Removal of helminth eggs by centralized and decentralized wastewater treatment plants in South Africa and Lesotho: health implications for direct and indirect exposure to the effluents

Isaac Dennis Amoah,Razak Seidu,Thor Axel Stenström,Poovendhree Reddy

doi:10.1007/s11356-018-1503-7

Abstract

Wastewater may contain contaminants harmful to human health; hence, there is the need for treatment before discharge. Centralized wastewater treatment systems are the favored treatment options globally, but these are not necessarily superior in reduction of pathogens as compared to decentralized wastewater treatment systems (collectively called DEWATS). This study was therefore undertaken to assess the soil-transmitted helminth (STH) and Taenia sp. egg reduction efficiency of selected anaerobic baffled reactors and planted gravel filters compared to centralized wastewater treatment plants in South Africa and Lesotho. The risk of ascariasis with exposure to effluents from the centralized wastewater treatment plants was also assessed using the quantitative microbial risk assessment (QMRA) approach. Eggs of Ascaris spp., hookworm, Trichuris spp., Taenia spp., and Toxocara spp. were commonly detected in the untreated wastewater. The DEWATS plants removed between 95 and 100% of the STH and Taenia sp. eggs, with centralized plants removing between 67 and 100%. Helminth egg concentrations in the final effluents from the centralized wastewater treatment plants were consistently higher than those in the WHO recommended guideline (≤ 1 helminth egg/L) for agricultural use resulting in higher risk of ascariasis. Therefore, in conclusion, DEWATS plants may be more efficient in reducing the concentration of helminth eggs in wastewater, resulting in lower risks of STH infections upon exposure.

Highlights

Municipal wastewater contains a variety of pathogens, reflecting the carrier state and infection levels in the community (Carr et al 2011; Hanjra et al 2012)
*p ≤ 0.05 enhanced and might increase the risks beyond what we reported for centralized wastewater treatment plants (WWTPs)
Soil-transmitted helminth and Taenia spp. prevalence and concentration were found to be consistent with other reports

Summary

Introduction

Municipal wastewater contains a variety of pathogens, reflecting the carrier state and infection levels in the community (Carr et al 2011; Hanjra et al 2012). The issue of costs of constructing and operating of wastewater treatment plants is mainly a challenge in poor settings (Massoud et al 2009); access to finance for these investments acts as the main stumbling block (Hanjra et al 2015; Duchin 2016). STHs are recognized as a major public health problem affecting over 1.5 billion people worldwide (WHO 2015), with Ascaris spp., hookworm, and Trichuris spp. infections the most common (Pullan et al 2014). These infections are associated with low-income countries, mainly occurring in Sub-Saharan Africa, Asia, and South America (WHO 2015)

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Results

Discussion

Conclusion