Moringa-Functionalized Rice Husk Ash for Potential Use in Water Disinfection

Moringa oleifera, a tree indigenous in tropical and sub-tropical areas, has been widely used in water purification in many low-income regions such as Africa, India, and Asia. Its seeds are known to contain proteins that possess coagulating and antimicrobial properties but its use in water treatment is compromised by the corelease of soluble organics in the seeds. These organics can serve as food for pathogen regrowth, causing problems with the storage of treated water. The current study investigated the potential for selective functionalization of the Moringa protein onto rice husk ash (RHA). RHA was soaked in different concentrations of Moringa solution until equilibrium sorption was achieved. The dissolved protein in solution was measured using an optical density meter at 280 nm. Moringa sorption on the RHA surface was also examined under a confocal laser scanning microscope (CLSM) by tagging the protein with green fluorescent dye. The potential leaching of bound Moringa was investigated by taking TOC (total organic carbon) measurements in water before and after addition of the functionalized RHA. Results show a strong potential for eliminating undesired organics in treated water through Moringa protein sorption onto RHA. Further, the Moringa protein binds strongly onto the RHA surface, and that the sorption process is irreversible. The antimicrobial property of the Moringa-functionalized RHA was also tested using different E. coli in water (103-105 CFU/mL). The functionalized RHA exhibited bactericidal property, and high E. coli removals were observed (%). E. coli removal in the control samples (bare RHA) was also observed but further CLSM analysis of tagged E. coli showed that the E. coli was inactivated in the functionalized RHA but not on the bare RHA. In summary, these results indicate a potential solution for the storage problem of water treated with Moringa, and that Moringa functionalization can effectively enhance the capability of typical adsorbents such as rice husk ash which inherently cannot inactivate bacteria.