1 Livestock and poultry Aquaculture wastewater Hazards to the environment

Large scale farms discharge large and concentrated wastewater every day, and the wastewater contains a large number of pollutants, such as heavy metals, residual veterinary drugs and a large number of pathogens. Therefore, if the wastewater is discharged into the environment or directly used for agriculture without treatment, it will cause serious pollution to the local ecological environment and farmland.
1.1 Water pollution
Aquaculture wastewater is a high concentration organic wastewater rich in a large number of pathogens, which can be directly discharged into the water body or stored in an inappropriate place. If it is washed into the water body by rainwater, it may cause serious deterioration of surface water or groundwater quality. Due to the strong leaching ability of livestock and poultry manure, the amount of nitrogen, phosphorus and water-soluble organic matter in manure is large. If not properly treated, it will enter the groundwater through surface runoff and infiltration to pollute groundwater. The impact on surface water is mainly shown as: after a large amount of organic matter enters the water body, the decomposition of organic matter will consume a large amount of dissolved oxygen in the water, making the water body smelly; When the dissolved oxygen in the water body drops significantly, a large amount of organic matter can continue to decompose under anaerobic conditions, which will produce methane, hydrogen sulfide and other toxic gases, leading to the death of a large number of aquatic organisms; A large amount of suspended solids in the wastewater can make the water body turbid, reduce the photosynthesis of algae in the water, restrict the normal activities of aquatic organisms, and gradually kill aquatic organisms sensitive to organic pollution, thus further exacerbating the oxygen deficiency at the bottom of the water body, and reducing the assimilation capacity of the water body; Nitrogen and phosphorus can cause eutrophication of the water body. The result of eutrophication will cause high concentrations of nitrate and nitrite in the water body. If people and animals drink for a long time, they will be poisoned. The growth and mass reproduction of some toxic algae will discharge a large amount of toxins into the water body, resulting in a large number of deaths of aquatic animals, thus seriously destroying the ecological balance of the water body; Some germs and viruses in feces and urine flow with water, which may lead to the spread of some epidemics.
1.2 Impact on farmland and crops
Livestock and poultry breeding wastewater contains more nitrogen, phosphorus, potassium and other nutrients. If it can be reasonably applied, it can effectively improve soil fertility, improve the physical and chemical properties of soil, and promote the growth of crops. However, if it is directly, continuously and excessively applied without any treatment, it will have adverse effects on the growth of soil and crops, such as causing crops to grow excessively, turn green and lodging, greatly reducing the yield, delaying the maturity period and affecting the production of subsequent crops. A large amount of organic matter in the wastewater accumulates continuously in the soil. Although it can provide nutrients and suitable environment for small animals, insects, fungi, bacteria, etc. inhabiting in the soil, it can also cause a large number of pathogenic bacteria to breed and cause the occurrence of diseases and pests; In addition, the accumulation of a large amount of organic matter will also make the soil show strong reducibility, and the conditions of strong reducibility will not only affect the root growth of crops, but also easily reduce and release harmful elements in the soil that were originally in an inert state; The accumulation of a large amount of inorganic salts in the soil will cause salt damage to crops.
1.3 Mineral element and heavy metal pollution
On the one hand, about 75% of the inorganic phosphorus added in livestock and poultry feed is phytate, which can not be absorbed by animals and directly discharged out of the body, causing pollution. On the other hand, feed mills and farms generally use high copper, high iron, high zinc and other trace element additives. Because the absorption rate and utilization rate of these metal elements are very low, they are easily discharged into the environment with feces, which has become a major environmental hazard in China.
