Articles
BIOLOGICAL PARAMETERS FOR COMPOST STABILITY ASSESSMENT AND PROCESS EVALUATION
There is a consensus that biological parameters, especially respirometry and germination tests, are more suitable for the evaluation of compost stability, although some chemical parameters (e.g.
C/N ratio) are still widely used and even appear in regulations.
Three different respirometric parameters were used for the assessment of stability; their common factor is that they all take advantage of the improved technology of the Clark-type polarographic dissolved oxygen probe.
The SOUR measures the rate of O2 consumption in an aqueous compost suspension; the TOD20 is the total O2 consumed by the same suspension in 20 hours; and the DSOUR is the rate of O2 consumption by a solid compost matrix.
The range of values obtained differed for each of three parameters, but they all showed similar variations with composting time, and had highly significant correlations with each other.
Cress seed germination, used to evaluate compost stability in terms of phytotoxicity, revealed strong inhibition during the thermophilic phase, which subsided later.
Of the chemical parameters, the reduction of volatile solids was the most useful, having a highly significant correlation with compost age and the respirometric parameters.
The C/N ratio and its variation during composting depended on the type of compost, and was thus of limited usefulness.