Articles
EXPERIENCES WITH THE OUR METHOD EN 16087-1: INTERPRETATION OF PRESSURE CURVES AND EFFECT OF METHOD DEVIATIONS
Article number
1034_31
Pages
255 – 261
Language
English
Abstract
Nowadays, a variety of organic materials are offered to be used as constituents for horticultural growing media.
Examples of these are bark, compost, coir products and more recently waste products such as digestate.
One of the important character-istics to be known is the biological stability or aerobic biological activity of these products.
This can be determined by measuring the oxygen uptake rate (OUR). The oxygen uptake rate (i.e., respiration) is an indicator of the extent to which bio-degradable organic matter is broken down within a specified time period by aerobic microorganisms.
A European Standard is established by the Comité Européen de Normalisation (CEN) to determine the OUR of materials (EN 16087-1). Principle of the method is that material is suspended in demineralised water, enriched with nutrient solution, pH buffer and nitrification inhibitor.
During breakdown of the product, oxygen is consumed and produced carbon dioxide is removed by sodium hydroxide pellets, resulting in a pressure drop in the headspace of the bottle.
Variables of the EN method were tested: stirring versus orbital shaking, tem-perature stabilisation, weight of sodium hydroxide pellets, non-sieved versus 10 mm sieved material and variability due to sampling.
At testing of new materials, atypical curves are found.
Atypical curves are presented and interpretation is discussed.
Stirring and orbital shaking have no effect on the OUR and neither does the weight of NaOH pellets.
Temperature stabilisation is necessary, as well as testing non-sieved material and getting representative samples.
For interpretation of atypical curves expert judgement is necessary.
Examples of these are bark, compost, coir products and more recently waste products such as digestate.
One of the important character-istics to be known is the biological stability or aerobic biological activity of these products.
This can be determined by measuring the oxygen uptake rate (OUR). The oxygen uptake rate (i.e., respiration) is an indicator of the extent to which bio-degradable organic matter is broken down within a specified time period by aerobic microorganisms.
A European Standard is established by the Comité Européen de Normalisation (CEN) to determine the OUR of materials (EN 16087-1). Principle of the method is that material is suspended in demineralised water, enriched with nutrient solution, pH buffer and nitrification inhibitor.
During breakdown of the product, oxygen is consumed and produced carbon dioxide is removed by sodium hydroxide pellets, resulting in a pressure drop in the headspace of the bottle.
Variables of the EN method were tested: stirring versus orbital shaking, tem-perature stabilisation, weight of sodium hydroxide pellets, non-sieved versus 10 mm sieved material and variability due to sampling.
At testing of new materials, atypical curves are found.
Atypical curves are presented and interpretation is discussed.
Stirring and orbital shaking have no effect on the OUR and neither does the weight of NaOH pellets.
Temperature stabilisation is necessary, as well as testing non-sieved material and getting representative samples.
For interpretation of atypical curves expert judgement is necessary.
Authors
W.H.C. Geuijen, J.B.G.M. Verhagen
Keywords
respiration, stability, oxygen uptake rate
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