A Mechanistic Model to Assess the Fate of Naphthalene and Benzo(a)pyrene in a Chilean WWTP

Antonia Arroyo,Ana L Prieto,Fabián Provoste,Montserrat Rodríguez

doi:10.3390/pr9081313

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a family of organic compounds of widespread presence in the environment. They are recalcitrant, ubiquitous, prone to bioaccumulation, and potentially carcinogenic. Effluent from wastewater treatment plants (WWTPs) constitutes a major source of PAHs into water bodies, and their presence should be closely monitored, especially considering the increasing applications of potable and non-potable reuse of treated wastewater worldwide. Modeling the fate and distribution of PAHs in WWTPs is a valuable tool to overcome the complexity and cost of monitoring and quantifying PAHs. A mechanistic model was built to evaluate the fate of PAHs in both water and sludge lines of a Chilean WWTP. Naphthalene and benzo(a)pyrene were used as models of low-MW and high-MW PAHs. As there were no reported experimental data available for the case study, the influent load was determined through a statistical approach based on reported values worldwide. For both naphthalene and benzo(a)pyrene, the predominant mechanism in the water line was sorption to sludge, while that in the sludge line was desorption. Compared to other studies in the literature, the model satisfactorily describes the mechanisms involved in the fate and distribution of PAHs in a conventional activated sludge WWTP. Even though there is evidence of the presence of PAHs in urban centers in Chile, local regulatory standards do not consider PAHs in the disposal of WWTP effluents. Monitoring of PAHs in both treated effluents and biosolids is imperative, especially when considering de facto reuse and soil amendment in agricultural activities are currently practiced downstream of the studied WWTP.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants formed during the incomplete combustion of organic materials [1]
LMW PAHs were in most cases present in higher concentrations in both influent and effluent in the dissolved phase only, whereas HMW PAHs tended to sorb to particulate matter present in the sewers, entering the wastewater treatment plants (WWTPs) sorbed to particles [9,13]
It has a influent flow of 8.8 m3 /s, treating approximately 50% of the city’s domestic discharged to the Mapocho river, downstream from the WWTP, where it is further used wastewater [38]

Summary

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants formed during the incomplete combustion of organic materials [1] They are hydrophobic, with low solubilities in water and low vapor pressure [2]. As their molecular weight increases, their hydrophobicity increases, and their water solubility and vapor pressure decrease, which makes these compounds more recalcitrant [3] Due to their persistence in the environment, and the carcinogenic and mutagenic effects of some PAHs, they are listed as US-EPA and EU priority pollutants to be monitored in the urban water cycle [4,5]. Several authors have studied and measured PAHs in WWTP [8,9,10,11,12], reporting a wide range of both influent and effluent concentrations (Table 1). The influent concentrations are highly variable and inherent to each specific case study

Methods

Results

Discussion

Conclusion