Biosand filters in Ghana contribute to a 60% overall reduction in diarrhoeal disease
An 8-month randomized controlled trial of the plastic biosand filter was performed in 6 rural communities in Tamale, Ghana, during 2008 by Stauber et al (2012). The trial was carried out in order to assess reductions in diarrheal disease and improvements in household drinking water quality. During the study, the longitudinal prevalence ratio for diarrhoea comparing households that received the filter to households that did not receive it was 0.40 (95% confidence interval: 0.05, 0.80), suggesting an overall diarrheal disease reduction of 60%. Further details are available here.
The effect of pause time on water quality: new research out
Research published by the University of North Carolina has confirmed the importance of residence time of water in a filter. Regarding the daily amount of water put through the filter, they found that microbial reductions were greater with a greater residence time within the filter, especially for water retained in the filter bed overnight. The researchers showed this through taking samples of filtered water at various stages when the filter was re-started after pause time – a significant drop in filtrate quality was noted after the pore volume threshold had been filtered. This showed that water that had been sitting in the filter during pause time had a much better quality, and this seems to be largely due to the increased contact time for biological and chemical processes in the sand. More information here.
Over 47% reduction in diarrhoea risk: new health impact studies on the BSF
A few health impact studies are starting to emerge on the biosand filter. These look at how much impact the filters have on diarrhoea in real life situations. So far, results are encouraging and confirm the anecdotal evidence that many of us hear from sand filter users in the field. Two studies carried out in the Dominican Republic and Kenya showed a reduction in diarrhoea risk of 47% and 54%, indicating a significant protective effect of the BSF against waterborne diarrheal disease. More information here.