AF-modified ABR anaerobic treatment process for high concentration dairy wastewater

Abstract

This invention discloses an AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater. It relates to the field of wastewater treatment technology. The process involves passing wastewater into a pre-AF unit for degreasing, deproteinization, and preliminary hydrolysis and acidification to obtain the first effluent. This first effluent is then passed into a three-stage modified ABR reactor, consisting of an acidification reaction section, a hydrogen and electricity generation reaction section, and a methanogenesis reaction section, for stepwise anaerobic treatment. The hydrogen and electricity generation reaction section employs an air cathode structure without a proton exchange membrane, utilizing electrons generated from the oxidation of organic matter in the wastewater to reduce oxygen, thereby generating electricity and powering the system itself. The ABR effluent is then passed into an electrochemical purification unit, where it undergoes deep purification through iron-carbon micro-electrolysis and micro-nano aeration before being discharged in compliance with standards. Simultaneously, a portion of the activated sludge from the methanogenesis section is recycled to the pre-AF unit and / or the hydrogen and electricity generation reaction section, combined with external enrichment culture and gradient temperature control, to form a gradient adaptation system of psychrophilic-mesothermic composite bacteria.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to an AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater. Background Technology

[0002] Dairy wastewater is characterized by high organic matter concentration (COD typically 3000~20000 mg / L), good biodegradability, but also contains large amounts of milk fat, milk protein, and lactose. Anaerobic biological treatment has become one of the mainstream technologies for dairy wastewater treatment due to its low energy consumption and the ability to recover biogas energy. Among them, the combined process of anaerobic filter (AF) and anaerobic baffle reactor (ABR) is widely used due to its simple structure and strong biological retention capacity.

[0003] However, the traditional AF-ABR process still faces several technical bottlenecks when treating high-concentration dairy wastewater. First, milk fat and protein are prone to acid-induced denaturation and coagulation under anaerobic conditions, forming floating scum or sedimentary sludge that clogs packing materials and pipelines, potentially leading to system acid death or calcification. Second, while conventional ABRs can achieve phase separation, the lack of effective electron transfer regulation between the acidification and methanogenic stages allows for excessive accumulation of volatile fatty acids (VFAs), inhibiting methanogenic bacteria activity and resulting in COD removal rates of only 70%–85% and low methane yields. Third, the peak dairy production season is often concentrated in winter (October to March of the following year), where the activity of mesophilic methanogenic bacteria drops sharply under low temperatures, requiring significant heating energy consumption in traditional processes or potentially worsening treatment efficiency. Fourth, existing ABR systems cannot recover the chemical energy of organic matter in wastewater, resulting in substantial energy loss as excess sludge and high sludge disposal costs. Fifth, to meet emission standards, subsequent aerobic treatment is often required, further increasing energy consumption and land occupation.

[0004] To address the aforementioned shortcomings, previous studies have attempted improvements through methods such as front-end air flotation for oil removal, the addition of external conductive materials, or microbial fuel cells. However, these methods suffer from problems such as complex equipment, severe membrane fouling, high investment costs, and poor low-temperature adaptability. Therefore, there is an urgent need to develop a novel anaerobic treatment process that integrates efficient degreasing and deproteinization, low-temperature adaptability, energy self-sufficiency, and sludge reduction. Summary of the Invention

[0005] In order to overcome the problems of low COD removal rate, poor methanogenesis efficiency, weak low temperature adaptability and high energy consumption in the existing technology of anaerobic treatment of dairy wastewater, this invention discloses an AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater, which can effectively solve the above-mentioned technical problems.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: An AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater, the process comprising: Wastewater is fed into the pre-AF unit, where it undergoes degreasing, deproteinization, and preliminary hydrolysis acidification to obtain the first effluent. The first effluent is fed into a three-stage modified ABR reactor, which consists of an acidification reaction section, a hydrogen and electricity generation reaction section, and a methanogenesis reaction section along the water flow direction. The wastewater is anaerobically treated step by step through the differentiated microbial communities and electrode system in each functional section to obtain the second effluent and biogas. The second effluent is fed into the effluent electrochemical fine treatment unit, where it is finely treated by iron-carbon micro-electrolysis and micro-nano aeration to obtain compliant discharge water. A portion of the activated sludge in the methanogenic reaction section is returned to the pre-AF unit and / or the hydrogen and electricity generation reaction section to supplement and enhance the functional microbial community. The hydrogen and electricity generation reaction section adopts an air cathode structure without a proton exchange membrane, which uses electrons generated by the oxidation of organic matter in wastewater to reduce oxygen, thereby generating electricity and supplying power to the system.

[0007] Furthermore, the step of passing the wastewater into the pre-filter AF unit for degreasing, deproteinization, and preliminary hydrolysis and acidification treatment to obtain the first effluent specifically includes: Wastewater is fed into the first-stage AF filter, where milk fat and milk protein are adsorbed and retained by the hydrophilic-hydrophobic composite packing layer. The effluent from the first-stage AF filter is fed into the second-stage AF filter, where it undergoes hydrolysis and acidification through packing material loaded with psychrophilic acidifying bacteria to obtain the first effluent. The first effluent is returned to the bottom of the first-stage AF filter at a return ratio of 0.5-1.0 to form a recirculation within the pre-AF filter.

