The Effect of Varied Nitrate Addition Rates on the Production of N2O During the Composting of Organic Space Refuse
The establishment of an advanced denitrifying compost system is integral to the pursuit of controlling the production of undesirable gases and on extended space missions. In this study, nitrate addition regimens were examined and the effect on production of N2O, and other undesirable substances will be measured. The use of Nitrate electrodes, CO2 measurements and CHN assays reveal that a lower addition rate (200 g/day) results in the production of less undesirable products, and allows for greater degradation of organic carbon sources.
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• Traditional composting of organic space trash could involve two types of bacteria:
-Aerobic: C + O2 — CO2 + H2O
Crew Oxygen Consumed (not desirable)
-Anaerobic: C — NH3 + VFA + H2O
VFA (Volatile Fatty Acids) –bad odor (not desirable)
• Denitrification is the solution:
Organic-C + NO3- — N2 + CO2 + H2O
Keep nitrate low and minimize N2O side products. Firestone (1982)
Methods/Procedure
Study examined NO3- addition rates in two trials, each 14 days using denitrifying bacteria.
TRIAL 1: 200g of KNO3 day-1 for 6 days
TRIAL 2: 1200g of KNO3 on the first day
Above: The Space Operations Bioconverter. This vessel will compost material using denitrifying bacteria. Photo by S. Lloyd
Above: Compost feed simulated space trash, with NaHCO3 and bacteria added.
Photo by S. Lloyd
Conclusions/Discussion
• TRIAL 1 with low addition rate yields less CO2, less C-degradation, Figure 1.
• TRIAL 2 has a CO2 spike later and is higher, but yields an enormous amount of harmful NO2
• Previous studies confirmed, lower rates provide optimal conditions for bacterial metabolism. Future studies should examin lower and more continuous nitrate addition regimens.
Above: Figure 1. Effect of denitrification on the production of CO2
Author: Shane Lloyd, CBS Trainee, SLSTP 2004
The University of British Columbia Vancouver, Canada
Principal Investigator: Dr. Richard Strayer, Dynamac Corp. Kennedy Space Center
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