Precision determination for the specific oxygen uptake rate (SOUR) method used for biological stability evaluation of compost and biostabilized products

Abstract Test validation needs to assure results quality when new methods are proposed as routinely matter. This work represents a first attempt to validate the Specific oxygen uptake rate method (SOUR) by precision, i.e. repeatability (r) and reproducibility limits (R), detection. Three laboratories were implied in an inter-laboratories test for respirometric analysis by SOUR on six biomasses (3 composts and 3 biostabilized) of different degree of biological stability. Both maximum specific oxygen uptake rate (SOUR peak) and cumulative data registered for 12 h (OD12) and 20 h (OD20) were investigated. Precision values expressed as relative standard deviation, were in the range of 9 and 41%. Linear regressions found for r and R, versus OD12 and OD20 allowed deriving precision values (r and R) for all levels contained in the operating range. OD12 and OD20 indexes seemed to be preferred to indicate biological stability as they are less influenced by random errors than SOUR index.