Biosolids

Complex Organics

Lipids Polysaccharides Proteins Nucleicacids

Phase I - Hydrolysis

Phase I - Hydrolysis

Figure 16.40 Anaerobic biosolids digestion metabolic phases.

the previously hydrolyzed organics are transformed into three substrate precursors (i.e., CO2, H2, and acetate) in preparation for the concluding methanogenesis transformation. Two different types of acidogenesis reactions are involved: one- and two-step conversions. The first such mechanism produces acetate primarily (i.e., by means of an acetogenic conversion, encompassing reactions that produce organic acids directly), whereas the second fermentative conversion involves intermediate production of volatile fatty acids (e.g., butyric and proprionic acid) and alcohols, which are converted subsequently to acetate, hydrogen, and carbon dioxide. The latter conversions are mediated by a wide range of gram-positive and gram-negative bacteria, whose classifications depend on the primary form of their fermentative products (Table 16.11).

TABLE 16.11 Fermentative Bacterial Types and Products

Anaerobic Reaction Products

Fermentative Bacterial Groups

Representative Bacterial Forms te at n o ri p o ra ty ut B

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