1 Pollution Status of Livestock and Poultry Breeding Industry
Livestock and Poultry Breeding Industry is an important part of China's agriculture and rural economy. The environmental pollution caused by the vigorous development of Livestock and Poultry Breeding Industry is becoming more and more serious, which not only affects economic development, but also endangers ecological security, and has become a social problem that people generally pay attention to. The feces and sewage produced by livestock and poultry farms cause serious pollution of surface water, groundwater, soil and ambient air, which directly affects people's health and normal production and life. The untreated sewage from livestock and poultry farms contains a lot of pollutants, and its pollution load is very high. See Table 1 for the excretory coefficients of various livestock and poultry manure. This kind of high-concentration organic wastewater is directly discharged into rivers and lakes or washed with rainwater, which consumes a lot of dissolved oxygen in the water body and makes the water body black and smelly. Water contains a lot of nutrients such as N and P, which is one of the important reasons for water eutrophication. When it is discharged into fish ponds and rivers, aquatic organisms sensitive to organic pollution gradually die, and in serious cases, fish ponds and rivers lose their use functions. Long-term infiltration of aquaculture sewage into the ground will increase the concentration of nitrate nitrogen or nitrite nitrogen in the groundwater, reduce the dissolved oxygen content in the groundwater and increase the toxic components, which will lead to the deterioration of water quality and even the loss of its use function, and endanger the quality of surrounding domestic water. High-concentration sewage can also lead to soil pore blockage, resulting in soil air permeability and water permeability decline, hardening and salinization, seriously reducing soil quality, and even hurting crops, resulting in reduced production and death.
in order to control the environmental pollution caused by waste water, waste residue and odor from livestock and poultry breeding, the State Environmental Protection Administration issued the Emission Standard of Pollutants from Livestock and Poultry Breeding, and began to control the pollution problems in livestock and poultry farms and breeding areas. This standard aims to encourage ecological farming and promote the sustainable and healthy development of livestock and poultry farming; Promote livestock and poultry farms to consider resource utilization in the process of waste treatment, and reduce the amount of terminal pollutants. See Table 2 for pollutant discharge standards of livestock and poultry breeding industry.
2 pretreatment of livestock and poultry wastewater
No matter what process or comprehensive measures are used to treat livestock and poultry wastewater, certain pretreatment measures should be taken. Through pretreatment, the pollutant load of wastewater can be reduced, and at the same time, large solids or sundries can be prevented from entering the follow-up treatment link, causing equipment blockage or damage. In view of the large particles or easy-to-settle substances in wastewater, livestock and poultry breeding industry adopts solid-liquid separation technologies such as filtration, centrifugation and sedimentation for pretreatment, and commonly used equipment includes grids, sedimentation tanks and screens. Grille is an essential part in the process of sewage treatment, and its function is to stop coarse floating and suspended solids in sewage, so as not to block holes, gates and pipelines, and to protect mechanical equipment such as pumps. Precipitation is a treatment process that separates suspended solids heavier than water from water under the action of gravity, and it is one of the most widely used methods in wastewater treatment. At present, all farms with wastewater treatment facilities basically connect two or three sedimentation tanks in series outside the house, and treat the manure water through filtration, sedimentation and oxidative decomposition. Screen is the facility used for screening. Waste water flows through the gap in the screen, while the solid part is intercepted by machinery or its own weight, or pushed to the edge of the screen to be discharged. Commonly used solid-liquid separation screens for livestock manure include fixed screen, vibrating screen and rotating screen. In addition, there are commonly used mechanical filtration equipment such as automatic drum filter, rotary drum filter press, centrifugal disc separator and so on.
