Long-term sampling of CO2 from waste-to-energy plants: 14C determination methodology, data variation and uncertainty

A dedicated sampling and measurement method was developed for long-term measurements of biogenic and fossil-derived CO 2 from thermal waste-to-energy processes. Based on long-term sampling of CO 2 and 14 C determination, plant-specific emission factors can be determined more accurately, and the annual emission of fossil CO 2 from waste-to-energy plants can be monitored according to carbon trading schemes and renewable energy certificates. Weekly and monthly measurements were performed at five Danish waste incinerators. Significant variations between fractions of biogenic CO 2 emitted were observed, not only over time, but also between plants. From the results of monthly samples at one plant, the annual mean fraction of biogenic CO 2 was found to be 69% of the total annual CO 2 emissions. From weekly samples, taken every 3 months at the five plants, significant seasonal variations in biogenic CO 2 emissions were observed (between 56% and 71% biogenic CO 2 ). These variations confirmed that biomass fractions in the waste can vary considerably, not only from day to day but also from month to month. An uncertainty budget for the measurement method itself showed that the expanded uncertainty of the method was ± 4.0 pmC (95 % confidence interval) at 62 pmC. The long-term sampling method was found to be useful for waste incinerators for determination of annual fossil and biogenic CO 2 emissions with relatively low uncertainty.