Quantification of greenhouse gas emissions from a biological waste treatment facility.

Whole-site emissions of methane and nitrous oxide, from a combined dry anaerobic digestion and composting facility treating biowaste, were quantified using a tracer dispersion technique that combines a controlled tracer gas release from the treatment facility with time-resolved concentration measurements downwind of the facility. Emission measurements were conducted over a period of three days, and in total, 80 plume traverses were obtained. On-site screening showed that important processes resulting in methane emissions were aerobic composting reactors, anaerobic digester reactors, composting windrows and the site's biofilter. Average whole-site methane emissions measured during the three days were 27.5±7.4, 28.5±6.1 and 30.1±11.4kg CH h, respectively. Turning the windrows resulted in an increase in methane emission from about 26.3-35.9kg CH h. Lower emissions (21.5kg CH h) were measured after work hours ended, in comparison to emissions measured during the facility's opening hours (30.2kg CH h). Nitrous oxide emission was too small for a downwind quantification. Direct on-site measurements, however, suggested that the main part of the emitted nitrous oxide came from the biofilter (about 1.4kg NO h). Whole-site emissions were compared to emissions previously measured at different point sources on-site. Whole-site fugitive emissions were three to eight times higher than the sum of emissions measured at on-site sources. The magnitude of the emissions had a significant influence on the overall environmental impact of the treatment facility, assessed by consequential life cycle assessment. Including the higher whole-site fugitive emissions led to an increase in global warming potential, from a saving of 97kgCO-eq.tonne of treated waste (wet weight) to a loading of 71kg CO-eq. tonne, ultimately flipping the environmental profile of the treatment facility.