The Risk Assessment And Treatment Of Industrial Heavy-metal Wastewater Ponds

Industry of China developed at high speed in recent years.Many factories discharged wastewater without treatment,which caused industrial wastewater ponds.Acid heavy-metal wastewater ponds pose a huge and permanent threat to ecological environment and human being’s health.This paper investigated three ponds in Tianjin and evaluated the risk.We also proposed treatment methods according to experiments.The pH of Pond A wastewater was 2.5.The average concentrations of Cl^-,Fe,Zn,Mn,Pb in the wastewater were respectively 20 g/L,1250 mg/L,40 mg/L,40 mg/L,0.1 mg/L.In the soil,C_Fe was 28000 mg/kg.Those of Pb,Ni and As were all 30mg/kg.Carcinogenic risk and non-carcinogenic risk of As,non-carcinogenic risk of Pb,total carcinogenic risk and total non-carcinogenic risk all exceeded the acceptable level.The total ecological risk was extremely strong.The pH of Pond B wastewater was 2.5.The average concentrations of Cl^-,Fe,Mn,Zn,Pb in the wastewater were respectively 18 g/L,2600 mg/L,35 mg/L,10mg/L,0.17 mg/L,0.10 mg/L.In the soil,those of Fe and Pb were respectively 16500mg/kg and 22 mg/L.Carcinogenic risk of As,total carcinogenic risk both exceeded the acceptable level.The total ecological risk was middle level.The H⁺concentration in Pond C wastewater was 10 mg/L.The average concentrations of Cl^-,Fe and Cr were respectively 50 g/L,3000 mg/L,20 mg/L.Those of Pb,Ni and Cu all were 1.10 mg/L.TOC was 500 mg/L.In the soil,those of Fe and Cr were 21000 mg/kg and 200 mg/L.Those of Pb and Ni in the soil were all50 mg/kg.Carcinogenic risk of As,total carcinogenic risk and total non-carcinogenic risk all exceeded the acceptable level.The total ecological risk was extremely strong.We added 2.00 g/L NaOH or 3.00 g/L CaO as a neutralizing agent into wastewater（pH=2.5）,making pH of reaction mixture 8.0⁹.0.Effluent pH will be7.0⁸.0,C_Fe,C_Zn and C_Mn will all decrease to 2.00 mg/L,and C_Pb will decrease to0.10 mg/L,reaching the codes.