Effect of different excipients on passivation of heavy metals in pig manure composting
Dehydrated pig manure from a large-scale pig farm was utilized as the primary composting material,and a self-made aerobic composting device was employed to investigate the effects of 3%superphosphate,3%humus and 5%bentonite on the morphological changes and passivation effect of heavy metals during the composting process.The findings revealed that among the heavy metals in pig manure samples,Zn had the highest content,followed by Cu,Cr,Pb and Cd.Notably,before composting treatment,the contents of available Pb and available Zn were high,accounting for 15.48%-40.30%and 19.17%-34.58%of the total contents of Pb and Zn,respectively.Moreover,post-composting analysis demonstrated that organic matter content ranged between 50%and 60%,total P ranged between 0.64%and 0.98%,pH remained stable within the range of 6.80-7.40,and EC value was lower than 4 mS/cm,which met mature composting standards.The concentration of heavy metals in each treatment increased by 7.91%-157.90%,compared with before composting,showing an evident"relative concentration effect".Specifically,the total amount of Zn in CK treatment exceeded standard levels by 23.10%after composting.The addition of various excipients facilitated the overall transformation of heavy metals towards reduced effectiveness,although the passivation performance varied for each individual metal.The passivation rates of Cu and Zn by 3%humus were 52.11%and 32.11%,respectively,and the passivation effect was good.The passivation rates of Cr,Cd and Pb by compound ingredients(3%superphosphate+3%humus+5%bentonite)were 46.43%,47.05%and 51.76%,respectively.There was a certain correlation between the main physical and chemical parameters of compost and the availability of heavy metals.The Nemero composting products from each treatment remained low and within safe levels.
heavy metal passivationpig manurehumusbentonitecalcium perphosphate
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