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Update on the progress made to date on AfOR's inter-laboratory trial
Background to the inter-lab trial
After a preparatory sampling exercise carried out during July 2011, which we informed you about in the Winter 2011 edition of our magazine ‘Organics Recycling, the official sampling round for the inter-lab trial took place on 16 October 2011. Emily and Kiara visited the composting site that kindly agreed to host the exercise and sampled approximately 120 kilograms of green/food waste derived compost. Between 5 and 10 replicate samples (depending on the analysed parameter) were posted to all laboratories taking part in the exercise and were tested for the following parameters (method of test in brackets):
Physical contaminants including stones (AfOR MT PC&S)
Stability (ORG0020)
E. coli (BS ISO 16649-2)
Loss on ignition / LOI (BS EN 13039)
Electrical Conductivity / EC (BS EN 13038)
Water soluble nitrogen (BS EN 13652)
Plant response test (OFW006-000)
Dry matter content (BS EN 13040)
Stability (ORG0020)
E. coli (BS ISO 16649-2)
Loss on ignition / LOI (BS EN 13039)
Electrical Conductivity / EC (BS EN 13038)
Water soluble nitrogen (BS EN 13652)
Plant response test (OFW006-000)
Dry matter content (BS EN 13040)
Parameters such physical contaminants, stability, E. coli, and Plant response test have been chosen as related test results between labs and within the same lab are likely to show the greatest level of variability when tested in material types like composts. Parameters such as LOI, dry matter, EC and Water soluble nitrogen have been selected as they are determined as a part of the stability and the plant response test methods and, thus, affect the results obtained for these tests.
Once the laboratories completed the testing, the related test results were collated by AfOR and provided to AfOR’s appointed contractor (WRc) for the statistical analysis.
Thanks to the composters and the approved laboratories’ financial contributions, WRc was contracted by AfOR to provide technical and statistical support to their inter-laboratory trial to evaluate precision and performance, between AfOR approved laboratories, for the test parameters specified above. The objectives of the statistical analysis of test data generated during the inter-laboratory trials were to:
a. determine the precision of compost sample testing achieved by AfOR’s six approved laboratories;
b. evaluate their performance in terms of precision; and
c. identify any precision performance improvements each laboratory should make.
b. evaluate their performance in terms of precision; and
c. identify any precision performance improvements each laboratory should make.
To achieve AfOR’s trial objectives, WRc collated and reviewed historic data held by AfOR on the PAS100 test parameters reported by all approved laboratories, provided input to the inter-laboratory trial sampling and testing methodology and following completion of the inter-laboratory trial, statistically analysed the data collated and provided by AfOR. The findings of the statistical analysis are presented in this report.
Latest developments:
A confidential first draft report focused on the repeatability and reproducibility of the stability test results was supplied to AfOR by WRc on 7 March 2012. Having read the report in detail, AfOR asked WRc to clarify a number of aspects and considerations made within it. WRc has verbally clarified the majority of these aspects; however written clarifications will only be made in WRc’s second draft of the report.
The second draft, which WRc will supply to AfOR shortly, will include the repeatability and reproducibility data related to all other parameters assessed (physical contaminants, stones, E.coli, Loss on Ignition, Electrical Conductivity, Water Soluble Nitrogen, plant response and weeds test and dry matter).
AfOR intends to make the final version of WRc’s report available in the public domain, after the report’s considerations and associated conclusions have been reviewed by AfOR and any necessary clarifications have been made by WRc.
AfOR has ALREADY undertaken a number of actions, based on WRc’s first draft report:
1) we have consulted the Project Technical Advisors and agreed with them what actions should be taken by AfOR as a matter of urgency;
2) we have individually contacted each involved laboratory, informed them of their results in the context of the repeatability and reproducibility data for the stability test (this was done on 3 & 4 May;
3) where appropriate, we have asked laboratories to look into their procedures, identify and address likely cause(s) of repeatability or reproducibility issues as a matter of urgency; and
4) we have informed the laboratories that we aim to project manage another inter-lab exercise focused on the stability test, to check their improved performances, as soon as practicable after we have received their feedback about procedures review and any corrective actions taken.
2) we have individually contacted each involved laboratory, informed them of their results in the context of the repeatability and reproducibility data for the stability test (this was done on 3 & 4 May;
3) where appropriate, we have asked laboratories to look into their procedures, identify and address likely cause(s) of repeatability or reproducibility issues as a matter of urgency; and
4) we have informed the laboratories that we aim to project manage another inter-lab exercise focused on the stability test, to check their improved performances, as soon as practicable after we have received their feedback about procedures review and any corrective actions taken.
N.B.: Item 4) is subject to AfOR having sufficient financial resource to carry out the exercise and allocating further time to manage the exercise.
In addition, after discussing the methodology with the Project Technical Advisors, AfOR has obtained WRAP’s permission to make improvements to the ORG0020[1] method of test as a matter of urgency.
The key improvements relate to the following aspects:
Storage period: the current method does not specify what the maximum storage period should be between receipt of the sample at the laboratory and the start of the test. Setting a maximum storage period at the laboratory and recommending sample testing straight after sample receipt will minimise any changes in sample characteristics.
Moisture content of the samples: the current method does not identify the acceptable range of moisture the sample should achieve prior to be tested for stability.
An additional issue that is being considered is:
Accuracy of CO2 devices: the current test method allows for alternative CO2 monitoring devices to be used instead of trapping the CO2 evolved and then titrating to determine its quantity. However, the method does not identify what accuracy should be achieved by CO2 monitoring devices and how their data should be converted into a stability test result. This aspect can be either clarified in the methodology, if appropriate, or further guidance can be provided by AfOR to the laboratories that are using these devises.
Once improvements to the method instructions have been drafted by AfOR, the revised methodology will be subject to WRAP’s review, with a view to approval and publication of the new version of this method as soon as practicable.
Last update: 10/05/2012
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