Baseline Performance Monitoring of Commercial Dairy Anaerobic Digester

Manure is generally a low quality wastewater for biogas production as much of the organics have already been biologically converted during animal digestion. Because of this, the resulting manure is composed to a large degree of stabilized or recalcitrant organics, resulting in only limited biogas production from its subsequent digestion. Despite the low production, though, manure provide stability to the digestion process as its organic loading is relatively low and it is highly alkaline which controls the pH throughout the digestion process (Callaghan et al., 2002; Hartmann and Ahring, 2005). In contrast, other wastewaters such as food processing wastes, industrial greases and oils, and organic fraction municipal solids (OFMSW) are rich in biodegradable organics and correspondingly contain a large biogas production potential. Unfortunately, these wastes are often difficult to digest in practice as they are often too high in organic loads, contain high levels of inhibitory substances, and contain low levels of alkalinity or buffering capacity to control pH adequately throughout the digestion process (Gallert and Winter, 1997). Notably, the biogas industry has recognized the beneficial effects that can be achieved by combining the digestion of manures with other organically-rich wastewaters or waste solids, namely increased biogas production and enhanced stability. This practice is called co-digestion, with the non-manure waste streams being referred to as substrates, and although considerable research has been done at laboratory scale (Alatriste-Mondragon et al., 2006; Braun et al., 2003), little demonstration of co-digestion has been done at commercial scale (DEA, 1995; Kaparaju et al., 2002; Kumke and Langhans, 2000).