China Environmental Protection (Linyi) Ecological Cycle Industrial Park takes“ environmental protection priority, resource sharing, facility co-construction, material circulation, and energy cascade utilization” as the construction concept, and relies on domestic waste treatment to achieve the harmlessness of other solid wastes., reduction, and resource-based collaborative disposal, plans and builds three categories of entry projects: solid waste treatment, park supporting facilities, and neighborly projects, including solid waste treatment projects such as domestic waste, kitchen waste, animal carcasses, and sludge, central heating, sewage treatment center, science and technology research and development center, digital management and control platform and other park supporting projects, publicity and education center, regional residents heating, Village-based warehousing poverty alleviation and other neighbor-friendly projects.

The disposal scope of the industrial park covers 5 districts and 6 counties in Linyi City, serves more than 7.3 million people in the old areas, solves the problem of harmless treatment and resource utilization of urban solid waste such as urban domestic waste, kitchen waste, sludge, and animal carcasses, and makes full use of the synergy between projects to realize secondary development and recycling of resources of each project to achieve the purpose of energy conservation and emission reduction.

When the ecological recycling industrial park was completed, landfill leachate, kitchen biogas slurry, sludge filter press fluid, and animal harmless wastewater were produced. In recent years, there have been many studies at home and abroad on the treatment of individual landfill leachate and kitchen biogas slurry, but there has been little research on mixed sewage treatment technology.

As the scale of cities becomes larger and the population gathers more, more urban wastewater will be produced. Research on mixed sewage treatment technology becomes particularly important. This requires the design and construction of an excellent process system to meet the needs of mixed industrial sewage in the park. The need for treatment and disposal.

Anaerobic biological treatment technology has been widely used in the treatment of high-concentration organic wastewater in recent years due to its low operating cost, low energy consumption, small amount of residual sludge, and ability to treat biodegradable organic matter under high concentration and aerobic conditions.

　　Common anaerobic reactors include upstream anaerobic sludge bed reactor (UASB), upflow anaerobic sludge bed-filter bed reactor (UBF), and anaerobic biological filter (AF). The UASB system has strong impact resistance, high load rate, and the process design parameters are supported by more leachate test data and operating effect analysis data.

　　Moreover, there are few successful application examples of UBF and AF in the more influential landfill leachate treatment projects in China, and it is difficult to confirm the more reliable design parameters. Therefore, the design of this project uses UASB as the structure selection of the anaerobic treatment unit.

　　Aerobic biological treatment is relatively mature in wastewater treatment, which can make organic matter degraded to the greatest extent and close to the discharge standard, reducing the difficulty and cost of deep treatment, mainly including membrane biological method (MBR), oxidation ditch, sequential batch activated sludge method (SBR) and other processes.

　　The MBR process is increasingly widely used in the treatment of high-concentration organic wastewater, and the MBR system has a high sludge concentration and a small area of the system, which can easily arrange biological denitrification, which is especially suitable for sewage treatment with high ammonia nitrogen. Due to the use of ultrafiltration membrane for slurry water separation, the effluent SS of the MBR process is low, which is conducive to subsequent deep treatment.

　　The aerobic unit of this project chooses the MBR system, in which the biochemical section is set up with two stages of AO, the nitrogen that cannot be removed in the first AO section is added later, and the hypoxic section is denitrified and removed by supplementing the carbon source beyond a part of the landfill leachate, and the final aerobic section controls the higher dissolved oxygen and oxidizes the remaining carbon source and organic matter.

　　Table 1 shows that the COD of landfill leachate is 60 000 mg/L, which is much higher than that of other wastewater, and only the landfill leachate is designed to enter the UASB for anaerobic fermentation to produce biogas to ensure gas production efficiency and stability. The scale of landfill leachate treatment is much larger than the sum of other sewage treatment volumes, so it is necessary to design the leachate control tank and monitor the effluent quality index of the UASB anaerobic tank in real time.

　　Ensuring that the water quality and quantity of landfill leachate are adjustable and controllable can ensure that the treatment effect of Type 4 wastewater directly after MBR mixing is stable and good, and there is no need to set up a homogeneous tank before MBR, which saves the cost of tank construction.

　　After MBR treatment, the COD and color intensity formed by refractory organic matter still exceed the standard, and the general coagulation treatment has a low removal rate and a large amount of sludge for this type of wastewater, which is troublesome to treat.

　　Other physical and chemical treatment technologies still lack the confirmation of productive related application technical parameters in the practical engineering application of high-concentration organic wastewater treatment.

　　At present, the only reliable deep treatment process is membrane treatment technology. According to the pore size of the membrane, membrane treatment can be divided into reverse osmosis, nanofiltration, ultrafiltration and microfiltration. Compared with reverse osmosis, the biggest advantage of nanofiltration is that it can discharge small molecule salts with the effluent to avoid the adverse effects of salt enrichment. There is little difference between nanofiltration membrane and reverse osmosis membrane in terms of equipment investment, but the power consumption of nanofiltration system is much smaller than that of reverse osmosis system. The depth treatment of this project adopts nanofiltration process.

