Effect Of Biochars On Adsorption And Desorption Of Phthalic Acid Esters In Soils

Phthalic acid esters (PAEs) are the most common plasticizers. They accumulate in soils throughusing plastic products such as agricultural film and plastic greenhouse roofing materials as well aswastewater discharge. Therefore, PAEs have been recognized as emerging soil organic pollutantsDiethyl phthalate (DEP）is one of the commonly used PAEs. When DEP is released to soils, it can betaken up by plants and enter to the human food chain.Biochar is the solid product from the pyrolysis ofbiomass residues from agricultural and forestry production. It is considered to have a great capacity foradsorption of organic pollutants. In this study, biochars derived from bamboo sawdust (BB) and rice straw(SB) were pyrolyzed at350°C,500°C and650°C. We investigated the effects of biochar application rates(0，0.1%，0.5%), biochar type and aging process of biochar (alternating wet and dry and humidistat) onthe adsorption ability of DEP in two vegetable garden soils (high and low organic carbon content). Theobjectives of this study were to understand the effect of biochar on DEP adsorption and desorptionhysteresis behaviors in soil, to clarify the effects of feedstock materials, pyrolysis temperatures andaging conditions on adsorption of DEP in soil and associated mechanisms, and to provide a theoreticalbasis for using biochar to remediate soils contaminated with DEP. The main results are as following.1. Soil with high organic carbon content had greater capacity for DEP adsorption than the soil with loworganic carbon content. Adding a small amount (0.1%) of biochar to soil can enhance the adsorptioncapacity of the DEP. The ability of soil to adsorb DEP increased with biochar application rates. Thepyrolysis temperature affected the adsorption capacity of biochar. For the straw biochar treated soils, theincrease of DEP adsorption followed the order350SB>500SB>650SB. However, for the bamboobiochars, the order was650BB>350BB>500BB. Compared to the untreated control soil with loworganic carbon, soil treated with0.5%650BB increased the adsorption capacity by4orders ofmagnitude. Feedstock material of biochar can also affect its adsorption capacity. Bamboo biochars weremore effective than the straw biochars in improving soils’ adsorption capacity and reducing thedesorption of DEP.2. A30-day alternating wet and dry aging treatment significantly (P<0.05) reduced the DEP adsorptioncapacity of biochar-treated soils, when they were compared with the fresh biochar treatments. Whenbiochar-treated soil was aged for30days under constant moisture, the adsorption capacity of the0.5%bamboo biochar and0.1%rice straw biochar treatments in the high organic carbon content soil was significantly (P<0.05) smaller than the corresponding fresh biochar treatments. There were nosignificant differences in adsorption capacity in other biochar treatments between the aged (underconstant moisture for30days) and fresh biochar treatments.. The reduction of adsorption capacity of thebiochar-treated soils was greater under the alternating wet and dry aging process than that underconstant moisture aging treatment.In conclusion, adding biochar to soil can enhance DEP adsorption to soil, and reduce the risk of DEPfrom leaching into the groundwater and entering the human food chain. Aging can reduce the DEPadsorption to soils treated with biochar, and the adsorption capacity was affected by different agingconditions.