Optimizing biological effluent organic matter removal for subsequent micropollutant removal

K Van Gijn,Y.L Chen,B Van Oudheusden,S Gong,H.A De Wilt,H.H.M Rijnaarts,A.A.M Langenhoff

doi:10.1016/j.jece.2021.106247

Abstract

Wastewater treatment plant effluent is an important point source for micropollutants emissions into the environment. These micropollutants can pose risks for ecosystems and humans; therefore, wastewater treatment plants should be upgraded to improve their micropollutant removal. Micropollutant removal can be improved by implementing tertiary treatment such as ozonation or activated carbon filtration. However, organic matter in the wastewater treatment plant effluent interferes with the micropollutant removal in these tertiary treatments, resulting in high energy demand and costs. To decrease the energy demand of tertiary treatment, biological pre-treatment can be introduced to remove effluent organic matter in an energy efficient manner. This biological pre-treatment was optimized by comparing three types of bioreactors; biological activated carbon, sand filter, and moving bed bioreactor. The reactors were operated at five flow rates (0.25, 0.5, 1, 2 and 4 L/h) in a continuous setup. The biological activated carbon filter achieved higher effluent organic matter removal than the sand filter and moving bed bioreactor (up to 72%, 41%, and 21% respectively). Additionally, effluent organic matter removal was negatively correlated to the flow rate in the biological activated carbon filter and the sand filter. The biological activated carbon filter also achieved average removal of 85% for the 18 analyzed micropollutants, although how long this high micropollutant removal can be sustained is unclear. To conclude, the biological activated carbon filter as pre-treatment can achieve high effluent organic matter removal, which would decreases the energy demand and cost of subsequent treatment for micropollutant removal.

Highlights

The occurrence of micropollutants (MPs), such as pharmaceuticals, personal care products, pesticides and industrial chemicals, is a growing global concern [1,2,3]
TOC is commonly used as guiding param eter in tertiary treatment, while UV254 absorbance and chemical oxygen demand (COD) can give more insight into the complexity of the effluent organic matter (EfOM) [36,37]
Results of our study indicate that biological activated carbon filters (BAC) is a promising technology to remove organic matter (OM) from WWTP effluent

Summary

Introduction

The occurrence of micropollutants (MPs), such as pharmaceuticals, personal care products, pesticides and industrial chemicals, is a growing global concern [1,2,3]. MPs occur in fresh and saline water systems at concentrations ranging from ng to μg/L. Despite their low concentra tions, toxicological risks of MPs are of concern for three reasons: the vast amount of compounds, synergistic mixture effects, and chronic or long term exposure. Every MP can be broken down by biological, chemical or physical processes, forming transformation products (TPs) that are sometimes difficult to mineralize into carbon dioxide and water [5,6,7,8]. Assessing the long term toxicological risk of a complex envi ronmental mixture with a large number MPs and TPs is difficult, because most available toxicological information is related to individual com pounds and short term effects [11,12,13,14]. Due to the widespread occur rence of MPs and the uncertainties related to their toxicological risks the precautionary principle should be applied to reduce emissions of MPs into the environment [15]

Methods

Results

Conclusion