Abstract:
The most widely reported groundwater-quality problems in Bangladesh include excessive
concentration of As and Fe. However, available groundwater quality data suggests that
excessive concentration of Mn is also a significant problem in many areas of the country.
The iron problem has long been recognized, and many technologies have been developed
for Fe removal at municipal, community and household levels. After the detection of As,
many municipal IRPs are now being used for removal of both and Fe and As, and many
community plants (AIRPs) have been developed for removal of both Fe and As from
tubewell water. The Mn issue, however, has attracted less attention and there is little data
available on the performance of these plants, especially with regard to Mn removal. The
study assessed the Fe, As and Mn removal efficiencies of six municipal IRPs, three ironcum-
hardness removal plants, and fifteen community IRPs/ AIRPs.
The municipal IRPs have been found effective in removing Fe from groundwater. Only
one municipal IRP had relatively high As concentration (108 Ilgll) in the raw water, and
the performance of this plant suggests that good As removal could be achieved in
municipal IRPs. However, very little removal of Mn could be achieved in the
conventional IRPs. The hardness-cum-iron removal plants, with flocculation and
sedimentation chambers, have been found to be very effective in removing Mn from
groundwater. Pilot studies may be carried out to see if such designs could be used for
simultaneous removal of Fe, As and Mn. Fecal coli forms were detected in the treated
water reservoir in most of the municipal plants; better disinfection processes need to be
employed in these plants to safeguard against bacterial contamination.
With few exceptions, the community IRPs/ AIRPs appear to be very effective in removing
Fe from groundwater. The AIRPs have been found to be effective in reducing As
concentration in raw water below the Bangladesh drinking water standard (50 Ilgll) when
As concentrations in the raw water are relatively low (around 100 Ilgll). The community
IRPs/ AIRPs differed significantly in terms of their ability to remove Mn from
groundwater. The removal efficiency appears to depend on a number of factors, e.g.,
provision for aeration, depth of filter bed, and filtration rate (face velocity). Currently,
typical designs are used for IRPs/AIRPs and no specific design criteria (e.g., detention
time, face velocity, surface over-flow rate, media size range and grading) are followed .
. Variation in raw water quality is also not taken into consideration in the designs. These
issues need to be assessed in more details in order to develop designs of community
plants for simultaneous removal of Fe, As, and Mn. Bacteriological contamination of
treated water from the community IRPs/ AIRPs is common. Effective disinfection process,
considering the field situation in Bangladesh, need to be developed to make the treated
water bacteriologically safe.
