Effect of initial moisture content and sample storage duration on compost stability using the ORG0020 dynamic respiration test.

Biological tests are widely used to assess composting process status and finished material stability. Although compost stability is known to be influenced by moisture content (MC) and storage duration, there is a lack of data supporting boundary limits for standardised testing. Using the ORG0020 dynamic respiration test we assessed the stability of materials from different commercial composting sites processing only green waste or mixed green and food waste. Samples were tested at three different MC following adjustment with the 'fist' test within the range 40-60%. The results showed manipulation of MC within this range could have significant impact on measured stability for some but not all samples. Two samples reported significantly higher activity when MC was manipulated from ~50% to ~60%. For storage duration, samples showed significant decrease in measured activity over several weeks of cold storage. However, there was no significant difference in stability for samples tested up to nine days from receipt. The results of this research will support decisions relating to the boundary limits for moisture content and storage time for the ORG0020 test. The results will also provide insight to the wider range of biological tests used to assess compost stability.