The influence of sludge retention time on mixed culture microbial fuel cell start-ups

In this work, the start-ups of air-cathode microbial fuel cells (MFCs) seeds with conventional activatedsludge cultivated at different solid retention times (SRTs) are compared. A clear influence of the SRT of theinoculum was observed, corresponding to an SRT of 10 days to the higher current density exerted, about0.2 A m−2. This observation points out that, in this type of electrochemical device, it is recommended touse high SRT seeds. The work also points out that in order to promote an efficient start-up, it is not onlynecessary to use high SRT seeds, but also to feed a high COD concentration. When feeding 10,000 ppmCOD and keeping SRT of 10 d differences of current densities up to 0.1 A m−2 were observed within acycle. Additionally it was observed that SRT influences direct and indirect electron transfer mechanisms,being the direct mechanisms the most relevant ones, accounting for more than 95% of the total electricityproduction.