This review investigates the modification, optimisation, and characterisation of plant-based natural coagulants applied to water treatment. The disadvantages of plant-based materials hinder their application as alternatives to chemical coagulants, necessitating their modification to alter and enhance their physicochemical properties, making them suitable for application. Modification via microwave-assisted grafting copolymerisation has been found to be the most preferred approach compared to conventional methods. Optimisation of the coagulation process using response surface methodology has been shown to be practical. Different techniques are used in determining the physicochemical properties of plant-based natural coagulants. Some of these techniques have been tabulated, describing the properties each technique is capable of investigating. In conclusion, modification and optimisation of plant-based natural coagulants will result in the production of new materials that are stable and suitable for application as coagulants in water treatment.

This study investigated the efficiency of LENFLOC^™ production using a microwave-assisted continuous-flow grafting process. The study discussed the contribution of plant-based coagulants for water and wastewater treatment toward the circular economy in water treatment. Lentil waste extract was used to produce LENFLOC^™ using (2-methacryloyloxyethyl) trimethyl ammonium chloride with 75 wt.% on H₂O as a chain monomer and cerium ammonium nitrate (≥98%) as an initiator. The continuous flow grafting process was conducted at a constant flowrate of 60 mL/min and reaction time of 30 s. The process was optimised using RSM to obtain optimum conditions of process factors. Characterisation studies were conducted using Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray. A comparison study was performed using a Jar test with LENFLOC^™, lentil waste extract, and a polymer as coagulants. The results obtained show that the continuous-flow grafting process was efficient with an optimum grafting percentage of 330%. The characterisation studies confirmed the grafting process. A 99% turbidity removal rate was achieved with LENFLOC^™ as a coagulant with a lower dosage compared to the lentil waste extract. Furthermore, microscope imaging showed improved floc compaction when using LENFLOC^™ as a coagulant. The continuous-flow grafting process has been shown to be effective; therefore, its potential for upscaling the process is possible.

The ever-present environmental crises are current research hotspots. Nature-based solutions have been shown to have multiple co-benefits toward solving these crises. Plant-based coagulants are known to be a cost-effective and environmentally friendly approach for coagulation and flocculation processes for drinking-water treatment. In this study, a natural coagulant was extracted from Annona diversifolia seed, and its effectiveness was investigated for turbidity reduction using jar test in kaolin suspension, river water, and evaluation of factors for sludge dewatering. The characterisation studies of Annona diversifolia seed extract were carried out using techniques including Fourier-transform infrared spectroscopy (FTIR), zeta potential analyser, and transmission electron microscopy (TEM). Response surface methodology (RSM) was also performed for the optimisation study. The results from FTIR showed that Annona diversifolia seed extract contains carboxyl and hydroxyl functional groups. The charge density was found to be negative. A web-like structure surface morphology was observed from TEM. The optimum treatment settings were found to be at pH 3 and a dosage of 25 mg/L for water treatment, and 50 mg/L for sludge dewatering, which were comparable to the metal–salts coagulants. Annona diversifolia seed extract has been shown to be a good natural coagulant. Further research can be conducted to modify and enhance its performance.