Invited review: Anaerobic fermentation of dairy food wastewater

• Published in: Journal of dairy science Vol. 95; no. 11; pp. 6188 - 6203
• Main Authors: Hassan, A.N., Nelson, B.K.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.11.2012; Elsevier
• Subjects: acetates; additives; anaerobic digesters; anaerobic digestion; Anaerobiosis; Animal Feed; Animal productions; Animals; Bacteria, Anaerobic - metabolism; Biological and medical sciences; carbon dioxide; carbon nitrogen ratio; Cattle; chemical oxygen demand; dairies; dairy food waste; Dairying; Fermentation; Food industries; food processing wastes; food waste; Fundamental and applied biological sciences. Psychology; hydrogen; Lactose - metabolism; long chain fatty acids; methane; methane production; methanogens; Milk and cheese industries. Ice creams; nutrient requirements; oxygen; Proteins - metabolism; Sewage - microbiology; sludge; surfactants; temperature; Terrestrial animal productions; Vertebrates; volatile fatty acids; Waste Water - microbiology; wastewater; whey; methane; whey; anaerobic digestion; dairy food waste; Methane; Dairy industry; Dairy product; Anaerobic fermentation; Review; Whey; Anaerobic digestion
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2012-5732

Dairy food wastewater disposal represents a major environmental problem. This review discusses microorganisms associated with anaerobic digestion of dairy food wastewater, biochemistry of the process, factors affecting anaerobic digestion, and efforts to develop defined cultures. Anaerobic digestion of dairy food wastewater offers many advantages over other treatments in that a high level of waste stabilization is achieved with much lower levels of sludge. In addition, the process produces readily usable methane with low nutrient requirements and no oxygen. Anaerobic digestion is a series of complex reactions that broadly involve 2 groups of anaerobic or facultative anaerobic microorganisms: acidogens and methanogens. The first group of microorganisms breaks down organic compounds into CO2 and volatile fatty acids. Some of these organisms are acetogenic, which convert long-chain fatty acids to acetate, CO2, and hydrogen. Methanogens convert the acidogens’ products to methane. The imbalance among the different microbial groups can lead not only to less methane production, but also to process failure. This is due to accumulation of intermediate compounds, such as volatile fatty acids, that inhibit methanogens. The criteria used for evaluation of the anaerobic digestion include levels of hydrogen and volatile fatty acids, methane:carbon ratio, and the gas production rate. A steady state is achieved in an anaerobic digester when the pH, chemical oxygen demand of the effluent, the suspended solids of the effluent, and the daily gas production remain constant. Factors affecting efficiency and stability of the process are types of microorganisms, feed C:N ratio, hydraulic retention time, reactor design, temperature, pH control, hydrogen pressure, and additives such as manure and surfactants. As anaerobic digesters become increasingly used in dairy plants, more research should be directed toward selecting the best cultures that maximize methane production from dairy food waste.