Aerobic Digestion

Whether collected within wastewater treatment plants, solid waste landfills, or simply on a forest floor, organic solids will naturally degrade and decay under aerobic conditions through the natural process of oxidative breakdown. The microbial cells found in raw sludge will therefore undergo much the same progressive sequence of cell lysis, release of cytoplasmic materials, and final oxidative conversion within an aerobic digester, whereby the organics released from lysed cells serve as a source of substrates for other living aerobic cells. The metabolic conversion of wastewater sludge through aerobic digestion, such as the unit depicted in Figure 16.47, subsequently converts an initially organic-rich sludge matrix into carbon dioxide and residual solids that include not only both inorganic and recalcitrant organic forms but also the remaining complement of meta-bolically active aerobic oxidizers. The resulting product has the advantage not only of

Raw sludge i HRT I A

Thermophilic "Acid-Phase" (Hydrolysis & Acidogenesis)

Digested sludge

Mesophilic 'Gas-Phase'

(Methanogenesis)

Mesophilic 'Gas-Phase'

(Methanogenesis)

Acid-Gas Phased "Therms—Mess" Total HRT 12+ days

Digested sludge

Raw sludge

Raw sludge

1-3 day

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