BTEX Concentration and Risk Assessment from Biological Activated Sludge in Municipal Wastewater Treatment Plants: Systematic Review

Abstract

Background: The municipal wastewater treatment plants are crucial for protecting the environment and the scarce water resource, but they also release volatile organic compounds like BTEX, Benzene (B), Toluene (T), Ethylbenzene (E) and Xylenes (X) during the treatment processes. BTEX emissions poses significant challenges due to their potential to endanger public health and environment, this is because the efficiency of the wastewater treatment plants (WWTP) and quality of influent determines the effluent quality and emissions. In this research report an attention was given to primary studies which evaluated the emissions of BTEX concentration from Municipal WWTP and subsequently undertake a health risk assessment. Aim: The study aimed to identify and synthesize existing literature on average BTEX emission concentrations from biological activated sludge in municipal wastewater treatment plants (WWTPs). Additionally, the study will evaluate the associated health risks from exposure to these emissions. Methodology: A systematic review was conducted to gather information from literature, focusing on the South African context while also exploring global studies in the absence of related research in South Africa. A total of 579 articles were reviewed using the PRISMA framework with some exclusion based on the criterion. Publications were sourced from several databases, including ScienceDirect, ProQuest, SCOPUS, and PubMed. For the health risk assessment, exposure assessment, and risk characterization, including carcinogenic risk (CR) and hazard quotient (HQ), the United States Environmental Protection Agency (U.S. EPA) method was used, summarizing data from relevant studies for the review paper. Results: Numerous studies have been conducted globally to investigate BTEX emissions from municipal wastewater treatment plants (WWTPs). However, South Africa remains underrepresented in this research area, with a notable lack of studies. Globally, biological activated sludge technology is widely used due to its effectiveness and efficiency in treating municipal wastewater. The BTEX concentrations emitted from WWTPs often exceed the South African Occupational Health and Safety (SAOHS) and National Institute for Occupational Safety and Health (NIOSH) occupational exposure limits (OEL). The carcinogenic risks (CRs) for benzene from macro-scale and average-scale WWTPs surpass the U.S. EPA threshold risk limit in ambient air of 1 x 10-4, indicating an average risk of two additional cancer cases per 10,000 individuals exposed in biological activated sludge (BAS) WWTPs. vi Conclusion: Overall, this report indicates that during the wastewater treatment process in biological activated sludge (BAS) wastewater treatment plants (WWTPs), BTEX compounds are released into the ambient air. The health risk assessment results suggest a potential carcinogenic risk from macro-scale and average-scale WWTPs, although the likelihood of developing non-carcinogenic health effects for both male and female workers is lower. However, due to limited available data, there remains some uncertainty regarding the risk. In summary, BTEX compounds are released into the ambient air, exposing employees in this microenvironment to potential inhalation. Consequently, employees might develop adverse health effects over time. More studies in this field are needed to reduce uncertainty and safeguard workers' health.