Synthesis of a New Flocculant from Waste Polystyrene: Plastic Recycling Industry Wastewater Treatability

Abstract

HDPE (high-density polyethylene), LDPE (low-density polyethylene), PET (polyethylene terephthalate), and PP (polypropylene) plastic washing wastewater contains high concentrations of turbidity, COD (chemical oxygen demand), SS (suspended solids), and oil grease that lead to an increase in the pollution load of the wastewater treatment plant. Plastics washed in plastic recycling plants produce large volumes of wastewater. In this study, the use of sulfonated polystyrene as a flocculant for the treatment of these wastewaters, which is not found in the literature, was studied. A flocculant was synthesized from waste polystyrene (FSPS) by sulfonation, by cyclohexane, H2SO4, and P2O5 modification. This flocculant was used in the coagulation-flocculation treatment of plastic washing wastewater. Turbidity, COD, SS, and oil grease were determined for the supernatant. Effects of pH were studied at pH 3-13 intervals. Alum and FeCl3 were used as conventional coagulants at 15-1000 mg/L doses. The FSPS and polyelectrolyte (PEL) were used as flocculants at between 5 and 50 mg/L dosage. For HDPE washing wastewater (FeCl3 + FSPS), turbidity, COD, SS, and oil grease removal efficiencies are 96%, 92%, 86%, and 50%, respectively. For LDPE washing wastewater (FeCl3 + FSPS), turbidity, COD, SS, and oil grease removal efficiencies are 99%, 60%, 35%, and 75%, respectively. For PET washing wastewater (alum + FSPS), turbidity, COD, SS, and oil grease removal efficiencies are 94%, 70%, 99%, and 55%, respectively. For PP washing wastewater (alum + FSPS), turbidity, COD, SS, and oil grease removal efficiencies are 98%, 82%, 93%, and 89%, respectively. It was observed that treatment of synthesized FSPS flocculant resulted in higher or similar results of PEL.