Preliminary Study Of Microbial Extracellular Polymeric Substances Delaying The Sedimentation Of Fluid Mud And Its Mechanism

China has many silt ports, needing to dredge the mud regularly, which bring great economic pressure to the port. The application of nautical depth alleviated some pressure, but there was still the problem that nautical thickness decreased due to the sedimentation of fluid mud. There were some reports that extracellular polymeric substances could delay the sedimentation of fluid mud, and promote the value of nautical depth. Extracellular polymeric substances (EPS), a complex high-molecular-weight mixture of biopolymers, were secreted by a variety of microorganisms in particular environment, and mainly composed of carbohydrate and protein. On this basis, the main goals of this paper are screening strains producing EPS, determining the property of EPS delaying the fluid mud settlement, realizing the characteristic of EPS and further more preliminarily elaborating the mechanism of EPS delaying the sedimentation of fluid mud.16 EPS producing strains were isolated from different port mud samples. Finally the strain zh-14 was chosen since its EPS yields were the highest, and identified as Burkholderia by sequencing of 16S rDNA. Further more, optimization for EPS production was conducted through the single factor experiment, confirmed that the optimal carbon and nitrogen source were sucrose and NH4Cl respectively. On the basis of single factor experiment, response surface optimization was proceed with sucrose, NH4Cl and MgSO4 as variables using the Box-Behnken design, ultimately determined the optimal combination for EPS production was sucrose 21.0 g/L, NH4Cl 1.1 g/L, MgSO4 0.2 g/L, KH2PO4 1.0 g/L, Na2HPO4·12H2O 2.0 g/L, CaCO3 1.5 g/L and the interaction between each two variables was unobvious.Results of EPS composition showed the predominant portion was polysaccharide, about 47%. We found that the intrinsic viscosity of polysaccharide after purified with DEAE ion exchange resin was 800.6 mL/g. Moreover, the measurement of monosaccharide composition was mannose, glucuronic acid, glucose, galactose and fucose, with the molar ratio at 0.06:0.19:1.00:0.09:0.48; Besides, there was also a small quantity of galacturonic acid.Finally, the sedimentation result of fluid mud in different EPS concentration showed that, the sedimentation became slow with the increase of EPS concentration; And when the EPS concentration was about 0.8 g/L, sedimentation was not observed within 24 hours. Through the measurement of surface charge, viscosity and size distribution, the mechanism of EPS delaying the fluid mud sedimentation was speculated. It was the EPS absorbed on the particles that created "steric repulsive energy", as a result, flocculation due to the trend of approaching and impacting to each other between fine particles was restrained and the particles were easier to disperse. Besides, the addition of EPS changed the water quality of fluid mud system, then the system viscosity increased. In the combined action between surface charge and viscosity, EPS approached to the result of delaying the fluid mud sedimentation.