[0008] Furthermore, when the first effluent is introduced into the acidification reaction section of the three-stage modified ABR reactor, the pH of the acidification reaction section is controlled to be 5.2-6.2, and the hydraulic retention time is 8-20 hours. The complex organic matter is converted into volatile fatty acids by acid-producing bacteria, and by-product hydrogen is collected.

[0009] Furthermore, the hydrogen and electricity generation reaction section includes an anode compartment and a cathode compartment. The anode compartment contains a graphene-modified carbon fiber brush electrode and is loaded with hydrogen and electricity-generating bacteria. The cathode compartment is equipped with a porous nickel-based air cathode. There is no proton exchange membrane between the anode compartment and the cathode compartment. Proton transfer and substrate separation are achieved through baffles and water flow channels.

[0010] Furthermore, the power density of the hydrogen production and power generation reaction section is controlled to be ≥2.5W / m². 3 The generated electrical energy is boosted and rectified and then reused in the pumping unit or control unit of the process, achieving 15-25% self-powered system.

[0011] Furthermore, the process also includes: controlling the water temperature of the acidification reaction section to 18-25℃, the water temperature of the hydrogen and electricity generation reaction section to 18-25℃, and the water temperature of the methanogenesis reaction section to 28-32℃ through an independent insulation jacket, thereby forming a gradient adaptation environment for a psychrophilic / mesothermic composite microbial community.

[0012] Furthermore, the recirculation of a portion of the activated sludge in the methanogenic reaction section specifically includes: recirculating 5-15% of the highly active anaerobic sludge in the methanogenic reaction section to the pre-AF unit and the hydrogen and electricity generation reaction section, for the purpose of introducing a low-temperature adaptation enzyme system into the low-temperature section.

[0013] Furthermore, the process also includes an external enrichment culture step: setting up an independent anaerobic enrichment tank, regularly replenishing whey culture medium and trace metal nutrients, selectively enriching hydrogen-producing and electrogenic bacteria and / or low-temperature methanogenic bacteria, and injecting the enriched bacterial solution into the corresponding compartment of the three-stage modified ABR reactor at least once a month.

[0014] Furthermore, when the second effluent is introduced into the effluent electrochemical fine treatment unit, the hydraulic retention time is controlled to be 2-4 hours; the Fe:C mass ratio in the iron-carbon micro-electrolysis is 1:1-1.5, and the filling rate is 40-60%; the bubble diameter of the micro-nano aeration is ≤100nm, and the air-to-water ratio is 2-5:1.

[0015] Furthermore, the process also includes a biogas collection and purification step: the biogas produced by the three-stage modified ABR reactor is collected and then purified sequentially through a gas-liquid separator and a dry desulfurization tower to obtain purified biogas with a methane content ≥65%, which is then stored in a dual-membrane constant pressure gas holder.

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention achieves significant beneficial effects through the synergistic effect of multiple innovative mechanisms, including efficient retention of milk fat and milk protein by the pre-filter AF unit, the three-stage functionalized modified ABR for step-by-step conversion of organic matter, the recovery of electrical energy by a membrane-free bioelectrochemical system, the gradient adaptation of psychrophilic-mesothermic composite microbial communities, and electrochemical fine treatment of effluent. The pre-filter AF unit has an extremely high interception rate for milk fat and milk protein, fundamentally avoiding acid-induced denaturation and blockage problems in subsequent reactors. Combined with the step-by-step optimization of the acidification section, hydrogen and electricity generation section, and methanogenesis section, the total COD removal rate of the system can reach an extremely high level, and the methane yield is improved compared to traditional ABR processes. Specifically, the hydrogen and electricity generation section adopts an air cathode structure without a proton exchange membrane, avoiding membrane fouling and high cost issues, and can stably output a high power density. The collected electrical energy can be boosted and rectified and reused in the system pumping and control unit, achieving a considerable proportion of self-sufficiency in the system's internal electrical energy supply and reducing external energy consumption requirements. Regarding sludge reduction, the pre-treatment AF unit periodically separates easily proliferating components such as milk fat and milk protein from the system's front end. Furthermore, the hydrogen and electricity generation section directly converts some organic matter into electrical energy instead of synthesizing new cells, reducing the amount of residual sludge and lowering sludge disposal costs and subsequent treatment burden. Addressing the challenge of low-temperature operation in dairy production during winter, the process constructs a gradient temperature control system from the low-temperature zone to the medium-temperature zone. Highly active methanogenic sludge is recycled to the low-temperature zone, and low-temperature adaptability enzymes such as cold shock proteins and antifreeze proteins are introduced. Simultaneously, an external enrichment culture tank is used to periodically supplement low-temperature resistant functional bacteria, thus maintaining stable and efficient anaerobic treatment performance without additional energy consumption in winter, overcoming the deficiency of traditional processes where activity is inhibited under low-temperature conditions. In addition, the effluent electrochemical refining unit further removes residual recalcitrant organic matter and total phosphorus from the effluent through the synergistic effect of iron-carbon micro-electrolysis and micro-nano aeration. The effluent quality meets the national Class I discharge standard and can be directly discharged or reused in the plant's production and cleaning processes. In summary, this invention achieves four objectives simultaneously: high COD removal rate, high methane yield, low sludge production, and self-sufficiency in internal power generation. It also possesses excellent low-temperature adaptability and economic efficiency, demonstrating significant technological advancements and broad engineering application value. Attached Figure Description

[0017] 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 described below are merely exemplary. For those skilled in the art, other embodiments can be derived from the provided drawings without creative effort.

