Pretreatment methods to enhance anaerobic digestion of organic solid waste
Biological pretreatment
Biological pretreatment includes both anaerobic and aerobic methods, as well as the addition of specific enzymes such as peptidase, carbohydrolase and lipase to the AD system. Such conventional pretreatment methods are not very popular with OFMSW, but have been applied widely on other types of OSW such as WWTP sludge and pulp and paper industries.
The hydrolytic-acidogenic step (first step) of a two-phase AD process is considered as a biological pretreatment method by some researchers [3], [95], [96] and [97], while others consider it as a process configuration of AD, but not a pretreatment method [31]. Physically separating the acidogens from the methanogens can result in a higher methane production and COD removal efficiency at a shorter hydraulic retention time (HRT) as to conventional single-stage digesters [98]. Parawira et al. reported that optimizing the first hydrolysis stage could stimulate the acidogenic microbes to produce more specific enzymes, thus resulting in more extended degradation of substrates [99]. Therefore, in this review paper the first step of the two-phase AD systems are considered as a pretreatment method.