Use of inhibitors to prevent bacterial artefacts in experiments

Within the frame of HLW disposal Boom Clay is studied as the reference host rock. In order to study Boom Clay an underground laboratory was constructed but due to the excavation the clay was perturbed and additional perturbations of Boom Clay are caused by drilling and piezometer installation. These perturbations appear to be accompanied by microbial activity This report investigates the possibility to use inhibitors to suppress bacterial activity, specifically the activity of nitrate reducing bacteria (NRB) and methane producing bacteria (MPB). Activity of NRB can cause problems in experiments designed to study the chemical effect of nitrate on Boom Clay. In order to study the abiotic influence of nitrate, which is present in large concentrations in bituminized waste, on Boom Clay any activity of NRB has to be eliminated. The upcoming PRACLAY heater test, where one of the goals is the measurement of pCO2 and hence pH, can be severely disturbed by bacterial activity. Either the production or consumption of CO2 will influence the measured values. Bacterial activity of for instance MPB could seriously alter the values of pCO2. The efficiency of several types of inhibitors (NaN3, HgCl2, formaldehyde, triclosan and chloramphenicol) is evaluated for both cases.