News
New Instructional Material on YouTube
We are pleased to report that there is new instructional material about using the “SOLVITA” test that can be viewed on YouTube.
The material is divided into three segments, two practical lessons which are "How-To" guidelines, and one showing “SOLVITA” in the field comparing it to other laboratory tests like the CO2- Alkali Trap method, Dewar Self Heating, and “Oxitop”.
We hope you find this information useful and interesting. It shows quite clearly how the Woods End “SOLVITA” Compost Maturity Test can be used effectively and economically to establish when compost is stable and mature. More frequent testing of material between the mandatory more expensive laboratory tests is important to ensure that the end product will be safe to move and safe to use.
Solvita Compost Test: How to Perform It - CLICK HERE
Preparing Compost for Solvita Maturity Test - CLICK HERE
Plant Damage by Immature Composts: Measuring Respiration with Solvita
- CLICK
HERE
Forthcoming news on Compost testing in Europe – regulations. Comparison of methods across the community are assessed.
Solvita Compost Maturity Test - The “Solvita” Test is now accepted in Ireland by the Environment Agency as a valid Compost Maturity Test. It is recognised as one of the 2 mandatory checks required for every batch of compost produced. It is also gaining increasing acceptance by major compost producers in the UK.
Under aerobic conditions CO2 production and O2 uptake are broadly equivalent (the process of aerobic respiration uses one mole of O2 and produces one mole of CO2), so it is possible to do a theoretical conversion between CO2 data and O2 data.
There are 3 ways of doing this:
1. Using the Woodsend Respiration Conversion Tool.
The AT4 method measures total O2 or CO2 produced over 4 days. So a value of 10 mgO2/gTS (=dry matter) over 4 days is equivalent to 2.5 gO2/gTS/day. This converts to an equivalent Solvita CO2 score of at least 7 or a PAS 100 value of 6.9 mg CO2/gVS/day (far more demanding that the PAS100 test limit of 16 mgCO2/gVS/day). This AT4 Oxygen figure equates to a DRI figure of 210 mgO2/kgVS/h.
The DRI method has a critical upper limit of 1000 mgO2/kgVS/h which is equivalent to 1 mgO2/gVS/h. From the conversion tool this is equivalent to a Solvita score of at least 4 or a PAS 100 value of 33 mg CO2/gVS/day (far less demanding that the existing PAS100 limit of 16 mgCO2/gVS/day).
2. Using a DCR (digital colour reader) and the Woods End Respiration Conversion Tool:
For this we need to know the mass of compost in the test jar (expressed as total solids or as volatile solids). Assume 100 cm3 of compost (the amount used in the Solvita test) has a bulk density of 0.5 g/cm3, so the fresh weight of the sample is 50g. Assume water content of 40%, so the dry weight of the sample is 30g. Assume the volatile solids content of 40% (dry weight basis), so the volatile solids of the sample is 12g.
An uptake rate of 1000 mgO2/kgVS/h is equivalent to 1 mgO2/gVS/h, so over a 4 hour test we would expect the O2 uptake to be 4 mgO2/gVS/h. If we have 12 g VS in the test jar, then the actual O2 uptake over 4 hours would be 48mgO2. Woods End estimate that the total amount of O2 available in the test jar is 55 mg O2, so there is more than enough O2 to detect the critical value of 1000 mgO2/kg/h. Using the DCR with the Solvita test will therefore enable a direct estimation of the O2 uptake for the purposes of meeting the regulatory requirements.
3. Experimental results
Experimental data from the Quebec Centre for Industrial Research (1998) which supports all the above theory shows very clearly the relationship between O2 uptake rate and Solvita (the units used are the same as in the European regulations so the 1000 mgO2/kgVS/h is the critical value). This confirms that a Solvita CO2 value of 4 definitely meets the regulatory requirement (assuming we use the DRI critical value rather than the AT4 value).
We believe the above demonstrates unequivocally the direct equivalence between O2 uptake and CO2 produced tests to establish compost stability, both being tried and tested methods.
