Towards a Predictive Model for Initial Chlorine Dose in Humanitarian Emergencies

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.

Decay of Free Residual Chlorine in Wells Water of Northern Brazil

“…Water samples were collected in January and February 2020. All amber glass bottles used in the experiments were previously washed with neutral detergent (Extran MA 02, Merck S/A, São Paulo, SP, Brazil) and 20.0 mg•L −1 of a sodium hypochlorite solution (Dinâmica ® Química, São Paulo, Brazil) to remove chlorine reactive substances and were subsequently rinsed with deionized water [12]. The water samples were collected in duplicate, the exit of each well, following all the Brazilian guide's recommendations for sample collection and preservation [17].…”

“…The reaction of chlorine with organic matter, mainly humic substances, leads to the formation of unwanted disinfection byproducts, such as organochlorine compounds (e.g., trihalomethanes), which can pose a risk to human health [10]. The result of these chemical reactions, added to the components of the distribution system, such as the type of material of the pipes and biofilms present on the inner walls of pipes and tanks, among others, contribute to reducing the residual chlorine over time [11] and can be compounded by environmental factors, such as temperature [12].…”

Influence of physical and water quality parameters on residual chlorine decay in water distribution network

“…Physical water parameters are pipe length [ 2 , 7 ], pipe diameter [ [7] , [8] , [9] ], pipe roughness [ 2 , 9 ], pipe age [ 2 , 9 ] and pipe material [ 10 ]. Water quality parameters include initial chlorine concentration [ 2 , 7 , 9 , [11] , [12] , [13] , [14] , [15] , [16] ], pH [ 4 , 7 , 12 , 15 , [17] , [18] , [19] , [20] , [21] , [22] ] and turbidity [ 2 , 4 , 7 , [11] , [12] , [13] , [14] , [15] , [16] , [18] , [19] , [20] , [21] , [22] ]. However, turbidity which is commonly used by water utilities as an indicator proxy surrogate for initial chlorine dosage for suspended and colloidal organic and inorganic impurities in water [ 16 , 21 ].…”

“…Water quality parameters include initial chlorine concentration [ 2 , 7 , 9 , [11] , [12] , [13] , [14] , [15] , [16] ], pH [ 4 , 7 , 12 , 15 , [17] , [18] , [19] , [20] , [21] , [22] ] and turbidity [ 2 , 4 , 7 , [11] , [12] , [13] , [14] , [15] , [16] , [18] , [19] , [20] , [21] , [22] ]. However, turbidity which is commonly used by water utilities as an indicator proxy surrogate for initial chlorine dosage for suspended and colloidal organic and inorganic impurities in water [ 16 , 21 ]. This therefore means that turbidity excludes dissolved chlorine reactants [ 16 ].…”

“…However, turbidity which is commonly used by water utilities as an indicator proxy surrogate for initial chlorine dosage for suspended and colloidal organic and inorganic impurities in water [ 16 , 21 ]. This therefore means that turbidity excludes dissolved chlorine reactants [ 16 ]. Instead, it is advised that a minimum Ct (concentration-time) factor with 30-min contact time is used instead of turbidity [ 16 ].…”