[0018] Figure 1 A structural diagram of an AF-modified ABR anaerobic treatment system for high-concentration dairy wastewater provided in this application embodiment; Figure 2 A flow chart of an AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater provided in this application embodiment. Detailed Implementation

[0019] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0020] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It is understood that the specific embodiments described herein are merely illustrative of the embodiments of this application and are not intended to limit the embodiments of this application. Furthermore, it should be noted that, for ease of description, the accompanying drawings only show the parts related to the embodiments of this application, not all structures. Those skilled in the art, after reading this specification, should be able to realize that any combination of technical features can constitute an optional implementation method, provided that the technical features do not contradict each other.

[0022] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship. In the description of this application, "multiple" means two or more, and "several" means one or more.

[0023] like Figure 1 As shown, Figure 1This invention provides a structural diagram of an AF-modified ABR anaerobic treatment system for high-concentration dairy wastewater, as illustrated in this embodiment. The anaerobic treatment system includes: an influent pumping station (including a bar screen), a pre-AF unit, a three-stage modified ABR reactor, an effluent electrochemical refining unit, a biogas collection and purification system, a flow-through microbial inoculation and reflux system, and a PLC automated control system. These units are arranged in series along the wastewater treatment process. The effluent outlet of the pre-AF unit is connected to the influent outlet of the three-stage modified ABR reactor, and the effluent outlet of the three-stage modified ABR reactor is connected to the influent outlet of the effluent electrochemical refining unit. The effluent outlet of the effluent electrochemical refining unit leads to a discharge or reuse pipeline. A sludge reflux pipeline is located at the bottom of the methanogenic reaction section of the three-stage modified ABR reactor, connecting to the bottom of both the pre-AF unit and the hydrogen and electricity generation reaction sections of the three-stage modified ABR reactor. Additionally, the system includes an independent anaerobic enrichment tank, connected to both the hydrogen and electricity generation reaction sections and the methanogenic reaction section via a supplementary pipeline. The biogas collection and purification system is connected to the three-phase separator outlet at the top of each compartment of the three-stage modified ABR reactor. The PLC automatic control system is electrically connected to each unit through sensors and actuators to achieve fully automatic monitoring and regulation.

[0024] The pre-filter (AF) unit consists of two anaerobic biological filters connected in series, employing an upward flow configuration. The first-stage AF filter (i.e., the defatting and deproteinizing filter) is filled with a hydrophilic-hydrophobic composite packing material, which consists of two layers: an upper layer of oleophilic polyurethane packing material with a thickness of 400 mm; and a lower layer of porous volcanic rock packing material with a thickness of 600 mm. A water distribution system is located at the bottom of the first-stage AF filter, allowing water to enter evenly from the bottom and flow upwards. A scum scraping device is located at the top of the first-stage AF filter, and an independent sludge discharge pipe is located at the bottom for periodically removing trapped milk fat, milk protein, and sediment.

[0025] The second-stage AF filter (i.e., the hydrolysis acidification filter) is located after the first-stage AF filter, and the two are connected by a flow pipe. The second-stage AF filter is filled with macroporous mesh polyethylene packing material with a specific surface area greater than or equal to 500 square meters per cubic meter. The packing material is supported by psychrophilic acid-producing bacteria acclimated to low temperatures, including microorganisms of the genera *Acidobacterium* and *Clostridium*. The outlet of the second-stage AF filter is divided into two paths: one path serves as the first effluent to the subsequent tertiary modified ABR reactor, and the other path connects to the bottom inlet of the first-stage AF filter via a return pipe. The return pipe is equipped with a return pump and a flow regulating valve to control the return ratio.

[0026] In addition, the outer wall of the front AF unit is equipped with an independent insulation jacket, and hot water or electric heating can be introduced into the insulation layer to maintain the temperature inside the unit between 10 degrees Celsius and 15 degrees Celsius.

[0027] The three-stage modified ABR reactor is a horizontal baffled reactor, longitudinally divided into six compartments along the water flow direction. Each pair of compartments forms a functional section, resulting in three tiered functional sections: the first functional section is the acidification reaction section (comprising compartments 1 and 2); the second functional section is the hydrogen and electricity production reaction section (comprising compartments 3 and 4); and the third functional section is the methanogenesis reaction section (comprising compartments 5 and 6). The compartments are connected in series via low-level flow holes located at the bottom of the reactor, with the flow velocity controlled between 0.2 m / s and 0.5 m / s. Each compartment has an independent three-phase separator at the top for gas-liquid-solid separation.

[0028] The internal structure of compartment 1 (initial acidification stage) is as follows: The downward flow zone is equipped with a fixed composite packing material, which is composed of polypropylene multifaceted hollow spheres; the upward flow zone contains the dominant acid-producing bacteria, including *Lactobacillus*, *Propionibacterium*, and *Clostridium*. A micro carbon brush electrode, serving as the anode, is located at the bottom of compartment 1. This electrode is made of graphene-modified carbon brush with a conductivity greater than or equal to 300 Siemens per centimeter. An online pH meter and temperature sensor are installed on the outer wall of compartment 1, connected to an acid or alkali solution dosing pump to control the pH between 5.2 and 6.0. A gas phase outlet is located at the top of compartment 1, connected to a hydrogen collection pipeline.

