Laboratory evaluation of the efficacy of bucket chlorination guidelines at inactivating Vibrio cholerae for waters of varying quality

Abstract

Bucket chlorination, where chlorine is dosed directly into water collection containers, is a point-of-source water treatment intervention commonly implemented in cholera outbreaks. There is little previous data on chlorine efficacy against Vibrio cholerae in different waters and appropriate dosage regimes. We evaluated V. cholerae reduction and free chlorine residual (FCR) in waters with four turbidities (1/5/10/50 NTU), two total organic carbon (TOC) concentrations (0.4, 1 mg/L), and two dosing schemes (fixed-dose of 2 or 4 mg/L, variable-dose based on jar testing) treated with three chlorine types (HTH, NaOCl, NaDCC). We found that chlorine was efficacious at reducing V. cholerae by ≥2.75 to ≥3.63 log reduction value (LRV); variably dosed reactors were dosed higher, met ≥0.5 mg/L FCR at 30 min, and had higher LRVs (p=0.024) than fixed doses; and low TOC reactors had more samples ≥0.2 mg/L FRC at 4 h (p=0.007). Our results are conservative, as internationally recommended additives to create test water increased chlorine demand, highlighting the challenge of replicating field conditions in laboratory testing. Overall, we found that chlorine can efficaciously reduce V. cholerae; recommend further research on appropriate chlorine demand for test waters; and recommend establishing appropriate chlorine doses based on source water and taste/odor acceptability in bucket chlorination programs.

Report of the Scientific Committee of the Spanish Agency for Food Safety and Nutrition (AESAN) on the microbiological criteria for Vibrio cholerae, as additional control measures at border control posts, applicable to imported frozen prawns and other fishery products

“…However, there is little data on its action in different types of water (fresh versus salt) or under different dosage regimens. For this reason, it is recommended to carry out more research to establish adequate chlorine doses and determine concentrations that do not affect sensory properties such as taste and smell (String et al, 2022). In aquaculture, chlorination is usually carried out in fish farming or fattening tanks, but the measure cannot be implemented in open water.…”