The treatment methods for large-scale livestock and poultry manure at home and abroad mainly include comprehensive utilization and standard discharge treatment. Comprehensive utilization is a good way to utilize biomass energy at multiple levels, build ecological agriculture, and ensure sustainable agricultural development. However, currently, due to the outdated management methods of livestock and poultry farms in China, coupled with inadequate anaerobic treatment before comprehensive utilization, many problems often arise in the process of comprehensive utilization of livestock and poultry manure water, such as large wastewater production, complex composition, high pollutant concentration after treatment, high dilution water used, and seasonal irrigation effects. For the treatment of compliant emissions, although the process flow used domestically and internationally is roughly the same, namely solid-liquid separation anaerobic digestion aerobic treatment. However, for the aquaculture industry in China, which is operating at a low profit level, the investment required to build such sewage treatment facilities is too high and the operating costs are too high. Therefore, exploring methods for treating livestock manure with low facility investment, low operating costs, and high efficiency has become the key to solving livestock pollution.

1. Solid-liquid separation

No matter what system or comprehensive measures are used to treat wastewater from livestock and poultry farms, solid-liquid separation must be carried out first. This is an essential process, and its importance and significance mainly lie in: firstly, the content of solid suspended solids in the wastewater discharged from general farms is high, up to 160000mg/L, and the corresponding organic matter content is also high, By solid-liquid separation, the pollutant load of the liquid part can be greatly reduced; Secondly, solid-liquid separation can prevent larger solids from entering the subsequent treatment process and prevent equipment blockage and damage. In addition, solid-liquid separation before anaerobic digestion can also increase the reliability of anaerobic digestion operation, reduce the size and required residence time of anaerobic reactors, reduce facility investment, and improve COD removal efficiency. Solid liquid separation technology generally includes processes such as screening, centrifugation, filtration, flotation, sedimentation, sedimentation, and flocculation. At present, China has mature solid-liquid separation technology and corresponding equipment, which mainly include screen type, horizontal centrifuge, filter press, hydrocyclone, rotary conical screen, and centrifugal disc separator.

2. Anaerobic treatment

Due to the high concentration of organic matter, high N, P content, and high number of harmful microorganisms, aquaculture wastewater belongs to the "three highs" of wastewater. Therefore, anaerobic technology has become an indispensable key technology in the treatment of livestock and poultry manure. For high concentration organic wastewater in aquaculture farms, anaerobic digestion technology can effectively remove a large amount of soluble organic matter at lower operating costs, with a COD removal rate of 85% to 90%, and can kill infectious bacteria, which is beneficial for the epidemic prevention of aquaculture farms. If aerobic processes are directly used to treat livestock wastewater after solid-liquid separation, although a one-time investment can be saved by 20%, due to its high power consumption, electricity and water consumption are as much as 10 times that of anaerobic treatment. Therefore, long-term operating costs will bring a heavy economic burden to the breeding farm.

At present, there are many anaerobic processes used to treat livestock manure, among which the most commonly used are anaerobic filters (AF), upflow anaerobic sludge beds (UASB), composite anaerobic reactors (UASB+AF), two-stage anaerobic digestion method, and upflow sludge bed reactors (USR). In recent years, anaerobic digestion, also known as biogas fermentation technology, has been widely used in the treatment of waste in livestock farms. By the end of 2002, the number of large and medium-sized biogas projects in China's livestock and poultry farms had reached more than 2000, making it one of the countries with the largest number of biogas facilities in the world. Although there are also many failed examples in the construction of biogas projects in China, with a success rate of only 85%, this technology is still the most effective technical solution to solve the problem of harmless and resource utilization of livestock and poultry manure wastewater. Animal manure and wastewater generated by breeding farms are valuable resources. Anaerobic digestion treatment can not only achieve harmless treatment, but also recover biogas and organic fertilizers. Therefore, constructing biogas projects will be the best choice for the treatment of fecal wastewater in small and medium-sized breeding farms.

3. Aerobic treatment refers to a process that utilizes aerobic microorganisms to treat aquaculture wastewater. Aerobic biological treatment methods can be divided into two categories: natural aerobic treatment and artificial aerobic treatment.

Natural aerobic biological treatment is a method of purifying wastewater using microorganisms in natural water and soil, also known as natural biological treatment. It mainly includes two types: water purification and soil purification. The former mainly includes oxidation ponds (aerobic ponds, facultative ponds, anaerobic ponds) and aquaculture ponds, etc; The latter mainly includes land treatment (slow infiltration, rapid method filtration, surface overflow) and artificial wetlands. The natural biological treatment method not only has low infrastructure costs and low power consumption, but also has a higher removal rate for nutrients such as difficult to biodegrade organic matter, nitrogen and phosphorus, and bacteria than conventional secondary treatment. Some can achieve the effect of tertiary treatment. In addition, under certain conditions, this method combined with sewage irrigation can achieve the utilization of sewage resources. The main drawbacks of this method are the large land area and the susceptibility of the treatment effect to seasonal influences. However, if the farm is small and there are abandoned ditches, ponds and mudflat nearby for use, this method should be selected as far as possible to save investment and treatment costs. Artificial aerobic biological treatment is a wastewater treatment method that uses artificial enhanced oxygen supply to enhance the activity of aerobic microorganisms. This method mainly includes activated sludge method

Biological filter, biological rotary table, biological contact oxidation method, sequencing batch reactor (SBR), anaerobic/aerobic (A/O) and oxidation ditch method, etc. In terms of treatment efficiency, the contact oxidation method and the biological rotary table method have better treatment effects than the activated sludge method. Although the treatment effect of the biofilter is also good, it is prone to filter blockage. The oxidation ditch, SBR, and A/O processes are all improved activated sludge processes. The effluent quality of the oxidation ditch is good, the amount of mud produced is small, and it can also be used for denitrification treatment of sewage. However, its treatment requires a small BOD load, occupies a large area, and has high operating costs. The SBR method has a high degree of automation control and can deeply treat sewage, but its disadvantage is that the BOD load is small and the one-time investment is also large. A/O system is an activated sludge treatment process that combines the removal of BOD and denitrification. Although its investment is relatively high, the water treated by this method is easy to meet the discharge standards. Therefore, for farms with large scale, high wastewater production, and strong economic capacity, the A/O method can be chosen, while for medium-sized farms, aerobic treatment processes such as contact oxidation and biological turntables can be chosen.