Anaerobic digestion of dairy wastewater: effect of different parameters and co-digestion options—a review

Increasing demand for dairy products resulted in the development of a large number of dairy industries, generating wastewater of high pollution potential. Main wastes generated include whey residues, milk fat and proteins, dairy sludge, and liquid effluents produced through different lines (cleaning, processing, and sanitary). Anaerobic digestion technology has got wide acceptance in recent times for treating highly organic effluents like dairy wastes due to its added benefits like energy recovery and high waste stabilisation with less energy requirement. This review paper is aimed at studying the effects of different key parameters (pH, carbon-to-nitrogen ratio, temperature, organic loading rate, solid retention time, hydraulic retention time, alkalinity, and mixing) on the successful operation of an anaerobic digester and thereby enhancing biogas production efficiency. Different waste streams generated in the dairy industry are identified along with their important characteristics. The process chemistry of anaerobic degradation of various effluents generated from the dairy industry is discussed. The need for pre-treatment technologies and the scope of co-digestion of dairy wastewater with other organic wastes are also covered. This critical review is intended to summarise the present knowledge on the application of anaerobic methods for treating dairy wastes most efficiently with proper control over operational parameters while maximising the biogas yield. Graphical abstract: [Figure not available: see fulltext.].