The Effects Of Passivators And Vermicomposting On Fractionations Of Cu,Zn And Land Application Of Vermicompost

This research focused on the effects of passivator and vermicomposting on fractionation of heavy metals(Cu and Zn)and their bioavailability during swine manure vermicomposting and land application vermicompost swine manure.In our experiment treatments,calcium-magnesium phosphate,bentonite,biochar,enzymes,EM bacteria,fly ash and zeolite were added to the swine manure as heavy metal passivators,while vermicomposting treatment without passivator was set as control.Our results indicated that:(1)Biochar,enzymes,EM bacteria,fly ash and zeolite treatments had a passivation effect on Cu fractionation.Meanwhile the bioavailable Cu was converted into immobilized Cu,and there was a significant difference between the treatmented group and the control(p<0.05);Biochar,enzymes and bentonitead a passivation effect on Zn fractionation.In terms of the distribution rates of available Cu and Zn,biochar was considered as the best passivator with up to 42.34%reduction of the distribution rate of available Cu,and up to 2.7%reduction of the distribution rate of available Zn.Enzymes were considered as the best passivator for available Zn(p<0.05)with a maximum reduction(3.77%)of the distribution rate.(2)The concentrations of various Cu forms in each fraction for the vermicompost swine manure were in the order of oxidizable Cu>residual Cu>reducible Cu>exchangeable Cu,while the concentrations of various Zn forms followed the order of exchangeable Zn>reducible Zn>oxidizable Zn>residual Zn.Oxidizied Cu was the dominant specie for Cu with a fraction up to 50%,while exchangeable and reduced Zn were the dominant species for Zn(>80%)in the vermicompost swine manure.Based on the BCR sequential specie analysis,the bioavailability of Cu and Zn decreased after vermicomposting.Passivators differed in their effect on the bioavailability of Cu and Zn:Zn was mostly available while Cu was mostly unavailable to plants after vermicomposting.Therefore,more attention should be paid to the risk of environmental pollution caused by Zn in compost application.(3)Pot experiments showed that,the biomass of pakchoi significantly increased by the application of vermicompost swine manure and the optimal additional amount of vermicompost manure was 1/3 of the soil mass(1/3M).The concentrations of Cu and Zn in the roots of pakchoi were higher than those in the stems and leaves.The concentrations of Cu and Zn in the treated soil decreased by 27.31%and 20.93%,respectively,in the 1/3M treatment.Indexes and levels of geo-accumulation of heavy metals in soils revealed that excessive application of manure may pose slight risk of Cu polluation but severe risk of Zn pollution.This research provided theoretical and technical information on vermicomposting of swine manure,which is of great significance to pollution prevention and risk management for heavy metals in land application of swine manure.