Optimized production of biomethane as an energy vector from low-solids biomass using novel magnetic biofilm carriers

Abstract Completely stirred tank reactors are the common type of bioreactors used for biogas production, however, efficient conversion of low-solids feedstocks to biomethane is restricted by the wash-out of microorganisms at short hydraulic retention times. Novel magnetic foam glass particles that can serve as biofilm carriers and retain active microbial biomass were investigated in high-rate biomethane production. A mesophilic completely stirred tank reactor containing 2% (w/w) magnetic carriers was operated at organic loading rates of 1.5 to 7.7 g VS L −1 d −1 feeding sugar beet silage, the hydraulic retention time was systematically decreased from 24.5 to 4.7 d. Magnetic foam glass particles clearly stabilized the methane production process, especially by supporting methanogenic microorganisms that presented 49% of the population living on the magnetic carriers. Even at an hydraulic retention time of 4.7 d, which is very low for completely stirred tank reactors, methane production remained stable at a high level of 2.2 L L −1  d −1 (organic loading rate 6.3 g VS L −1 d −1 , methane yield 0.353 L g VS −1 ). Results suggest that magnetic foam glass particles are an attractive option for increasing the process stability and performance of anaerobic completely stirred tank reactors fed with low-solids feedstock, enabling high-rate production of energy from slurries and wastewaters representing waste materials in agriculture and industry.