Changes Of Heavy Metal Speciation And Analysis On Contributing Factors Of Maturity During The Pig Manure And Straw Co-composting

Due to the excessive addition of heavy metal elements in feed,the livestock manure contains a variety of pathogenic microorganisms and carries a large of heavy metal elements that were not absorbed.The soil heavy metals content were above the national standard when entered the soil with the abuse of manure.The heavy metal may be allowed greater absorption of the plants and through food chain into the body to cause chronic poisoning.Composting is an effective way for reducing,harmless and resource utilization of livestock and poultry manure.The changes of the compost maturity,the concentration and chemical morphology of heavy metals(Cu,Zn)during pig manure and straw co-composting were researched in the paper.The correlation and influence mechanism between the physical and chemical parameters and the compost maturity in the composting were analyzed through the Redundancy analysis,Monte Carlo test and Pearson correlation.We attempt to clarify the changes of heavy metal speciation and the influencing factors of composting maturity to provide technical support for the subsequent composting.The main research results of research are as follows:(1)At the end of composting,the high temperature duration of the composting was more than 8d,which satisfys the temperature requirements of “the Hygienic Standard for Hazardous Feces GB7959-2012”.The organic matter content and total nitrogen(TN)content decreased by 48.69% and 18.4%,respectively.During the composting,the carbon nitrogen(C/N)ratio always showed a downward trend,while the germination index(GI)kept an increasing trend.At the end of composting,the C/N ratio was 15.55 and the GI was 102.3%,which met the requirement of compost maturity.(2)The content of humic substances(HE)and humic acid(HA)increased by22.79% and 464.51%,respectively and fulvic acid(FA)content decreased by 66.72%when the composting is over.According to the increasing degree of humification and humus structure,it is showed that microorganisms degraded organic matter into small molecular organic matter,condensed fulvic acid,then synthesized more stable humic acid through the condensation polymerization reaction of microorganisms in pig manure composting.And humic acid is the main component of humus.Compared with pre-composting,the molecular weight,condensation and aromatization degree of humic acid were lower with the composting,which indicated that the nutrients were more easily absorbed into the soil.(3)Due to the "concentration effect" of heavy metals,Cu and Zn concentration increased by 33.15% and 37.02%,respectively after composting.The distribution rates of non-bioavailability Cu and Zn increased by 11.85% and 3.3% respectively.The decrease rates of BF-Cu and BF-Zn were 39.13% and 5.56%,respectively.The results showed that the composting could stabilize the bioavailable state of heavy metals and reduced their fluidity and biotoxicity.However,the change of the bioavailable state of Zn is relatively small.(4)According to the redundancy analysis,the seven environmental factors which selected for the analysis indicated the important factors affected the changes.They could account for the 99.9% variation of different evaluation indexes for maturity,Monte Carlo test showed that organic matter,TN,HA,FA and HE can change the maturity significantly.According to the two-dimensional sorting diagram of RDA and Pearson correlation analysis,it could promote the stability of heavy metals,reduce the portability and bioavailability of heavy metals in the compost and effectively improve the degree of compost decay when the organic matter convert to humus as much as possible,especially increase HA in humus during the composting.