A Review of Natural Polysaccharides-Based Flocculants Derived from Waste: Application Efficiency, Function Mechanism, and Development Prospects

The application of conventional flocculants always causes degenerative diseases, whereas natural polysaccharide (NPs)-based flocculants exhibit great potential, due to their biosafety. Considering material costs and sustainable development, NPs derived from waste have been extensively researched as a substitute for conventional flocculants, promoting the development of flocculation process toward safety, economy, and low-carbon direction. This review summarizes various waste polysaccharides (WPs) derived from ocean waste, agricultural waste, food waste, and invasive species. It then compares the treatment effects of typical WPs-based flocculants in water treatment. Flocculation mechanism of WPs-based flocculants was emphasized based on their respective structures and physicochemical properties. Moreover, flaws in WPs application have been noted, and strategies to deal with them have also been proposed. Benefiting from the environmental and economic benefits of WPs, the progress of using WPs-based flocculants is promising. However, some threats should be overcome, especially in terms of the stability and broad-spectrum applicability of WPs.