Passivation Of Heavy Metals Of Copper And Zinc In Composts From Animal Manure

Along with the rapid development of animal breeding industry, the production of animal manure increased greatly, and the wide usage of feed additives containing trace elements (including Cu, Zn, etc.) resulted in the heavy metal pollution in the soil after land application of animal manure and endangered the safety of agricultural products. In order to reduce the biological effectiveness of heavy metals in animal manure and ensure the quality and safety of agricultural products, this study took the pig manure from a typical pig feeding plant in Shanghai suburbs as raw material mixed with the mushroom residues, and selected biochar, chemosorbent and microorganism as heavy metal passivators, to conduct an aerobic composting for 46 days. The effect of passivator additions on the physical and chemical properties (temperature, pH and moisture) during animal manure composting process, and the influence of land application of composts with different passivators on the copper and zinc contents in leafy vegetables (Chinese cabbage) and solanaceous vegetables (pepper) were studied. The passivator with better passivation effect was determined, according to the assessment of vegetables biomass, absorption coefficient of Cu and Zn, safety and passivator cost. The main results were as follows:1. During the composting process, all the piles had experienced the stages of temperature rising, high temperature keeping, temperature decreasing and maturity stability, and maintained above 55? more than 10 days, which reached the standard of non-hazardous treatment. The piles with the additions of biochar, chemosorbent and microorganism performed longer period of high temperature. The pH values in all the piles appeared the tendency of increasing firstly then tending to be stable, and finally stabilized in the range from 8.45 to 9.00, which reached the composting maturity standard. The pH values had no significant difference in the piles with or without passivator addition. The moisture contents in all the piles gradually reduced during the composting process, and there were no significant influence on moisture contents in the piles with the additions of biochar and microorganism, while the moisture contents in the piles with the addition of chemosorbent were higher remarkably than the control after 14 days'composting. 2. The composting products with biochar treatment could reduce the adsorption and accumulation of Cu and Zn in the cabbage and pepper plants (stems, leaves and fruits), the S4 treatment (1.25% of biochar addition) reduced Zn contents in the cabbage and Cu and Zn contents in the pepper fruits and leaves significantly. The composting products with chemosorbent treatment could reduce the Zn contents in the pepper stems and leaves greatly. The composting products with microorganism treatment of W2 (1.00% of microorganism addition) and W3 (1.33% of microorganism addition) could reduce Cu and Zn contents in the pepper plant (stems, leaves and fruits) remarkably.3. The absorption coefficients of Cu in the cabbage were the lowest in the treatments of S1 (0.50% of biochar addition), S3 (1.00% of biochar addition) and W2, which were 0.88%, 0.82% and 0.85%, respectively. The absorption coefficients of Cu in the pepper fruits were the lowest in the treatment of SI, S4 and W2, which were 1.71%,1.61% and 1.73%, respectively, indicating better passivation effect on Cu. The absorption coefficients of Zn in the cabbage and pepper fruits in the treatment of S4 were the lowest, which were 2.60% and 1.09%, respectively, performing better passivation effect on Zn.4. The passivation effect of passivators on Cu and Zn showed that: biochar>microorganism>chemosorbent, and biochar was determined as a good passivator accoding to the comprehensive evaluation of biomass, passivation effect and passivator cost, in which S3 and S4 were the best.