Laboratory Efficacy and Disinfection by-Product Formation of a Coagulant/Disinfectant Tablet for Point-of-Use Water Treatment

Abstract

Coagulant/disinfection products (CDPs) are a point-of-use (POU) water treatment technique that can improve microbial quality, reduce turbidity, and produce a free chlorine residual (FCR), serving as a potentially effective option for decentralized water treatment in a variety of contexts, including humanitarian emergencies. A novel CDP with a sodium dichloroisocyanurate-based disinfectant was evaluated with regard to its laboratory water treatment efficacy and generation of disinfection byproducts (DBPs). The CDP water treatment performance was assessed relative to bacteriological (E. coli) humanitarian water quality objectives, World Health Organization recommendations for evaluating POU water treatment options, and available DBP regulations and guidelines. At least 4 log10 E. coli reductions, for a “highly protective” status with regard to bacterial reductions, were attained in the tested conditions. Treated waters were consistently below 10 MPN/100 mL with regard to E. coli concentrations, with the majority of samples showing no detectable E. coli. For most conditions, target FCR values were not attained. Treated water turbidity levels were mostly between 5 NTU and 10 NTU. DBP levels were below the regulatory and health-based targets for both families of DBPs studied. This study has served to identify the performance envelopes of the CDP tested under challenging conditions.

Characterization of Disinfection By-Products Levels at an Emergency Surface Water Treatment Plant in a Refugee Settlement in Northern Uganda

“…Interestingly, Lantange et al [7,8] in their study of TTHM production in household chlorination programs in Kenya and Tanzania observed that chloroform was the dominant THM species in the samples they analyzed, contributing on average 78% and 83% of TTHM content across multiple water types in either country, respectively. Similarly, Légaré-Julien et al [34] also found the speciation of TTHMs to be primarily chloroform when natural surface waters were chlorinated. This reinforces the assumption that the DBP/THM reading produced by the Hach THM Plus method can meaningfully be compared to the WHO chloroform guideline as the majority species is indeed likely to be chloroform.…”

“…Similarly, Nhongo et al [40] found THMs to generally be within WHO guideline limits in their investigation of DBP levels in the piped water supply system of Harare, Zimbabwe. Légaré-Julien et al [34] found THM levels in the range of 50 ppb when natural surface waters from Quebec, Canada were treated using a point-of-use coagulant-disinfectant product that included NaDCC as the disinfecting agent. On the other hand, Werner et al [41] found levels of chloroform and TTHMs approaching and even exceeding the 300 ppb WHO guideline at 24 h when point-of-use chlorine dioxide tablets were used to treat natural surface waters in the Northern British Isles.…”

Differences in laboratory versus field treatment performance of point-of-use drinking water treatment methods: research gaps and ways forward

“…This applies even if laboratory assessments are intended to simulate challenging conditions, for example the use of a high-turbidity, high-organic-content test water 25,29,39 . Laboratory assessments can be effectively employed to identify water quality-or treatmentrelated limitations of products and screen performance between several design conditions 40,41 , options or products 42,43 .…”