Removal Of Multiple Contaminants From Water By Modified-biochar Derived From Cassava Dregs

Water pollution caused by heavy metals and antibiotics has posed a potential threat to aquatic organisms and human health.However,Numerous studies focus on the removal of single heavy metals and antibiotics.Less attention is paid to the highly mixed characteristics of contaminants in water,which makes it difficult for many technologies to apply in practice.Therefore,the attention and exploration on the removal of pollutants in compound polluted water is beneficial to the practical application of pollution control technology.In addition,biochar derived from agricultural and forestry wastes are used as adsorbents,which can effectively reduce the waste of resources and obtain cost-effective adsorption materials.Furthermore,the enhanced surface properties of biochar can be got by modification,and the modified biochar promotes the adsorption of heavy metals and antibiotics in water,which can achieve a win-win of ecological and economic.In this study,cassava residue,a common agricultural waste,was selected as raw material to prepare biochar(CW)by slow pyrolysis,and modified by soaking CW in KOH and NH4CI solutions.The modified biochars(KCW and NCW)had stronger adsorption abilities and its physio-chemical properties were characterized.The removal ability of modified biochars for ternary-solutes systems of heavy metals(Cu2+,Cd2+ and Ni2+),ternary antibiotics(norfloxacin(NOR),sulfamerazine(SMR)and oxytetracycline(OTC)),and binary-solutes systems of single heavy metal and antibiotic(Cu2+-OTC and Cd2+-OTC)in the water,and their competitive adsorption mechanisms were studied.The main conclusions of this study are as follow:The specific surface area and CEC of biochar were enhanced by chemical modification.The KOH modified biochar has higher pH value and ash content,while the results of the NH4CI modified biochar are opposite.The surface of modified biochars was rougher and the pore size of the modified biochars was reduced.The surface of the biochars(CW,KCW and NCW)was negatively charged,and the numbers of oxygen functional groups on the surface of biochars were increased by the two kinds of chemical modification.KCW showed significantly higher adsorption capacities for Cue+,Cd2+ and Ni2+ than CW.For the temary-heavy-metals system,the competitive effect was found on the surface of CW and KCW with multiple reactions,and the adsorption rate was higher than the single system.The Langmuir model was best suited to describe the isotherm adsorption process with r2>0.90.Electrostatic interaction was the main mechanism for the adsorption of the three heavy metals.The increase of pH may promote the adsorption by enhancing the complexation between heavy metal ions and OH-,while the weak alkali conditions could inhibit the adsorption of Ni2+.For antibiotics,kinetics results highlighted that the sorption process had a fast initial sorption phase,which was followed by slower sorption processes.The adsorption process in the ternary-solute system was relatively single,and only the pseudo-second-order model fit well.Among the three biochars,KCW had the highest sorption capacities for NOR(96.5%)and OTC(96.2%),NCW had the highest sorption capacity for SMR(81.4%).The Langmuir model was better fit for the adsorption of NOR,while both the Freundlich and Langmuir models were fit for that of SMR and OTC.All the adsorption of the three biochars was a spontaneous endothermic process,and the increase of the temperature enhanced the process.Electrostatic interaction was the main mechanism for NOR,SMR and OTC sorption on CW and NCW.However,in the case of antibiotic sorption on the KCW in mixed solution,?-? interaction and H-bonding were considered as the potential mechanisms.For Cu2+-OTC or Cd2+-OTC system,contaminants sorption on CW and KCW were influenced by the concentration of them.High concentration of Cu2+or OTC increased the competition between Cu2+ and OTC.At a low level of Cu2+or OTC,Cu2+ acted as cationic bridge to promote the adsorption of OTC,but the competition on KCW was not significant.For Cd2+-OTC system,high concentration of Cd2+(OTC)inhibited the adsorption of OTC(Cd2+).The sorption of Cd2+ on KCW was enhanced by a moderate increase of OTC concentration.