Potential Ecotoxicity Of Modified Composite Biochars And Its Control On Ecotoxicity Of Sediments Contaminated With Perfluorooctanoic Acid

Sediments are core components of aquatic ecosystems,which are not only the sink and source of various persistent organic pollutants.Consequently,the development of high-efficiency and low-cost in situ remediation technologies for polluted sediments is essential for protecting aquatic ecosystems.Biochar is an important green amendment for in situ remediation.However,the direct use of raw biochar as an adsorbent has some limitations such as limited adsorption capacity and poor adsorption selectivity,while modified biochar can significantly enhance or improve the adsorption capacity of pollutants.Recent attention has been mainly paid to modified biochar based on some single materials.A new modified composite biochar derived from activated sludge and biomass waste may not only facilitate maximum utilization of activated sludge but also improve the adsorption capacity of biochar.In this research,for the first time,KOH-or H₃PO₄-modified composite biochars were generated from corn straw and activated sludge through co-pyrolysis in different blending ratio at 650?,tested for adsorption properties,and characterized for physical and chemical properties.Among composite biochars,KCA82 had maximum adsorption capacity optimal adsorption capacity.Next,KCA82was selected as model absorbent,perfluorooctanoic acid?PFOA?was selected as targeted contaminant,and Bellamya aeruginosa was used as a test organism.A 30-day sediment bioassay by using sediments spiked with PFOA(10?g g^-1),and/or KCA82 with different particle size?100 mesh and 200 mesh?and different dosage?1%,3%and 5%?to investigate the potential ecotoxicity of KCA82 to B.aeruginosa and its control efficacy on the ecotoxicity of PFOA in the sediments.Our objects are to obtain the optimal process for preparing modified composite biochar based on corn stalks and activated sludge and optimized conditions for controlling the ecological toxicity of PFOA in sediments.This research may provide a scientific basis for the future application of modified composite biochar to remediate PFOA-contaminated sediments with and its formulation of long-term application to the contaminated environment.The results showed that the adsorption capacity of modified composite biochars were highly dependent on blending ratio of corn straw and activated sludge,type of modifier and modification method.Both KOH-modification and H₃PO₄-modification before carbonization could markedly enhance adsorption capacity of composite biochars,moreover,KOH-modification was more favorable to improve adsorption capacity than H₃PO₄-modification.Due to significantly improved surface texture,surface properties and increased oxygen-containing functional groups and aromaticity through KOH-modification before carbonization,the adsorption capacity of the composite biochars were significantly enhanced.However,modification after carbonization could not enhance adsorption capacity.The relatively high proportion of activated sludge in the composite was unfavorable to improve the adsorption capacity.The optimal blending ratio of corn straw vs activated sludge was 8:2?w:w?.Among the modified composite biochars,KCA82 has demonstrated the highest iodine value(900.20 mg g^-1)and adsorption capacity for MB(186.48 mg g^-1).The enhancement of KCA82 adsorption capacity was mainly ascribed to surface complexation,electrostatic attraction and surface properties.Therefore,KCA82 has the potential used as a high-efficiency adsorbent to remediate the polluted environment.The bioassay with sediments showed that,KCA82 could cause slightly DNA damage and oxidative stress in hepatopancreas of B.aeruginosa.Therefore,KCA82 has relatively lower ecotoxicity risk,and these effects were enhanced with the increase of KCA82 dosage,but did not depend on particle size.When exposed to sediments spiked only PFOA,significant PFOA accumulation in the visceral mass of B.aeruginosa and DNA damage and oxidative damage had been observed,and thus PFOA exhibited obvious toxicity to B.aeruginosa.When exposed to sediments contaminated with KCA82 and PFOA,KCA82 could significantly decreased the bioaccumulation of PFOA in the visceral mass of B.aeruginosa by markedly reducing the concentration of PFOA in the sediment interstitial water,consequently weakened the oxidative stress of PFOA to B.aeruginosa.Within the experimental concentration range?1%?5%?,the higher the proportion and the finer the particles of KCA82,the more significant the effectiveness of its controlling PFOA toxicity.Integrating above results including the toxicity of KCA82 to B.aeruginosa,its control efficacy on bioavailability,bioaccumulation and ecotoxicity of sediments contaminated with PFOA,and its potential preparation cost,it was suggested that appropriate KCA82 dosage in sediments should be 3%fine particles?200 mesh?.