Treatment of oily wastewater from metal processing by thermochemical decomposition process

Abstract

This paper investigates the treatment of oily wastewater (emulsions) originating from metal processing via thermochemical decomposition. The treatment aimed to purify the wastewater to meet the regulatory standards, that is, specifically targeting a hydrocarbon index concentration of less than 10 mg/l. Experimental investigations included testing the influence of flocculant addition, sulfuric acid dosage, temperature and process duration on applied treatment efficency. The results indicate that the addition of flocculants is not necessary. The optimal parameters for the thermochemical decomposition of oily wastewater are defined as: acid dosage of 2.4 g H2SO4/l of emulsion, process temperature of 90 ⁰C and a duration time of 24 hours. Under these optimal conditions, the hydrocarbon index was reduced to 1.89 mg/l. However, due to the resulting low pH value (1.6), an additional neutralization step to a pH range of 6-13 is required before discharging the purified water into the recipient.