Study On The Preparation Of Sludge-derived Biochar And Its Effect On The Sorption And Degradation Of Carbendazim In Soil

Biochar,an emerging soil amendment,has been received an increasing attention all over the world due to its unique physicochemical properties and potential application in environmental remediation.In the present study,we used the municipal sludge as raw material to prepare sludge-based biochar with different pyrolysis temperatures（100-700℃）,and then characterize the properties of these biochars.The sorption-desorption behavior and degradation of typical pesticide carbendazim in soil by biochars was also explored,as compared to that of raw sludge and activated carbon.The main conclusions are as follows:（1）The physicochemical properties of biochar were varied with the pyrolysis temperatures.The results showed that the ash contents,pH,specific surface area and surface pore size of biochar increased with the pyrolysis temperature increased,whereas the content of carbon,hydrogen,oxygen and nitrogen,soluble K⁺,Ca²⁺and Mg²⁺,surface total acid functional groups,and surface oxygen functional group showed a decrease tendency.In addition,the contents of heavy metals in biochar varied with the metal species.For example,the contents of Cu²⁺、Zn²⁺、Pb²⁺increased with the pyrolysis temperature increased,whereas the contents of Cr²⁺、Cd²⁺decreased correspondingly.（2）The sorption of carbendazim in soil by biochar varied with the pyrolysis temperatures and ratios of biochar.The sorption-desorption behavior of carbendazim in soil was explored by biochars produced at different pyrolysis temperatures,in order to reveal their application potential in soil remediation as compared to the raw sewage sludge and activated carbon.The results indicated that the adsorption efficiency of carbendazim in soil by biochar increased with the pyrolysis temperature increased,whereas the desorption efficiency presented an opposite trend.For example,the highest adsorption efficiency of carbendazim was found in the biochar produced at 700°C（BC700）,which could be an irreversible sorption.Additionally,the sorption efficiency of carbendazim was elevated with the ratios of BC700increased,whereas the desorption efficiency decreased.As compared to the sorption behaviors of carbendazim by raw sewage sludge and activated carbon,the BC700 showed a higher sorption efficiency than raw sewage sludge but a lower sorption than activated carbon,implying that BC700 may be suitable for the soil remediation.Further studies on the sorption mechanism indicated that the partition effect may be the main mechanism for the sorption of carbendazim in soil by biochar.（3）The degradation of carbendazim in soil varied with the soil types and microorganisms,and the addition of biochar could alter the degradation because of the biochars produced at different pyrolysis temperatures and the ratio of amendments.The results showed that microorganisms in soil played an important role in the degradation of carbendazim,which the degradation half-life time increased from 20.9 days in non-sterilized soil to 61.1 days in sterilized soil.The degradation of carbendazim in soil were affected by biochars produced at different pyrolysis temperatures.For example,biochar produced at high temperature（such as BC700）could promote the degradation of carbendazim in soil,whereas the biochar produced at low temperature could have an inhibition effect on the carbendazim degradation.The appending ratio of BC700 had also affected the degradation of carbendazim in soil,which the degradation half-life time decreased from 30.3 days in 0.5%BC700 to 15.3 days in 10%BC700.