Efficacy of chlorine dosage recommendations on the microbiologic quality of turbid waters Open Access

Oliver, Shannon Thomas (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/td96k259f?locale=en
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

Rights statement
  • Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.
School
Department
Degree
Submission
Language
  • English
Research field
Keyword
Committee Chair / Thesis Advisor
Committee Members
Partnering Agencies
Last modified

Primary PDF

Supplemental Files