　　In summary, the anaerobic system of this project adopts UASB process, aerobic treatment adopts MBR system (two-stage A/O+ external tube ultrafiltration), and nanofiltration process adopts deep treatment.

Kitchen biogas slurry and landfill leachate are treated together, and part of the landfill leachate in the regulating tank enters the anaerobic system for anaerobic fermentation, and part goes beyond the biochemical system, which can supplement the carbon source required for the biochemical treatment of kitchen biogas slurry, without additional carbon sources, which greatly saves operating costs. The denitrifying bacteria use the carbon source supplemented by the leachate to greatly improve the TN removal effect of the system, and the removal rate of organic matter in the leachate in the biochemical system is also improved accordingly.

　　The sludge filtration fluid enters the MBR system and mixes with the landfill leachate, because the landfill leachate treatment volume is large, the two collaborative treatment plays a dilution role in the sludge filtrate without adding acid to adjust the pH of the sludge filtrate, saving a lot of chemical costs.

　　In addition, the oil content of the four kinds of sewage was greatly diluted in the collaborative treatment of the kitchen biogas slurry and animal harmless sewage, which weakened the influence of oil content on the biochemical system microorganisms and the later membrane system treatment.

Landfill leachate, kitchen biogas slurry, sludge filtration solution, animal harmless wastewater

Mixed industrial wastewater treatment process

　　The leachate generated by the waste-to-energy plant flows into the pretreatment section, and the grille machine intercepts the large suspended solids in the water to prevent the rear section from blocking the equipment. The filtered sewage from the grille flows into the leachate conditioning tank.

　　Part of the leachate in the conditioning tank is quantitatively lifted to the UASB anaerobic tank by the lift pump, and part is transcended to the MBR system. The biogas generated by the anaerobic system is collected and entered into the biogas treatment system for treatment or utilization. The anaerobic treatment effluent flows into the intermediate sedimentation tank to remove the aged anaerobic sludge flowing out with the water to avoid its adverse effects on the back-end biochemical system.

　　The effluent from the sedimentation tank in the anaerobic section flows into the MBR system. The MBR system adopts external type, the membrane system adopts the form of tubular ultrafiltration membrane, and the biochemical part adopts two-stage A/O biochemical process.

　　The MBR system includes five parts: primary denitrification tank, primary nitrification tank, secondary denitrification tank, secondary nitrification tank, and tubular ultrafiltration system. The nitrification liquid forms a part of the ultrafiltration produced water under the circulating pressure of the tubular ultrafiltration system, and flows into the ultrafiltration tank under the pressure.

　　The sludge filtrate generated by the sludge harmless treatment center enters the filtrate conditioning tank, enters the intermediate tank after passing through the pH adjustment tank, sedimentation tank, and hydrolysis tank, and then is pumped into the MBR system by the lift pump.

　　The biogas slurry produced by the anaerobic tank of the kitchen harmless project and the animal harmless sewage generated by the animal harmless project are stored in the pre-storage tank of their respective projects after being pretreated with slag removal, and then pumped into the MBR system by lifting pump after slag removal by automatic filter cleaner.

　　The sewage treated by the MBR process enters the nanofiltration treatment system. Under the action of a certain pressure, part of the clean water and small molecule substances form a clear liquid through the membrane, and the remaining substances and water form a concentrate, which is reused or discharged to meet the standard, and the concentrate is discharged into the concentrate collection tank, and after further concentration by the dish tube reverse osmosis (DTRO) system of the concentrate treatment station, it enters the mechanical vapor compression (MVR) system for evaporation, and the reclaimed water is used as a circulating cooling tower to replenish water, and the mother liquor is sprayed back to the waste incinerator.

  Since the commissioning of this project in October 2018 to the official operation, the treatment effect of the mixed sewage treatment station has been stable, and the treated effluent has been discharged into the municipal sewage pipe network or reused after meeting the requirements of Table 2 of the "Domestic Waste Landfill Pollution Control Standard" (GB 16889-2008).

　　At present, the mixed sewage treatment station is overloaded during peak period, and the actual average water intake is 698 m³/d, of which the average inlet of leachate, biogas slurry, sludge filtration and animal harmless sewage is 462, 145, 20 and 42 m³/d, respectively. Through the company's routine monitoring and third-party monitoring, the effluent water quality is stable and meets the design standard.

　　The treatment and disposal of mixed industrial sewage in this project is for the purpose of protecting the ecological environment and controlling environmental pollution, and the overall emission of pollutants in the industrial park is reduced after the operation of the project, making great contributions to energy conservation and emission reduction. The reuse of reclaimed water effectively reduces the consumption of water resources, reduces the pollution caused by leachate to the environment, and realizes the harmless and reduced treatment of leachate, kitchen biogas slurry, animal harmless sewage and sludge press, which has huge environmental benefits.

　　Since its official operation, as of April 2021, a total of 615,200 tons of sewage have been treated, including 397,600 tons of leachate, 155,200 tons of kitchen biogas slurry, 39,800 tons of animal harmless sewage, and 22,500 tons of sludge filtrate. COD, ammonia nitrogen and total nitrogen emissions decreased by 16 719, 1 015 and 1 288 t, respectively.