Efficacy of chlorine dosage recommendations on the microbiologic quality of turbid waters Público
Oliver, Shannon Thomas (2011)
Published
Abstract
ABSTRACT
Efficacy of chlorine dosage recommendations on the microbiologic
quality of turbid
waters
By Shannon Oliver
Background: Recent figures indicate that 884 million
people lack access to improved
water supplies, and 2.6 billion people do not have access to
improved sanitation. The
World Health Organization and Centers for Disease Control and
Prevention have
therefore promoted the use of sodium hypochlorite (chlorine bleach)
as a cheap and
readily available point-of-use water treatment intervention in an
effort to alleviate the
disease burden associated with unclean water and unimproved
sanitation. Objective:
The goal of this
research project was to understand the efficacy of sodium
hypochlorite
(NaOCl) treatment in turbid waters. Specifically, each of two
chlorine dosages (1.875
and 3.75 mg/L NaOCl) were tested on their ability to achieve the
following: 1) maintain
recommended chlorine residual levels (0.2-2.0 mg/L free chlorine);
and 2) reduce
microbiologic contamination to <1 CFU. Methods: A
field study to investigate these
dosing recommendations was completed in which source waters were
collected for the
efficacy trial. Three jerry cans were filled to 10 liters each from
sources identified as >10
nephelometric turbidity units (NTUs), and randomly assigned to
treatment arms (control,
1.875 mg/L and 3.75 mg/L). Source water characteristics were
collected at the source
location and chlorine dosing occurred in the lab. Follow-up
analyses were complete at
one-hour (T1), eight-hour (T8) and twenty-four-hour (T24)
increments to quantify
follow-up contamination ( E. coli MPN) and free chlorine
residual. Results: No major
differences were seen between the two dosing levels with regard to
follow-up
microbiologic water quality. The higher chlorine dose was more
effective at meeting
chlorine residual standards, but no significant differences were
seen between the two
dosages in meeting the E. coli standard or for meeting both
standards concurrently.
There were no consistent associations noted between source water
characteristics and
follow-up level of contamination or residual chlorine.
Discussion: Point-of-use
interventions relying on chlorination as the primary means of water
treatment may be
effective in lower turbidities. When turbidity is of concern
(>10 NTUs) as presented here
however, an increased chlorine dose was not shown to significantly
improve the
microbiologic quality of otherwise untreated source
water.
RESUMEN
La eficacia de las recomendaciones para la dosis de cloro en la
calidad microbiológica de
las aguas turbias
Por Shannon Oliver
Fondo: Las cifras recientes indican que 884 millones
de personas no tienen acceso a las
fuentes de agua mejoradas, y 2,6 billones de personas no tienen el
acceso a las
condiciones mejoradas de salubridad. Por lo tanto, la
Organización Mundial de la Salud
y el Centro para el Control y la Prevención de las
Enfermedades han fomentado el uso del
hipoclorito de sodio (cloro común) como un método barato
y disponible para tratar el
agua al punto-del-uso para aliviar el peso de las enfermedades que
están asociadas con el
agua sucia y las condiciones rudimentarias de salubridad.
Objetivo: La meta de esta
investigación fue comprender la eficacia del uso de
hipoclorito de sodio (NaOCl) en las
aguas turbias. Específicamente, se examinó la capacidad
de cada una de las dos dosis de
cloro (1,875 y 3,75 mg/L NaOCl) para lograr lo siguiente: 1)
mantener niveles
recomendados (0.2-2.0 mg/L cloro libre) de cloro residual; y 2)
reducir la contaminación
microbiológica al <1 UFC. Métodos: Se
completó un estudio de campo para investigar
las dosis recomendadas y se recolectaron aguas de la fuente para
las pruebas de eficacia.
Se llenaron tres pomas con 10 litros cada una, de las fuentes
identificados como >10
unidades de turbiedad nephelometric (UTNs), y asignadas al azar a
los brazos del
tratamiento (control, 1,875 mg/L y 3,75 mg/L). Se recogieron las
características del agua
de la fuente en su lugar de origen y se administro' la dosis del
cloro en el laboratorio. Se
recogió el análisis siguiente en incrementos de una hora
(T1), ocho horas (T8) y
veinticuatro horas (T24) después para cuantificar la
contaminación en esos momentos
(UFC de E. coli) y el residual del cloro libre.
Resultados: No se observaron diferencias
importantes entre los dos niveles de dosis con respecto a la
calidad microbiológica
inmediata del agua. El nivel elevado del cloro fue más eficaz
al cumplir con el nivel
estándar del cloro residual, pero no se observaron diferencias
significativas entre las dos
dosis con respecto a cumplir con el criterio de E. coli ni
con respeto a cumplir con los dos
criterios al mismo tiempo. No hubo asociaciones constantes entre
las características del
agua de la fuente y el nivel inmediato de contaminación ni el
cloro residual. Discusión:
Las intervenciones en el punto-del-uso que dependen de la
cloración como el primer
tratamiento del agua podrían sean efectivas en aguas de baja
turbiedad. Sin embargo,
cuando la preocupación es la turbiedad (>10 UTNs) tal como
se presenta aquí, una dosis
elevada de cloro no demostró una mejoría en la calidad
microbiológica de aguas no
tratadas.
Table of Contents
TABLE of CONTENTS
INTRODUCTION
...........................................................................................................................1
Background..................................................................................................................................1
Impact of Turbidity
......................................................................................................................1
Chlorine as a Disinfectant
...........................................................................................................2
Microbiologic Water Quality
Standards......................................................................................4
Context.........................................................................................................................................5
Purpose
........................................................................................................................................6
METHODS
......................................................................................................................................7
Study
Site......................................................................................................................................7
Study Design
................................................................................................................................8
Sampling
Methods........................................................................................................................9
Laboratory
Methods...................................................................................................................11
Data Analysis
Methods..............................................................................................................13
Data entry and cleaning
.........................................................................................................13
Sample Population and Variables of
Interest.........................................................................14
Log reductions in E.
coli........................................................................................................15
Impact of
Turbidity................................................................................................................15
Impact of Source Contamination
...........................................................................................16
Comparison of
Standards.......................................................................................................16
Linear Regression
..................................................................................................................17
Multiple Linear
Regression....................................................................................................18
RESULTS
......................................................................................................................................19
Summary statistics
.....................................................................................................................19
Log reductions in E.
coli............................................................................................................21
Impact of Source Contamination
...............................................................................................24
Comparison of Standards
..........................................................................................................24
Simple Linear Regression
..........................................................................................................30
Log Reductions in E.
coli.......................................................................................................31
Follow-up Contamination
......................................................................................................34
Multiple Linear
Regression........................................................................................................36
Log reductions in E.
coli........................................................................................................36
Free Chlorine Residual
..........................................................................................................37
Follow-up Contamination
......................................................................................................37
DISCUSSION................................................................................................................................38
Log Reductions in E.
coli...........................................................................................................38
Free Chlorine
Residual..............................................................................................................40
Follow-up
Contamination..........................................................................................................42
Implications for Point-of-use
Interventions...............................................................................44
Limitations.................................................................................................................................45
CONCLUSION..............................................................................................................................47
REFERENCES
..............................................................................................................................49
APPENDIX of TABLES and
FIGURES.......................................................................................52
About this Master's Thesis
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