Mass balances and life-cycle inventory for a garden waste windrow composting plant (Aarhus, Denmark)

Abstract

A comprehensive life-cycle inventory of all consumptions and emissions of environmental relevance was made for the windrow composting plant treating garden waste in Aarhus (Denmark). The flows of materials and substances within the facility were balanced using the mass-balance model STAN. The overall fuel and electricity use at the facility (3.04 L diesel Mg—1 wet waste (ww) and 0.2 kWh Mg—1 ww) was low whereas the emissions of CH 4 and N2O from the windrows (2.4 ± 0.5 kg CH 4—C Mg—1 ww and 0.06 ± 0.03 kg N2O—N Mg—1 ww) were relatively high compared to data reported in similar studies. The loss of carbon during the 14-month-long composting was 56%. CH4 made up 2.1% of the C lost. Loss of nitrogen-containing compounds was identified as the most sensible and uncertain parameter and could be relevant for global warming (N 2O emissions), acidification (NH3 emissions), and eutrophication (NH3 and NO3 emissions). The compost produced had a very low content of heavy metals and was suitable for use in gardens and/or agriculture.