The Application of Microbial Technology in Harbor Engineering: The Impact of Extracellular Polymeric Substances on the Sedimentation and Properties of Fluid Mud

Abstract

Extracellular polymeric substances (EPS) are complex biopolymers secreted by a variety of microorganisms. There are reports that EPS played important roles in stabilization of fluid mud, which can solve the problem of fluid mud settling too fast in harbor engineering. In this study, one EPS-producing strain Burkholderia sp. TKS1 isolated from fluid mud of one muddy port in China was utilized, which has showed effectiveness in delaying the sedimentation of fluid mud in our preliminary study. The main component of EPS was polysaccharide accounting for 47.2%, which was defined as heteropolysaccharide composed of mannose, glucuronic acid, glucose, galactose and fucose, the proportion of the composition were 0.06:0.19:1.00:0.09:0.48 and the EPS possessed high intrinsic viscosity of 802.1 mL/g. No obvious sediment settling was observed with EPS concentration more than 0.8 g/L in 24 h. The viscosity of fluid mud increased from 1.5 to 3.2 mPa·S with the increase of EPS concentration. The surface charge density of fluid mud decreased after adding EPS, and would remain stable when the density from initial |−0.7 meq/g MLSS| fell to |−0.3 meq/g MLSS| due to positively charged EPS. The sediment particles size significantly increased with the increase of EPS concentration. Based on the results, the possible mechanism for EPS delaying the sedimentation of fluid mud was finally proposed. These results will shed light on novel strategies for the application of microbial technology in harbor engineering.