A review of selected natural coagulants in water and wastewater treatment

Water treatment by inorganic coagulants and synthetic polymers poses environmental challenges tied to trace metals and sludge quality/quantity. With the popularisation of chemical precipitation during the last 50 years, these challenges have become more apparent. As a way to combat the environmental challenges posed by the use of inorganic coagulants and synthetic polymers, natural coagulants have been explored for water treatment. Natural coagulants are biodegradable, non-toxic, and do not pose any of the environmental challenges that inorganic coagulants and synthetic polymers do. This literature review aims to research the treatment efficiency and coagulation mechanism of two of the most promising natural coagulants, chitosan and Moringa oleifera, and compare them to more traditional inorganic coagulants and synthetic polymers. In this context, natural coagulant refers to natural polymers used as a primary coagulant for water treatment. Based on a review of literature on water treatment by the natural coagulants chitosan and Moringa oleifera seeds, a table for each of the natural coagulants were made where key information such as treated water type, experimental setup, achieved removal efficiency, and reported coagulation mechanisms were noted. Analysis of the results of researched literature showed that both natural coagulant excelled at removing pollutants commonly found in portable water treatment, however, few studies were found on their use in wastewater treatment. The coagulation mechanisms reported were adsorption, charge neutralization, bridging, and electrostatic patch mechanism. The results indicate that both reviewed natural coagulants can compete with inorganic coagulants for portable water treatment, but more research is needed on the treatment of wastewater before a fair comparison can be made. Further research should be directed at the implementation of chitosan in combined processes, and the use of purified protein from Moringa oleifera seeds in water treatment