Treating mechanical washing wastewater with iron-in-oil characteristics by changing the fate of iron

Abstract

The mechanical washing wastewater contained a large amount of oil, and the iron wrapped in the oil was slowly released into water. This caused the effluent quality to fluctuate, causing common polymeric aluminum chloride (PAC) to ineffectively remove the water-in-oil. The method uses Ca2+ to demulsify and ClOx− to destroy the water-in-oil structure, which releases Fe from the oil droplets. The active oxygen produced by NaClOx further converts Fe2+ into Fe3+ and then combines with NaOH to form Fe(OH)3-flocs core, which improves the flocculation efficiency of PAC. The optimal ratio was approximately 400 μL of NaClOx, 200 μL of 1 mol L−1 CaO, and 12 mL of 12.8 g L−1 PAC. The oil removal rate reached 99.88% and the residue density was 178.42 mg L−1. The maximum Fe and chemical oxygen demand (COD) removal rates were close to 49.2 and 99.89%, respectively. In field applications, wastewater should be acidified first, and acidification oxidation is more effective than direct oxidation. In short, a novel way for treating mechanically washed wastewater with iron-in-oil characteristics by changing the environmental fate of iron is provided. HIGHLIGHTS 49.2% of Fe and 99.89% of COD were removed by NaClOx + CaO + PAC.; The optimal ratio was 400 μL of NaClOx, 200 μL of 1 mol L−1 CaO, and 12 mL of 12.8 g L−1 PAC.; NaClOx destroys the water-in-oil and alters the environmental fate of Fe to Fe(OH)3 for promoting flocculation.; Acidification prior to NaClOx oxidation benefits the removal of COD and iron.;

Keywords

• coagulation–flocculation
• fate of fe
• mechanical washing wastewater
• naclox
• water-in-oil structure