3 Main treatment technologies of livestock and poultry breeding wastewater
3.1 Natural treatment method
Natural treatment method is the most traditional method of livestock and poultry breeding wastewater treatment technology. Natural treatment is to use the physical, chemical and biological comprehensive effects of natural water, soil and organisms to purify sewage. Its purification mechanism mainly includes filtration, interception, precipitation, physical and chemical adsorption, chemical decomposition, biological oxidation and biological absorption. Its principle involves the principle of species growth, material recycling in the ecosystem, the principle of coordination between structure and function, and the mechanism of multi-level interception, storage, utilization and transformation of nutrients. This method has the advantages of low investment, simple process and low power consumption, but the purification function is restricted by natural conditions. The main modes of natural treatment are oxidation pond, soil treatment and constructed wetland treatment. Oxidation pond, also known as biological stabilization pond, is a kind of structure that uses natural or artificial renovated pond for biological treatment of sewage. The purification process of sewage is very similar to the self-purification process of natural water. The sewage stays in the pond for a long time, and the organic pollutants are degraded through the metabolic activities of microorganisms in the water. The dissolved oxygen is provided by algae through photosynthesis and reoxygenation on the pond surface, or by artificial aeration. As an environmental engineering structure, oxidation pond is mainly used to reduce the organic pollutants in water, increase the content of dissolved oxygen, and properly remove nitrogen and phosphorus from water to reduce the degree of eutrophication of water. Different from seasonal sewage irrigation, soil treatment is a perennial sewage treatment method. Sewage is applied to the land, and a series of physical, chemical and biological purification processes are carried out on pollutants in the wastewater by using an ecosystem composed of soil, microorganisms and plants, so that the water quality of the wastewater is purified, and green plants grow and reproduce through the recycling of nutrients and water in the system, thus realizing the resource, harmlessness and stability of the wastewater. Constructed wetland can remove < P > suspended solids, organic matter, nitrogen, phosphorus and heavy metals from wastewater through precipitation, adsorption, barrier, microbial assimilation and decomposition, nitrification, denitrification and plant absorption. In recent years, more and more attention has been paid to the study of constructed wetlands. Ye Yong and others used mangrove plants Bruguiera gymnorrhiza and Kandelia candel to treat nutrients N and P in livestock wastewater. The results showed that the two plants had better removal effects on N and P. Liao Xin-zhuo and Luo Shi-ming used Vetiveria zizanioides and Cyperus alterniflora as vegetation, respectively, and established constructed wetlands. With different seasons, the removal rate of pollutants was different, with the removal rate of COD Cr reaching over 9% and BOD 5 reaching over 8%. Due to the low investment and operating cost, natural treatment is an economical treatment method, especially suitable for wastewater treatment of small livestock and poultry farms, provided that there is enough land available.
3.2 anaerobic treatment technology
In 195s, the process of anaerobic contact appeared. Then, with the invention of anaerobic filter A F(anaerobic filter) and upflow anaerobic sludge bed UASB (Upflowanaerobic sludge bed), a series of high-load anaerobic reactors based on increasing sludge concentration and improving the mixing effect of wastewater and sludge were promoted and gradually applied to livestock wastewater treatment. 1/2 12 The anaerobic treatment of the last page is characterized by low cost, less land occupation, low energy demand and biogas production. Moreover, the treatment process does not need oxygen and is not limited by oxygen transfer ability, so it has high organic matter loading potential and can degrade some parts that aerobic microorganisms cannot degrade. Commonly used methods include: fully mixed anaerobic digester, anaerobic contact reactor, anaerobic filter, upflow anaerobic sludge bed, anaerobic fluidized bed, upflow solid reactor, etc. Deng Liangwei and Chen Chroming used the internal circulation anaerobic reactor (IC) process to treat piggery wastewater. The removal rates of TP, COD, BOD5, SS and biogas were 53.8% ,COD 8.3%, 95.8% ,SS 78% and 1.5 ~ 3 m 3-d-1, respectively. Zhang Guozhi and others selected Chlorella, Oscillatoria and other algae, and used suspended algae method and fixed algae method to purify the anaerobic wastewater of pig manure, which also achieved good results. At present, domestic farm wastewater treatment mainly adopts upflow anaerobic sludge bed and upflow solid reactor process. In recent years, scholars have done a lot of research on various anaerobic reactors, and believe that the new ultra-efficient anaerobic reactor has broad prospects for treating organic pollutants in pig farm sewage.
3.3 Aerobic treatment technology
The basic principle of aerobic treatment is to use microorganisms to decompose organic matter and synthesize their own cells (activated sludge) under aerobic conditions. In aerobic treatment, biodegradable organic matter can eventually be completely oxidized into simple inorganic matter. This method mainly includes activated sludge process and biofilter, biological turntable, biological contact oxidation, sequencing batch activated sludge, A/O and oxidation ditch. Aerobic technology is used for biological treatment of livestock and poultry wastewater, and the combination of hydrolysis and SBR is studied in this respect. SBR (sequencing batch reactor) process, namely sequencing batch activated sludge process, is an intermittent activated sludge process improved and developed based on the traditional Fill- Draw system. It transforms sewage treatment structures from spatial series to time series, and carries out periodic cycles such as water inflow, reaction, sedimentation, drainage and idleness in the same structure. When SBR is combined with hydrolysis to treat livestock wastewater, the hydrolysis process has a high removal rate of COD Cr, the removal rate of total phosphorus by SBR is 74.1%, and the removal rate of high concentration ammonia nitrogen is over 97%. In addition, other aerobic treatment technologies are gradually applied to livestock wastewater treatment, such as intermittent drainage extended aeration (IDEA), circulating activated sludge system (CASS) and intermittent circulating extended aeration activated sludge process (ICEAS).
