Development of emission factors to estimate discharge of typical pharmaceuticals and personal care products from wastewater treatment plants

Highlights

• A simple approach was proposed for calculation of PPCP emission factors (EFs).

• EFs focused on biological treatment and disinfection (UV and chlorine) processes.

• EFs of 9 PPCPs were established for low, medium and high emission scenarios.

• Mass of 9 PPCPs in the Yangtze River valley was 8808 kg for medium scenario in 2018.

Abstract

Due to the potential ecological and human health risks, pharmaceuticals and personal care products (PPCPs) are considered as contaminants of emerging concern. PPCPs can be discharged to the aquatic environment from various sources, including municipal wastewater treatment plants (WWTPs), animal feeding operations, hospitals, and pharmaceutical manufacturers. A major challenge to regional characterization of ecological and human health risks is identification of the environmental emissions of PPCPs. This study established a facile approach for calculation of PPCP emission factors from raw wastewater and wastewater effluent. Using reported concentrations from WWTPs, nine PPCPs, namely carbamazepine, ciprofloxacin, erythromycin, ibuprofen, ketoprofen, ofloxacin, sulfadiazine, sulfamethoxazole, and trimethoprim, were identified as priority contaminants based on environmental significance (i.e., high detection frequency and potential ecological risk) and data availability. Emission factors were calculated for the nine PPCPs in raw wastewater, secondary effluent, and tertiary effluent for low, medium and high emission scenarios according to the concentration distributions of these nine PPCPs. The emission factors were used to estimate the mass of the PPCPs discharged from the nine provinces and two municipalities of the Yangtze River valley. The total mass of the nine PPCPs emitted into the watershed was estimated as 3867 kg, 8808 kg and 21,464 kg for low, medium and high emission scenarios respectively in 2018. Although uncertainty is inevitable in the emission factors, the reported approach provides a viable alternative to top-down and multimedia fugacity estimation strategies that require an abundance of sewershed-, WWTP-, and compound-specific information that is difficult to collect in developing countries.

Introduction

Pharmaceuticals and personal care products (PPCPs) are necessary to maintain human health and quality of life. While PPCPs improve our lives, these specially-designed molecules are sometimes over-prescribed, overused, and improperly disposed (Zhang et al., 2015b; Zhang et al., 2019). For instance, many PPCPs can be obtained over-the-counter with little restriction in China and other Asian countries (Tran et al., 2018). As a result, relatively high PPCP concentrations have been detected in the following downstream environmental systems: surface water (Barbosa et al., 2018; Ebele et al., 2017; Hopkins and Blaney, 2016; Veras et al., 2019); sediment (da Silva et al., 2011; Xie et al., 2019); soil (Dodgen et al., 2014; Gottschall et al., 2012); domestic, industrial, hospital, and agricultural wastewater (He et al., 2015; Liu et al., 2017; Oliveira et al., 2015; Petrie et al., 2015; Sim et al., 2011; Van Epps and Blaney, 2016); groundwater (Sharma et al., 2019; Sui et al., 2015); landfill leachates (Sui et al., 2017; Yu et al., 2020a; Yu et al., 2020b); and, aquatic organisms (He et al., 2019; He et al., 2017). Wastewater treatment plants (WWTPs) receive a high load of PPCPs due to incomplete metabolism of pharmaceuticals in humans, wash-off of personal care products during/after use, and improper disposal down the drain (Dong et al., 2016a; Michael et al., 2013). Due to their incomplete removal in most WWTPs (He et al., 2015; Verlicchi et al., 2012), a fraction of the PPCPs in raw wastewater is discharged into receiving water bodies.

The emission of PPCPs to the environment causes certain ecological and human health risks, including antibiotic resistance (Gago-Ferrero et al., 2015; Oaks et al., 2004; Wang et al., 2018) and endocrine disruption (Abdel-Moneim et al., 2017; Golden et al., 2008; Wang et al., 2018), among others (Jepsen et al., 2019). More importantly, the discharged PPCPs could also be migrated to further influence the ecosystem of protected area (e.g. Amazon Estuary) (Chaves et al., 2020). To assess downstream ecological impacts, the mass loading of individual PPCPs into the environment must be identified. The most common methods to quantify PPCP concentrations and loads in wastewater effluent involve grab or composite sample collection followed by liquid chromatography with tandem mass spectrometry analysis (Dong et al., 2016b; Subedi et al., 2017; Zhang et al., 2020; Zhong et al., 2019). These techniques are labor-intensive and expensive, making them unsuitable for widespread deployment in developing countries. For this reason, more convenient methods are needed to estimate PPCP emissions to the environment.

To date, two main strategies for estimating PPCP emissions have been explored: top-down approaches (Carballa et al., 2008; Franquet-Griell et al., 2017; Tarpani and Azapagic, 2018; Tran et al., 2018); and, multimedia fugacity models (Khan and Ongerth, 2004; Trinh et al., 2016; Zhang et al., 2015a). Top-down prediction of PPCP concentrations and loads requires knowledge of WWTP capacity (i.e., volumetric flow rate), the population served by the WWTP, and PPCP consumption per capita. For example, predicted environmental concentrations (PECs) of anticancer drugs in Spanish wastewater effluent were calculated using the population, drug consumption data from pharmacies, daily per capita water consumption, drug excretion factors, and previously determined removal efficiencies for the WWTP (Franquet-Griell et al., 2017). Similarly, Carballa et al. (2008) applied four parameters (i.e., population, per capita consumption, excretion factor, and average wastewater flow rate) to determine PECs for pharmaceuticals, fragrances, and hormones. The influent and effluent concentration ranges in WWTPs have also been evaluated with the daily raw wastewater flow rate, sewershed population, and PPCP concentrations from previous studies (to calculate removal efficiency) and used to estimated freshwater concentrations (Tarpani and Azapagic, 2018). Compared with top-down strategies, multimedia fugacity models require media-specific information to calculate PECs for PPCPs (Khan and Ongerth, 2004; Trinh et al., 2016; Zhang et al., 2015a). In addition to the PPCP consumption and population data, the transfer and distribution coefficients of compounds between different phases are needed in these models. Fugacity models have been combined with Geographic Information Systems to estimate PPCP concentrations and emissions within specific catchments (Boxall et al., 2014; Pistocchi et al., 2012). Both top-down and fugacity methods require a great deal of compound-, catchment-, and WWTP-specific information to accurately estimate PPCP emissions; however, this information is often challenging to acquire and update. Given the aforementioned limitations of the top-down and multimedia fugacity modeling approaches, a bottom-up strategy of acquiring PPCP emission factors was investigated. Here, emission factor is defined as the amount of PPCPs discharged for per liter wastewater treated by WWTPs, which is just the PPCPs concentration in WWTP effluent. This simple strategy only required information about the wastewater treatment train to predict PPCP emissions of WWTPs. The PPCP emission through PPCPs can be roughly calculated by emission factors combined with sewage amount.

The main objective of this work was to develop a conceptual framework to predict the mass of PPCPs discharged into the environment based on extensive literature analysis. Emission factors of different PPCPs, as an output of the conceptual framework, were used for subsequent estimation. The emission factors of different scenarios were defined corresponding to different wastewater treatment processes, which were further applied to calculate the environmental discharge of nine PPCPs by WWTPs in Yangtze River valley.