Sorption Of Typical Pharmaceutically Active Compounds To Wheat Straw-derived Biochars

Pharmaceutically active compounds（PhACs）are a group of emerging organic pollutants that have potential environmental risks.Biochar can be used as a stabilizer to control the transport of organic pollutants from soil to groundwater.In this study,two wheat straw-derived biochars at 300°C（WS300）and 700°C（WS700）were produced by pyrolyzing feedstock under oxygen-limited conditions.Four typical PhACs（ketoprofen（KTP）,triclosan（TCS）,atenolol（ATL）and carbamazepine（CBZ））with different dissociation properties were selected as sorbates.Sorption of different species of the PhACs to biochars（with varying carbonization degrees）and biochar-amended soil as affected by dissolved organic matter fractions was investigated by batch experiments and microscopic characterization.The main conclusions are as follows:（1）Dissociation of KTP and TCS reduced their sorption to the negatively charged biochar surfaces due to the formation of hydrophilic anionic species.π-πinteractions are the main mechanisms in sorption of KTP and TCS to biochars.Partition of neutral species of KTP and TCS in WS300 can also occur.WS700 with higher specific surface area and total pore volume had higher sorption coefficient（K_d）for KTP and TCS than WS300.In bisolute system,KTP and TCS competed for the sorption sites on carbonized organic matter of WS300 and WS700（in a molar ratio of1:1）.TCS was more competitive than KTP because of its higher hydrophobicity.（2）Hydrophobic acid（HoA）fraction(30 mg L^-1)of dissolved organic matter inhibited KTP sorption to biochars due to its competition with KTP on sites of biochars.The inhibitory role of HoA was more obvious on WS300 than that on WS700 because of the fewer sorption sites of WS300.Solubility of KTP decreased（22%）in the presence of hydrophilic neutral（HiN）fraction(30 mg L^-1)of dissolved organic matter.The decreased solubility of KTP by HiN exerted a more dominant influence than the competition between HiN and KTP,leading to apparent enhanced KTP sorption to biochars.Sorption enhancement of KTP was more obvious on WS700 than that on WS300 because WS700 contained more sorption sites.（3）Sorption affinity of different species of PhACs to loessial soil and biochars followed the order:ATL（cationic）>CBZ（neutral）>KTP（anionic）.The sorption capacity for KTP,ATL and CBZ was enhanced by soil amended with biochars（especially WS700）at a mass ratio of 5%.Competitive sorption of KTP,ATL and CBZ on WS700-amended soil occurred when each two of them coexisted in solution,which led to the smaller K_d values than those in single solute system.Even so,the K_d values of KTP,ATL and CBZ to WS700-amended soil in both single solute and bisolute systems were higher than those on soil.The experimental results indicated that addition of WS700 can effectively control the transport of KTP,ATL and CBZ from soil to groundwater.