Applying rhamnolipid to enhance hydrolysis and acidogenesis of waste activated sludge: retarded methanogenic community evolution and methane production.

Recently, bio-surfactants, like rhamnolipid (RL), have been used as efficient pre-treatments to enhance the accumulation of short-chain fatty acids (SCFAs) from waste activated sludge (WAS). The current study found that SCFA accumulation occurred with evolutional variation in methanogen with RL (0.04 g RL g -1 TSS), resulting in a retarded methane production over a period of 20 days. However, a slow methane production was only detected before the 18 th day, while the concentration of acetic acid (HAc) accumulated to a peak at 2616.94 ± 310.77 mg L -1 in the presence of RL, which was 2.58-fold higher than the control assay. During the retarded methane production, the concentration of dissolved hydrogen also increased to 49.27 ± 6.02 μmol L -1 , in comparison with 22.45 μmol L -1 of control WAS without RL. According to the analysis of archaea communities induced by RL, hydrogenotrophic methanogens, like Methanobrevibacter , had been substantially promoted at the beginning of quick SCFA and hydrogen production, but their percentage decreased from 70% to 35% with time. Intrinsically, the growth of acetotrophic methanogens were postponed but they contributed most to the methane production in this research according to the correlation analysis.