Biodegradable plastic bags in biowaste treatment 

The project (Biologisch abbaubare Beutel in der Bioabfallverwertung – Biodegradable plastic bags in bio-waste treatment), led jointly by the German Fraunhofer Institute and the University of Bayreuth, examined the fate of bio-waste collection bags made of biodegradable plastic (BDP) starting from bio-waste collection, treatment, to their degradation behaviour in soil. Particular emphasis was placed on particles measuring less than 1 mm, which, as per the current German Biowaste Ordinance, are not obligatory to trace.

The following research questions are an extract of those that were addressed during the project:

  1. Will BDP bags substantially displace conventional plastic bags when provided to the public for free?
    The gratuitous distribution of BDP bags did not significantly improve the quality of bio-waste by reducing impurities, considering the provided ones were on the positive catalogue.
  2. Are certified BDP bags fully aerobically degraded into CO2, water, minerals and biomass in industrial composting facilities?
    BDP bags do not fully degrade, neither in composting nor in combination with anaerobic digestion under industrial conditions (2 weeks intensive rotting, 4 weeks maturation). Particles < 1 mm mainly comprised polybutylene adipate terephthalate (PBAT) which is among the main ingredients of BDP bags.
  3. Do BDP bags cause more or less microplastics in compost compared to conventional plastic bags?
    BDP bags cause a larger fraction of microplastics particles (< 1 mm, mainly PBAT) compared to conventional plastics. The design of BDP bags as well as the treatment plant technology influence the fragmentation process. BDP bags made of Mater-Bi® cause a higher degree of fragmentation compared to those made of Ecovio®.
  4. How is the further degradation behaviour of BDP in soil with and without aerobic (and anaerobic) pre-treatment?
    The mineralisation in soil depends on the material composition of BDP. The main ones investigated were Ecovio® and Mater-bi®, two standard blends of BDP used for the production of BDP bags. Ecovio® showed an improved degradation with the material being pre-treated (25%) compared to untreated (5%) after 5 months under ideal conditions. The treatment conditions did not significantly influence the mineralisation of Mater-bi® (14% in both cases). Reference materials wax-coated paper (43%) and the polymer polyhydroxybutyrate (PHB, 46%) showed significantly higher degradation in both cases.

The authors state, that further investigations are necessary, particularly with regards to conducting long-term evaluations of BDP behaviour in soil. Additionally, a revision of the current standards (DIN; EN) governing the certification of BDP bag degradability is advocated.

The project report can be found here.