Delaying Effect of Extracellular Polymer Substances on Fluid Mud Consolidation and Application for Nautical Depth

Abstract

Microorganisms have been used to delay fluid mud consolidation and to keep fluid mud navigable. However, bacteria and extracellular polymer substances (EPSs) that delay sediment consolidation have not been studied widely, and it has taken many years to make inorganic chemoautotroph bacteria and EPSs effective. To understand the effect of EPSs on consolidation and to find new methods of applying EPSs at nautical depths, a strain of bacteria, Burkholderia vietnamiensis, was recently isolated and screened from sediment; it was cultured to secrete EPSs to be added directly to fluid mud in a series of consolidation experiments. The experimental results showed that the EPS consisting of polysaccharides as the main component can greatly reduce sediment settling and consolidation velocity. Also, when the EPS content was relatively high, the fluid mud consolidated at a slower rate. A self-weight consolidation in the settling regime was best predicted by an exponential equation, and a permeability regime was best predicted by a logarithmic equation. The equilibrium density of mud in the effective stress regime decreased exponentially with increasing EPS content. The application time of the nautical depth might be delayed greatly by adding .68 g/L EPS directly into the Cangnan Power Plant Harbor, Zhejiang Province, China. The new concept of direct EPS addition into fluid mud might be a solution to the problem of slow growth of inorganic chemoautotroph bacteria and EPSs, and it might be helpful to promote the application of EPSs at nautical depths in new harbors.