[0029] The internal structure of compartment 2 (acidification enhancement section) includes: a downward flow zone with carbon felt packing material on which facultative acid-producing bacteria, including *Escherichia coli* and *Klebsiella*, are attached. Compartment 2 is equipped with an independent air-lift internal circulation device, comprising an air-lift pipe and a circulation pump, to lift the mud-water mixture at the bottom of the compartment to the upward flow zone. A hydrogen collection port is located at the top of compartment 2, connecting to the hydrogen collection pipe of compartment 1 via a pipeline. The pH of compartment 2 is controlled between 5.5 and 6.2. A cathode is located at the bottom of compartment 2 (creating a potential difference with the anode of compartment 1), with a potential control range of 0.2 volts to 0.4 volts.

[0030] Inside compartment 3 (hydrogen production core area): A multilayer graphene-modified carbon fiber brush electrode is installed. This electrode is an anode array, with each layer independently connected to a variable resistor, forming an adjustable electro-generation circuit. Compartment 3 contains a specific hydrogen-producing and electro-generating bacterial community, including a mixed enrichment culture of *Enterobacter cloacae*, *Enterobacter aerogenes*, and *Shewanella*. A baffle-type hydraulic lift is located at the bottom of compartment 3 to elevate the mud-water mixture to the electrode area. A gas collection port is located at the top of compartment 3, connected to a hydrogen collection pipeline.

[0031] Inside compartment 4 (electrogenous cathode area): a porous nickel-based air cathode is built-in. This air cathode has a composite structure, including a waterproof and breathable layer, a catalytic layer, and a conductive layer. This air cathode does not require external aeration and directly utilizes oxygen in the air as an electron acceptor. The anode of compartment 3 and the cathode of compartment 4 are connected via an external circuit. A variable resistor bank is connected in parallel to the external circuit, with an adjustable resistance range of 100 ohms to 5000 ohms. A DC-DC converter circuit (boost circuit) is also connected in series to the external circuit to boost the collected electrical energy to 5 volts to 12 volts before it is fed back to the boost pump and PLC control unit of the pre-AF unit. No proton exchange membrane is installed between compartments 3 and 4. Instead, proton transfer and substrate separation are achieved by utilizing the modified baffle flow channels of the ABR itself and the dense layer of the microbial membrane. The cathode potential of compartment 4 is controlled between -0.1 volts and -0.05 volts (relative to the Ag / AgCl reference electrode). The pH of both compartments 3 and 4 was controlled between 6.0 and 6.8.

[0032] Inside compartment 5 (the main methanogenic zone): The downflow zone contains a granular sludge bed inoculated with a mixed mesophilic methanogenic microbial community and psychrophilic methanogenic bacteria acclimated to low temperatures. The mixed mesophilic methanogenic microbial community is dominated by *Methanococcus* and *Methanotherium* genera, while the psychrophilic methanogenic bacteria include *Methanophilic Bacteria* and *Phytotrophoblastus*. The upflow zone is equipped with a stacked corrugated baffle plate made of high-density polyethylene (HDPE) with a corrugation height of 80 mm. The pH of compartment 5 is controlled between 6.8 and 7.4. The outer wall of compartment 5 is equipped with an independent insulation jacket to control the temperature between 28°C and 32°C.

[0033] Inside compartment 6 (methanogenic refining zone): The downflow zone is primarily filled with bio-carbon-based granular packing material, a mixture of ceramsite and bone char at a mass ratio of 1:1, with a particle size ranging from 3 mm to 5 mm. This packing material exhibits high biofilm density. The top biogas collection system of compartment 6 is equipped with a return pipe, which introduces a portion of the biogas into the bottom of compartment 6 for micro-aeration and agitation, maintaining a gas-to-water ratio (biogas volume to wastewater volume) between 1:1 and 3:1. The pH of compartment 6 is controlled between 6.8 and 7.4, and the temperature is maintained between 28°C and 32°C via an insulation jacket.

[0034] To ensure the gradient adaptation of the psychrophilic / mesothermic bacterial community, the outer wall of the pre-AF unit is equipped with a first insulation jacket to maintain the water temperature within the unit at 10°C to 15°C. The outer walls of the acidification reaction section (compartments 1 and 2) and the hydrogen and electricity production reaction section (compartments 3 and 4) of the three-stage modified ABR reactor are equipped with a second insulation jacket to control the water temperature at 18°C ​​to 25°C. The outer walls of the methanogenesis reaction section (compartments 5 and 6) are equipped with a third insulation jacket to control the water temperature at 28°C to 32°C. Each insulation jacket is independently controlled, and the heating power is automatically adjusted via a PLC system based on feedback from online temperature sensors.

[0035] A sludge return pipeline is located at the bottom of compartment 6 (methanogenic refining zone). This pipeline is connected via a sludge return pump to the bottom of the first-stage AF filter in the pre-AF unit and the bottom of compartment 3 in the third-stage modified ABR reactor. The return pipeline is equipped with a flow meter and a regulating valve to control the return flow rate to 5% to 15% of the treatment capacity.

[0036] In addition, the system is equipped with an external anaerobic enrichment tank, the effective volume of which is 5% to 8% of the total volume of the main reactor (a modified three-stage ABR reactor). The enrichment tank is a closed anaerobic container equipped with a stirring device, a temperature control device, a feed inlet, and a discharge outlet. The feed inlet is used to periodically replenish whey culture medium and trace metal nutrients, the trace metal nutrients including nickel ions (Ni). 2+ ), cobalt ions (Co) 2+ ) and ferrous ions (Fe 2+ The outlet of the enrichment tank is connected to compartments 3 and 5 via pipelines and a transfer pump, respectively, for injecting the selectively enriched bacterial culture into the corresponding compartments. The selectively cultured bacterial populations in the enrichment tank include hydrogen-producing and electrogenic bacteria (such as Shewanella) and low-temperature methanogenic bacteria.