3.4 mixed treatment method
The natural treatment method, anaerobic treatment method and aerobic treatment method mentioned above have their own advantages and disadvantages and scope of application. In order to learn from each other's strong points and obtain good and stable effluent quality, other treatment units are added in practical application. Mixed treatment is to design a combination of the above three kinds, or with them as the main body and combined with other treatment methods to treat livestock wastewater according to the quantity and specific conditions of livestock wastewater. This method can achieve better results with lower processing cost.
Peng Jun and others chose the anaerobic-facultative biological pond as the main process, and transplanted the upflow anaerobic sludge bed to the facultative pond. After treatment, the BOD 5, COD Cr and NH 4-N of pig farm wastewater can be reduced from 9 , 14 and 1 2 to 2, 6 and 65 mg-L -1 respectively, which successfully solved the problem of high sewage pollution load of large-scale pig farms in tropical areas. Hangzhou Xizi Farm adopted the anaerobic-aerobic treatment process. After treatment, the COD Cr and BOD 5 in the water were about 4 mg-l-1 and 14 mg-L -1, which basically reached the wastewater discharge standard. Li Han adopts the method of directly adding dominant bacteria, which can greatly improve the capacity of the original natural treatment system and improve the degradation capacity of refractory organic matter in water or soil. The process flow of wastewater treatment project of Shenzhen Agriculture and Animal Husbandry Industry Company is sewage → solid-liquid separation → regulating tank → upflow anaerobic digestion → plant pond → fish pond → discharge, and the treated wastewater can also meet the wastewater discharge standard of Shenzhen. Li Jinxiu and others adopt ASBR- SBR combined reactor system, in which ASBR is used as pretreatment (anaerobic) and SBR (aerobic) is used for biological nitrogen removal. Membrane bioreactor is a new biochemical reaction system which combines membrane separation technology with bioreactor. It replaces the traditional secondary sedimentation tank with membrane, which has the characteristics of stable effluent, high activated sludge concentration, strong impact load resistance, less residual sludge, compact structure and less land occupation. In recent years, it has been gradually applied to the treatment of various sewage. Jianwei Fan and Jason used membrane bioreactor to treat the wastewater from a livestock farm in Shanghai suburb. After a period of adjustment, the treatment system gradually stabilized and the effluent reached the national first-class discharge standard. Livestock and poultry breeding wastewater is an organic wastewater that is difficult to treat, mainly because of its large discharge, low temperature, mixed solid and liquid, high organic content and small solid volume, which makes it difficult to separate, and the washing time is relatively concentrated, making the treatment process impossible to continue. Because the indexes such as COD and BOD in wastewater seriously exceed the standard, the amount of suspended solids is large, the content of nitrogen and phosphorus is rich, and the content of ammonia nitrogen is high and difficult to remove, it is difficult to meet the discharge requirements simply by physical, chemical or biological treatment methods. Therefore, the wastewater treatment of general farms needs to use a combination of various treatment methods. According to the characteristics and utilization ways of livestock wastewater, the above different treatment technologies can be adopted. The typical process flow is shown in Figure 1.
4 Conclusion
There are still many methods to treat livestock and poultry wastewater. Whether a certain treatment method can be accepted depends not only on the technical advantages of this treatment method, but also on the investment, daily operation cost and convenience of operation. In order to prevent and control the pollution of livestock and poultry breeding, realize the recycling of wastewater, reduce the discharge of wastewater and the input of chemicals into the environment, and minimize the pollution, we should not only realize the harmlessness of the treatment process, but also realize the resource utilization of the treatment process, effectively protect and improve the rural ecological environment, and promote the sustainable and coordinated development of the livestock and poultry breeding environment and economy.
for more information about the engineering/service/procurement bidding, and to improve the winning rate, you can click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd