Wastewater treatment in dairy industries — possibility of reuse

The reuse of wastewater from the dairy industry was investigated using coagulation, adsorption and membrane separation. Dairy industry was chosen as it requires huge volume of water. In recent times, development of newer membranes with high flux/rejection characteristics have increased the probability of water reuse and recycling up to a greater extent. In this investigation thorough pretreatment studies were done using different types of coagulants categorized as inorganic, polymeric, and organic having biological origins. The coagulant treatment was performed at various pH using different dosages and it was followed by activated charcoal treatment. The combined effects of these two pretreatment methodologies were evaluated. The color and the odor were removed completely and permanently after charcoal treatment. The pretreated water was passed through a cross flow reverse osmosis membrane system and the permeate water was found to have very good quality. This was compared to the process water used by the dairy farm and was found that the water can be recycled or reused.

Chitosan at very low dosage, 10 mg/L was found to be a better coagulant compared to inorganic and organic coagulants. PAC treatment after chitosan was found to be useful in complete removal of color and odor of the wastewater before membrane processing. Performance of chitosan and PAC is pH dependent. Chitosan and PAC work efficiently at the same pH 4.0 and comprise the RO pretreatment step suitable for dairy wastewater. Pilot scale experiment using spiral wound RO membrane yields better water quality compared to flat sheet membranes used in bench scale experiments. The quality of water after reverse osmosis was found to be comparable to that of process water used in the Dairy and can be recycled back.