ALTERNATIVE OPTIONS FOR SAFE DRINKING WATER IN ARSENIC AND SALINITY AFFECTED NARAIL DISTRICT, BANGLADESH

The study area, Bornal-Ilisabad union of Narail district, Bangladesh is one of the most vulnerable parts of the country in terms of access to safe drinking water. Shallow groundwater is highly arsenic contaminated (mostly >250 µg/L) and deep groundwater is saline (EC ranges 1-8 mS/cm). Local communities rely on rainwater for drinking and cooking purposes during the monsoon. But remaining periods of the year they use surface water from the ponds which are mostly polluted. In areas where surface water is not available people are compelled to use arsenic contaminated groundwater and thus exposing themselves to a serious health hazard.

The principal objective of this research is to evaluate the effectiveness of managed aquifer recharge (MAR) in mitigating groundwater salinity and arsenic problem; whereas subsurface arsenic removal (SAR) technology in reducing arsenic concentration in groundwater.

For the MAR system, surface water (pond water) and rainwater collected from the roofs are used as source water to be recharged into the target aquifer. The source water is filtered through a sand filtration unit to remove turbidity and microorganisms before recharging through infiltration wells. On the other hand, for SAR system a certain volume (2000L) of groundwater is abstracted from the target aquifer and then aerated about an hour to saturate with oxygen. The oxygenated water is injected into the aquifer. After injection, the whole system is kept undisturbed for 6-8 hours to allow chemical reactions.

The MAR system is found very effective in reducing both salinity and arsenic within six months of injection. The EC of the groundwater has been reduced 72-81% from the initial EC value (3.4 mS/cm). A significant improvement in arsenic and iron concentration is also observed. Before the introduction of MAR, arsenic concentration was 100 µg/L but now the system is yielding groundwater where the arsenic concentration is less than WHO drinking water standards (10 µg/L). The SAR system is also found effective in reducing groundwater arsenic. This system reduced arsenic concentration well within WHO drinking water standards form the initial concentration of 100 µg/L. The system is now capable of yielding about 1500L of low arsenic and low iron water per cycle injection of aerated water which is 70- 80% of the injected volume (2000L).