1.4 Pollution of residual veterinary drugs
In the process of livestock and poultry breeding, in order to prevent and control the multiple diseases of livestock and poultry, antibiotics and other drugs are often added to the feed. These drugs enter the animal's digestive tract with the feed and enter the animal's blood circulation in a short time. Finally, most drugs are filtered by the kidney and discharged out of the body with urine, and only a small part of drugs and antibiotics remain in the animals. A large number of studies have shown that most feed antibiotics have residues, but the amount of residues is different. With the continuous improvement of science and technology, people found that the use of antibiotics as feed additives has caused serious negative consequences for the breeding environment. First of all, drug resistant pathogens or mutant pathogens in livestock and poultry are constantly produced and discharged into the environment; Secondly, livestock and poultry continuously excrete these antibiotics or their metabolites into the environment, so that drug-resistant pathogens and mutant pathogens in the environment continue to produce. These two in turn stimulate producers to increase drug dosage and update drug varieties, which leads to a vicious circle of "drug pollution → drug resistance or mutation of pathogenic bacteria → increased drug dosage → further environmental pollution". In addition, drug residues in livestock and poultry products may be converted into environmental hormones or precursors of environmental hormones after entering the environment, thus directly destroying ecological balance and threatening human health.
1.5 Microbial pollution
Microbes in livestock and poultry are mainly discharged from the body through the digestive tract, and enter the environment through the discharge of farm waste, thus causing serious microbial pollution. If these feces are not treated innocuously, once a large number of harmful bacteria enter the environment, they will not only directly threaten the survival of livestock and poultry, but also seriously endanger human health.
2 Basic methods and steps of livestock and poultry breeding wastewater treatment
At home and abroad, the treatment methods for fecal water of large-scale livestock and poultry farms mainly include comprehensive utilization and treatment of up to standard discharge. Comprehensive utilization is a good way for multi-level utilization of biomass energy, construction of ecological agriculture and guarantee of sustainable agricultural development. However, at present, due to the backward feeding management mode of livestock and poultry farms in China, and the 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 amount of wastewater, complex composition, high concentration of pollutants after treatment, large amount of dilution water used and seasonal irrigation. For the treatment of up to standard discharge, although the process flow used at home and abroad is roughly the same, that is, solid-liquid separation anaerobic digestion aerobic treatment. However, for China's aquaculture industry, which operates at a low profit, the investment required for the construction of such fecal sewage treatment facilities is too large and the operating costs are too high. Therefore, it has become the key to solve the pollution of aquaculture industry to explore a method of fecal sewage treatment with low facility investment, low operating cost and efficient treatment.
2.1 Solid liquid separation
No matter what system or comprehensive measures are adopted for the treatment of livestock and poultry farm wastewater, solid-liquid separation must be carried out first. This is an essential process link, and its importance and significance mainly lie in: first, the content of suspended solids in wastewater discharged from general farms is very high, up to 160000mg/L, and the corresponding organic content is also very high, Through solid-liquid separation, the pollutant load of the liquid part can be greatly reduced; Secondly, through solid-liquid separation, large solids can be prevented from entering the subsequent processing link to prevent equipment blockage and damage. In addition, solid-liquid separation before anaerobic digestion treatment can also increase the reliability of anaerobic digestion operation, reduce the size of anaerobic reactor and the required residence time, reduce the investment in facilities and improve the removal efficiency of COD. Solid liquid separation technology It generally includes: screening, centrifugation, filtration, floatation, sedimentation, sedimentation, flocculation and other processes. At present, China has mature solid-liquid separation technology and corresponding equipment, and the equipment types mainly include screen type Horizontal centrifuge , filter press, hydrocyclone, rotary cone screen, centrifugal disc separator, etc.
2.2 Anaerobic treatment
The aquaculture wastewater belongs to the "three high" wastewater with high organic concentration, high N, P content and high number of harmful microorganisms. Therefore, anaerobic technology has become an indispensable key technology in the manure treatment of livestock and poultry farms. For the high concentration organic wastewater of the breeding farm, the anaerobic digestion process can effectively remove a large amount of soluble organic matter at a lower operating cost. The COD removal rate can reach 85%~90%, and can kill infectious bacteria, which is conducive to the epidemic prevention of the breeding farm. If the aerobic process is directly used to treat the aquaculture wastewater after solid-liquid separation, although the one-time investment can be saved by 20%, because of its large power consumption, the power and water consumption is 10 times more than that of anaerobic treatment, so the long-term operation cost will bring heavy economic burden to the farm.
