A novel pre-treatment of brewery spent grains using mycelium-bound cellulase from Aspergillus oryzae for biogas production

Abstract

Large amounts of waste are generated by brewing manufacturing processes, mainly brewery spent grains (BSG) and trubs. To overcome such disposal issue and valorize waste, the present work assesses a new technology for BSG pretreatment employing biological and enzymatic techniques for biogas production. Its approach consisted in using the activated metabolism of Aspergillus oryzae cells to degrade BSG while simultaneously producing mycelium-bound cellulase complexes. Aspergillus oryzae whole cells have been cultivated under submerged fermentation using 20 g L−1 BSG as main carbon source to induce mycelium-bound cellulase production, in addition to using trubs as an additional substrate and source of nutrients. It was found that the addition of a saline solution with no trubs resulted in higher enzyme activity (4.77 UI g−1) and 86 % of BSG initial degradation. To increase BSG degradation, whole cells were submitted to a hydrolysis step and the resulting product underwent a BMP test after 72 h. Compared to control tests through commercial enzymatic pretreatment of BSG and no enzymes addition, the use of whole cells has substantially increased biomethane production, given that values of 226.87 ± 2.43 Nml/gVS were found at the end of 39 days of incubation. Data from pH variation and COD removal evidence such a great performance of BMP with whole cells. There was no pH variation during anaerobic digestion, thus favoring methanogenesis. Furthermore, COD removal reached 85.2 %, thus evidencing the treatment success. These findings reveal the potential of this new approach towards biogas production from brewery waste.