In laboratory studies, the bio-sand filter has been found to remove about 98-99% of bacteria. In removal of Escherichia coli it was found that the bio-sand filter may increase due to biofilm formation over about two months. The removal after this time ranged from 97-99.99% depending on the daily water volume and percent primary effluent added. The addition of primary effluent or waste water facilitates growth of the biofilm which aids bacterial die-off. Research shows that bio-sand filters in use in the field remove fewer bacteria than ones in a controlled environment. In research conducted in 55 households of Bonao, Dominican Republic, the average E. coli reduction was about 93 percent.
Lab tests have shown that while the filters reduce significant quantities of E. coli, they remove significantly fewer viruses because viruses are smaller. In a study using bacteriophages, virus removal ranged between 85% and 95% after 45 days of usage. A recent study has suggested that virus removal increases significantly over time, reaching 99.99% after approximately 150 days.
In one lab test the bio-sand filter removed more than 99.9% of protozoa. In tests for one type of protozoa, Giardia lamblia, the filter removed 100% over 29 days of use. It removed 99.98% of the oocysts of another protozoa, Cryptosporidium sp., possibly due to their smaller size. This removal was comparable with that of the slow sand filter.
Studies in the Dominican Republic and Cambodia conducted by the University of North Carolina and the University of Nevada show that BSF use reduced occurrence of diarrheal diseases by 47% in all age groups. In a study conducted by CAWST in Haiti, 95% of 187 households believed their water quality had improved since using bio-sand filters to clean it. 80% of users stated that their families’ health had improved since implementation. Such health perceptions on the use of bio-sand filter has shown to be more positive in long-term users.
Concrete bio-sand filter
Concrete filters, of concrete, are the most widespread type of bio-sand filter. Concrete is generally preferable to other materials because of the low cost, wide availability and the ability to be constructed on-site. The plans for the concrete filter are distributed openly by CAWST. Several versions have been developed. The CAWST Version 9 bio-sand filter is constructed with a higher maximum loading rate. Although the filtered water passes EPA water quality standards, it is not optimal. Recent research establishes that contact time between the water and the granular material is the leading determinant in purifying water. The CAWST Version 10 bio-sand filter takes this into account; the volume of the water reservoir is equal to the pore space volume of the sand layer. The maximum loading rate was decreased by 33% to ensure stagnant water is in constant contact with granular material.
In a natural or man-made disaster, water is more vital to survival than food for the first 20 to 40 days! You can easily live forty to 60 days without food if you have clean health drinking water. The SRV conserves every drop, wastes none! All the grey water (from sinks, shower and washing machine) is recycled through a unique system of filtration and distillation. The 100 gallons stored under the raised bathroom floor, can be used over and over indefinitely with no fear of using or drinking unsafe water. There is an additional 50 gallons of pure clean distilled drinking water.