Biodegradation and methane production from glycerol-containing synthetic wastes with fixed-bed bioreactor under mesophilic and thermophilic anaerobic conditions

In this study, efficient biodegradation of glycerol-containing synthetic wastes using an immobilization bioreactor was examined. A fixed-bed bioreactor packed with polyurethane was used in semi-continuous mode for glycerol removal under mesophilic and thermophilic anaerobic conditions. The best performance was obtained from the reactor under the thermophilic (55 °C) conditions. The average removal of dissolved organic carbon was 86.7% at an organic loading rate of 1.00 g/(l-reactor d). Molecular cloning of 16S rRNA gene sequences indicated that the archaeal clones in the thermophilic reactor were affiliated with two main groups, the hydrogenotrophic Methanobacterium sp. (17 out of 20 clones) and the aceticlastic Methanosarcina sp. (3 out of 20 clones). The bacterial clones were mostly affiliated with Bacillus sp., Clostridium sp., Desulfotomaculum sp., and Ruminococcus sp. Scanning electron microscopy (SEM) observation of the main cellular morphologies present in the biofilm on the colonization indicated that the immobilized microorganism was primarily composed of coccus, diplococci-shaped Methanosarcina-like cells, rods of Methanobacterium-like cells, rods of Bacillus sp., rods and coccus of Clostridium sp. and Desulfotomaculum sp., and coccobacillus of Ruminococcus sp.-like bacteria. They presumably form a syntrophic association.