ABSTRACT
This chapter deals with anaerobic processes designed to ferment waste materials to methane and carbon dioxide. Anaerobic processes offer two unique advantages compared to their aerobic cousins. First, anaerobic processes can be a net producer of energy because methane is produced that has significant fuel value. Second, anaerobic redox reactions yield a significantly lower Gibb’s free energy change compared to aerobic reactions. Anaerobic treatment is probably the most used process for the stabilization of municipal sludge, including both primary and waste activated sludge. Anaerobic filters are best applied to wastes that are largely soluble because particulates would tend to plug the packed bed. Early designs of conventional anaerobic digesters often included a first-stage, mesophilic digester that was well mixed followed by an unmixed, unheated second stage. Maintaining near neutral pH levels during anaerobic digestion is important because the methane formers are sensitive to low pH conditions.
