Coagulation and Flocculation before Primary Clarification as Efficient Solutions for Low-Density Microplastic Removal from Wastewater

Abstract

Microplastic (MP) removal from wastewater was investigated using various types and doses of commercial coagulants (PIX, PAX) and flocculants (FPM, PEL, FCT) before primary clarification in a wastewater treatment plant (WWTP). Dosing with FPM, PIX, and PEL caused small MPs (180–212 µm) to be transferred mainly to the settled sludge (up to 86.4% of MP at a dose of 5 mL FMP/m3), while dosing of FCT and PAX caused these MPs to be transferred to the floated sludge (up to 64% MP at a dose of 5 mL PAX/m3). The efficiency of MP removal from wastewater was the highest (90%) with 2.5 mL PAX/m3; the generated primary sludge had a low MP content and could be safely managed in subsequent stages of sludge treatment. At the highest doses, PIX significantly increased the removal of P-PO4 (up to 94%) and COD (up to 73%). FPM and FCT resulted in over 40% efficiency of ammonium removal—such disturbance in wastewater composition may negatively affect further biological treatment. Effective removal of MP in the mechanical part of WWTP resulting from coagulation and flocculation enables the safe use of the excess sludge for agricultural purposes.