Different standards for impurities in compost
According to Porterfield et all (2023)[1] plastic contamination can impede circular economy efforts by making composts and digestates less attractive to farmers and consumers (Friege & Eger, 2021; Roy et al., 2021). “Biodegradable” and “compostable” plastics have been touted as a more environmentally friendly alternative compared to conventional petroleum-based plastics (European Commission, 2018; Folino et al., 2020; Shaikh et al., 2021), but are problematic for multiple reasons and do not yet represent a clear solution (Calabrò & Grosso, 2018; Haider et al., 2019; Markowicz & Szymaoska-Pulikowska, 2019; Serrano-Ruiz et al., 2021).[2]
Recent regulatory actions in the EU and in specific European countries have resulted in stricter limits for plastic contamination in recycled organic waste products.[3] In the (near) future, the limit values for the presence of (plastic) impurities will be lowered further.
ECN-QAS
In the last 20 years, quality assurance schemes for compost and digestate products were successfully established in various European Member States and contributed significantly to the sustainable recycling of organic waste. The example of the advanced countries clearly demonstrates that for the sustainable recycling of biowaste, strict quality standards are essential. The quality assurance of compost and digestate products guarantees environmental safety and supports a successful marketing and application. Based on existing experiences in countries with running quality assurance schemes, the European Compost Network ECN has developed a European Quality Assurance Scheme (ECN-QAS) for compost and digestate products. National Quality Assurance Organisations can benchmark their national scheme with ECN-QAS. This helps to create a level playing field for compost and digestate quality.
The current limit value for impurities in ECN-QAS is 0,5 w/w% on dry matter for impurities >2mm.
EU Fertilising Products Regulation (FPR)
A new EU Fertilising Products Regulation (EU) 2019/1009 was approved on 5 June 2019. A new key element is the opening of the market for CE labelled bio-based fertilisers. The fertilising products are divided into different product function categories (PFC), according to their main properties. The material that is used to assemble these PFC’s, is subdivided into so-called CMC’s (Component Material Classes). Compost derived from waste materials is categorised as CMC3, digestate from waste materials as CMC5. The EU FPR proposes limit values for impurities for both CMC3 and CMC5. These standards are given in the table below.
Most of the EU countries have national standards for impurities in compost. A selected overview for some member states is given in table 1. There are two types of analytical standards: (a) a standard based on the weight fraction of the impurities and (b) a standard based on the visual assessment of impurities by determination of the surface area. Both methods have their advantages and are complementary. This is illustrated by the figure below: a higher degree for standard (a) in sample A doesn’t necessarily imply a higher degree of visual impurities (which is clearly higher in sample B).
Sample A Sample B
|
Standard |
Parameter |
Unit |
Limit value |
|
EU level |
|
|
|
|
ECN-QAS |
Impurities > 2mm |
w/w% DM |
0,5 |
|
ECN-QAS growing media |
Impurities > 2mm |
w/w% DM |
0,25 |
|
EU Fertilising Products Regulation |
Impurities > 2mm (sum) |
w/w% DM |
0,5 |
|
EU Fertilising Products Regulation |
Plastics, glass, metal >2mm |
w/w% DM |
0,3 |
|
EU Fertilising Products Regulation 16.07.2026 |
Plastics >2mm |
w/w% DM |
0,25 |
|
EU Countries |
|
|
|
|
Flemish Region: Reference value |
Impurities > 2mm |
w/w% DM |
0,5 |
|
Flemish Region: Quality target |
Visual assessment of impurities by determination of the surface area |
cm²/l |
25 (2023), 20 (2024) and 15 (2025) |
|
Austria |
Plastics > 2mm |
w/w% DM |
0,2 |
|
Austria |
Impurities > 2mm |
w/w% DM |
0,5 |
|
Austria (draft compost ordinance) agriculture and hobby gardening |
Impurities > 2mm |
w/w% DM |
0,2 |
|
Austria (draft compost ordinance) agriculture and hobby gardening |
Visual assessment of plastics by determination of the surface area |
cm²/l |
15 |
|
Austria (draft compost ordinance) |
Metals |
w/w% DM |
0,2 |
|
Austria (draft compost ordinance) |
Glass |
w/w% DM |
0,1 |
|
Scotland |
Impurities > 2mm |
w/w% DM |
0,25 |
|
Scotland |
Plastics > 2mm |
w/w% DM |
0,06 |
|
Germany |
Film plastics > 1mm |
w/w% DM |
0,1 |
|
Germany |
Impurities > 1mm |
w/w% DM |
0,4 |
|
Germany |
Visual assessment of impurities by determination of the surface area |
cm²/l |
15 |
|
Germany organic farming |
Visual assessment of impurities by determination of the surface area |
cm²/l |
10 |
|
Netherlands keurcompost A |
Glass 2-20mm |
w/w% DM |
0,05 |
|
Netherlands keurcompost A |
Other impurities 2-20mm |
w/w% DM |
0,05 |
|
Netherlands keurcompost B |
Glass 2-20mm |
w/w% DM |
0,1 |
|
Netherlands keurcompost B |
Other impurities 2-20mm |
w/w% DM |
0,1 |
Table 1: National standards for impurities in compost
Situation in Germany
In Germany, the following contaminant-relevant parameters are routinely analysed at certified composting plants as part of the quality assurance of the Bundesgütegemeinschaft Kompost (BGK): foreign matter (deformable plastics, other), stones >10 mm (w/w % dry matter) and the degree of contamination as a surface sum (cm²/L compost). In studies conducted by TUHH together with the Technical University Bergakademie Freiberg, they determined a range up to >0.5 mm for composts from two agricultural and two municipal composting plants. Small plastic particles were detected in all plants. A dependence on the input materials and also on the processing method in the plant was shown. The results are currently being evaluated and will be published in the TUHH report on Microplastics in compost from different composting facilities after project completion.
