Partitioning of removal of microplastics and other anthropogenic particles among influent, biosolids and final effluent in a tertiary wastewater treatment plant

Abstract

Influent, final effluent, biosolids, ultrafiltration membrane module inflow and outflow samples were collected in a tertiary wastewater treatment plant to enumerate and categorize anthropogenic particles, including microplastics in the 250 µm - 5 mm size fraction. Samples were digested with 50% hydrogen peroxide, filtered, and examined via microscopy at 40-50x magnification. Most (99%) anthropogenic particles were present in biosolids compared to final effluent (<1%), with fibres numerically dominating influent and final effluent, and fragments dominating biosolids and ultrafiltration inflow and outflow. Assessment of ultrafiltration (pore size = 0.02 µm) inflow and outflow before and after membrane deep cleaning and repair revealed high variability in source abundance and a general, yet non-significant reduction in particle counts in module permeate over 20 weeks. Removal techniques require assessment to explore effective options to mitigate the potential impacts, particularly to freshwater environments, of anthropogenic microparticle release. Our data reveal the utility of quantification and removal options for anthropogenic particles in wastewater treatment plants as they are conduits between municipal and industrial wastewater sources and freshwater and terrestrial receiving environments.