In order to develop a more effective and eco-friendly treatment technology, a full-scale tannery wastewater treatment plant with a sludge digestion system was augmented with a novel microbial consortium (BM-S-1). The aim of this study was to determine if the BM-S-1 could successfully treat the tannery wastewater in a full-scale treatment system without chemical pretreatment and to investigate effect of the augmentation on sludge production. Chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), chromium (Cr) and mixed liquor suspended solids (MLSS) were measured to monitor treated water quality and treatment efficiency. Microbial community structures in the treatment were also examined using pyrosequencing analysis of 16S rRNA gene and quantitative PCR (qPCR) of the nitrous oxide reductase gene (nosZ). The removal efficiencies of COD, TN, TP, and Cr were estimated to be 98.3%, 98.6%, 93.6%, and 88.5%, respectively, while the system without a continuous augmentation was broken down. The pyrosequencing analysis showed Brachymonas denitrificans to be the most dominant microbial population in the buffering tank (B; 37.5%). Potential polymeric substance degraders (Clostridia), sulfate reducers (Desulfuromonas palmitatis), and sulfur oxidizers (uncultured Thiobacillus) were dominant in the sludge digestion (SD) tank. The denitrifiers assayed by nosZ qPCR were dominant in B and SD. These microbial communities appeared to play important roles in removing nutrients and odor, and reducing sludge in the wastewater treatment plant without chemical pretreatment.