Performance Evaluation of Gravity-Fed Water Treatment Systems in Rural Honduras: Verifying Robust Reduction of Turbidity and Escherichia coli during Wet and Dry Weather

Abstract

Abstract.This is the first study to document the reduction of turbidity and Escherichia coli throughout the processes of full-scale gravity-fed drinking water plants (GFWTPs) and their downstream distribution systems in rural Honduras. The GFWTPs, which in these cases were designed by AguaClara, use standard treatment processes: coagulation, sedimentation, filtration, and chlorination. During the dry season, we measured E. coli, turbidity, and chlorine residual at five GFWTPs with < 1,000 connections and at three alternative piped-water systems in neighboring communities. Samples were evaluated from the raw water, settled water, filtered water, post-chlorination in the distribution tank, and at a distant-piped household connection. During the dry season, the treated water and household connections serviced by the GFWTPs met World Health Organization (WHO) recommendations for E. coli (< 1 most probable number [MPN]/100 mL). Alternative plants with the same water sources had comparable or higher E. coli and turbidity measurements posttreatment. We examined the performance robustness of two GFWTPs during the transition into the rainy season. The turbidity of the filtered water met WHO recommendations (< 1 nephelometric turbidity units). Escherichia coli was not detected in treated water, indicating that the two GFWTPs can consistently remove particulates and E. coli from source waters containing varying levels of turbidity. During two sampling events during the rainy season, E. coli was detected at the household connection of a GFWTP system with intermittent service and a substandard chlorine residual (geometric mean = 1.0 MPN/100 mL). Strategies to avoid contamination or inactivate E. coli in the distribution system are needed to ensure safe drinking water at the points of delivery, especially for systems with intermittent service.

Passive In-Line Chlorination for Drinking Water Disinfection: A Critical Review

“… 21 , 38 , 39 For studies evaluating existing chlorinators installed prior to the evaluation, the study period was often not more than a few weeks to a few months. 20 , 28 , 29 The results from our NGO survey suggest that longer-term evaluations could be conducted for many chlorinators that have already been deployed and are currently in use in resource-constrained communities.…”

“…In general, evaluations spanning longer time periods are needed to better understand the long-term sustainability and effectiveness of passive chlorinators. In most studies discussed in this review, chlorinators were installed only for the duration of the study and then removed. ,, For studies evaluating existing chlorinators installed prior to the evaluation, the study period was often not more than a few weeks to a few months. ,, The results from our NGO survey suggest that longer-term evaluations could be conducted for many chlorinators that have already been deployed and are currently in use in resource-constrained communities.…”

“…Depending on the source water turbidity and chlorine demand, pretreatment steps may be necessary to ensure consistent dosing. The AguaClara treatment system incorporated coagulation, flocculation, and settling tanks to account for the variable turbidity of incoming source water . Several other evaluations reviewed here coupled chlorinators with other forms of treatment such as gravity-driven membrane filtration systems or natural (gravel and sand) filtration upstream of chlorination. , …”

A Hybrid Centralized-Point-of-Use Drinking Water Treatment System in a Rural Community in Chiapas, Mexico

“…Recognizing that conventional drinking water treatment utilized in larger urban contexts may not be appropriate for rural or low-income communities, more suitable alternatives have been and continue to be developed and tested (Skinner, 2001;Montgomery and Elimelech, 2007;Smyth, 2011;Pickering et al, 2015Pickering et al, , 2019Amin et al, 2016;Brooks et al, 2018) providing more options to communities, government agencies, and other organizations to better serve a wider range of contexts (Hunter et al, 2010a;González Rivas et al, 2014;Mihelcic et al, 2017). Technologies are usually classified based on the scale or level at which the water is treated, including centralized or community-level, point-of-entry, and point-of-use (POU) systems, each presenting advantages and disadvantages in terms of treatment efficiency as well as the social dimensions to ensure proper and sustained use, maintenance, and monitoring.…”