Could Plant-Based Flocculants Substitute the Conventional Synthetic Chemicals in the Sludge Dewatering Process?

Due its high water content, sewage sludge dewatering is not just a simple operation; rather, it is a challenging process and a costly management task. Its final handling is usually preceded by several dewatering steps, and among them is the conditioning process known as the flocculation stage, which is carried out using synthetic chemical reagents. Despite the abilities of these additives to reduce sludge volume and extract its bound waters, they are suspected to cause serious environmental and health threats. Their substitution by natural and efficient additives originating from plant extracts could thus be a safe and an eco-friendly alternative, overcoming ecosystem damages. It is within this context that the present review paper critically investigates the efficacy and feasibility of plant-based flocculants, aiming to enhance sludge dewatering and dispense with environmental burdens. To do so, the types of the conventional chemical flocculants, their drawbacks, and their impacts on the ecosystem and human health were addressed. In parallel, the potential dewatering efficiency of plant extracts toward sludge treatment was compiled, and their mechanistic dewatering paths performances were thoroughly discussed. The challenges associated with dewatered sludge and its potential exploitation were also highlighted to motivate scientific communities to further explore green resources for sludge processing. It is suggested that green resources such as Moringa, Cactus, Aloe, and Okra could be used as green flocculants instead of chemical ones, which would provide a promising and eco-sustainable approach to sludge dewatering and might represent a path towards an environmentally friendly and clean technology.