Investigation of Ceramic Pot Filter Design Variables

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Investigation of Ceramic Filter Design Variables

Molly Klarman

Background: Over four billion cases of diarrhea occur worldwide each year that result in about 2.2 million deaths. Household water treatment and safe storage (HWTS) methods, such as ceramic pot water filters, are one of four proven HWTS methods and have been shown to reduce diarrheal prevalence by an average of 45% among users in a randomized control field trial. Although ceramic filters have been proven effective for improving water quality, users and implementers often express concern over their inability to produce a sufficient quantity of water due to their slow flow rate of approximately 1-2 liters per hour (L/H). If flow rate could be increased by altering the current filter design, it would improve the ceramic pot filter’s viability as a scalable HWTS option.

Objective: The main objective of this study was to determine if the flow rate of ceramic pot filters could be increased without sacrificing filter effectiveness, in terms of bacterial removal, by examining the effect of altering specific design variables.

Methods: At the FilterPure ceramic manufacturing facility in the Dominican Republic, eight new filter designs were created by changing one of three design variables: 1) type of combustible material, 2) the ratio of combustible material to clay, or 3) the size of the screen used to sift combustible material. These eight new filter designs were produced in triplicate, along with six control filters. Local river water was passed through the filters daily, and they were tested once a week for five weeks for total coliforms (TC), turbidity, pH, conductivity, and flow rate. 

Results: The flow rate of all filter designs increased from the first to fifth week by an average of 44.1%. The filters made with alternative combustible materials (coffee husks and rice husks) had average flow rates of 9.9 and 5.0 L/H and average TC reductions of 96.1% and 97.6%. The control filters had an average flow rate of 0.95 L/H and average TC reduction of 99.8%. As the proportion of clay to combustible material decreased from 60% clay:40% sawdust to 40% clay:60%sawdust, the average flow rate increased from 0.38L/H to 5.9L/H and the percent reduction of TC decreased from >99.9% to 98.1%. Once initial flow rate increased above 1.7L/H, TC reductions fell below 99%.

Discussion:Minor alterations in filter design or raw materials can affect the performance of locally produced ceramic pot filters to thepoint where their ability to produce safe drinking water is compromised. The results of this research suggest that the maximum initial flow rate for a properly functioning FilterPure filter is 1.7 L/H. None of the alternative designs, that had faster flow rates had better TC reduction than the control filters. This indicates FilterPure should not produce filters with a clay to sawdust ratio lower than 53% clay to 47% sawdust and different combustible materials cannot be used interchangeably without first identifying optimal proportions.



The author of this thesis is:
NAME: Molly Klarman
Address: 32 Lovejoy RD
Andover, MA 01810
The advisor for this thesis is:
NAME: Christine Moe, PhD
Rollins School of Public Health
ADDRESS: 1518 Clifton Road
Atlanta, Georgia 30322
Other committee members for this thesis are:
NAME: Daniele Lantagne, PE
Centers for Disease Control and Prevention
ADDRESS: 1600 Clifton Rd.
Atlanta, GA 30333

Molly Klarman
BA Lewis and Clark College

A thesis submitted to the Department of Environmental and Occupational Health and the Hubert
Department of Global Health
Rollins School of Public Health
Emory University
in partial fulfillment of the requirements
for the degree of Master of Public Health
May, 2009


Independent Appraisal of Ceramic Water Filtration Interventions in Cambodia: Final Report

Joe Brown and Mark Sobsey
University of North Carolina School of Public Health
Department of Environmental Sciences and Engineering
Submitted to UNICEF – Cambodia, 5 May 2006

This study is an independent follow-up assessment of two large-scale implementations
of the household-scale ceramic water filteration after 2 and 4 years in use.
Approximately 1000 household filters were introduced by Resources Development
International (RDI) in Kandal Province from December 2003 and 1000+ filters by
International Development Enterprises (IDE) in Kampong Chhnang and Pursat provinces
from July 2002. The American Red Cross, CIDA, AusAID, UNICEF, and the World Bank
Development Marketplace Programme have supplied support to these two NGOs for
various parts of the production and distribution cycle of the filters.

In October 2003, IDE completed a field study of the ceramic water filtration devices after one year in use,
yielding promising results. The study used bacterial analyses of water samples and user
surveys to measure the performance, acceptance and use of ceramic water filtration devices in 12 rural villages.
The field study also assessed health improvements, time savings, and expense savings.
In August 2005, RDI completed a similar internal study for the filter distribution in Kandal
province, although findings from this assessment have not yet been released. The
present study follows up on these previous assessments and represents an independent
appraisal of the performance of the ceramic water filtration projects undertaken by IDE and RDI. It is
hoped that the findings produced will aid in assessing the water quality and health
impacts of the ceramic water filtration interventions to date and yield useful information on the
sustainability of the filters as implemented.

The study was carried out in two parts:

(1), a cross-sectional study of households
that originally received filters to determine uptake and use rates and associated factors;

(2), a nested longitudinal prospective cohort study of 80 households using filters and
80 control households to determine the microbiological effectiveness and health impacts
of the filters in household use. We measured (i) the continued use of the filters over
time as the proportion of filters still in use since introduction, and identified factors
potentially associated with filter uptake and long term use; (ii), the microbiological
effectiveness in situ of the filters still being used, as determined by the log10 reduction
values of the indicator bacterium E. coli; and (iii), the health impacts of the filters as
determined by a prospective cohort study using data on diarrheal disease prevalence
proportions among filter users versus non-users. We also collected a variety of other
survey data intended to elucidate successes and challenges facing the long-term
sustainability of this intervention in Cambodia. Stratified analyses, logistic regression,
and log-risk regression with Poisson extension of generalized estimating equations
(GEE) were employed in analysis of cross-sectional and longitudinal data to determine
factors associated with long term filter use and effectiveness of filters currently in use.

Major findings are that (i), the rate of filter disuse was approximately 2% per
month after implementation, due largely to breakages; (ii), controlling for time since
implementation, continued filter use over time was most closely positively associated
with related water, sanitation, and hygiene practices in the home, cash investment in the
technology by the household, and use of surface water as a primary drinking water
source; (iii), the filters reduced E. coli/100ml counts by a mean 95.1% in treated versus
untreated household water, although demonstrated filter field performance in some
cases exceeded 99.99%; (iv), microbiological effectiveness of the filters was not
observed to be closely related to time in use; (v), the filters can be highly effective
against microbial indicator organisms but may be subject to recontamination, probably
during regular cleaning; and (vi), the filters were associated with an estimated 46%
reduction in diarrhea in filter users versus non users (RR: 0.54, 95% CI 0.41-0.71).

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