Natural coagulants have been the focus of research of many investigators through the last decade owing to the problems caused by the chemical coagulants. Optimization of process parameters is vital for the effectiveness of coagulation process. In the present study optimization of parameters like pH, dose of coagulant and mixing speed were studied using natural coagulants sago and chitin in comparison with alum. Jar test apparatus was used to perform the coagulation. The results showed that the removal of turbidity was up to 99 % by both alum and chitin at lower doses of coagulant, i.e., 0.1–0.3 g/L, whereas sago has shown a reduction of 70–100 % at doses of 0.1 and 0.2 g/L. The optimum conditions observed for sago were 6 and 7 whereas chitin was stable at all pH ranges, lower coagulant doses, i.e., 0.1–0.3 g/L and mixing speed—rapid mixing at 100 rpm for 10 min and slow mixing 20 rpm for 20 min. Hence, it can be concluded that sago and chitin can be used for treating water even with large seasonal variation in turbidity.

Dependency on sea food has increased owing to its nutrition as well as being complete food. As the production of seafood is enhanced through aquaculture, wastewater release has also improved. The composition of wastewater from aquaculture production has been a concern as it has oil and grease, organic content, etc., which makes its treatment challenging. The present study aims at treating aquaculture wastewater using two natural coagulants—chitin and seeds of Moringa oleifera. The efficiency of the natural coagulants was compared against inorganic chemical coagulant ferric chloride. A blended coagulant with two natural coagulants seeds of Moringa oleifera and chitin was also tested. Jar test apparatus was used in the current experiments, and four coagulant doses were tested against 3 pH ranges, from 6 to 8. The study results showed that the coagulants showed a 30–50% reduction in various physicochemical parameters. Further, the most promising result was obtained with the blended coagulants (di-blend) with 70–81% removal of total nitrogen and total phosphorus and the highest reduction of chloride with 95%. The Fourier-transform infrared spectroscopy showed functionalized groups responsible for coagulation, and X-ray powder diffraction analysis of the blended coagulant indicated the crystallinity and amorphous nature of the compounds. Scanning electron microscope analysis presented a firm and dense structure indicating adsorption of impurities onto the coagulant. Thus, it is evident that natural coagulants can be the solution for the challenges of aquaculture wastewater and specifically the di-blend used in the present is ascertained to be a promising solution.

Coagulation is an essential and easy process to treat water and wastewater and also to adopt for point of use solutions. Coagulants have played a significant role in providing safe and potable water. Nevertheless, the ill effects of chemical coagulants, such as health effects and substantial sludge quantities, cannot be ignored. Under given conditions, the search for alternative coagulants has been the need of the hour, and researchers have presented those natural coagulants are promising alternatives. The exploration and evaluation of plant-based coagulants have shown that these are fit to substitute chemical coagulants sustainably. Previous studies have presented the efficacy of various coagulants but could not fill in the gap existing in terms of a cumulative database of natural coagulants. In these lines, the focus of the current review is to present the history of natural coagulants, the science involved and studies carried out to evaluate them at different levels. Furthermore, a cumulative database of 57 natural coagulants with their efficacy in removing impurities from raw water is presented.