Tracking pollutants in a municipal sewage network impairing the operation of a wastewater treatment plant

Mariana F.T Sá,Verónica Castro,Ana I Gomes,Daniela F.S Morais,Rui V.P.S Silva Braga,Isabel Saraiva,Bianca M Souza-Chaves,Minkyu Park,Victoria Fernández-Fernández,Rosario Rodil,Rosa Montes,José Benito Quintana,Vítor J.P Vilar

doi:10.1016/j.scitotenv.2021.152518

Abstract

This work provides a screening of organic contaminants and characterization of the dissolved organic matter in the sewer network until the municipal wastewater treatment plant (WWTP), identifying the network areas with a higher degree of contamination and their impact on the WWTP performance, particularly in the activated sludge reactor. Three monitoring campaigns were carried out at six selected locations of the sewage system (PVZ-1, PVZ-2, PS-F, PS-VC, CP-VC, and PS-T), influent (WWTPINF) and effluent (WWTPEFF) of the WWTP. Advanced analytical techniques were employed, namely excitation/emission matrix fluorescence-parallel factor analysis (EEM-PARAFAC), size exclusion chromatography with organic carbon detector (SEC-OCD), and liquid chromatography with high-resolution-mass spectrometric detection (LC-HRMS). EEM-PARAFAC showed higher fluorescence intensity for the protein-like component (C2), particularly at CP-VC (near seafood industries) associated with the presence of surfactants (~50 mg/L). SEC-OCD highlighted the WWTP efficiency in removing low molecular weight acids and neutrals. LC-HRMS tentatively identified 108 compounds of emerging concern (CEC) and similar detection patterns were obtained for all wastewater samples, except for PVZ-2 (lower detection), many of which occurred in the effluent. Eight CECs included on relevant Watch-Lists were detected in all WWTPEFF samples. Furthermore, 111 surfactants were detected, the classes more frequently found being alcohol ethoxylates (AEOs), nonylphenol polyethoxylates (NPEOs) and linear alkylbenzene sulphonates (LAS). The continuous presence of LAS and NPEOs allied to surfactants concentrations in the WWTPINF of 15–20 mg/L, with CP-VC location (linked with food industries) as an important contributor, explain the morphological changes in the activated sludge and high LAS content in the dewatered sludge, which may have impacted WWTP performance.

Highlights

Industrial effluents are known to contain a wide variety of pollutants, such as persistent organic pollutants (POP) and many other contaminants of emerging concern (CECs), culminating in a highly complex matrix (Saghafi et al, 2019; Yu et al, 2019)
3D-excitation-emission matrix (EEM) coupled with parallel factor (PARAFAC), and supported by size exclusion chromatography with organic carbon detector (SEC-OCD) analysis and physicochemical parameters concluded that protein-like and soluble microbial product (SMP)-like components, usually predominant in urban and food industry wastewaters, are the dominant contributors to dissolved organic matter (DOM) in the sewer network samples
The liquid chromatography with high-resolution-mass spectrometric detection (LC-HRMS) screening of the samples detected several compounds of emerging concern (CEC) along the sewage network, many of which occurred in treated wastewater, which may be partly attributed to the inefficient operation of the plant

Summary

Introduction

Industrial effluents are known to contain a wide variety of pollutants, such as persistent organic pollutants (POP) and many other contaminants of emerging concern (CECs), culminating in a highly complex matrix (Saghafi et al, 2019; Yu et al, 2019). WWTPs performance is routinely verified by assessing wastewater influents and effluents in terms of chemical and biochemical oxygen demand (COD and BOD, respectively), total nitrogen (TN), and phosphorous (TP) contents, among other current physicochemical parameters These general wastewater quality parameters are normally required to overview legal compliance and are used as the basis for the design of WWTPs. These general wastewater quality parameters are normally required to overview legal compliance and are used as the basis for the design of WWTPs Those parameters are indicative and do not provide detailed information on the properties of specific components of dissolved organic matter (DOM), nor the presence or identification of contaminants that reach the WWTP and that may impact the treatment performance, especially the biological treatment stage (Ignatev and Tuhkanen, 2019). To ensure the proper operation of WWTPs, it is essential to check the presence of (organic) microcontaminants and characterize DOM throughout the sewage network, allowing the detection of specific hotspots and the implementation of preventive measures at their source

Methods

Results

Conclusion