(edited June 1) A variety of compost stability tests under development in Europe “have the potential to be as confusing as they are important”, according to Will Brinton of Woods End. The UK has announced a standard CO2-respiration assay, based on work by a single private lab. Elsewhere, O2-uptake tests seem to dominate, especially “DRI" – dynamic respiration – which is alleged to indicate higher O2 consumption rates than shown by other tests including SRI, SOUR, OUR, Sapromat and Oxitop. Yet, few labs are comparing methods adequately on equal footing, according to Brinton "partly because of sheer logistics, but also because each lab seems to have its favorite pick". Presently, there is more than one variant of each protocol, including the DRI, the original Italian (Adani) version employing a large 140-liter self-heating vessel and a similar but scaled down ASTM version which is easier and less costly to set up and run.
Along with methodological developments comes setting acceptable stability thresholds. “Setting numerical limits that are meaningful requires perspective and considerable experience,” says Brinton. The proposed DRI cutoff between waste being considered fresh vs. compost is suggested to be a DRI of 1000 mg O2/kg VS/hr, and “has been somewhat extrapolated too far ”. The new British PAS100-2005 compost guideline sets a respiration guideline of 16 mg CO2/g OM/day, but without any justification for the number “except that it is very lenient” says Brinton. Whether 1000 DRI or 16 CO2, Woods End believes setting either single numerical limits or too lenient ones is misleading, conveying the impression that compost achieves a right state at one value. “People should read our Solvita Test manual” Brinton said, “.. and grasp that a varying range of compost maturity may be usefully interpreted”. Just what the correlation of one test is to another is currently left to anyone’s guess, according to Woods End. This will be a topic of research at Woods End during 2005, with a project underway to compare DRI, Solvita, Oxitop and CO2-trapping methods. "Ultimately, to make this useful to industry and the end-user, you need a combination of one or two standard lab protocols plus reliable, inexpensive field test kits – like Solvita – that are the same anywhere in the world. The idea of there being only one proper test is unrealistic and very impractical”.
A Task Force on Stability methods met in Vienna in 2004, but did not achieve a clear consensus on how to move forward.