Fabrication and Monitoring of Single and Double Unit Ceramic Filters for Arsenic Removal

Abstract

Arsenic contamination of groundwater is one of the vital concerns of human health all over the world, especially in Bangladesh, India, Argentina, Vietnam, Mexico, etc. Among those, Bangladesh and West Bengal of India are most adversely affected. Many technologies have been tried to be induced, but a cheap, easy and more effective technology is yet to come. The project focused on the development, and also the checking of the performances of that filter unit. The filter unit worked in the biological oxidation process by the cultured iron bacteria for arsenic removal. The treatment unit was composed of a ceramic filter, iron net, iron oxidizing bacteria, clay pot reactor, stand, and bucket for the effluent storage. The ceramic filter was made of locally available cheap materials (i.e. clay soil and rice bran). This filter unit was firstly installed with iron net as the source of the iron. After that, single unit filter systems with different iron options as iron net, scrap iron and iron rod were installed and run for long time. These two attempts were taken to check the suitability of single unit filter systems in case of household tubewells with highly arsenic contaminated water. Double unit filter systems were then developed and installed in the field. Firstly double unit filter systems with both 'W-system' and 'Connect system' were installed and nm to compare the performances. There was no big difference found between the performances of these two ways of double unit filtration. Then double unit filter systems with 'Connect system' were being run continuously for the long run. In case of arsenic removal, the single unit system was not able to reduce the arsenic concentration level to allowable limit, as the raw waters of all the sites were highly contaminated. The average removal efficiency for two single unit filter systems was 65.56% and 67.34% respectively. Average iron removal efficiency was almost 100%. The comparison among the results of single unit filter systems with iron net, scrap iron and iron rod showed that whatever the iron producing option in the single unit filter system the performances remain almost same. Average arsenic removal efficiency for single unit filter systems with net, scrap and rod ion was 73.63%, 74.42% and 73 .73%, respectively during the long run of the filter units in the field. Iron removal was successfully accomplished by every option as iron net, scrap iron or iron rod and average iron concentration was reduced from 7.90 mg/L to almost zero. The color removal efficiency for filter units with iron net, scrap iron and iron rod were as follows 97.15%, 94.70% and 97.11%. Also the turbidity of the raw water samples was reduced significantly by the filtration process. Influent and effluents with iron net, scrap iron and iron rod contained turbidity of average values 98.99, 10.25, 10.65 and 10.79 NTU, respectively. Prior to the long run of the double unit filter system in field level; a short study was performed in the same household to choose the way of double filtration ('W-system' or 'Connect system'). Arsenic removal efficiency was nearly same in case of double unit filter systems with 'W-system' and 'Connect system'. In 'W-system', the removal efficiency in 1st effluent and 2nd effluent were as 63% and 86.21%, respectively and in 'Connect system', the final removal efficiency was 83.96%. The average values of influent, 1St effluent, 2nd effluent and final effluent were 406 µg/L, 149 µg/L, 57 µg/L and 65 µg/L for 'R1double'; while 421 µg/L, 151 µg/L, 57 µg/L and 62 µg/L for 'R2double' respectively. Also from the performances with respect to other water quality parameters it was found that whatever the way of double unit filtration the performances had a little difference. Most of the cases, the double unit filter system was proved effective to reduce the arsenic concentration to the allowable standard limit (Bangladesh standard 50 µg/L). Average removal efficiency of 'R1double' and 'R2double' for the long monitoring study was 88.19% and 87.33% respectively. Average influent and final effluent arsenic concentrations were 419 µg/L and 50 µg/L for 'R1double', and 416 µg/L and 53 µg/L for 'R2double'. Iron removal efficiency was 100% for both 'R1double' and 'R2double'. Also the average color and turbidity removal efficiency was above 95%. Flow rates for different filter options were important factor. It was found that the flow was reduced with time due to the clogging of the filter core. For good filtration rate and removal efficiency, the filter core was cleaned in very 30 days. The cost of the treatment unit was approximately 150 200 BDT only and the maintenance was very easy and economic. Thus, the filter unit could be widely used in different arsenic contaminated rural areas of Bangladesh.