Effects Of Modified Biochar On Heavy Metal Passivation In Pig Manure Compost

With the intensive and large-scale development of livestock and poultry breeding industry,the total emission of livestock and poultry manure has increased dramatically,and livestock and poultry manure generally contains Cu,Zn,Pb,Cd and other heavy metals,which has become the main source of heavy metal pollution in agriculture and greatly limits the sustainable development of agriculture.Aerobic composting technology can not only realize resource utilization and harmlessness of livestock manure,but also effectively reduce the activity of heavy metals.Therefore,fresh pig manure was used as raw material,corn straw was used as conditioner,and apricot shell biochar,coconut shell biochar and Chinese fir biochar at 5%,10%and 15%addition levels were used as heavy metal passivation agents for aerobic composting of pig manure.Through the analysis of the basic physical and chemical properties of materials and the change of heavy metal morphology,the types and addition levels of biochar with the best passivation effect of heavy metals were determined.Then,the biochar was modified by Na OH,Fe Cl₃ and H₃PO₄,and the composting experiment was carried out.According to the passivation effect of heavy metals,the optimal modified biochar was determined,which provided technical guidance for the passivation of heavy metals in livestock manure.The main research results and conclusions are as follows:（1）The effects of different types and addition levels of biochar on the passivation of Cu,Zn,Pb and Cd in pig manure composting were investigated,and the types and addition levels of biochar with the best passivation effect on heavy metals were selected.The high temperature period of the ten experimental groups was more than 7d the seed germination index GI was more than 80%,the humification coefficient HA/FA was more than 1.80,and the materials were all matured to achieve harmless treatment.Among them,adding biochar test group can effectively shorten the time to reach the highest temperature and can prolong the high temperature period of1～3d;The addition of biochar in the experimental group increased the seed germination index by19%–39.5%,effectively reduced the toxicity of compost products,and the material humification coefficient increased by 2%–27%,indicating that the addition of biochar could effectively promote the humification of organic matter in the pile and improve the maturity of compost products.Through the overall analysis of the passivation effect of four heavy metals in each experimental group,when adding 15%apricot shell biochar,the passivation effect of four heavy metals was the best.The passivation rates of Cu,Zn,Pb and Cd were 60.80%,41.10%,60.05%and 46.59%,respectively,which were 26.28%,13.09%,24.37%and 15.16%higher than those of CK group.（2）The apricot shell biochar was modified by Na OH,Fe Cl₃ and H₃PO₄,and the composting experiment was carried out with three kinds of modified biochar as additives.The results showed that the addition of modified biochar could not only further prolong the high temperature time,improve the seed germination index,reduce the toxicity of compost products,significantly improve the maturity of compost products,but also enrich the microbial diversity of compost.The analysis on the passivation effects of four heavy metals shows that the modified biochar can effectively enhance the passivation of heavy metals.Among them,H₃PO₄ modified biochar had the best passivation effect on heavy metals.The passivation rates of Cu,Zn,Pb and Cd were 79.45%,51.30%,70.65%and 61.05%,respectively,which were 20.03%,11.00%,11.08%and 12.66%higher than those of the unmodified biochar group.