Microalgae as sustainable producers of bioplastic

Abstract

Extensive exploitation of nonrenewable resources for various products has showed its undesirable consequence on the environment following its limited availability. Plastics have impacted the environment in a negative way polluting terrestrial and marine life to a great extent. Biodegradable products from renewable resources are the possible alternative solution. Bioplastics are one such promising replacements with characteristics similar to fossil fuel-derived polymers, with increased biodegradability and blending property. Bacterial and algal systems accumulate polyhydroxyalkanoates (PHA) as part of their metabolic processes depending on the availability of carbon source. PHA from bacterial systems has proved to be efficient in accumulation, but their commercialization is challenging due to the high cost involved. Bacterial systems demand critical process parameters which makes scaling-up expensive. The shortcomings of bacterial PHA commercialization can be overcome by employing microalgal biomass that accumulates PHA. The versatility in carbon source utilization enables cultivation on different resources. This eliminates the dependence on single substrate, thus aiding in mixed growth population. Current studies indicate an accumulation of 27% PHA by Chlorella pyrenoidosa. Taking blending properties into consideration, the whole biomass of Chlorella to glycerol (4:1) showed improved plasticity with polyolefins. Interestingly, direct incorporation of 50% Spirulina platensis biomass into polyolefin shows properties comparable to petroleum-derived plastics. Further developments in the strain could be achieved through metabolic engineering by directing flux toward PHA accumulation. But the maintenance of genetically modified microalgae for continuous production is critical, taking the doubling time of the organism into account. In order to have a sustainable bioplastic recovery from microalgal biomass, an integrated biorefinery approach should be adopted.