5. Conclusions
Anaerobic digester performances in terms of volatile solids
removal, biogas and methane generation were greatly influenced
by internal environmental conditions. Changes in internal environmental
conditions were able to stimulate the growth of different
microbial guilds able to operate methanogens in a more efficient
way. The performance of sludge anaerobic digesters can be
improved if co-digestion with fruit and vegetable waste (FVW) is
performed. Introducing an adequate amount of FVW together with
sludge in digesters represents a suitable solution for improving the
amount of methane generated per unit of volatile solids introduced,
even if at reduced retention time. Key findings of this effect
were related to some changes occurring in the methanogenic pathway.
In particular a partial shift of methanogenesis from fully
acetoclastic to partially hydrogenotrophic and acetoclastic pathways
was able to increase both the amount of methane generated
and the amount of volatile solids removed. Ammonium concentration
plays a key role in modifying the populations of microbial
guilds responsible for these different methanogenic pathways.