A Pilot Study Combining Ultrafiltration with Ozonation for the Treatment of Secondary Urban Wastewater: Organic Micropollutants, Microbial Load and Biological Effects

Cátia A L Graça,Célia M Manaia,Joana Abreu-Silva,Sara Ribeirinho-Soares,Ana R Ribeiro,Olga C Nunes,Adrián M T Silva,Marcela A Segundo,Inês I Ramos,Sérgio M Castro-Silva

doi:10.3390/w12123458

Abstract

Ozonation followed by ultrafiltration (O3 + UF) was employed at pilot scale for the treatment of secondary urban wastewater, envisaging its safe reuse for crop irrigation. Chemical contaminants of emerging concern (CECs) and priority substances (PSs), microbial load, estrogenic activity, cell viability and cellular metabolic activity were measured before and immediately after O3 + UF treatment. The microbial load was also evaluated after one-week storage of the treated water to assess potential bacteria regrowth. Among the organic micropollutants detected, only citalopram and isoproturon were not removed below the limit of quantification. The treatment was also effective in the reduction in the bacterial loads considering current legislation in water quality for irrigation (i.e., in terms of enterobacteria and nematode eggs). However, after seven days of storage, total heterotrophs regrew to levels close to the initial, with the concomitant increase in the genes 16S rRNA and intI1. The assessment of biological effects revealed similar water quality before and after treatment, meaning that O3 + UF did not produce detectable toxic by-products. Thus, the findings of this study indicate that the wastewater treated with this technology comply with the water quality standards for irrigation, even when stored up to one week, although improvements must be made to minimise microbial overgrowth.

Highlights

Urban wastewater reuse is considered an important strategy when addressing water scarcity issues [1]
From the chemical organic micropollutants analysed in fresh (WW)
The results of this study indicate that UF performed after ozonation can be a suitable approach to allow the safe reuse of urban wastewater for irrigation

Summary

Introduction

Urban wastewater reuse is considered an important strategy when addressing water scarcity issues [1]. These new rules will be put into practice in 2023 and are expected to promote water reuse This regulation demands an established water reuse risk management plan that should consider the environmental quality standards for priority substances and certain other pollutants, as well as additional requirements, such as heavy metals, pesticides, disinfection by-products, pharmaceuticals, and other substances of emerging concern, including micropollutants and microplastics. It addressed the identification of some preventive measures that can be taken to limit risks, namely additional disinfection or pollutant removal measures

Methods

Results

Conclusion