Effects of rhamnolipid on degradation of granular organic substrate from kitchen waste by a Pseudomonas aeruginosa strain

The effect of rhamnolipid produced by a Pseudomonas aeruginosa strain on the aerobic degradation of granular organic substrate from kitchen waste by the bacterium was studied and compared with that of two synthetic surfactants, SDS and Triton X-100. The adsorption of rhamnolipid on the substrate, the surfactant-interfered adhesion of bacteria on the substrate as well as physicochemical and microbial conditions of the substrate during degradation were investigated. The adsorption isotherm of rhamnolipid on the substrate fit Freundlich law and its interactions with the substrate and bacteria weakened the adsorption of the bacteria on the substrate. The two synthetic surfactants, however, did not have such microbial effects. During degradation, rhamnolipid slowed down water evaporation in the substrate and significantly strengthened the dispersion of organic matter into the substrate water phase. The number of cells in the rhamnolipid treatment was higher than that in control and the remaining organic matter content in the substrates also had faster decreasing. SEM examination showed the on-site degradation of the substrate organic matter without rhamnolipid and the transfer of the degradation site in the presence of rhamnolipid. The results indicated that interference of rhamnolipid in the substrate matrix plays a potential role, physicochemically or microbially, on the degradation of the granular organic substrate. SDS and Triton X-100 may have the above physicochemical effects, but not so significant.