The TUHH has also entered into a cooperation with the University of Hamburg with the objective of further developing microplastics analysis by means of pyrolysis GC/MS, which can also cover the smallest particle range and enable mass-related statements.
Prevention of plastics in compost
Strict limit values are essential. But ensuring separately collected bio-waste remains an important option for recycling through composting and anaerobic digestion. Therefore we also need to consider the technical ability of the treatment facilities to meet these strict limit values. We see 2 key principles. On the one hand, the effort in prevention should be increased: the occurrence of plastics or other impurities ending up in bio-waste must be minimised. Sensitising citizens is essential for achieving this goal. On the other hand, the producers of compost and digestate should invest in the best available techniques to remove the impurities that are still present in the compost or digestate, and the occurrence should be closely monitored through sampling and analysis.
Too soon for additional regulations for microplastics!
According to the paper Microplastics in compost, digestates and food wastes: a review1, there are multiple limitations to the existing regulatory approach to microplastic contamination in compost and digestate products.
- Regulatory standards are in units of w/w, while 44% of the studies we reviewed reported microplastic abundance in composts and/or digestates exclusively on a count per weight basis. This results in a mismatch between science and policy whereby a large fraction of the existing body of knowledge cannot effectively assess the results.
- Due to an incomplete understanding of the risks posed by microplastics in soils under different conditions (e.g. dosing rates, edaphic factors, polymer types, size distributions etc.), allowable contamination levels and lower particles size thresholds may instead be determined by aesthetic concerns and detection limits rather than known risk (USEPA, 2021a).
- Regulating microplastics content in finished products, without considering the fertilizer value of the material or application rate, does not limit the ultimate flow of microplastics to soils via organic amendments. For example, under the current regulatory structure, it may be permissible to apply a large amount of microplastics in a dilute form on land, but not a smaller amount of microplastics in a more concentrated form.
- Regulating contamination levels in organic amendments alone may be insufficient to fully mitigate the flow of microplastics into agricultural soils given the existence of other entry points. There are other examples of narrowly focused microplastics policy that similarly do not address multiple pathways of introduction to the environment.
For analysing microplastics in compost or digestate the main problem is that there is no agreement about how to get the microplastics in solution to count/weight them. Each lab, research centre uses its own method. Collecting data is difficult and comparing these results is even less obvious.
Together for a Premium compost quality
Last years, within the SOILCOM project around 170 interviews were conducted among growers. In almost 70% of the companies more compost was used. In decision making and application especially price and certification were leading. Companies which didn’t use any compost were in 10% of the cases concerned about the presence of impurities in compost, or had bad experiences with compost in the past (15%). Surprisingly, 50% of the non-users didn’t think of using compost. Researchers as well as the composting industry engaged themselves, strengthened by the Soilcom project, to optimise the quality of compost concerning the degree of impurities. The goal is to develop an additional standard for premium quality compost complementary with the ECN-QAS quality requirements. This will be presented it at the final meeting of the project.
[1]Microplastics in Composts, Digestates and Food Wastes: A Review Katherine K. Porterfield, Sarah A. Hobson, Deborah A. Neher, Meredith T. Niles, Eric D. Roy
[3]USEPA. (2021). Emerging issues in food waste management: Plastic contamination (Report No.
EPA/600/R-21/116). https://www.epa.gov/system/files/documents/2021-08/emerging-issuesin-
food-waste-management-plastic-contamination.pdf