Laboratory and field studies to compare fecal coliform counts in water from biosand filters following periods of either intermittent use or following a pause in use in Boston MA and san juan del Sur, Nicaragua

Guidelines indicate that biosand filters should be primed with source water every two days and not paused for longer than 48h1. Once paused, it is not clear how quickly the filters can be re-primed. The efficacy of filters following intermittent priming and re-priming following pause is reported here. River water in Boston was filtered through a plastic filter and field testing was conducted on disused, re-primed concrete filters in Nicaragua. All filters were based on CAWST specifications1. Fecal coliform counts were analyzed from source and filtered water. The water was tested using either MPN count or membrane filtration. Intermittent mean data ranged from 99.7% and 99.8% removal of fecal coliforms whereas re-primed data for a paused plastic filter ranged from 92%-98.3%, mean 95.5%. This did not meet MANZ standards but fell within WHO ‘low risk' for drinking water in developing countries2. For re-primed concrete filters in Nicaragua, the mean fecal coliform count in well water samples was 647/100 ml. The mean count in filtered water samples was 17/100 ml. Of eight filters tested, three showed zero fecal coliforms, giving an average 96.95% removal efficiency. The filters that did not meet MANZ and WHO standards were those where the source water was most heavily contaminated. Of eight concrete filters tested following pause, removal efficiency ranged from 88% to 100%. Whilst all of the re-started filters showed reduction in fecal coliforms compared to source water, further investigation is required to better understand why some of the paused, re-primed biosand filters under-performed