Graduation Year

2022

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Engineering

Major Professor

Sarina Ergas, Ph.D.

Co-Major Professor

Kebreab Ghebremichael, Ph.D.

Committee Member

Katherine Alfredo, Ph.D.

Keywords

Biochar, Biosand Filter, Pumice, Sand

Abstract

There are over 20 countries whose citizens consume groundwater containing high levels of fluoride, including Nigeria, Mexico, India, China, and Ghana, which all have major health crises when it comes to the safety of their drinking water. Minerals like fluorite contain fluoride which is often found in groundwater aquifers. The minerals release fluoride into the groundwater. Per the World Health Organization (WHO) standard, the maximum contaminant limit for fluoride consumption should be less than 1.5 mg/L. Chronic exposure of elevated levels of fluoride can cause people to suffer debilitating health effects, such as dental and skeletal fluorosis. Dental fluorosis causes teeth to be pitted, have a damaged enamel, and have yellow or brown stains. Skeletal fluorosis causes pain and stiffness in the muscles and joints and causes crippling changes in the bone structure.

The aim of this study was to modify and improve the design of biosand filters with distinct types of media coated with aluminum hydroxide to maximize its performance for the removal of fluoride, turbidity, organic matter, and E. coli, while also maintaining an adequate filtration rate. There were three specific objectives in this research. The first objective was to compare long term fluoride removal of BSFs with the different media (sand, coated pumice, and coated biochar). The second objective was to compare performance of the different media materials for the removal of turbidity, E. coli, and dissolved organic carbon (measured as UV254). The third objective was to assess the fluoride removal efficacies of uncoated sand and recoated media (coated biochar, and coated pumice).

Initially, adsorption fluoride screening studies were performed to see whether sand and aluminum hydroxide coated media materials (pumice and biochar) could remove fluoride from contaminated drinking water. A bench-scale column study was performed by constructing three biosand filter (BSFs) columns. Of the three, one was filled by uncoated sand as a control, one was filled with aluminum hydroxide coated pumice, and one was a mixture of coated biochar with an additional uncoated sand layer on top. The column study was used to test the efficacy of removing multiple contaminants from drinking water sources (fluoride, E. coli, turbidity, organic matter). Other parameters measured were aluminum concentration, pH, and alkalinity. After the fluoride breakthrough occurred in the biochar and pumice columns, the media materials were recoated to compare the fluoride removal efficacy of uncoated sand and recoated media (coated pumice, and coated biochar) with the initial adsorption fluoride screening studies.

Long term performance studies conducted over a one-year period showed that BSFs with aluminum hydroxide coated biochar and pumice effectively removed fluoride to below the WHO maximum contaminant level (1.5 mg/L). Coated pumice was the most effective at removing turbidity, at up to 98 to 99%, and E. coli. The coated biochar was the most effective at removing organic matter, with removal efficiencies greater than 80%. After fluoride breakthrough in the biochar column, the biochar was recoated with aluminum hydroxide and achieved an effective fluoride removal; thus, demonstrating that the media could be reused. This suggests that the biosand filter can be used for longer periods of time, providing safe drinking water to communities at a household level. The filters are simple to use, and are effective at removing pathogens, turbidity, and fluoride from the water. On the other hand, the coated pumice showed that the pumice exhausted its adsorption capacity, even after recoating. The coated pumice was able to remove the fluoride for a total of 418 days with a fluoride removal of 98% and higher. Coated biochar was able to remove fluoride for 313 days with a fluoride removal of 90% and higher. Although pumice had the greatest fluoride removal, the coated pumice filtered water pH was low and required adjustment. Post treatment using columns filled with oyster shells showed that oyster shells restored the pH to within drinking water standards without compromising other water quality parameters.

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