At present, there are many anaerobic processes used to treat the feces of breeding farms, among which the following are commonly used: anaerobic filter (AF), upflow anaerobic sludge bed (UASB), composite anaerobic reactor (UASB+AF), two-stage anaerobic digestion and upflow sludge bed reactor (USR). In recent years, anaerobic digestion, that is, biogas fermentation technology, has been widely used in the waste treatment of livestock farms. By the end of 2002, the number of large and medium-sized biogas projects in livestock farms in China had reached more than 2000, which is one of the countries with the largest number of biogas devices in the world. Although there are many failures in the construction of biogas projects in China, with a success rate of only 85%, this technology is the most effective technical solution to the problem of harmless and resourceful treatment of livestock and poultry manure sewage. Livestock manure and wastewater from farms are valuable resources. Anaerobic digestion treatment can not only achieve harmless treatment, but also recover biogas and organic fertilizers. Therefore, the construction of biogas project will be the best choice for the treatment of feces and wastewater from small and medium-sized farms.
Aerobic treatment is a process that uses aerobic microorganisms to treat aquaculture wastewater. Aerobic biological treatment methods can be divided into natural aerobic treatment and artificial aerobic treatment.
Natural aerobic biological treatment is a method of purifying wastewater by using microorganisms in natural water and soil, also known as natural biological treatment, which mainly includes water purification and soil purification. The former mainly includes oxidation ponds (aerobic ponds, facultative ponds, anaerobic ponds) and aquaculture ponds; The latter mainly includes land treatment (slow infiltration, rapid filtration, overland flow) and constructed wetlands. The natural biological treatment method not only has low infrastructure cost and low power consumption, but also has higher removal rate of nutrients and bacteria such as organic matter, nitrogen and phosphorus that are difficult to be biodegraded than the conventional secondary treatment, some of which can achieve the effect of tertiary treatment. In addition, under certain conditions, this method can be used together with sewage irrigation to realize sewage recycling. The disadvantages of this method are that it covers a large area and the treatment effect is easily affected by seasons. However, if the farm is small and there are abandoned ditches, ponds and beaches nearby for use, this method should be selected as far as possible to save investment and treatment costs. Artificial aerobic biological treatment is a kind of wastewater treatment method that adopts artificial enhanced oxygen supply to improve the activity of aerobic microorganisms. This method mainly includes activated sludge method
Biological filter, biological rotating disk, biological contact oxidation, sequencing batch reactor (SBR), anaerobic/aerobic (A/O) and oxidation ditch methods. As far as the treatment effect is concerned, the treatment effect of contact oxidation method and biological rotary table is better than that of activated sludge method. Although the treatment effect of biological filter is also very good, it is prone to filter blockage. Oxidation ditch, SBR and A/O processes are all improved activated sludge processes. The effluent quality of oxidation ditch is good, and the amount of sludge generated is small. It can also remove nitrogen from sewage, but the BOD load of the treatment is small, the area occupied is large, and the operation cost is high. SBR method has a high degree of automation control and can carry out advanced treatment of sewage, but its disadvantage is that the BOD load is small and the one-time investment is large. A/O body is an activated sludge treatment process with dual functions of BOD removal and nitrogen removal. Although its investment is relatively large, the water treated by this method is easy to discharge up to the standard. Therefore, A/O method can be selected for those farms with large scale, large amount of wastewater and strong economic capacity, while aerobic treatment processes such as contact oxidation and biological rotary table can be selected for medium-sized farms.
This article is written by Zhejiang Zhengda Environmental Protection Equipment Co., Ltd, Horizontal screw centrifuge Arrangement and release of professional manufacturing experts

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