Bagwell, C.E., D.L. Saunders, J.W. Morad, J.R. Wells, and K.C. Johnson.
PNNL-28021, 27 pp, 2018

Contaminated groundwater in the 200W Area of the Hanford Site is being treated ex situ by pump and treat, and the subsurface plume is under hydraulic containment. The treatment facility removes uranium, technetium, carbon tetrachloride, and nitrate from the groundwater, but its capacity is constrained by biofouling of the injection wells, which limits efficient injection of treated effluent water to the subsurface. The treatment facility's fluidized bed reactor (FBR) was identified as a principal source of biofouling, and further investigation led to the following main findings: (1) Iodine is accumulating on the granulated activated carbon in the FBR. (2) FBR enrichment cultures were found to attenuate nitrate by dissimilatory nitrate reduction to ammonia, which does not eliminate nitrate from the system but rather converts it to a biologically available form that can lead to microbial contamination in the effluent distribution pipelines and contribute to biofouling at the injection wells. (3) Ferrocyanide was not inhibitory to the FBR enrichment cultures at concentrations <50 µM (FeCN in Hanford groundwater is 0.5 µM), but exposure did slow growth in a concentration-dependent manner under aerobic and anaerobic conditions with the potential for an eventual negative effect on FBR activity and sustained performance. Results demonstrate that careful management of complex biological processes is needed to control biofouling at the 200W P&T injection wells. http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-28021.pdf