Biopolymers as an Alternative to Petroleum-Based Polymers for Soil Modification, ESTCP ER-0920: Treatability Studies

Abstract

Abstract : Rhizobium tropici, a catalogued symbiotic nodulator of leguminous plants, is also known for its production of a gel-like extracellular polymeric substance (EPS). The natural functions of the biopolymer in the rhizosphere include surface adhesion, self-adhesion of cells into biofilms, formation of protective barriers, water retention around roots, and nutrient accumulation. We performed three treatability studies to evaluate the effectiveness of the biopolymer as a soil amendment to increase slope stability and reduce transport of solids in runoff water, reduce the transport of heavy metals associated with suspended sediment from small arms firing ranges, and reduce the generation of dust. Four soil types were used: Silty Sand (SM), Sandy Silt (ML), Silt (S), and Silty Clay (CL). These soil types were selected because they are prone to wind and water erosion thus presenting possible worst case scenarios. The study of sediment transport demonstrated that the biopolymer soil amendment was able to significantly reduce surface water erosion and particulate and heavy metal transport in leachate. The biopolymer soil amendment effectively maintained the slope stability of a simulated berm. In addition, biopolymer added to the Silty Sand soil at 0.5% (w:w) loading rate reduced dust production compared to the control at all relative humidities, indicating it should perform well in both arid and tropical environments.