The Implications of the Spatial Distribution of Nitrifiers in Advanced Life Support Systems

Human urine represents a major problem with respect to ammonia vapors in the crew cabin and the amount of water necessary for human hydration (2 kg/person/day). Bacterial nitrification represents an important element of the solution to water resource limitations in extended space flight missions. Nitrifiers convert potentially volatile NH3 to NO3 eliminating the problem of volatile ammonia in the cabin, and the NO3 is potentially removable by another biological process, denitrification, leaving water that can be easily finished by physical-chemical means for reuse by the crew. Nitrifiers form biofilms on reactor surfaces, and the distribution of nitrifiers in biofilms (which can affect the efficiency of the process) is controlled by gradients of O2 and NH3. Changes in organism distribution can impact the rates at which the two genera of nitrifiers (i.e. ammonia oxidizing and nitrite oxidizing bacteria, AOB and NOB, respectively) function. Fluorescent in situ Hybridization (FISH) and microscale electrodes are used to study the distribution of these organisms, precursors, and products within the biofilms. Current results in planktonic cultures show growth and oxidation rates where uniform distribution of microorganisms and nutrient resources are maintained. Cell doubling time for AOB and NOB combined is 1.4 days. Data from these studies will be compared to rates found in biofilms to determine how these biofilms will benefit advanced life support systems.