[0037] The effluent electrochemical refining unit is a sealed tank containing an iron-carbon micro-electrolysis packing layer. The Fe to C mass ratio in the packing layer is 1:1 to 1.5, and the filling rate (the percentage of packing volume to the effective tank volume) is 40% to 60%. Below the packing layer is a micro-nano aeration system that generates bubbles with a diameter of 100 nanometers or less. The aeration system is connected to an air source (air compressor), and the air-to-water ratio is controlled between 2:1 and 5:1. The inlet of the refining unit is located at the bottom, and the outlet is at the top; water flows upward through the packing layer. An exhaust pipe is located at the top of the unit to remove excess gas.

[0038] The gas outlets of the three-phase separators at the top of compartments 2 to 6 are collected into the main collection pipe via a gas collecting pipeline. The main collection pipe is sequentially connected to a gas-water separator, a dry desulfurization tower, and a dual-membrane constant-pressure gas holder. The dry desulfurization tower is filled with iron oxide desulfurizing agent to remove hydrogen sulfide from the biogas (H2S removal rate ≥95%). The dual-membrane constant-pressure gas holder is used to store the purified biogas. The gas holder outlet is equipped with an online gas composition analyzer (for detecting CH4 and H2 content) and a flow meter. The gas holder outlet is divided into two paths: one path connects to the plant's gas pipeline network for combustion and heating; the other path connects to a pressure swing adsorption (PSA) separator for separating and purifying hydrogen (purity ≥99%).

[0039] The PLC automated control system includes a central controller, a touchscreen, field sensors, and actuators. Sensors include: online pH meters for each compartment, platinum resistance temperature sensors, online oxidation-reduction potential monitors, voltage and current acquisition modules (for power generation parameters), thermal biogas flow meters, and online near-infrared COD monitors for influent and effluent. Actuators include: influent pumps, reflux pumps, dosing pumps, heating devices, variable frequency stirrers, valves, etc. The PLC has a built-in algorithm model that automatically adjusts the reflux ratio, insulation temperature, and external resistor values ​​based on predicted fluctuations in influent water quality, achieving unattended optimized operation.

[0040] The following describes in detail the AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater according to an embodiment of the present invention, based on the above system structure. Figure 2 As shown, Figure 2 A flow chart of an AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater provided in this application embodiment is shown. The process includes the following steps: Step 1: Pretreatment and pre-AF (Anaerobic Filter) for defatting and deproteinization. High-concentration wastewater generated during dairy production first passes through a screen channel to remove large suspended solids and floating matter with a particle size of 5 mm or greater. It then enters a regulating tank with a hydraulic retention time of 6 to 12 hours for homogenization and flow equalization. The effluent from the regulating tank is pumped into the pre-AF unit by a lift pump.

[0041] After entering the pre-filter AF unit, the wastewater first flows upward through a 400 mm thick layer of oleophilic polyurethane packing and a 600 mm thick layer of porous volcanic rock. During this process, the milk fat and milk protein in the wastewater are efficiently adsorbed and retained by the oleophilic polyurethane, while the porous volcanic rock layer further intercepts suspended solids and provides a surface for microbial attachment. The hydraulic retention time in the first-stage AF filter is controlled between 4 and 8 hours. The retained milk fat and milk protein form a scum layer or sediment. The top scum scraper is operated once or twice a week to remove the scum from the system; the bottom sludge discharge pipe is opened once or twice a week to remove the settled sludge.

[0042] The effluent from the first-stage AF filter flows out from the top and enters the second-stage AF filter (hydrolysis acidification filter). The second-stage AF filter is filled with macroporous mesh polyethylene packing material, on which are attached psychrophilic acidifying bacteria (Acid-producing Bacillus and Clostridium species) acclimated to low temperatures. Wastewater flows upwards in the second-stage AF filter, with a hydraulic retention time of 6 to 10 hours, and the water temperature is maintained at 10 to 15 degrees Celsius through an insulation jacket. The psychrophilic acidifying bacteria further convert the small-molecule organic matter from the hydrolysis of lactose and milk protein into volatile fatty acids (VFA), achieving a COD removal rate of 25% to 35% and a VFA accumulation concentration of 800 mg / L to 1500 mg / L (calculated as acetic acid).

[0043] A portion of the effluent from the second-stage AF filter is used as the first effluent and enters the subsequent three-stage modified ABR reactor. The other portion is returned to the bottom of the first-stage AF filter via a recirculation pipeline, with the recirculation ratio (the ratio of recirculation flow to influent flow) controlled between 0.5 and 1.0. This recirculation operation not only dilutes the influent concentration and reduces shock load, but also utilizes the hydrolytic enzymes contained in the effluent from the second-stage AF filter to further decompose the milk fat and milk protein retained in the first-stage AF filter, forming an internal cycle of retention, decomposition, and re-retention.

