(best examples and good practices) on household organic waste ...

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The duration of the composting process varies with the technology employed,
<strong>and</strong> the maturity <strong>and</strong> stability of the compost required. The assessment of
compost maturity <strong>and</strong> stability is not easy, since there is not a single acceptable
method that is commonly applied within the scientific committee. Therefore
several methods have been established which are described in the next section.
(Richard., 1993)
2.1.4. Compost stability/maturity determination
Compost stability is today recognized as maybe the most important
characteristic. The main reason for that is because in specific situations,
immature, poorly stabilized composts may be problematic. Continued active
decomposition when these composts are added to soil or growth media may
have negative impacts on plant growth due to reduced oxygen in the soil-root
zone, reduced available nitrogen, or the presence of phototoxic compounds.
Consequently, tests have been developed to evaluate the maturity of compost
materials. It should be mentioned, however, that no clear agreement on the
<strong>best</strong> approach exists. (Brinton., 2000)
1. Carbon-based analysis – compost maturity can be assessed by the
carbon/nitrogen (C/N) ratio of the material, which falls from around 20 in raw
organic waste to around 12 in a mature compost after some 12–14 weeks. This
method suffers from a lack of sensitivity <strong>and</strong> the results vary depending on the
C <strong>and</strong> N content of the starting material. Application to soils of immature
composts with high residual microbial activity <strong>and</strong> high C/N ratios can result in
uptake of the nitrogen from the soil by the compost, which will reduce, rather
than enhance the soil fertility.
2. Enzyme assays – different enzymes change in concentration during the
composting process. Further research is required to develop an accurate
measure of stabilization using such assay techniques.
3. Respiration measurements – respiratory activity falls as composting
proceeds. It has been proposed that compost may be considered stable when its
oxygen uptake is less than 40 mg/kg dry matter per hour at 20°C.
4.Phytotoxicity assays – the presence of phytotoxins (organic materials toxic
to some plants) can be assessed using cress seed emergence tests <strong>and</strong> assays for
individual phytotoxins such as acetic, propionic, butyric <strong>and</strong> valeric acids <strong>and</strong>
phenolic acids.