Investigation of microplastic removal from greywater by coagulation and dissolved air flotation

Microplastics (MPs) have recently become a controversial issue, mainly due to their eco-toxicological effects on aquatic environments. Although a typical wastewater treatment plant (WWTP) removes a large number of MPs from the wastewaters, final effluents are yet considered to be the primary sources of MP contaminations into the environment. Hence, there should be a tertiary treatment called advanced wastewater treatment technology for efficient MP removal. In the current research, Al-based and Febased coagulants were used in a dissolved air flotation (DAF) cell as an advanced wastewater treatment technology to remove polyethylene (PE) MPs from greywater, which is one of the most predominant types of MPs found in the greywater. PE reduction up to 96.10 % and 70.56 % were observed for Al- and Fe-based coagulants, respectively. The operative parameters, including pressure, pH, coagulant dosage, and water flow rate into the flotation cell, were identified. The experimental design was developed using DesignExpert software to investigate and maximize the PE removal efficiency. As a result, some sufficiently accurate statistical models were proposed to obtain the optimum quantities of the respective factors. It was determined that the most effective removal was achieved with 5.95 bar saturation pressure, pH 6, 14.46 mg/L coagulant concentration, and 680.5 mL/min water flow rate into the flotation cell using AlCl3.6H2O as the coagulant. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

Microplastics have raised concerns for their eco-toxicological effects on aquatic environments. While wastewater treatment plants remove a large number of microplastics, final effluents are still considered the main source of contamination. Advanced wastewater treatment technologies such as using aluminum and iron-based coagulants in dissolved air flotation cells have been shown to effectively remove polyethylene microplastics from greywater.