Treatment of waste cutting fluid by coagulation-anaerobic hydrolysis (with or without cosubstrate glucose)-aeration process

Abstract

A coagulation-anaerobic hydrolysis-aeration process was used to treat the waste cutting fluid, which was discharged from a metalworking plant, and the operating conditions of each unit were optimized in this paper. The results showed that 9 g/L poly-aluminum chloride and 0.3 g/L cationic polyacrylamide were added in the coagulation stage, the TOC was removed by 78.94% and the BOD5/COD of the waste cutting fluid increased from 0.046 to 0.312 before and after coagulation. The coagulation effluent was further treated by anaerobic hydrolysis-aeration, and the TOC removal efficiencies of the biological process and the whole chemical-biological process were 92.77% and 98.48% respectively. Adding glucose as a cosubstrate into the anaerobic hydrolysis can improve the TOC removal efficiency; when the TOC content ratio of coagulation effluent to glucose solution was 7:3, the TOC removal efficiencies of the biological process and the chemical-biological process reached 97.16% and 99.40%, and the total oil removal efficiency of the whole process reached 99.99%. The effluent quality parameters of the coagu-lation-anaerobic hydrolysis (with cosubstrate glucose)-aeration process met the Class C limits specified in the Wastewater Quality Standards for Discharge to Municipal Sewers (GB/T 31962-2015); that is, the effluent COD, TN, TP and total oil were below 300 mg/L, 25 mg/L, 5 mg/L and 110 mg/L, respectively, and the effluent pH was between 6.5–9.5.