  The aim of this study is to evaluate the integration of microbial
electrochemical technologies (MET) with anaerobic digestion (AD) to overcome AD
limitations caused by propionate accumulation. The study focuses on
understanding to what extent the inoculum impacts on the behaviour of the
integrated systems (AD-MET) from the perspective of propionate degradation,
methane production and microbial population dynamics. Three different inocula
were used: two from environmental sources (anaerobic sludge and river sediment)
and another one from a pre-enriched electroactive consortium adapted to
propionate degradation. Contrary to expectations, the reactor inoculated with
the pre-enriched consortium was not able to maintain its initial good
performance in the long run, and the bioelectrochemical activity collapsed
after three months of operation. In contrast, the reactor inoculated with
anaerobic sludge, although it required a relatively longer time to produce any
observable current, was able to maintain the electrogenic activity operation
(0.8 A.m-2) as well as the positive contribution of AD-MET integration to
tackle propionate accumulation and to enhance methane yield (338 mL.gCOD-1).
However, it must also be highlighted that from a purely energetic point of view
the AD-MET was not favorable.
