Exhibit I
Compost Respiration
Comparison of Oxygen Uptake vs. CO2 Evolution
Respiration: Heterotrophic organisms (require carbon from organic compounds for
their growth). Oxygen is consumed and CO2 is evolved. Both are
somewhat related since they both involve the same biological process by
different microorganisms (aerobes, anaerobes and fungi). Both
measurements and determinations are accepted by TMECC/USDA, with
reservations listed for both methods.
Aerobic activity is a function of the composts stability; therefore
respiration is directly related to the compost maturity.
CAN/BNQ 0413-220/1998 Determination of Oxygen Uptake/ Respiration
TMECC Method 05.08-A Specific Oxygen Uptake Rate (SOUR)
TMECC Method 05.08-B Carbon Dioxide Evolution
Specific Oxygen Uptake Rate
Method determines the amount of Oxygen consumed by compost over a period of time
due to heterotrophic microbial activity. Generally, biological activity and the oxygen
uptake diminish as the composting process reaches completion. Therefore determining
the amount of oxygen that compost uptakes gives an indication of the compost’s
maturity.
Advantages:
Oxygen consumption is a good estimate of the amount of biological activity, indicating
whether or not the compost is mature.
Disadvantages:
Measurements of oxygen uptake by the instrument are tedious and precision across
replicates is difficult to maintain due to limits in the procedure and equipment
capabilities. Therefore, the confidence level of the test is low to accurately predict
whether maturity has been reached.
The level of instrument precision requires skilled chemist personnel to operate.
Saprophylic (organisms feeding off of dead and decaying matter) fungi can artificially
exaggerate and increase oxygen uptake (false positive).
Method Differences of Oxygen uptake
Oxygen Uptake Equipment
• Specialized equipment Arthur Automatic Respirometer (Single or Double
unit) developed primarily for monitoring waste treatment plants
• Equipment cost estimates (2004) $20,000 U.S. $30,000 cdn.
• Instrument Capacity 2 samples per 24 hours (8-10 per 5 day week).
• Instrument Capacity does not include controls, or blanks
• Internal calibration of instrument is conducted according to
manufacturer’s guidelines (Manually calibrated using a calibrated syringe
measuring a volume of air).
• The level of error is high using the O2 evolution method and the
recommended instrument. There is limited or no external calibration
available for the Arthur Instrument available. The O2 evolution method has
poor precision and replication of results as noted by both TMECC 05.084.2 and the BNQ standard method. The BNQ standard method
document notes the procedure’s “Precision and Accuracy” has not
been determined.
• O2 Equipment supplier has yet to be able to get the instrument endorsed by
the U.S. Composting Council. They feel that there are not sufficient
advantages to proceed with the testing protocols and presently it is not cost
effective versus the CO2 respiration procedure.
• Oxygen uptake equipment currently used by laboratories for compost
maturity is very limited.
Carbon Dioxide Evolution Rate
Method to determine the amount of carbon dioxide evolved from compost over the period
of time due to the microbial activity. It is an indicator of compost’s relative stability and
maturity index (05.08-4.4)
Advantages:
Extensive testing and scientifically peer-reviewed, TMECC endorsed as an official
method for the evaluation of biological activity and compost maturity index.
Apparatus for CO2 measurements is inexpensive to set up and more practical for the
application (Can be set-up to conduct multiples, including blanks, and controls
simultaneously)
CO2 measurements have more precision and reproducibility due to the relatively simple
laboratory procedures, method precision, and quality control measures, all of which leads
to a higher confidence level for the results.
Disadvantages:
All biological activity does not always result in complete oxidation of C to CO2 (CO2
evolved may be slightly low).
Individual tests are completed over a four-day period though there are no restrictions on
the number of tests capable of completing.
Summary
• TMECC recognizes the use of both determinations: O2 uptake and CO2 evolution
as measures of biological activity and indicators of relative stability of compost.
The BNQ only recognizes the Oxygen method as the standard method.
• The precision and accuracy of the Respirometer instrument used for the BNQ
method CAN/BNQ 0413-220/1998 has not been determined. TMECC method
05.08-4.2 notes CO2 measurements are precise and simple whereas O2 uptake
measurements are tedious and precision across replicates is poor.
• Major cost differences exist between both tests. Apparatus and instrumentation
for CO2 measurements are generally far more inexpensive than O2 allowing for
these cost savings to pass on to submitter.
• Experienced trained chemists may be required to operate the O2 uptake instrument
vs. CO2 evolution capable of being conducted by laboratory technicians.
• U.S. Composting Council has adopted the CO2 evolution test as a measure of
compost stability due to the correlation of results, the relative ease of conducting
the test, and its precision and accuracy. They passed on working with the
respirometer instrument since the CO2 evolution was universally available to the
peer group to study.
• Lastly, the respiration test is a relative indicator only of maturity, to be used in
conjunction with other physical, chemical, and microbiological measurements to
determine that the compost is mature for use.