Removal Of Diuron And Phosphorus From Surface Runoff By Mixing Sludge Based Biochar With Steel Sludge

Organic pesticides and phosphorus pollution exist in surface water.In this study,sludge based biochar was prepared from dewatered sludge after mesophiloic anaerobic digestion.The influence of pyrolysis temperature on the physicochemical properties of biochar was studied,and the adsorption characteristics and mechanisms of diuron on biochar were revealed.Bioretention tank is an important facility for controlling surface runoff pollution.Adding modifiers into the packing layer of bioretention tank could realize the simultaneous removal of various pollutants.Steel sludge had excellent adsorption performance for phosphorus.To simulate the simultaneous removal of organic pesticides and phosphorus by bioretention tank,the sludge based biochar and steel sludge were mixed as the modifiers of sand based filter column fillers,and the simultaneous removal performance of diuron and phosphorus on sand based filter column was explored,which provided basis for strengthening bioretention to remove organic pesticides and phosphorus pollution in surface runoff.Sludge based biochar was prepared at pyrolysis temperatures of 400,500,600,700 ℃,named as SBBC-400,SBBC-500,SBBC-600,SBBC-700 respectively.With the increase of pyrolysis temperature,the yield of biochar decreased,the bulk structure of biochar surface decreased,the slit pores increased,the content of C decreased,and the content of metal oxides increased.The average pore size of biochar decreased with increasing pyrolysis temperature,but the specific surface area did not change with pyrolysis temperature.The surface of biochar was rich in oxygen-containing functional groups.Hydrogen bonds formed between oxygen-containing functional groups such as O-H and C-O and diuron molecules were the main adsorption forces.In addition,π-π conjugated bond and hydrophobicity also contributed to adsorption.The sludge based biochar prepared at high temperature had better adsorption performance for diuron,and the removal rate of SRBB-700 to diuron could reach94.94%.When the initial concentration of diuron was 3 mg/L,the optimal biochar dosage was 2 g/L,and the optimal reaction time was 6 h.The Langmuir model fitted the adsorption process best,and the adsorption was mainly on the single molecular layer of homogeneous surface.The maximum theoretical adsorption capacity of SBBC-500,SBBC-600 and SBBC-700 was 3.20,4.53,5.45 mg/g,respectively.A sand based filter column was set up,and SBBC-700 was mixed with steel sludge as the modifiers of sand based filter column fillers.It was found that the breakthrough time and exhaustion time of the column were prolonged with the increase of modifiers mass,but shortened with the increase of initial solution concentration and hydraulic loading rate.When the volume ratio of sludge based biochar and steel sludge was 0.22% and 0.35%,the maximum removal rate of diuron and phosphorus by sand based filter column was 66.39% and 47.37%,respectively.The addition of modifiers could significantly improve the adsorption capacity of diuron and phosphorus on sand based filter column,adsorption was the dominant step.The sludge based biochar and steel sludge can be used as modifiers for bioretention to alleviate organic pesticides and phosphorus pollution in surface runoff.