Implications of natural coagulants and the development of a chemical coagulation reactor for dairy wastewater treatment with product recovery from waste sludge

The dairy sector in India faces water wastage since the dairy industry is an example of a wet industry. Globally, India ranks first in milk output and population; therefore, the treatment and reusability of water is a hot topic in this present context. Coagulant-aided wastewater treatment is an emerging trend. Even though the chemical sludge generated in chemical coagulant–mediated wastewater treatment is still a problem to be managed. This research aims to evaluate the performance of Hibiscus rosasinensis, lemon peel, and orange peel coagulants as natural coagulant sources for dairy wastewater treatment. The water treatment using natural coagulants is time-consuming. Among the selected natural coagulants, the lemon peel coagulant achieves impressive results, with a maximum turbidity removal of 75.15% and COD removal of 78.44% after 24 h of reaction time. In comparison, the orange peel coagulant attains a maximum turbidity removal of 65.15% and COD removal of 84.48% but requires a slightly longer reaction time of 48 h. A chemical coagulation reactor (CCR) is designed with a working volume of 9.05 L and operated continuously using chemical coagulant (FeSO₄) for 48 h. The achieved turbidity removal was 82 to 84.43%, reducing at an optimized coagulant dosage of 18 g/L. A limited number of studies have suggested sludge biomass management and utilizing natural coagulant–mediated dairy sludge for product recovery. As a result, this study recommends using dairy sludge made after wastewater treatment by natural coagulation as a source for producing animal feed and using chemical coagulation sludge for making compost. The results show that an efficient composition for compost production is a 1:1:1:1 compost mixing ratio of dry leaves, chemical coagulant dairy sludge, industrial sludge, and coir pith.