The Reaction Front Hypothesis in Solid-State Digestion: Estimation of Minimum Size of Viable Seed Body

Abstract

An alternative mechanism for the anaerobic digestion of a bed of solids was recently proposed. A multizoned reaction front might form around a suitable body of seed material, then advance through the bed, within the solid phase. Such a solid-phase mechanism might coexist with liquid-phase digestion but one or the other of these two parallel mechanisms might generally be dominant. It is envisaged that solid-phase digestion would be favored by the presence of viable seed bodies: single particles of a suitable seed material above a minimum size or equivalent aggregates. A key determinant of the feasibility of this mechanism is expected to be the minimum viable size for a seed body (d _min). This would depend on the thickness of the reaction zones, some of which must initially be accommodated within the seed body. In this article, we present some theoretical estimates of d _min, which indicate a magnitude of 7–700 mm. Such values suggest that solid-phase digestion might be the norm in semi-dry waste digesters. Such digestion might be rare in unseeded landfills but it would appear likely that it could easily be initiated by suitable seeding.