Effects Of Biochar On The Adsorption/Desorption And The Potential Mobility Of PAEs And Heavy Metals In Soils

Nowadays,facility agriculture is being quickly adopted in China,and plays a very important role in our country's agriculture development.The wide uses of plastic products such as mulching film and roofing material for facility agriculture have contributed to complex contamination of soils with heavy metals and emerging organic pollutants such as phthalic acid esters(PAEs).The co-occurrence of heavy metals and emerging organic pollutants in soils is an issue of great concern affecting human health and ecosystems.Previous studies showed that biochar may be used as adsorbent for adsorption of heavy metals and PAEs,and subsequently reduce their mobility in contaminated soils.In this study,biochars derived from dead pig(PB),chinar sawdust(CB),and bamboo sawdust(BB)were pyrolyzed at 650 oC.We investigated the effects of biochar application rates(0,0.5%,1%),biochar type and interaction on the abilities of adsorption and desorption,and the potential mobility of PAEs and heavy metals in co-contaminated soils(high and low organic carbon content).A batch adsorption/desorption experiment was carried out to determine the factors affecting the immobilization of DEP,Cd,and Zn by biochars in soils.In addition,a laboratory leaching study was conducted to evaluate the effect of BB and PB on the leachability of DBP,Cd,and Pb through soil columns packed with two soils with low or high organic carbon content(LOC;0.35% C: HOC;2.24% C)and spiked with DBP,Cd,and Pb.The main results are as following.(1)Adding of biochar to soil could significantly(P<0.05)increase the p H,EC,CEC,and TOC of soils,especially in the soil with low organic carbon content.Results show that Freundlich adsorption equation could well describe the isothermal adsorption/desorption processes of DEP,while the adsorption/desorption isotherm datas of Cd and Zn obeyed the Langmuir model.The organic carbon significantly affected the DEP,Cd,and Zn adsorption/desorption in soils.Application of PB and CB significantly(P<0.05)enhanced the adsorption capacity of the DEP and Zn,and reduced the desorption of DEP and Zn;nevertheless,there was no significant effect on Cd.The ability of soil to adsorb DEP and Zn increased with biochar application rates,especially the PB.The competitive adsorption among DEP,Cd,and Pb reduced the adsorption capacity of DEP,and increased the desorption extent of DEP in soils.(2)Application of PB to the LOC soil significantly(P<0.05)reduced the leaching loss by up to 88% for DBP,38% for Cd,and 71% for Pb,whereas its impact was insignificant in the HOC soil.The higher efficacy of PB in reducing the leaching of DBP,Cd,and Pb in the LOC soil than that of BB might be related to PB's higher specific surface area,surface alkalinity,p H,and mineral contents compared to those of BB.Co-contamination of Cd and Pb enhanced leaching of DBP in the LOC soil treated with PB,possibly by competition for the sorption sites.Leaching of DBP,Cd,and Pb were significantly(P<0.05)higher in the LOC soil than in the HOC soil.This study revealed that the effectiveness of biochars was dependent on the soil organic carbon content.In conclusion,pig biochar could enhance the soils adsorption capacity of PAEs and heavy metals and reduce the leachability.Co-contamination of Cd,Zn,and Pb reduced the adsorption capacity of DEP and DBP,and enhanced the desorption and eluviation of PAEs in soils,especially in the soil with low organic carbon content.Application of pig biochar to the soil was effective in immobilization of PAEs and heavy metals and reduced those leaching risk.