[0044] Step 2: Enhanced tertiary anaerobic treatment of the modified ABR. The first effluent from the pre-AF unit enters the tertiary modified ABR reactor from the bottom, with the total hydraulic retention time controlled between 24 and 60 hours. The wastewater flows sequentially through the acidification reaction section, the hydrogen and electricity generation reaction section, and the methanogenesis reaction section.

[0045] Acidification reaction section treatment: Wastewater first enters compartment 1 (initial acidification section). The pH of compartment 1 is controlled between 5.2 and 6.0 by automatic acid / alkali addition, and the water temperature is controlled between 18°C ​​and 25°C by an insulation jacket. Under the action of the dominant acid-producing bacteria (Lactobacillus, Propionibacterium, Clostridium), the complex organic matter in the wastewater (including residual carbohydrates, proteins, etc.) is rapidly converted into volatile fatty acids (mainly acetic acid, propionic acid, and butyric acid). At the same time, a potential difference of 0.2 volts to 0.4 volts is formed between the micro-carbon brush anode at the bottom of compartment 1 and the cathode of compartment 2. The micro-electric field promotes the metabolic activity of acid-producing bacteria, and excess electrons drive proton reduction to produce a small amount of hydrogen gas. The hydraulic retention time of compartment 1 is 4 to 10 hours.

[0046] Wastewater enters compartment 2 (acidification enhancement section) through a low-level flow orifice. The pH of compartment 2 is controlled between 5.5 and 6.2, and the temperature is also maintained between 18°C ​​and 25°C. Compartment 2 is filled with carbon felt packing material, on which facultative acid-producing bacteria (Escherichia coli and Klebsiella spp.) are attached. An airlift internal circulation device elevates the bottom sludge-water mixture to the upward flow zone, enhancing sludge-water mixing and mass transfer. Byproduct hydrogen is collected at the top of compartment 2, with a hydrogen production rate of 0.5 cubic meters per cubic meter of reactor per day to 1.2 cubic meters per cubic meter of reactor per day. The hydraulic retention time of compartment 2 is 4 to 10 hours. The total hydraulic retention time of the acidification reaction section is 8 to 20 hours.

[0047] Hydrogen and electricity generation reaction section treatment: The effluent from the acidification reaction section enters compartment 3 (hydrogen generation core area). The pH of compartment 3 is controlled between 6.0 and 6.8, and the temperature is controlled between 18°C ​​and 25°C. Hydrogen-producing and electricity-generating bacteria (Enterobacter cloacae, Enterobacter aerogenes, Shewanella, etc.) mounted on the multilayer graphene-modified carbon fiber brush anode array in compartment 3 metabolize small molecule organic acids (mainly acetic acid, butyric acid, etc.) under anaerobic conditions, producing electrons and protons. Electrons are transferred to the air cathode in compartment 4 through an external circuit, while protons migrate with the water flow through the baffle channels and the dense layer of the microbial film to compartment 4. The baffle-type hydraulic lifter at the bottom of compartment 3 enhances the contact between the mud-water mixture and the anode brush, improving electron transfer efficiency. Hydrogen is collected at the top of compartment 3 and combined with the hydrogen collected in the acidification section. The hydraulic residence time in compartment 3 is 4 to 9 hours.

[0048] Chamber 4 (the cathode generation zone) houses a porous nickel-based air cathode with a cathode potential controlled between -0.1 volts and -0.05 volts (vs. Ag / AgCl). Oxygen in the air gains electrons at the cathode surface and is reduced to water or hydroxide ions. Electrons generated at the anode in chamber 3 flow to the cathode via an external circuit (a parallel variable resistor group, with resistance adjusted according to the generated power), forming a closed loop and generating current. Since there is no proton exchange membrane between chambers 3 and 4, there are no membrane fouling or membrane cost issues, and protons can freely transfer through the aqueous phase. The power density can reach over 2.5 watts per cubic meter of reactor volume. The electrical energy collected by the external circuit is boosted to 5 to 12 volts by a DC-DC converter and then reused for the booster pump, PLC control system, and other low-voltage electrical equipment in the pre-AF unit, achieving 15% to 25% self-sufficiency in the system. The hydraulic retention time in chamber 4 is 4 to 9 hours. The total hydraulic residence time of the hydrogen and electricity production reaction section is 8 to 18 hours.

[0049] Methanogenic reaction section treatment: The effluent from the hydrogen and electricity generation reaction section enters compartment 5 (the main methanogenic zone). The pH of compartment 5 is controlled between 6.8 and 7.4, and the temperature is controlled between 28°C and 32°C via an insulation jacket. The downflow zone of compartment 5 contains a granular sludge bed enriched with a mixed mesophilic methanogenic microbial community (mainly *Methanococcus* and *Methanotherium*) and psychrophilic methanogenic bacteria acclimated to low temperatures (*Methanophilic Bacteria* and *Methanobacterium*). The stacked corrugated baffles in the upflow zone extend the water flow path, increase the sludge-water contact time, and promote the shearing and separation of biogas bubbles. Compartment 5 converts 65% to 80% of the volatile fatty acid load into methane. The hydraulic retention time of compartment 5 is 6 to 12 hours.

