Sequentially Coupled Moringa oleifera Seed Extract and Electrocoagulation Technology for Fluoride Removal

Abstract

Fluoride is an inorganic mineral found naturally in groundwater because of the presence of fluorine bearing rocks and minerals. The presence of fluoride in water has both beneficial as well as harmful effects. Prolonged exposure to high concentrations of fluoride in drinking water can cause serious health effects such as dental and skeletal fluorosis. Moreover, endemic fluorosis is exacerbated in tropical countries where people drink large volumes of water because of the hot climate. Hence, removing excess fluoride from water is critical to ensure access to clean and safe drinking water, especially in rural communities. The Moringa oleifera (MO) plant extract coupled with electrocoagulation (EC) technology has proven to have high fluoride removal rate. The technology presents an ideal alternative to remove excess fluoride as it uses locally available materials, has low maintenance costs, and is a relatively simple process. The MO-EC technology had > 90% fluoride removal rate for all the fluoride concentrations tested at 1, 5, 10, and 15 mg/L. The results showed that higher initial fluoride concentrations required longer time to reach the same defluroidation rate. At 5 mg/L, the MO-EC technology required a run time of less than 5 minutes, at 10 mg/ it required between 5-10 minutes, and at 15 mg/L, it required around 10 minutes to reach the World Health Organization guideline limit for optimal fluoride concentration of 1.5 mg/L. The results also showed that the performance of the MO-EC was not affected by the type of MO extracts tested in the study (leaf, seed, and equal mix of seed and leaf). The MO-EC technology energy costs for water treatment were calculated to be United States Dollar (USD) 0.40/m3 for fluoride concentration of 5 mg/L, USD 0.69/m3 for fluoride concentration of 10 mg/L, and USD 0.88/m3 for fluoride concentration of 15 mg/L. The results also indicate that optimal fluoride removal rates were achieved at 28.8 m2/m3 surface area to volume ratio.Modeling the estimated energy costs based on reported fluoride concentration and optimal fluoride concentration as a function of the daily maximum temperature shows that the energy costs varies according to different regions. Taking additional features such as power supply (solar photovoltaic panels, where required) and sludge filtration into account may be necessary to improve the MO-EC technology and ensure successful implementation of the project in rural communities. Hence, while developing the MO-EC technology parameters, the specifications will have to be developed as per the specific conditions of the individual communities.