Abstract:
Groundwater salinity and Arsenic contamination are the main causes of the drinking water crisis in the coastal areas of Bangladesh, particularly, in the south-west region. People have been using conventional Arsenic treatment technologies, which show little promise in providing Arsenic safe drinking water especially at the community-scale. Subsurface Arsenic Removal (SAR) technology could be a viable option to provide potable water at the community-scale with Arsenic within acceptable limit. Previous study suggested that high pH in groundwater may improve the SAR system's efficiency. Therefore, the current study explored the effect of increased pH in SAR system through batch experiments and a pilot-scale test. In order to evaluate this, the pH of groundwater was raised by adding Sodium Hydroxide (NaOH). There were three different kinds of batch experiments (Control, Regular, and Modified) conducted in this study. In Control condition, no interventions were adopted, wherein groundwater used in Regular condition was oxygen saturated through aeration, and in Modified condition, groundwater was oxygen saturated through aeration and pH was adjusted using NaOH. Regular and Modified SAR conditions were implemented out at Manikganj, Dhaka, as part of the in-situ field test. In Modified field experiment, the pH of the groundwater was increased by adding NaOH. Additionally, SAR applicable suitable sites in the south-west coastal areas of Bangladesh were identified using literature data. The SAR batch studies show the possibility of co-removal of Iron, Arsenic, and Manganese from groundwater. For the field experiments, the Modified condition improved the subsurface oxidation zone, resulting in better Arsenic mass removal compared to Regular SAR. Besides, the Arsenic concentrations in extracted groundwater up to V/Vi = 4 were always below the native groundwater Arsenic concentration (0.082 mg/L) and the acceptable limit 0.05 mg/L. The Na+ concentrations in extracted groundwater within V/Vi = 4 of both conditions were below the acceptable limit 200 mg/L. Furthermore, the Modified SAR field test had showed a great capability to remove Iron, Arsenic, and Manganese simultaneously from groundwater. From areas in the south-west coastal zones with low groundwater salinity of less than 2,000 µS/cm and the Arsenic concentration of more than 0.05 mg/L, SAR applicable areas were identified, considering native groundwater's Iron to Arsenic ratio (mg/mg) above 40. It is expected that successful implementation of Modified SAR would benefit approx. 75 number of families in a community with Arsenic safe drinking water.