Final Report: Novel reactor design for enhanced removal of fluoride using a modified Nalgonda methodEPA Grant Number: SU836117
Title: Novel reactor design for enhanced removal of fluoride using a modified Nalgonda method
Investigators: Weber-Shirk, Monroe
Institution: Cornell University
EPA Project Officer: Page, Angela
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $14,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , Sustainability , P3 Challenge Area - Water
Ground water is a feasible source of drinking water for many communities. In India, more than 80 percent of water is obtained from ground water sources (The World Bank, 2012). Dependence on ground water becomes a health concern when the aquifer’s composition contains minerals that cause fluoride contamination. Fluoride ions are highly soluble in water, which makes treatment extremely difficult. In developing countries and rural villages, fluoride removal becomes an even greater challenge because technology and funding are limited. AguaClara seeks to overcome obstacles by creating innovative solutions focused on promoting environmental, social, and economic sustainability.
Few fluoride remediation methods are available, and most of them are expensive or are not effective at high fluoride concentrations (Singh, 1999). Fluoride removal by adsorption to aluminum sulfate precipitate is known as the Nalgonda method (Venkobachar, 1997). In this method, aluminum sulfate is added to a batch of fluoridated water and the solution is mixed and allowed to settle. However, high aluminum sulfate concentrations are necessary and result in a large sludge volume and elevated sulfate concentration in the treated water (Fawell, 2006). The proposed research uses Polyaluminum chloride (PACl) and a continuous flow reactor to dramatically reduce the required chemical concentration. Previous research demonstrated that arsenic readily adsorbs to PACl (Zhi, 2015). Given that adsorption techniques are also an effective fluoride removal method, the proposed research tested PACl as the coagulant in the continuous flow reactor.
A direct filtration reactor system for the removal of fluoride was tested with an influent fluoride concentration of 10 mg/L (Figure 1). PACl was added at 20, 40, and 50 mg/L as Al. As expected, fluoride removal increased with PACl dose. Results showed that a PACl dose of 50 mg/L as aluminum (Al) effectively reduced fluoride concentrations from 10 mg/L (Dao et al., 2015) to meet the World Health Organization (WHO) fluoride standard of 1.5 mg/L (WHO, 2011). The 50 mg/L Al as PACl is much lower in contrast with the 1,200 mg/L Al as aluminum sulfate required to treat similar fluoride concentrations (Dahiet al., 1996). These results suggest that a continuous flow PACl based fluoride reactor system provided effective removal and significant improvement in performance over the Nalgonda method.
Ground water fluoride contamination poses a health threat to more than 66 million people in India (Arlappa, 2013). According to the WHO, dental damage can occur at a fluoride concentration above 1.5 mg/L and crippling skeletal damage can arise at a concentration above 10 mg/L (WHO, n.d.). Therefore, access to safe drinking water is critical in maintaining the health and productivity of a community. In Phase I research, the student team demonstrated that fluoride contamination of 10 mg/L can be successfully treated to safe drinking standards using PACl in combination with sand filtration.
Although the highly soluble fluoride ions are difficult to remove from water, results from Phase I demonstrated the potential for efficient removal using PACl and direct filtration. Experimentation proved that PACl and continuous flow direct filtration removed enough fluoride to reach WHO standards of 1.5 mg/L (WHO, 2011). Compared to previously documented values (Dahi et al., 1996), the apparatus used in Phase I required 24 times less mass of aluminum per mass of fluoride removed.
AguaClara’s improved fluoride removal technique incorporates the elements of People, Prosperity, and the Planet into a sustainable water treatment system (Rivas, 2014). The technologies are designed to use non-proprietary materials available in the national supply chain, and leverage community engagement and municipal resource management. Advanced technologies that deliver operational simplicity can decrease failure modes and improve economic efficiency. The long-term goal of AguaClara is to create and implement reliable and intuitive designs so communities can independently maintain their own water treatment system. The improved PACl fluoride treatment system embodies the idea of optimization by accomplishing fluoride removal with 24 times less mass as aluminum than the Nalgonda method. As a result, less residual sludge is generated. Since less coagulant and physical labor is necessary, the improved fluoride treatment technique has the potential to improve access to safe drinking water in villages with contaminated groundwater.
Supplemental Keywords:Continuous flow reactor, arsenic removal, floc blanket, fluidized bed, hazardous waste reduction, ground water treatment