Control measures of heavy metal pollution in pig manure
Abstract: With the rise of large-scale pig farming, the problem of manure pollution in pig farms has become a focus of attention. In actual production, pig manure is often used as organic fertilizer for agricultural production. However, due to the abuse of trace element additives in feed, the content of heavy metals in pig manure exceeds the standard, which poses a serious threat to human health. This paper analyzes the harm of heavy metal pollution in pig manure, and puts forward control measures from strengthening the control of manure source, using organic trace elements, using compost fermentation, and using passivation agent adsorption. Governance provides lessons.
Key words:pig farm manure treatment; heavy metal pollution; control measures
With the rapid development of the pig industry in the direction of large-scale and intensification, the problem of manure pollution from pig production is becoming more and more serious. life has had a serious impact. The content of heavy metals such as copper and zinc added in feed often exceeds the absorption capacity of livestock and poultry, and most of them are excreted. Heavy metals have the characteristics of refractory degradation and long-lasting effect, which will cause environmental pollution. Excessive heavy metal content in manure will lead to the accumulation of heavy metals in agricultural products and cause certain harm to human health. Therefore, controlling the discharge of heavy metals in pig manure is very important to reduce external environmental pollution.
1 Harmful effects of heavy metal pollution in pig manure
Trace elements are essential nutrients for the growth and development of livestock and poultry, but they are also the main source of heavy metal pollution in animal husbandry. In order to unilaterally emphasize the growth-promoting effect of feed, some feed factories add excessive trace element additives to the feed, resulting in the feed rich in copper, zinc, manganese, chromium and other heavy metals, which can only be absorbed by pigs after feeding. Large amounts of heavy metals are excreted in feces. There are many ways to treat pig manure, and a large part of it is made into organic fertilizer for crop cultivation . Because heavy metals have the characteristics of persistence and non-degradation, continuous use of fecal organic fertilizers rich in heavy metals will increase the content of heavy metals in soil and crops. Studies have shown that vegetables are the crops with the most enriched heavy metal elements, and the content of heavy metal elements in some vegetables seriously exceeds my country's food safety standards, which seriously endangers human health . In addition, heavy metals in manure will seriously affect water sources, soil, groundwater, etc., threatening the ecological environment.
2 Control measures
2.1 Strengthen the control of manure source
Disorderly discharge of manure from pig farms is one of the important reasons for heavy metal pollution. Many pig farms return the manure directly to the fields without treatment, resulting in excessive heavy metal content in the soil. More importantly, once the soil is polluted, it is very difficult to control it. Soil contaminated with heavy metals can be effectively treated by deposition of insoluble or stable compounds, but it takes a long time, the treatment cost is high, and the practical operation is not feasible enough. Therefore, the control of heavy metal pollution in pig manure is focused on prevention, and prevention is better than cure. In pig production, the proportion and dosage of various elements in the feed should be strictly controlled, especially the addition of trace elements of heavy metals should not exceed the standard . Feed mills must strictly follow production standards to prevent excessive addition of heavy metal elements in feed.
2.2 Use of organic trace elements
The use of organic trace elements can effectively reduce the discharge of heavy metals in livestock and poultry manure, and reduce the pollution of heavy metals in livestock and poultry manure to the environment. Organic trace elements are mainly made by chelation technology, which not only absorbs quickly, but also consumes low energy, and has no competition with free amino acids during the absorption process. Studies have shown that there is mutual antagonism between different trace elements in the feed, so the appropriate dosage and ratio must be set. The use of organic trace elements can significantly improve the production performance of pigs, reduce the loss of trace elements, and reduce the content of heavy metals in pig manure, thereby reducing the pollution of heavy metals in soil and agricultural products.
2.3 Adopting composting and fermentation technology
Composting and fermentation is the most common way of resource utilization of manure in large-scale pig farms. It can not only improve the utilization rate of organic matter in pig manure, but also effectively kill pathogenic microorganisms and reduce the spread of diseases. Composting fermentation mainly converts the organic matter in the manure into humus and organic matter under the action of aerobic thermophilic microorganisms, which can improve the soil structure of the soil after fertilization. Studies have shown that the accumulation and fermentation of manure can passivate heavy metals and lose metal activity . The principle is that the organic matter produced in the composting and fermentation process of manure can complex and fix heavy metals, reduce their biological availability, and effectively reduce the pollution of heavy metals from manure to the soil environment.
2.4 Adsorption with passivating agents
Commonly used passivating agents in production can be divided into three types: physical, chemical and biological. Physical passivating agents mainly use strong adsorption capacity to adsorb heavy metals, and commonly used activated carbon, zeolite, etc. Physical passivators have the advantages of simple operation method, low cost, easy to use, etc., but they also have disadvantages such as weak adsorption and difficult separation from compost products . Compared with physical passivators, chemical passivators have a better adsorption effect on heavy metals, but due to chemical reactions, they will cause secondary pollution to the surrounding environment. Biological deactivators are rarely used in practice due to the limitations of their scope of application and target. For manure with high heavy metal content, a combination of physical and chemical passivators is often used in practice.