Biokinetic and Sediment Structural Controls on Gas Release from Contaminated Sediments

Gas ebullition in sediment results from biogenic gas production by mixtures of bacteria and archaea. It often occurs in organic-rich sediments that have been impacted by hydrophobic organic compounds and other anthropogenic pollutions. What is less understood is the role that substrate structure plays in the rate of methanogenesis and sediment mechanical characteristics that drives gas ebullition. This study investigated the factors affecting gas ebullition and anaerobic biodegradation of contaminants in non-aqueous phase liquids (NAPLs) in sediment systems. The biogenic gas fracture model was developed based upon the hypothesis that when biogenic methane gas becomes oversaturated in sediment porewater, gas bubbles nucleate on sediment surfaces and grow by linear elastic fracture of the surrounding sediment matrix. Model input data were obtained directly from experimental studies on sediment samples collected from an estuarine urban waterway. The results showed that the simultaneous effect of organic contaminants on sediment mechanical properties and biological activity controls the gas ebullition rate and source in sediment. Thus, by determining active-ebullition zones in sediment, methane emission can be better managed by means of remediation.