Microbial gas generation under expected Waste Isolation Pilot Plant repository conditions

Gas generation from the microbial degradation of the organic constituents of transuranic (TRU) waste under conditions expected in the Waste Isolation Pilot Plant (WIPP) was investigated. The biodegradation of mixed cellulosic materials and electron-beam irradiated plastic and rubber materials (polyethylene, polyvinylchloride, hypalon, leaded hypalon, and neoprene) was examined. We evaluated the effects of environmental variables such as initial atmosphere (air or nitrogen), water content (humid (~70% relative humidity, RH) and brine inundated), and nutrient amendments (nitogen phosphate, yeast extract, and excess nitrate) on microbial gas generation. Total gas production was determined by pressure measurement and carbon dioxide (CO2) and methane (CH4) were analyzed by gas chromatography; cellulose degradation products in solution were analyzed by high-performance liquid chromatography. Microbial populations in the samples were determined by direct microscopy and molecular analysis.. The results of this work are summarized below. • Over 10.8 years, under initially aerobic conditions 0.84 ± 0.10 mL of total gas was produced per g cellulose without a nutrient amendment, while samples with a nutrient amendment supplemented without and with excess nitrate produced 1.71 ± 1.03 mL and 12.2 ± 0.0 mL total gas g cellulose, respectively. Over the same period, 16.3 ± 1.3 μmol CO2 was produced g cellulose in the absence of a nutrient amendment; 41.4 ± 7.8 μmol CO2 g cellulose with nutrient amendment, and 186 μmoles CO2 g cellulose when excess NO3 was present. The overall rate of total gas production from these treatments was 2.3 x 10, 4.0 x 10, and 1.9 x 10 mL total gas g cellulose day, respectively, and CO2 production was 3.7 x 10, 4.5 x 10, and 4.1 x 10 μmol CO2 g cellulose day, respectively. • Under anaerobic conditions, 2.48 ± 0.31 mL total gas g cellulose was produced without a nutrient amendment, 4.12 ± 0.76 mL total gas g cellulose with nutrients, and 18.1 ± 0.38