Optimum Operating Conditions of Drinking Water Treatment System for Fluoride Removal using High Adsorption Bone Char

摘要

Objectives:Bone char is used in many eastern countries in Africa to remove high levels of fluoride from groundwater. However, due to the low adsorption efficiency of bone char, it is necessary to replace bone char frequently, which cause significant burden to the people in those areas. In this study, we developed a water treatment system to remove high level of fluoride in groundwater using a high efficiency bone char. Methods:In order to make a high efficiency bone char, cow bones were washed, dried and cut into small pieces. Then the bones were burned for 1, 3 and 5 hours at 350, 450 and 550℃ in electric furnaces. After that, the burned bones were sieved with 600~2,000 µm to match the size of bone char being used in Ethiopia. Surface analysis of bone char was performed using SEM and BET. The removal efficiency of bone char was conducted with various level of turbidity, TOC, and fluoride concentration for 90 minutes under the flow rate conditions of 100, 200, 300, and 400 L/day with an initial fluoride concentration of 4.8 mg/L.Result and Discussion:There was a significant difference between the bone char from Ethiopia and our study in terms of their surface roughness and specific surface area according to SEM and BET analysis. The adsorption capacity of the bone char produced in this study was 3.7 mg F/g, compared to 1 mg/L from the one from Ethiopia. In terms of turbidity and organic matter removal with column test, 200 L/d showed the shortest operating time to reach turbidity of less than 0.5 NTU, and was an effective operation for TOC removal. However, It took the longest to 1.5 mg/L of fluoride after breakthrough under 100 L/d operating conditions. In terms of operating time, bed volume, and energy efficiency, 100 L/d was found to be an effective operating condition. Conclusions:We developed a high efficiency bone char in this study with modification of its production process and tested it at various operating conditions. Our study showed that the bone char developed in this study is about 4 times more effective than traditional bone char and it is most effective at operation with low flow rates. Column operation is most effective at 100 L/d for fluoride removal under operating time and bed volume and energy efficiency. Therefore operating condition of drinking water treatment system for the fluorine removal using bone char in developing countries is effective in low flow rate operation.