In this study, fermentation liquor from rice straw was used to produce bioflocculants during a dry fermentation process. Acetic acid and butyric acid were the predominant VFAs during the process. A compound bioflocculant producing inoculum, F+ was inoculated into compound media in which fermentation liquor and conventional bioflocculants medium at different ratios. The maximum flocculation activity, 92.45% was achieved when 100-day fermentation liquor and conventional bioflocculants medium were mixed at an equal ratio. Furthermore, 454-pyrosequencing technology was used to measure bacterial diversity on the 25th day of operation, which was a period of rapid VFA accumulating. A total of 2110 sequences were obtained, and were found to be affiliated with 8 phylogenetic groups, including Actinobacteria, Acidobacteria, Bacteroidetes, Firmicutes, Proteobacteria, Chloroflexi, Spirochaetes and Synergistetes. Notably, Firmicutes (92.3%) was the dominant microbial population, followed by Actinobacteria (2.37%) and Proteobacteria (1.04%). (C) 2011 Elsevier Ltd. All rights reserved.