Field
Performance Testing – Village of El Venu
Dr. Pedro Bernal – Department of Chemistry, Rollins College
Dr. Robert Quick – Centers for Disease Control
Associated Colleges of the South
Introduction:
This document reports the result of a rather comprehensive study of
the field performance of 60 of the Mission Filters in the village
of El Venu in the Dominican Republic, some of which have been in use
for over 2 years. The investigation consisted of chemical and microbiological
measurements of the water produced by the filters, and the water sources
used by the villagers, as well as epidemiological studies of the health
impact of the filters. Dr. Pedro Bernal, of the Chemistry Department
at Rollins College, and his students, performed the chemical and microbiological
measurements. The epidemiological surveys were conducted by graduate
students in Public Health from Emory University under the supervision
of Dr. Robert Quick of the Centers for Diseases Control (CDC).
Water
Sources and Filters:
The primary sources of water for the community of El Venu consist
of two rivers and rainwater. Both the river water and rainwater is
frequently stored in or around the household in large steel drums
(sometimes cement-lined), large plastic containers, buckets, or wide-neck
ceramic containers known as “tinajas”.
Sources:
The two local rivers are highly contaminated. As indicated the levels
of fecal contamination of the rivers can rise as high as 3500 cfu/100mL.
This level of fecal contamination places anyone who would drink this
water without some form of disinfection at “high risk”
of diarrheal illness. The stored rainwater typically has lower levels
of fecal contamination (0 – 1000+ cfu/100mL), yet almost half
(44%) of the water presented an “intermediate” or higher
risk.
Results:
A total of 75 analyses were made of 60 filters, with 12 filters having
been visited more than once. As shown by the table below, approximately
90% of the filters were shown to produce water that presents “Little”
or “No Risk”. Given that some users refuse to chlorinate,
this is a very good result.
Risk |
CFU / 100ml |
# of Filters |
Percentage |
No Risk |
0 |
43 |
58% |
Little Risk |
1 - 10 |
21 |
28% |
Intermediate Risk |
11 - 50 |
7 |
9% |
High Risk |
>50 |
4 |
5% |
Chemical
Results:
The filters are also performing well chemically. As shown below, all
of the tests (100%) indicated that the filters were producing water
of acceptable turbidity and more than three quarters (84%) of acceptable
pH. The residual chlorine content presents a problem since at least
three quarters (76%) of the tests indicate that the water in the filters
is below the recommended range of 0.2 – 0.5 ppm. This is, in
the main, a result of the fact that the carbon cartridge of the filter
is very efficient at chlorine removal.
|
Under Acceptable Range |
Within Acceptable Range |
Over Acceptable Range |
Turbidity
< 5 NTU |
--- |
100% |
0% |
Residual Chlorine
0.2 - 0.5 |
76% |
15% |
9% |
pH
6.5 - 8.5 |
0% |
84% |
16% |
Conclusion:
These results show that the Mission Filter, when properly used, can
turn highly contaminated water, not fit for human consumption, into
water that presents little or no risk to consumers.
