Reduction of water hardness with a compact slow sand filtration system

Hardness has a marked effect on the taste of water and it is very important in the manufacture of food. Consequently, water treatment plants in regions with high levels of water hardness typically treat the water chemically before filtering and processing it for further use. We examined the effectiveness of slow sand-filtration for reducing water hardness. Specifically, we examined whether the method, which is safe, simple, inexpensive, and does not employ chemicals, could be used to soften very hard water and produce water that is suitable for producing food. We devised a small, pilot-scale, slow sand-filtration system consisting of three gravel filters and one sand filter connected in series. First, we circulated the water samples through the three gravel filters only, and then measured the hardness of the water by chelatometry. The results showed that water hardness was markedly reduced by filtration through the gravel filters only. The amount of reduction in water hardness was found to correspond to the temporary hardness component of the water samples. By investigating the structure of coarse filter columns in use at water purification plants, it may be possible to soften hard water and produce high-quality water suitable for both food production and drinking without the need for chemical treatment.