Sustainable bio-plastic production through landfill methane recycling

Plastics are an indispensable part of day-to-day life. Environmental implications of these non-biodegradable plastics in landfills raise major concerns. Use of biodegradable plastics is the best alternative as they are environmental friendly, with great recycling potential, and can be produced using renewable resources such as waste materials, methane (CH₄) and simple carbon sources. Whilst the biodegradable plastics are eco-friendly, they pose a risk of emitting CH₄ under anaerobic conditions in landfills. As a cradle-to-cradle approach, landfill CH₄ could be effectively used for biodegradable plastic production by methanotrophs. This review briefly reviews approaches to plastic disposal, alternatives to plastic waste management and outlines issues arising. The focus of the review is to examine the potential for cost-effective production of polyhydroxybutyrate (PHB) using methanotrophs for manufacturing biodegradable plastics. The data input into this analysis is derived from Australian landfill CH₄ emissions, the average PHB content of methanotrophs and applied to a case-scenario in Sydney, Australia. The results suggest that this approach to biodegradable plastic production can be economically viable and price-competitive with synthetic plastics. In our case study, landfills were sized small, medium and large (5,000, 35,000 and 230,000 t of waste per year, respectively). In small landfills, 162 t of CH₄ can be recovered to produce 71 t of PHB per year, whilst in large landfills 7,480 t of CH₄ can be recovered to produce 3,252 t of PHB. The cost of PHB production can be reduced to 1.5–2.0 AUD meeting the market value of synthetic plastic by increasing production volumes through building a centralised extraction and refinement facility suitable for large metropolitan cities.