Design and Evaluation of a Household Chlorination System for Treating Cistern Water in the US Virgin Islands

Abstract

In the US Virgin Islands, >90% of households have rain catchment systems that utilize large cisterns; however, these systems are at high risk of microbial contamination. Available water treatment technologies provide varying levels of protection from microbial contamination and can be expensive. Therefore, we evaluated a low-cost water treatment train that included a passive chlorinator, carbon filter, and membrane filter to provide whole-house treatment for microbial contamination in a mock, pressurized, intermittent-use water system. Two types of locally available passive pool chlorinators were modified and tested for free chlorine residual (FCR) levels across a set of different water use scenarios. Additionally, tracer dye tests were conducted to evaluate chlorine contact time in the system, a carbon filter was evaluated for chlorine removal efficiencies, and a 1-micron nominal filter was evaluated for its effect on system pressure and microbial removal efficiencies. Results suggested the modified passive chlorinators provided relatively consistent chlorine dosing (offline: standard deviation range 0.54 to 0.79 ppm FCR, 3 trials, n=43; inline: standard deviation 0.53 ppm FCR, 1 trial, n=16) and tracer dye tests identified a minimum contact time for high flow rates (18.9 LPM, 5 GPM) of >45 s. The carbon filter reduced FCR levels from as high as 18.5 ppm to <0.13 ppm (n=9), while the 1-micron nominal filter had negligible effects on system pressure and provided 0.7 log 10 MPN/100 mL removal of total coliforms (n=9). The data suggest that passive chlorination can potentially be a low-cost option for whole-house water treatment for microbial contamination, but further research is needed to demonstrate system stability in a wider range of use cases over a longer period of time along with simplified practitioner protocols for field use.