The Effect of Varied Nitrate Addition Rates on the Production of N2O During the Composting of Organi

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The Effect of Varied Nitrate Addition Rates on
the Production of N2O During the Composting of
Organic Space Refuse

• Shane Lloyd
• CBS Trainee - SLSTP 2004 The University of
  British ColumbiaVancouver, Canada

Dr. Richard Strayer, PI Dynamac Corp.Kennedy
Space Center, FL 32899
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Introduction

• 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.
• 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)

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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

Picture 1. The Space Operations Bioconverter.
This vessel will compost material using
denitrifying bacteria. Photo by S. Lloyd
Picture 2. Compost feed simulated space trash,
with NaHCO3 and bacteria added. Photo by S. Lloyd
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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.

Figure 1. Effect of denitrification on the
production of CO2