Abstract:
Pond Sand Filter (PSF), a small scale filtering unit has been widely used in the saline
problem areas of Bangladesh. Recently it has been tried in arsenic problem areas of
the country too. But performance of the units is not up to the mark. Recent study
shows that the performance of existing PSFs is not satisfactory. Out of 61 visited PSF
in study areas only 48 (78.68%) PSF are functioning.
In this study the performance of the existing PSF in 13 upazilas with arsenic and
saline problem areas were investigated. The major problems of the existing PSFs
include slow production, poor fecal coliform removal, shorter filter run and poor
operation and maintenance. The study reveals that performance of PSF is declining
due to design faults including wrong placement of intake pipe, insufficient depth of
filter bed, inadequate pre.filter chamber, weak top lid, absence of overflow pipe in
clear water reservoir. A survey was carried out among the beneficiaries about their
opinion towards the existing PSFs to evaluate the social aspect of PSF.
The study also compared the DPHE, NGO Forum and Danida model PSFs. It covers
pond selection, intake system, pre-filter, sand bed depth, out let structure. turbidity,
color, fecal coliform removal efficiency. The study examined the effectiveness of
various treatment units of three model PSFs and analyzed the findings. Turbidity,
color, fecal coliform were tested for the raw and treated water at various steps of
treatment processes. Removal of bacteria, particularly fecal coliform, time interval of
washing, filter depth and filter run lenh>1hwere also analyzed based on observational
and experimental findings.
The average turbidity and color removal of the PSFs under the study were compared.
Turbidity removal of DPHE, NGO Forum and Danida model was 93.69%, 95.62%
and 92.12% respectively. Color removal of DPHE, NGO Forum and Danida model
was 88.16%, 93.76% and 88.22% respectively Beneficiaries participation in O&M for
NGOs installed PSFs were better than others. Turbidity removal was satisfactory in
all thee model PSFs. Effluent water color and fecal coliform did not meet drinking
water standards. Only 6% of PSF treated water found coliform free. Performance
assessment of PSF's was done in terms of quality of filtered water, ease of operation
and maintenance, efficiency of filter and acceptability of existing PSFs.
