Decay of Free Residual Chlorine in Wells Water of Northern Brazil

Taise Ferreira Vargas,Caetano Chang Dórea,Tatiana Lemos Da Silva Machado,Wanderley Rodrigues Bastos,Célia Ceolin Baía

doi:10.3390/w13070992

Abstract

The concentration of chlorine in water declines as it reacts with various substances, causing decay of the residual free chlorine until its total consumption. In light of the typical characteristics of the water from protected dug wells and tube wells, this study aimed to evaluate the decay kinetics of free chlorine in the water of alternative individual supply (AIS) solutions used in the city of Porto Velho in the Brazilian Amazon region. The free chlorine decay constant in the water was evaluated by “bottle tests,” applying a first-order model. According to the results, the type of well and initial chlorine concentration significantly influences the free chlorine decay speed. The water samples from the tubular wells had lower chlorine demand levels, attributed to their better water quality. The simulation of the residual chlorine decay in the different supply sources is an important tool to support safe disinfection processes.

Highlights

IntroductionThe free chlorine decay constant in the water was evaluated by “bottle tests,” applying a first-order model
The water samples tested in this study, both from protected dug wells and tube wells, did not undergo any type of treatment before being distributed to each house’s storage tank and later for daily use
Heterotrophic bacteria were present in water from all ten wells, with counts below 500 colony-forming unit (CFU) mL−1 in the five tube wells, while in the five protected dug wells, the count exceeded that limit indicated by Brazilian regulations [8] for human consumption

Summary

Introduction

The free chlorine decay constant in the water was evaluated by “bottle tests,” applying a first-order model. The simulation of the residual chlorine decay in the different supply sources is an important tool to support safe disinfection processes. Trata Brazil Institute [1], only 36.7% of the urban population of the city of Porto Velho (state of Rondônia) received treated water from the piped supply system. More than half of the population must resort to alternative individual supply (AIS) solutions to meet their needs (different from the public water network), mainly in groundwater obtained on shallow dug wells and tubular wells [2]. Contamination can occur in several ways, especially domestic sewage, since only 4.8% of the population of the city of Porto Velho is served by sewage collection systems [1], posing a direct risk of groundwater contamination from decentralized sanitation that serves a large portion of the urban population

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