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SEPA report on plastic in food waste derived digestate and soil

Earlier this year, SEPA investigated plastic in food waste derived digestate and soil. The objectives of this project were:
  1. Understand previous work on plastic in digestates and soils

  2. Through laboratory analysis, develop a knowledge base of the types, quantity and particle size of plastic that may be found in food waste derived digestate

  3. Through field work and laboratory analysis, develop a knowledge base of the behaviour and distribution of plastic in agricultural soils that have had digestate applied in the past and assess the likely impact on soil function. 

Regarding the lab analysis of plastic in digestate 15 discrete digestate samples were collected from three UK based PAS110 certified sites and analysed. Weight, surface area and size data for plastic contamination from a fourth PAS110 site was also made available for this project. 

The weight based analysis showed that three of the four sites assessed were producing digestate of suitable quality (in plastic contamination terms) to meet SEPA’s 2017 and 2018 limits through high selectivity of feedstocks and post digestion screening. However, the more stringent 2019 limit could cause periodic failures with current feedstock selection and screening practices.


For the soils work, samples were taken from agricultural soils that have had digestate applied in the past. Samples were collected from four fields on one farm representing arable and grassland with and without history of multiple PAS110 certified digestate application. Five locations with three depths were sampled per field. An original wet sieving approach was trialled and validated in this project. Using this approach plastic fragments less than 2 mm were recovered from the grassland field with digestate application at surface (0-5 cm) depth only. No plastic fragments >2 mm were recovered from the arable field with digestate application. 


The full report can be found here.


Published: 16/11/17

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