Combined bioaugmentation with anaerobic ruminal fungi and fermentative bacteria to enhance biogas production from wheat straw and mushroom spent straw

Bioaugmentation with anaerobic ruminal fungi and a pool of hydrogen-producing fermenting bacteria was tested on wheat straw (WS) and mushroom spent straw (MSS) with the aim of improving anaerobic digestion performance. Batch tests were set up to simulate a Bioaugmentation Anaerobic Digestion (BAD) treatment comparing single-(I-BAD) and two-stage (II-BAD) process configurations, at two reactor scales, 120 and 1200 ml (x10). In both cases, higher CH4 cumulative production was obtained in the II-BAD configuration on WS (65.1 +/- 8.9 Nml and 922 +/- 73.8 Nml respectively). The II-BADx10 tests allowed increasing CH4 production (similar or equal to 290% and similar or equal to 330% on WS and MSS, respectively) when compared to the unaugmented condition. Final results highlighted the achievable advantages of the two stage configuration in terms of CH4 production enhancement. Microbial community investigations confirmed the efficiency of the bioaugmentation treatment and revealed that such a result was mainly related to the Methanosarcinales increase, mostly composed by Methanosaeta.