Behaviour of compostable waste collection bags in industrial composting

21 December 2021 - Published by Hanne Lakkenborg Kristensen
Written by: Ina Körner and Stefan Deegener, TUHH, December 2021. Compostable plastics bags are increasingly used in households to dispose food waste. Their use might be helpful to improve biowaste separation. But often German composting companies do not accept them.

They fear insufficient biodegradability during their operations and remains of bio-based plastics particles in composts. Visible compost impurities are a hindering reason for extended compost application, which was also shown by the SOILCOM-questionnaire « Compost in Agriculture » distributed to farmers in 2020. To judge the usability of compostable plastic bags as integrated part of regional waste management concepts, the degradation behaviour during municipal composting and the resulting compost quality has to be known.  

TUHH carried out an investigation into this direction, supported by composting facilities in Neumünster and Lübeck, as well as the Association for Compostable Products. Four different types of commercially available, certified compostable and bio-based waste collection bags (two with starch- and two with PLA-based ingredients) were composted in the municipal composting plant of Neumünster, Germany. The bags, filled with food waste rich biowaste, were given into specifically constructed sacks and surrounded by biowaste. 20 bags from one material type were included in one sack, 32 sacks were prepared in total. The sacks were introduced into a conventional municipal composting process. Composting was done for two weeks in containers followed by four weeks in a windrow. Composting conditions were monitored and sampling was carried out after 2, 3, 4, 5, or 6 weeks.

The remaining bio-based plastics particles found in the sacks after opening were divided into the following fractions: Macro particles (easy visible fragments), meso particles (≥2-8mm), and micro particles (≥1-2, <1mm). The report with the results is to be expected early in 2022.



Placement of sacks into a composting container. The sacks contain biowaste and compostable waste collection bags filled with food-waste rich biowaste. The sack are further covered with layer of biowaste (Foto: Deegener, TUHH, 2021).