A modified dynamic respiration test to assess compost stability: effect of sample size and air flowrate.

Goal of this work was to study the effect of the unit air flowrate on dynamic respiration activity indexes during the assessment of compost stability. A MSW compost was used and six experimental runs were performed with variable compost masses and variable air flowrates, so that to achieve six unit air flowrates (6, 9, 16, 17, 23 and 30 L air kg(-1) organic matter h(-1)). Six respiration activity indexes were quantified, namely a dynamic respiration index (DRI24), the cumulative O2 consumption at 4 and 7 days (DCRI4, DCRI7), a CO2 index, the cumulative CO2 generation after 7 days (Total CO2) and the respiratory quotient. Results indicate that the CO2 related indexes and the respiratory quotients had a strong negative correlation with the unit air flowrate, whilst the DRI24 and both DCRIs slightly increased with increasing unit air flowrates.