The role of orthophosphate and dissolved oxygen in the performance of arsenic-iron removal plants in Bangladesh

Abstract

Arsenic iron removal plants (AIRPs) are used in some locations in Bangladesh to remove arsenic from groundwater to provide access to safer drinking water. In this study, the influence of orthophosphate in influent water on the performance of 21 (of 105) AIRPs installed in the Manikganj District was evaluated. The degree of aeration was also estimated, and the role of dissolved oxygen in AIRP performance is discussed. AIRP installations were done by a local non-governmental organization (The Society for People's Action in Change and Equity) with financial assistance from the Australian High Commission, Dhaka under the Direct Aid Program of the Australian Government. The presence of orthophosphate in the influent did not influence arsenic removal efficiency in the tested AIRPs, likely due to the high iron concentrations at all sites. The high iron provides adequate surface area for both orthophosphate and arsenic to be removed. Orthophosphate co-precipitated with iron oxides much more quickly than arsenic, in one cleaning cycle study, and is expected to play a more significant role in interfering with arsenic removal at sites with much lower iron concentrations. The aeration trays studied are estimated to introduce at least 2.4–3.7 mg/L of dissolved oxygen. In normal operation, sufficient oxygen is introduced through the aeration tray to fully oxidize all influent iron. The AIRPs studied show promise for use in areas of Bangladesh with high natural iron, where users are concerned with arsenic, iron, or both, in their drinking water.

Keywords:

• Arsenic
• Bangladesh
• drinking water
• AIRP
• phosphate
• dissolved oxygen
• iron
• groundwater
• water treatment

Acknowledgments

Particular thanks to Mr. Azahar Pramanik at SPACE for his continued support and hospitality, Mehrun, and Sharif at SPACE for field-level logistical support, and fellow researchers Mr. S.M. Abu Darda and Mr. Zahidul Islam Miah for their dedication, hard work, thoughtful contributions, and guidance during data collection. Additional thanks to Dr. Md. Mujibur Rahman at BUET for his advice and guidance. Also at BUET, Ehsan and all of the Environmental Laboratory employees, and Dr. Borhan Badruzzaman helped lab testing go (relatively) smoothly. Dr. Khosrow Farahbakhsh, Dr. Shafiul Ahmed, and Dr. Heather Murphy from the University of Guelph have provided invaluable guidance on this entire project.

Funding was provided by the Canadian International Development Agency (CIDA) through the Association of Universities and Colleges of Canada (AUCC) Students for Development program, and the Natural Sciences and Engineering Research Council (NSERC) of Canada through the Michael Smith Foreign Studies Supplement and the Canada Research Chairs program.