I-DEV0304: Measurement of percentage of biogas that is methane

This request is to allow deviation of measurement of percentage of biogas that is methane as specified by ID21 in Table D.2.1.3 of the revised monitoring plan by measuring the CO2 content of biogas and calculating the methane content instead of directly measuring the methane content. This request for deviation would apply for the first monitoring period from 1 October 2006 to 30 September 2007 and a portion of the second monitoring period which has yet to close.

The project developer has undergone an extensive evaluation and selection process to find the most reliable and durable equipment for measuring methane at its project activities. This process took considerably longer than anticipated by the project developer. At this time, the project developer has identified and begun using this monitoring equipment and, as of 9 April 2009, the direct measurement of methane has been implemented in accordance with the monitoring methodology and the monitoring plan and this practice will be used for all subsequent monitoring periods.

Prior to measuring the methane content the project developer has monitored the methane content of biogas using practices considered to be correct during validation and identical to the monitoring practices at other registered and verified projects by the same project developer applying AM0016 version 02.

Biogas consists of mainly CO2 and CH4. Recent measurements of both the methane and CO2 content of biogas taken from sites within this project activity showed that the sum of CO2 and CH4 averaged 98.86% with a 95% confidence level of 96.46%. An earlier analysis other similar advanced Animal Waste Management Systems (AWMS) in Brazil and Mexico, developed by the same project developer and applying the same project technology showed that the sum of CO2 and CH4 averaged 99.0% with a 95% confidence level of 96.7%. However, in order to be most conservative, the project developer has opted to use the minimum value of the sum of CO2 and CH4 found in its testing as the value to be applied across the all projects of this methodology version. This value is 94% for the sum of CO2 and CH4 with 6% trace or other gas. Hence, if this request for deviation is accepted, the percentage of methane in biogas will be calculated as 94% minus the percentage of CO2.

Measurements of the percentage of CO2 in biogas have the same accuracy as measurements of the percentage of methane. Hence, the monthly measurement of the percentage of CO2 and the calculation of the percentage of methane as described above ensures in our opinion the same level of accuracy.

As of 9 April 2009, the direct measurement of methane has been implemented in accordance with the monitoring methodology and the monitoring plan and this practice will be used for all subsequent monitoring periods. To use measurements of the CO2 content of biogas to calculate the CH4 content instead of directly measuring the CH4 content is required due to the project participants initially not finding reliable and durable equipment for measuring methane at its project activities. Hence, a request for deviation is suitable in accordance with paragraph 209 of the validation and verification manual (Version 01.1).

The deviation is project-specific and does not deviate from the methodology. Hence, no revision of the methodology is required.

The deviation is expected to result in an underestimation of the emission reductions as it is conservatively assumed that biogas contains 6% trace gases.