Coagulation and flocculation are basic chemical engineering operations employed to remove suspended solids from water. The growing concern for environmental and ecological issues warrants the use of the biodegradable flocculants in wastewater and industrial effluent treatment. In this work, unconventional coagulant, namely lactic acid, calcium lactate, sodium lactate, and citric acid were studied in comparison with AlCl3, a usual coagulant widely employed to remove water turbidity. It was observed that lactic acid and calcium lactate were able to reduce the water turbidity similarly to AlCl3. This fact can be very interesting because lactic acid salts can be produced by biotechnological process, and contrarily to aluminium salts, they are biodegradable, reducing the risk for human and animal’s health.

A novel tannin-based coagulant has been synthesized at lab scale. A multiparameter optimization was performed on the production process, and up to five variables were studied according to the response surface methodology in a face-centered design of experiments which included two temperatures, two pH levels, and the reaction time in the chemical process. The coagulant involved diethanolamine, formaldehyde, and a tannin extract from Acacia mearnsii de Wild. The results revealed an average optimum combination for dye and surfactant removal which was able to remove either Alizarin Violet 3R and sodium dodecylbenzene sulfonate efficiently from water effluents.

The occurrence of fluoride in groundwater has been reported in many countries, mainly because the excess fluoride in drinking water can lead to dental or skeletal fluorosis. Fluoride removal by coagulation with Moringa oleifera seeds, followed by separation with membranes, was investigated in this work. Artificially fluoridated water, at a starting fluoride concentration of 10 mg L⁻¹, was submitted to a coagulation process with aqueous extracts of M. oleifera seeds. The coagulation process was followed by ultrafiltration with membranes at different pressures. The coagulation process with 2.5 g L⁻¹ of M. oleifera promoted a reduction of 90.90 % in the fluoride content of the treated water, making it possible for poor communities to consume this water. It is noteworthy that the combined coagulation/filtration process using raw coagulant showed the highest values of colour and turbidity, which, however, were still below the limits set for drinking water by Brazilian legislation. The advantage of proposing a sequential process using membrane separation is that it removes colour and turbidity, caused by the use of M. oleifera as a coagulant, resulting in water that meets potability standards.