Towards a Predictive Model for Initial Chlorine Dose in Humanitarian Emergencies

Hongjian Wu,Caetano C C Dorea

doi:10.3390/w12051506

Abstract

Free chlorination is a widely employed disinfection method in humanitarian water provision due to its many advantages. However, its effective application is hindered by the challenge in determining adequate initial doses to achieve free chlorine residuals that satisfy both health and aesthetic requirements. Current guidelines show varying recommended dosing strategies, and many do not adequately consider chlorine decay mechanisms that occur during water storage. Even though turbidity is commonly used as a criterion for deciding chlorine dose, it may not be an adequate proxy for the water quality in many cases. This paper addresses the fundamental relationships between chlorine decay kinetics and selected key water parameters (i.e., natural organic matter, water temperature, chlorine demand) by conducting chlorine decay tests in controlled conditions and in jerrycans (i.e., simulating humanitarian water treatment conditions). Chlorine decay constant from the Feben and Taras’s empirical model and first order model formed linear and exponential relationships with two water parameters (UVA254 and 30-min chlorine demand). With these relationships, the two chlorine decay models can be calibrated quickly and frequently in the field, allowing effective determination of initial chlorine dose. These two models calibrated based on the suggested water parameters from the study could predict chlorine decay in water having a main chlorine demand-inducing constituents as natural organic matter. However, they underpredicted chlorine decay in surface water with additional chlorine reactants. Further research on additional chlorine decay mechanisms is needed to expand the applicability of the models.

Highlights

Humanitarian emergency situations arise when natural or man-made hazards bring serious disruptions to a society, causing widespread human suffering, and stretch the community’s coping mechanisms to a breaking point [1]
The two models explored in the study could be calibrated using either actual water quality parameters (UVA254 and temperature) or using the 30-min chlorine demand, which is a proxy for the chlorine decay property of the water
This study proves the possibility of chlorine decay model calibration using actual water parameters (UVA254, temperature, and 30-min chlorine demand) in the field, and this strategy satisfies the need for a practice-oriented, emergency-adapted dose prediction approach

Summary

Introduction

Humanitarian emergency situations arise when natural or man-made hazards bring serious disruptions to a society, causing widespread human suffering, and stretch the community’s coping mechanisms to a breaking point [1]. Insufficient quantity of water for consumption and hygiene, together with poor water quality, underlies most public health problems such as transmission of diarrheal diseases during crisis situations [2]. It is critical for humanitarian relief organizations to provide water of safe drinking quality and in adequate volume to support lives and hygiene in the community [2,3,4]. Based on the chemistry of chlorine reactions, major contributors to the rapid decay phase are oxidizable substances, metals, fast reacting NOM, ammonia, etc. The temperature dependence of chemical reaction rates can be described using the Arrhenius equation (Equation (1)) [12].

Methods

Results

Discussion

Conclusion