This project aims to improve sampling and testing methodologies for physical contaminants in compost and digestates. Led by Dr. Thomas Aspray, the project will work with composting and anaerobic digestion facilities to determine if current sampling methods are robust. It will also study variability in contaminant test results across laboratories by testing materials with known contamination levels. The goals are to minimize variability in test results and understand if the German approach to measuring film plastics could be adopted in the UK. The project will address these objectives through site visits, statistical studies, laboratory assessments and research.

1. Project concept
Sampling and Testing for Physical Contaminants in
PAS100 Compost and PAS110 Digestates
(OIN008-001)
This WRAP funded project is led by Dr Thomas Aspray of Heriot Watt University in collaboration with
Dr Mary Dimambro and Dr Joachim Steiner (Cambridge Eco Ltd), Dr Phil Wallace (Phil Wallace Ltd)
and Dr Stéphane Pietravalle (Fera). The project will take place during the period December 2014-
March 2015.
The overall project aim is to improve sampling and testing methodologies related to physical
contaminants in quality (PAS100 and PAS110) compost and digestate. The project has four main
objectives:
1. To work with a number of composting and AD facilities to determine whether the current
sampling methods (specified by the Biofertiliser and Compost Certification Schemes) are
sufficiently robust to deliver truly representative results.
2. To work with the Renewable Energy Associate Ltd (REAL) appointed laboratories to
understand intra and inter-laboratory variability in physical contaminant results through the
testing of materials with known levels of physical contaminants.
3. To work with the REAL appointed laboratories to minimise variability so far as is practicable,
across the tested range of contaminants and different substrates.
4. To work with REAL appointed laboratories to understand whether the German approach to
film plastics could be adopted in the UK, and at what cost.
Objective 1 will be addressed through a combination of site visits and telephone discussions with
compost and digestate producers. Objective 2 will be addressed through a statistically robust study,
where by samples containing known contamination levels will be analysed by commercial laboratories.
Objective 3 will use information gained from the above laboratory work together with commercial
laboratory visits to unravel intra and inter-laboratory variability in physical contaminant analysis.
Finally, Objective 4 will involve desk based research and in-house laboratory assessment of a potential
alternative method for film plastics quantification based on area rather than weight determination.
For further details please contact Dr Thomas Aspray (t.j.aspray@hw.ac.uk).