Improvement of Log Reduction Values Design Equations for Helminth Egg Management in Recycled Water

Daryl P Stevens,Andrew S Ball,Leadin S Khudur,Vivek Daniel,Arturo Aburto-Medina,Dan Deere,Jonathan Schmidt,Nick O’Connor,Nicholas D Crosbie,Aravind Surapaneni,Esmaeil Shahsavari,Basma Khallaf,Sarvesh K Soni,Judy Blackbeard,James Hampton,Alexandra Keegan

doi:10.3390/w13223149

Abstract

Understanding and managing the risk posed by helminth eggs (HE) is a key concern for wastewater engineers and public health regulators. The treatment processes that produce recycled water from sewage at wastewater treatment plants (WWTPs) rely on achieving a defined log10 reduction value (LRV) in HE concentration during the production of recycled water from sewage to achieve the guideline concentration of ≤1.0 HE/L. The total concentration of HE in sewage reaches thousands of HE/L in developing countries and therefore, an LRV of 4.0 is generally accepted to achieve a safe concentration in recycled water, as this will meet the guideline value. However, in many developed countries with good sanitation and public health standards, the HE concentration in sewage is generally <10 HE/L. Therefore, validation of the sewage treatment process relied on to achieve an LRV of 4.0 can be difficult. Because of these limitations, design equations to predict LRVs from hydraulic retention times (HRT), which are geographically non-specific, are commonly relied on to ensure the production of safe quality recycled water with respect to HE. However, these design equations could be further refined by defining the design and management of the treatment process in greater detail and thus be used more effectively for determining the LRV required. This paper discusses the limitations and possible improvements that could be applied to LRV design equations for predicting HE removal at WWTPs and identifies the data requirements to support these improvements. Several options for LRV design equations are proposed that could be validated experimentally or via the ongoing operation of WWTPs. These improvements have the potential to assist the rationalization of the HE removal requirements for specific treatment options, exposure scenarios and use of recycled water in agriculture.

Highlights

Due to climatic and demographic changes, there is an increasing demand around the world for finite freshwater resources
This review aims to determine if the management of helminth eggs (HE) removal from sewage can be improved and identify any future research needs to achieve this
The HE found in sewage varies considerably in size and shape some species are similar to each other (Figure 2)

Summary

Introduction

Due to climatic and demographic changes, there is an increasing demand around the world for finite freshwater resources. The recycling of water from a range of. Due to high intrinsic loads of pathogens and chemical contaminants, water resources [1,2]. Due to high intrinsic loads of pathogens and chemical contaminants, treating sewage effluent to the highest quality (e.g., potable) possible, is genertreating sewage effluent to the highest quality (e.g., potable) possible, is generally ally considered too challenging and expensive; lesser degrees of treatment are considered too challenging and expensive; lesser degrees of treatment are satissatisfactory for use in irrigated horticulture including pasture production for livestock, as factory for use in irrigated horticulture including pasture production for livestock, as well well as a variety of other uses.

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