Investigation of effective coagulants for oily wastewater treatment by coagulation method

One of the most important contaminants in water are oils. Within the scope of this study, effective coagulants in the treatment of oily wastewater by coagulation were investigated. In the study, aluminum sulfate, iron (III) sulfate and polyaluminum chloride, which are traditional coagulants, and chitosan, iron-grafted chitosan, cellulose, iron-grafted cellulose, activated cellulose by acids, aloe vera and waste paper were used as natural coagulants. In coagulation studies, pH and initial concentration are the main parameters examined. At the end of the treatment, turbidity, suspended solids amount (SS), chemical oxygen demand (COD), and oil recovery values were recorded. In studies conducted with aluminum sulfate, the best turbidity removal, COD removal and oil recovery (%), in 5 wt% oily wastewaters, were 99.6%, 97.99% and 72%, respectively, at pH 5 and 16000 mg/L dose has been obtained. For iron (III) sulfate, in 5 wt% oily wastewater, pH 4 and 30000 mg/L dose, turbidity removal was 97.4%; COD removal was achieved as 90.4% and oil recovery as 84.6%. High removal efficiency could not be achieved as a result of coagulation with polyaluminum chloride, cellulose, acid-activated cellulose, iron-grafted cellulose, iron-grafted chitosan and aloe vera. The best efficiency of natural coagulants was obtained with chitosan and waste paper (30 g/L solution-1 hour). The best turbidity and COD removal in 5 wt% oily wastewaters with chitosan was obtained as 99.89% and 96.2%, respectively, at pH 8 and 1000 mg/L dose of chitosan. The best turbidity, COD removal and oil recovery (%) was obtained with waste paper (30 g/L solution-1 hour; at pH 8.96 and 29000 mg/L dose) respectively as 93.1%, 95.9% and 77.1%. Two-stage coagulation was performed for 5 wt% oily wastewaters. Waste paper (30 g/L solution-1 hour) was applied in the first stage, followed by aluminum sulfate in the second stage, and a total of 77% oil recovery, 99.5% COD removal and 98.1% turbidity removal was achieved.