[0050] The effluent from compartment 5 enters compartment 6 (the methanogenic refining zone). The pH of compartment 6 is controlled between 6.8 and 7.4, and the temperature is also maintained between 28 and 32 degrees Celsius. The downflow zone of compartment 6 is filled with bio-carbon-based granular packing material (ceramsite + bone char), which has a high biofilm density, deeply converting residual volatile fatty acids. The return pipe of the biogas collection system at the top of compartment 6 introduces a portion of the biogas (gas-to-water ratio 1:1 to 3:1) to the bottom of compartment 6, creating micro-aeration and agitation, replacing mechanical stirring, saving energy while promoting mud-water mixing. The hydraulic retention time of compartment 6 is 4 to 8 hours. The total hydraulic retention time of the methanogenic reaction section is 10 to 20 hours.

[0051] After treatment by a three-stage modified ABR reactor, the second effluent and biogas are obtained. The COD in the second effluent has been significantly reduced, and the biogas contains hydrogen (5% to 15% by volume), methane (50% to 70% by volume), and carbon dioxide (20% to 30% by volume).

[0052] Step 3: Microbial Recirculation and Gradient Temperature Control Enhancement. During system operation, highly active anaerobic sludge is extracted daily from the bottom of compartment 6 (methanogenic refining zone), at a rate of 5% to 15% of the daily treatment capacity. This sludge is then pumped back to the bottom of the first-stage AF filter in the pre-AF unit and the bottom of compartment 3 in the tertiary modified ABR reactor via sludge recirculation pumps. The highly active sludge returned to the pre-AF unit carries various low-temperature adaptive enzyme systems (such as cold shock proteins and antifreeze proteins) secreted by mesophilic methanogenic bacteria. These enzyme systems promote the metabolic activity of psychrophilic acidifying bacteria under low-temperature conditions, improving treatment efficiency in winter. The activated sludge returned to compartment 3 supplements the hydrogen-producing and electrogenic bacteria with necessary coenzymes and growth factors, enhancing their electrogenic performance.

[0053] Meanwhile, through independent insulation jackets, the water temperature of the pre-AF unit is stabilized at 10 to 15 degrees Celsius, the water temperature of the acidification reaction section and the hydrogen and electricity generation reaction section is stabilized at 18 to 25 degrees Celsius, and the water temperature of the methanogenic reaction section is stabilized at 28 to 32 degrees Celsius. This creates a gradient adaptation environment for psychrophilic bacteria, transitional bacteria, and mesophilic bacteria, ensuring that the system can operate efficiently in winter without the need for external energy consumption.

[0054] Step 4: External enrichment culture of microbial communities. The anaerobic enrichment tank (effective volume 5% to 8% of the total volume of the main reactor) is used for microbial community enrichment every 20 to 30 days. Whey culture medium and trace metal nutrients (containing Ni) are pre-added to the enrichment tank. 2+ Co 2+ Fe 2+ Then, a small amount of mixed sludge from compartments 3 and 6 is inoculated and cultured under anaerobic conditions at a constant temperature (25°C) with stirring for 7 to 10 days. During the culture, hydrogen-producing and electrogenic bacteria (such as Shewanella) and low-temperature methanogens are selectively enriched. After the culture is completed, the enriched bacterial solution is injected into compartments 3 and 5 via a transfer pump, with the injection volume being approximately 1% to 3% of the effective volume of each compartment. The above-mentioned bacterial replenishment operation is performed at least once a month to maintain the dominant position of key functional microbiota in the system.

[0055] Step 5: Electrochemical Refining of Effluent. The second effluent from the three-stage modified ABR reactor, after three-phase separation, enters the electrochemical refining unit. The hydraulic retention time in the refining unit is controlled at 2 to 4 hours. Within the unit, the iron-carbon micro-electrolysis packing layer (Fe:C mass ratio 1:1 to 1.5, filling rate 40% to 60%) undergoes a galvanic cell reaction under micro-nano aeration conditions (bubble diameter ≤100 nm, air-to-water ratio 2:1 to 5:1), generating a large number of highly oxidizing hydroxyl radicals and iron ions. These active substances further oxidize and degrade residual recalcitrant organic matter (such as humic acids) in the second effluent, increasing the COD removal rate by an additional 8% to 12%. Simultaneously, iron ions combine with phosphates in the wastewater to form iron phosphate precipitates, removing total phosphorus through flocculation and co-precipitation, achieving a total phosphorus removal rate ≥85%. The treated effluent has a COD ≤ 80 mg / L, BOD5 ≤ 20 mg / L, SS ≤ 30 mg / L, and total phosphorus ≤ 0.5 mg / L, fully meeting the Class I standard of GB8978-1996 "Integrated Wastewater Discharge Standard". The effluent can be discharged directly or reused for washing factory and workshop floors or as cooling water replenishment after simple sand filtration.

[0056] Step Six: Biogas Collection, Purification, and Resource Utilization. Biogas collected by the three-phase separators at the top of compartments 2 to 6 enters a gas-water separator via a gas collection pipeline. After removing condensate, it enters a dry desulfurization tower where iron oxide is used to remove hydrogen sulfide (removal rate ≥95%). The purified biogas is stored in a dual-membrane constant-pressure gas holder, with a methane content ≥65% in the outlet gas. The purified biogas can be used as fuel for boiler heating in the plant area. If hydrogen separation is required, a portion of the biogas can be passed through a pressure swing adsorption (PSA) unit to separate hydrogen with a purity ≥99%, which can then be sold as a byproduct or used for hydrogen energy utilization within the plant (e.g., hydrogen fuel cell forklifts).

