Defluorination Effectiveness of Modified Biosand Filters

Abstract

The most substantial sources of fluoride exposure are located in the Rift valley. It has been reported that people in the Rift Valley are consuming water with up to 33 mg/L of fluoride. The WHO has set 1.5 mg/L as the maximum permissible limit for fluoride in potable water. The use of water with high fluoride concentration poses a health threat to millions of Kenyan residents. Biosand filter (BSF) is a low-cost technology that has been implemented in Kenya. Several studies have shown that the BSF can reduce the turbidity and microbial contaminants effectively however, limited studies have focused on removal of fluoride. Various low-cost materials like bamboo activated charcoal, bone char, diatomite and steel wool were investigated to assess their capacity to remove fluorides from water by batch adsorption studies. Experiment was also conducted to determine the effect of the modified filter on bacteria reduction using E. coli as an indicator. The measurements of the standard Biosand filter were scaled down and 18 modified filters were designed. The modified and standard Biosand filters were subjected to trials in the laboratory where 1.5, 2.26 and 3.0 mg/L initial fluoride concentration were subjected to 30, 60 and 90 minutes contact time in order to reduce fluoride concentration to the desired level of below1.5 mg/L. E. coli was cultured and serially diluted into sterile saline deionised water and passed through modified biosand filters. Data obtained was subjected to Microsoft Excel t- test and analysis of variance. The modified filters absorbed a significant amount of fluoride (p>0.05). It was also observed that there was a significant removal on the contact time (p>0.05). Modified filter performed significantly better (p<0.05) than the standard filter, removing 97% of fluoride after 24 hours and treating the water to below the WHO fluoride limit of 1.5 m/L. This study also indicated that the standard biosand filter removed the highest amount of E. coli bacteria with removal rate of 96%. bamboo activated charcoal, diatomite, bone char and iron oxide (Fe0) removed 90, 85, 81 and 70% respectively. This study's findings indicate that the modified filters can be an effective in removing fluoride from water so the study recommends that it be manufactured using locally available materials and implemented for local communities.