended sludge from the liquid, reducing the load on subsequent treatment; the two-stage filtration of quartz sand filter 301 and activated carbon filter 302 in staged filtration can effectively remove odors, pigments and some small molecule impurities from the liquid, improving the clarity of the liquid; the targeted purification unit 4 achieves simultaneous sulfide recovery and further impurity removal through diversion treatment, which not only recovers useful resources but also optimizes the water quality for subsequent deep treatment; the reverse osmosis membrane system 501 of deep treatment unit 5 can further remove trace impurities and salts from the liquid, ensuring that the effluent water quality meets the reuse standards; the disinfection device 602 can effectively kill harmful microorganisms in the purified water, ensuring safe reuse. The entire treatment process is progressive, ensuring that the treated water quality consistently meets standards, satisfying the requirements for recycling and reuse, and fundamentally avoiding the pollution of the environment caused by the direct discharge of by-product liquids.

[0125] This system features a dedicated sludge treatment unit 7, which centrally collects and dewaters the sludge settled in the sedimentation tank 202 of the pretreatment unit and the sludge generated by the ultrafiltration membrane module 403 of the targeted purification unit 4. The dewatered sludge is then transported to the sludge storage area 702 for centralized storage, facilitating further resource utilization (such as for organic fertilizer processing or incineration power generation), thus avoiding soil and water pollution caused by indiscriminate sludge dumping. Simultaneously, the filtrate generated during sludge filtration is returned to the liquid collection unit 1 for reprocessing, achieving the recycling of liquid entrained in the sludge. This completely solves the problem of secondary pollution during sludge treatment, ensuring that the entire treatment system meets environmental emission requirements and helping enterprises achieve green production.

[0126] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

[0127] The terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

Claims

1. A process for recovering and utilizing the liquid byproduct of a filter press during biogas purification, characterized in that, Includes the following steps: S1. Collect the sulfur-containing waste liquid, dust-containing sewage, and condensate generated by the filter press of the biogas purification system into the collection tank, adjust the pH to weak alkalinity, and control the liquid temperature within the preset constant temperature range to obtain the raw liquid to be treated. S2. After removing large impurities through a grid filter, the raw liquid to be treated is introduced into a sedimentation tank, where polyaluminum chloride and polyacrylamide are added. After stirring and mixing, the mixture is allowed to stand for 30-60 minutes to remove suspended solids with a particle size ≥10μm and some colloids, thus obtaining a pretreated liquid. S3. The pretreated liquid is filtered sequentially through a quartz sand filter and an activated carbon filter to obtain a clarified liquid; the suspended solids content in the clarified liquid is ≤10mg / L, and the COD is ≤100mg / L. S4, Targeted Purification: a. If the by-product liquid is sulfur-containing waste liquid, the clarified liquid is passed into the sulfide recovery reactor, ferrous chloride solution is added to generate ferrous sulfide precipitate, and ferrous sulfide by-product is obtained by separation by plate and frame filter press; b. If the by-product liquid is dusty wastewater or condensate, the clarified liquid is passed into the ultrafiltration membrane module to remove trace suspended solids and macromolecular organic matter, and ultrafiltration permeate is obtained; S5. The liquid treated in S4 is passed into the reverse osmosis membrane system for desalination and purification, with the recovery rate controlled at 70%-85%, to obtain recycled water; the conductivity of the recycled water is ≤100μS / cm, the sulfide content is ≤0.5mg / L, and the suspended solids content is ≤1mg / L. S6. The recycled water is divided into two streams: one stream is used as supplementary water for the biogas desulfurization tower and dehydrator, and the other stream is disinfected and used as flushing water for the filter press or workshop floor, thus realizing the recycling of water resources.

2. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 1, characterized in that, In S1, the pH value of the waste liquid is adjusted to 7.0~8.5, and the temperature of the raw liquid to be treated is controlled at 20~40℃; In S2, the dosage of polyaluminum chloride is 50~150 mg / L, and the dosage of polyacrylamide is 5~10 mg / L; In S3, the particle size of the quartz sand filter media is 0.5~2.0mm, the specific surface area of ​​the activated carbon filter media is 800~1200m² / g, and the filtration flow rate is controlled at 5~10m / h. The filtration removes suspended solids, color and some organic matter from the water. In S4a, the mass concentration of ferrous chloride solution is 10%~20%, the molar ratio of ferrous ions to sulfur ions is controlled at 1.2:1~1.5:1, the reaction temperature is 25~35℃, the stirring rate is 100~200r / min, and the reaction time is 30~45min. In S4b, the pore size of the ultrafiltration membrane module is 0.01~0.1μm, the filtration operating pressure is 0.1~0.3MPa, and the operating temperature is 25~35℃; In S5, the operating pressure for desalination and purification of the reverse osmosis membrane system is 1.0~2.5MPa, and the operating temperature is 20~35℃; In S6, the disinfection is ultraviolet irradiation disinfection, with an irradiation dose ≥30mJ / cm².

3. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 1, characterized in that, In S3, the quartz sand filter and activated carbon filter adopt a backwashing regeneration mode. The backwash water is the concentrated water produced by S5. The backwashing flow rate is 15~20m / h, the backwashing time is 10~15min, and the backwashing cycle is 8~12h. After regeneration, the quality of the filter effluent meets the requirements of the clarified liquid index.

4. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 2, characterized in that, The sulfide recovery reactor in S4a is equipped with an online pH monitoring and automatic dosing system. When the pH of the reaction system is less than 7.0, calcium hydroxide solution is automatically added to adjust the pH to 7.5-8.0 to ensure that the ferrous sulfide precipitation reaction is complete.

5. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 1, characterized in that, The S4b ultrafiltration membrane module uses hollow fiber membranes. During operation, it is chemically cleaned periodically. The cleaning agents are alternating between sodium hydroxide solution with a mass concentration of 0.5%~1.0% and hydrochloric acid solution with a mass concentration of 0.1%~0.3%. The cleaning cycle is 3~5 days, restoring the membrane flux to more than 85% of the initial flux.

6. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 1, characterized in that, The reverse osmosis membrane system in S5 uses spiral wound composite membranes. After the concentrate is collected in the concentrate storage tank, part of it is used for filter backwashing, and the remainder is treated by evaporation and crystallization. The crystallized salt can be recovered as an industrial raw material, and there is no wastewater discharge.

7. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 1, characterized in that, The sedimentation tank in S2 is equipped with inclined tube packing. The sludge at the bottom of the sedimentation tank is transported to the filter press for dewatering by a sludge pump. After dewatering, the sludge has a moisture content of ≤60% and can be used as raw material for organic fertilizer or disposed of safely.

8. The process for recovering and utilizing the by-product liquid of a filter press during biogas purification according to claim 7, characterized in that, The inclined tube packing has an inclination angle of 60° and a tube diameter of 25~50mm.

9. A system for recovering and utilizing liquid by-products from a filter press during biogas purification, characterized in that, It includes a liquid collection unit, a pretreatment unit, a staged filtration unit, a targeted purification unit, an advanced treatment unit, a recycling unit, and a sludge disposal unit; The liquid collection unit includes a liquid collection tank and a pH adjustment device, wherein the pH adjustment device is connected to the liquid collection tank; The pretreatment unit includes a bar screen filter, a sedimentation tank, and a sludge conveying device. The bar screen filter is connected to the collection tank, the sedimentation tank is connected to the bar screen filter, and the sludge conveying device is connected to the bottom of the sedimentation tank. The graded filtration unit includes a quartz sand filter, an activated carbon filter, and a backwashing system. The quartz sand filter is connected to the sedimentation tank, the activated carbon filter is connected to the quartz sand filter, and the backwashing system is connected to both the quartz sand filter and the activated carbon filter. It is used to rinse and regenerate the filter media of the quartz sand filter and the activated carbon filter. The backwashing wastewater generated by the backwashing system is returned to the sedimentation tank of the pretreatment unit through a pipeline. The targeted purification unit includes a targeted purification diversion module, a sulfide recovery reactor, and an ultrafiltration membrane assembly. The activated carbon filter is connected to the targeted purification diversion module, and the targeted purification diversion module is connected to both the sulfide recovery reactor and the ultrafiltration membrane assembly. The advanced treatment unit includes a reverse osmosis membrane system and a concentrate storage tank. The sulfide recovery reactor and the ultrafiltration membrane module are both connected to the reverse osmosis membrane system. The concentrate storage tank is connected to the reverse osmosis membrane system and is used to store the concentrate produced by the reverse osmosis membrane system. The concentrate storage tank is also connected to the sedimentation tank through a pipeline to realize concentrate reflux and reprocessing. The recycling unit includes a recycled water storage tank, a disinfection device, and a delivery pump. The recycled water storage tank is connected to the reverse osmosis membrane system and is used to store purified water after deep purification. The disinfection device is connected to the recycled water storage tank and is used to pressurize and send the disinfected purified water out for recycling. The sludge treatment unit includes a sludge filter press and a sludge storage area. The sludge filter press is connected to the sludge conveying equipment and the ultrafiltration membrane module, respectively, and is used to dewater and compress the sludge generated throughout the process. The sludge storage area is connected to the sludge filter press and is used to centrally store the dewatered dry sludge. The filtrate produced by the sludge filter press is returned to the collection tank of the liquid collection unit through a pipeline.

10. A system for recovering and utilizing by-product liquid from a filter press during biogas purification according to claim 9, characterized in that, The pH adjustment device includes a reagent storage tank, a metering pump, and a mixer. The reagent storage tank stores an alkaline adjusting agent. One end of the metering pump is connected to the reagent storage tank, and the other end is connected to a collection tank. It is used to meter and deliver the adjusting agent. The mixer is installed inside the collection tank to fully mix the adjusting agent with the by-product liquid.

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