Natural flocculants for the treatment of wastewaters containing dyes or heavy metals: A state-of-the-art review

Flocculation is a water and wastewater treatment technology whereby the large aggregation of flocs in water can be formed and be later separated through sedimentation. This review aims to provide the recent developments in the field of natural flocculants and their prospects for the effective removal of dyes or heavy metals from aqueous solutions. It provides a concise information on the types, characteristics and toxicity of dyes or heavy metals. It also covers a comprehensive list of natural flocculants, namely chitosan, starch, microbial, tannin, cellulose, and gelatin (including their derivatives where applicable). In addition, the performances and mechanisms for the removal of dyes or heavy metals as demonstrated by the natural flocculants (and their derivatives) are summarized and thoroughly discussed. Furthermore, the economic analysis of the natural flocculants is elucidated in order to give a perspective on the practicality of this technology in real application. Finally, the future prospects, challenges and recommendations are presented in order to advance the research in natural flocculants. It is anticipated that natural flocculants have a great potential to be further harnessed. By conducting more in-depth scientific research on natural flocculants, more significant breakthroughs can be discovered and this sustainable water treatment will be able to enhance the global water security in the long term.