[0057] Those skilled in the art will understand that the specific values ​​in the above embodiments (such as packing thickness, pH range, residence time, temperature, reflux ratio, etc.) can be adjusted according to the actual wastewater quality and treatment scale. For example, for wastewater with particularly high milk fat content, the hydraulic residence time of the first-stage AF filter can be appropriately extended or the thickness of the oleophilic polyurethane packing layer can be increased. For extremely cold regions in winter, an additional insulation layer can be added outside the insulation jacket, and the set value of the temperature transition zone of the hydrogen and electricity generation section can be appropriately increased (e.g., adjusted to 20-26℃). In addition, the external variable resistor of the hydrogen and electricity generation section can be automatically adjusted according to the real-time power generation to maximize energy recovery efficiency. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0058] The same or similar labels correspond to the same or similar parts; The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. An AF-modified ABR anaerobic treatment process for high-concentration dairy wastewater, characterized in that, The process includes: Wastewater is fed into the pre-AF unit, where it undergoes degreasing, deproteinization, and preliminary hydrolysis acidification to obtain the first effluent. The first effluent is fed into a three-stage modified ABR reactor, which consists of an acidification reaction section, a hydrogen and electricity generation reaction section, and a methanogenesis reaction section along the water flow direction. The wastewater is anaerobically treated step by step through the differentiated microbial communities and electrode system in each functional section to obtain the second effluent and biogas. The second effluent is fed into the effluent electrochemical fine treatment unit, where it is finely treated by iron-carbon micro-electrolysis and micro-nano aeration to obtain compliant discharge water. A portion of the activated sludge in the methanogenic reaction section is returned to the pre-AF unit and / or the hydrogen and electricity generation reaction section to supplement and enhance the functional microbial community. The hydrogen and electricity generation reaction section adopts an air cathode structure without a proton exchange membrane, which uses electrons generated by the oxidation of organic matter in wastewater to reduce oxygen, thereby generating electricity and supplying power to the system.

2. The process according to claim 1, characterized in that, The process of passing wastewater into a pre-treatment (AF) unit for degreasing, deproteinization, and preliminary hydrolysis and acidification to obtain the first effluent specifically includes: Wastewater is fed into the first-stage AF filter, where milk fat and milk protein are adsorbed and retained by the hydrophilic-hydrophobic composite packing layer. The effluent from the first-stage AF filter is fed into the second-stage AF filter, where it undergoes hydrolysis and acidification through packing material loaded with psychrophilic acidifying bacteria to obtain the first effluent. The first effluent is returned to the bottom of the first-stage AF filter at a return ratio of 0.5-1.0 to form a recirculation within the pre-AF filter.

3. The process according to claim 1, characterized in that, When the first effluent is fed into the acidification reaction section of the three-stage modified ABR reactor, the pH of the acidification reaction section is controlled to be 5.2-6.2, and the hydraulic retention time is 8-20 hours. The complex organic matter is converted into volatile fatty acids by acid-producing bacteria, and by-product hydrogen is collected.

4. The process according to claim 1, characterized in that, The hydrogen and electricity generation reaction section includes an anode compartment and a cathode compartment. The anode compartment is equipped with a graphene-modified carbon fiber brush electrode and a hydrogen- and electricity-generating bacterial community. The cathode compartment is equipped with a porous nickel-based air cathode. There is no proton exchange membrane between the anode compartment and the cathode compartment. Proton transfer and substrate separation are achieved through baffles and water flow channels.

5. The process according to claim 4, characterized in that, The power density of the hydrogen-generating and power-generating reaction section is controlled to be ≥2.5 W / m². 3 The generated electrical energy is boosted and rectified and then reused in the pumping unit or control unit of the process, achieving 15-25% self-powered system.

6. The process according to claim 1, characterized in that, The process further includes: controlling the water temperature of the acidification reaction section to 18-25℃, the water temperature of the hydrogen and electricity generation reaction section to 18-25℃, and the water temperature of the methanogenesis reaction section to 28-32℃ through an independent heat preservation jacket, thereby forming a gradient adaptation environment for a psychrophilic / mesothermic composite microbial community.

7. The process according to claim 1, characterized in that, The recirculation of a portion of the activated sludge in the methanogenic reaction section specifically includes: recirculating 5-15% of the highly active anaerobic sludge in the methanogenic reaction section to the pre-AF unit and the hydrogen and electricity generation reaction section, in order to introduce a low-temperature adaptation enzyme system into the low-temperature section.

8. The process according to claim 1, characterized in that, The process also includes an external enrichment culture step: setting up an independent anaerobic enrichment tank, regularly replenishing whey culture medium and trace metal nutrients, selectively enriching hydrogen-producing and electrogenic bacteria and / or low-temperature methanogenic bacteria, and injecting the enriched bacterial solution into the corresponding compartment of the three-stage modified ABR reactor at least once a month.

9. The process according to claim 1, characterized in that, When the second effluent is introduced into the effluent electrochemical fine treatment unit, the hydraulic retention time is controlled to be 2-4 hours; the mass ratio of Fe:C in the iron-carbon micro-electrolysis is 1:1-1.5, and the filling rate is 40-60%; the bubble diameter of the micro-nano aeration is ≤100nm, and the air-to-water ratio is 2-5:

1.

10. The process according to claim 1, characterized in that, The process also includes a biogas collection and purification step: the biogas produced by the three-stage modified ABR reactor is collected and then purified sequentially through a gas-liquid separator and a dry desulfurization tower to obtain purified biogas with a methane content ≥65%, which is then stored in a dual-membrane constant pressure gas holder.

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