As stated above, a successful economic outcome for anaerobic digesters may be dependent on co-digestion of, for example, animal manures with other organic feedstocks (only when other feedstocks are available locally). In addition to crops and crop residues, the use of food and organic industrial wastes offers excellent possibilities to develop waste management opportunities for these wastes and to avoid increasingly costly and limited landfill disposal. Manure co-digestion increases the buffering capacity of substrate mixtures and adds nutrients that can increase methane yields and substrate affinities compared with digestion of one substrate (Mladenovska and Ahring 2000; Mladenovska et al. 2003). Despite the perceived benefits of co — digestion, the overall and specific knowledge of adding organic feedstocks relative to single substrates is very limited (both the synergistic and antagonistic effects). Therefore, we initiated a study to evaluate the potential of co-digestion of dairy manure with a variety of organic substrates. The results of ~175 individual biochemical methane potentials (BMPs) on more than 30 different substrates showed that substrates rich in lipids and/or carbohydrates with a high VS content are good candidates for co-digestion with dairy manure (Figure 4.1; Labatut and Scott 2008). A critical parameter to estimate the BMP of a myriad of substrates is the substrate biodegradability and we suggest that future research needs to develop models to estimate the methane potential of the numerous farm waste options based on biodegradability of substrates.

From a logistic and economic perspective, the availability of food wastes and distance from source to farm anaerobic digester is critical because of transportation costs and energy con­sumption. The development of geographical information systems (GIS) offers a useful way to connect food waste sources to existing digesters (Ma et al. 2005). We developed a web site (http://wastetoenergy. bee. cornell. edu/) to identify the location of dairy farms and sources of food waste from food processors, restaurants (including fast food), universities and col­leges, K-12 public schools, supermarkets, correctional facilities, hospitals, and nursing homes. This tool has proven effective to link the mutual interests of the farmer and food waste sources.