Volume 3, Issue 6 (June 2006)
Optical Tests on the Slow Release of Biogenic Gas Bubbles in Sediment
The anaerobic decomposition of organic matter in marine or fresh water sediments can generate methane, carbon dioxide, hydrogen sulphide, and hydrogen as biogenic gases. In addition, innovative technologies are being used to remediate contaminated sediments and groundwater by releasing biogenic gases from the fermentation of carbon substrates as electron donors. Both scenarios can result in large discrete gas bubbles being present in sediment, which can affect aqueous permeability and mechanical strength. Furthermore the movement of gas bubbles can affect bioavailability as electron donors. In order to investigate bubble dispersion and movement in sediments, a series of novel optical experiments were carried out to observe the release and movement of discrete bubbles in artificial coarse-grained sediment. The results showed that buoyancy-induced movement depended on the clustering together of individual bubbles to achieve a critical depth of gas pocket to overcome the capillary force acting across the pore throat between sediment grains.