Research on the removal of chemical oxygen demand and surfactants from commercial laundry wastewater by the coagulation-flocculation process

Abstract

Wastewater from public commercial laundry facilities has significantly higher concentrations of chemical oxygen demand (COD) and total surfactant concentration compared to domestic wastewater. As the number of these facilities increases, the volume of wastewater generated also rises, necessitating classification and treatment to meet standards before being discharged into the common drainage system. The Jartest experiment in this study demonstrates that poly aluminium chloride (PAC), under optimal conditions (pH 7; dosage of 60 mg/l), is more effective than FeSO₄·7H₂O for treating commercial laundry wastewater. Specifically, after treatment, the parameters total suspended solids (TSS), turbidity, and color all comply with the requirements of column A of QCVN 40:2011/ BTNMT. Although the COD concentration post-treatment remains elevated (341 mg/l), PAC has significantly reduced non-biodegradable organic substances and improved the five-day biochemical oxygen demand/chemical oxygen demand (BOD₅/COD) ratio to 0.52, facilitating subsequent biological treatment processes. Notably, the close correlation between COD removal and total surfactants indicates that the coagulation-flocculation mechanism, along with the micelle adsorption mechanism, aids in reducing the concentration of surfactants, nearly achieving the standard of column B of QCVN 40:2011.