Research Of The Passivation Of Heavy Metals In The Composting Process Of Livestock Wastes

In recent years,heavy metals in livestock and poultry wastes have gradually become an important factor affecting their resource utilization,and they have also become an important factor threatening food security.This study selected large-scale pig farms and chicken farm wastes from Dongliao County,Liaoyuan City,Jilin Province as the research objects.The heavy metal copper(Cu),Zinc(Zn)of passivation and stabilization research was performed by adding different passivators and mixing them with corn stalks for aerobic composting.Through aerobic composting control experiments,adjusting composting conditions and optimizing harmless treatment process parameters,the high-efficiency heavy metal passivators were selected based on the changes of bioavailability of heavy metals,and the passivation and stabilization efficiencies of heavy metal were further optimized through outdoor composting.The study has established an optimized coupling technology system of heavy metal passivation stabilization and compost humification,and provided a basis for the resource utilization of livestock and poultry breeding waste.It is of great significance to improve the ecological environment in the source area of the Dongliao River,promote rural economic growth,increase farmers ’income,and achieve sustainable agricultural development.The main results are as follows:Using calcium magnesium phosphate,bentonite and fly ash as passivating agents significantly reduced the bioavailability of heavy metals Cu and Zn in pig manure and chicken manure compost.When the addition amounts of calcium magnesium phosphate fertilizer,bentonite,and fly ash were 5%,3%-4%,and 3% respectively,the Cu in the compost had highest passivation rates with 46%-52%,47%-55%,and48%-51%,respectively;when the addition amounts were 5%,5%,and 4%-5%,respectively,the Zn had highest passivation rates with 57%-58%,48%-54%,and48%-60%,respectively.In outdoor composting,using the bentonite as a passivating agent and compound addition with modified or unmodified biochar could passivate and stabilize the Cu and Zn in the compost..After acid-base modification of biochar,the passivation efficiencies were significantly improved.The passivation rates of Cu and Zn reached to 48%-60% and 60%-68%,respectively.The passivation effect of passivator on heavy metals was verified through freeze-thaw cycle processing or lower the p H.The effects of freeze-thaw cycles on Cu were as follows: fly ash treatment>bentonite treatment> calcium magnesium phosphate fertilizer treatment> no passivation agent treatment.When the moisture content was 150%,the bioavailability of heavy metals was reduced by more than 10%,and the effect on Zn was small,which proves that the freeze-thaw cycle will weaken the passivation effect of the passivator.on Cu.Within the soil p H range in Northeast China,the bioavailability of Cu and Zn was basically unchanged.Therefore,in areas with rainy and snowy weather,more attention should be paid to the influence of freeze-thaw cycles on the passivation effect.