Influence of biodegradable plastics on composting processes

  • Zhabiz Vilkiji

Student thesis: Phd


Poly(vinyl alcohol) is a biodegradable water soluble polymer that is widely used in agricultural mulch films. Since PVA is biodegradable, those mulch films can be composted after use. PVA's long-term contact with farm soil during its use, and its presence in compost after its disposal, could potentially have impact on the diversity and composition of microbial communities in compost and soil with potential consequences for carbon (C) and nitrogen (N) cycling. In turn, PVA effects on compost and soil microbial communities and C and N cycling could have knock-on consequences for plant and animal health. Further, the molecular features of PVA as well as composting temperature may affect the nature of PVA's impacts on microbial communities, as might the nature of PVA addition, for instance whether it is continuous long-term rather than one-off addition. My thesis presents three experiments that collectively aimed to advance understanding of how PVA addition impacts on compost and soil microbial communities, and aspects of C and N cycling. In the first experiment, six types of PVA with three different molecular weights and two degrees of hydrolysis were added to soil by a one-off addition. Fungal community of soil was then monitored for two months using terminal restriction fragment length polymorphism (TRFLP). Addition of PVA caused a temporary change in the fungal community composition, and a temporary reduction in richness, evenness, and diversity (i.e. Simpson's index) of the fungal community. None of the individual attributes of the PVA molecule (i.e. molecular weight and degree of hydrolysis) had an effect on the nature and rate of changes caused by PVA. However, a cumulative effect can be associated to both molecular weight and degree of hydrolysis of PVA molecule, since changes was observed in the effects of PVAs with different combinations of these two attributes. Based on my findings, PVA, regardless of its molecular weight and degree of hydrolysis, temporarily alters the composition and diversity of fungal community of soil. This could consequently affect the ecosystem functions and plant health. The second experiment aimed to test the effects of PVA on bacterial and fungal communities of compost at different incubation temperatures. PVA was added to compost as a one off addition at the start of the experiment, and incubated for 80 days at four different temperatures ranging from 25 °C to 55 °C. Bacterial and fungal communities were monitored using amplicon-based next generation sequencing (NGS) targeting 16S and ITS2 regions. The effects of temperature were much more intense than that of PVA. The richness, evenness, and the diversity (i.e. Simpson's index) of the bacterial and fungal communities was reduced at higher temperatures. Further, PVA affected different taxa at varied temperatures, since the bacterial and fungal communities were different depending on the incubation temperature. For example, PVA caused an increase in the population of Sphingopyxis, Altereythrobacter, Caulobacter, and Phenylobacterium, (all at 25 °C and 37 °C) and Steroidobacter (only at 37 °C), and an unidentified genus of the Steroidobacterales order (at 45 °C). Among the fungal species, Cymatoderma and Vrystaatia aloeicola grew in the presence of PVA at 25 °C, and Aspergillus stellatus at 45 °C. My findings show PVA can potentially alter both mesophilic and thermophilic microbial communities in compost. The changes caused by PVA in the composition of microbial communities of compost can interfere with the proper composting process at both mesophilic and thermophilic stages of composting and impact compost quality and maturity. In the third experiment, the effects of continuous addition of PVA on compost bacterial and fungal communities, and C and N availability were examined. PVA one-off addition was compared to two different frequencies of continuous PVA addition at three different concentrations. In general, PVA addition reduced the
Date of Award31 Dec 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRichard Bardgett (Supervisor) & Jon Pittman (Supervisor)


  • Biodegradable polymers
  • Biodegradation
  • Terminal restriction fragment length polymorphism (TRFLP)
  • Compost carbon and nitrogen analysis
  • Amplicon-based next generation sequencing
  • Soil fungal community
  • Microbial community profiling
  • Poly(vinyl alcohol) (PVA)
  • Compost microbial community

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