Microbial activity of the inoculum determines the impact of activated carbon, magnetite and zeolite on methane production

The conversion of organic matter to methane through anaerobic digestion (AD) process can be enhanced by different materials. However, literature reports show inconsistent results on the effect of materials in different AD systems. In this study, we evaluated the influence of the inoculum's activity on methane production (MP) efficiency in the presence of different materials (activated carbon (AC), magnetite (Mag), and zeolite (Zeo)). The inocula included pure cultures of methanogens, syntrophic cocultures, and complex microbial communities, and the kinetic parameters assessed were the lag phase duration and methane production rates (MPR). The results showed that the microbial activity of the inocula is an important factor determining materials' effect on MP kinetics. AC, Mag, and Zeo significantly enhanced the MP profiles of less active microbial communities or low-active microorganisms by decreasing lag phases duration up to 85 %, consequently increasing MPR up to 15 times. Contrarily, these materials did not affect highly active microbial communities or pure cultures, as MP profiles tend to be similar with and without materials. These results indicate that from an applied point of view, the addition of materials to anaerobic bioreactors should be considered only when the methanogenic activity of the sludge is low or compromised. [Display omitted] •Materials do not improve methane production efficiency by active inocula•Materials accelerate methane production rates up to 15× by low-active methanogens•Inoculum activity should be evaluated prior to materials supplementation in AD