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

Abstract

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.