Microbiological water quality of Managed Aquifer Recharge systems in the salinity-prone southwest coastal Bangladesh

Abstract

Managed aquifer recharge (MAR), a hydro-geological intervention designed to dilute groundwater salinity, pumps pond water treated through a slow sand filter into the underground aquifers. We evaluated the microbiological safety of the resulting MAR water at sites from three districts in southwest coastal Bangladesh. We collected monthly paired pond-MAR water samples from July 2016-June 2017 and enumerated fecal coliforms and E. coli using the IDEXX quanti-tray technique, by the most probable number (MPN) method. We used WHO risk categories for microbiological quality; no risk (<1 MPN), low risk (1-10 MPN) and moderate to high risk (>10 MPN per 100 mL water). We estimated the difference in mean log10 MPN in pond and MAR water using linear mixed effect models with random intercepts and cluster adjusted robust standard error. Almost all pond water samples (292/299, 98%) had moderate-to high-risk level (>10 MPN) fecal coliforms and E. coli (283/299, 95%). In contrast, 81% (242/300) of MAR water samples had no or low risk level fecal coliforms (0-10 MPN), of which 60% (179/300) had no fecal coliforms. We detected no or low risk level E. coli in 94% (283/300) of MAR water samples of these 80% (240/300) had no E. coli. MAR samples had lower mean log10 MPN fecal coliforms (-2.37; 95% CI: -2.56, -2.19) and E. coli (-2.26; 95% CI: -2.43, -2.09) than pond water; microbial reductions remained consistent during the wet (May-October) and dry seasons. MAR-systems provided water with reduced fecal indicator bacteria compared to infiltered pond water.

Drinking Water Supply Options in Arsenic and Salinity Affected Areas of Bangladesh: A Case Study

“…The water samples from the MAR systems contain fecal coliform (FC) ranging from 20 to 76 cfu/100 ml. It should be noted that Doza et al (2018) reported fecal coliform in the range of 1-10 MPN or more in water samples from 40% MAR units studied (in Satkhira, Khulna and Bagerhat), compared to 99% in the source pond water. There was no latrine pit within 30 feet around the MAR recharge wells in our study area.…”

Consequences of access to water from managed aquifer recharge systems for blood pressure and proteinuria in south-west coastal Bangladesh: a stepped-wedge cluster-randomized trial

“…Another possible benefit of the MAR system is the improved microbiological quality of MAR water over the pond water. 48 MAR systems filter the pond water when it passes through the sand and gravel layers of the MAR infiltration wells. 14 …”

Assessing the Feasibility of Managed Aquifer Recharge in California

“…Anticipating the influence of MAR on water quality is often not as straightforward as the dilution effect that many of the GSPs rely on, as specific regional aspects of each MAR project can provide numerous mechanisms to improve or degrade water quality. MAR can improve water quality by using recharge water chemistry to drive natural reactions during infiltration and storage that improve water quality (Bekele et al, 2011;Dillon et al, 2003Dillon et al, , 2010Doza et al, 2020) or by preventing or minimizing reactions linked to groundwater extraction that degrade water quality (Smith et al, 2018). However, geochemical and biological responses are specific to aquifer characteristics (e.g., geologic composition, hydrologic composition, microbe population, structure, and temperature) and added water temperature and chemical composition (e.g., contaminants, pH) (Page et al, 2018).…”