Introduction

Throughout the modern age crude oil has become the essential resource upon which we have become ever reliant, not only for transportation and heating but also for all manner of chemicals from plastics to lubricants, sulfuric acid to asphalt. Petroleum however is a finite resource, driving the incentive to find alternative feedstocks or manufacturing processes. In juxtaposition to this, the combustion of crude oil and its derivatives has resulted in an alarming increase in carbon dioxide and the devastating effect it has had on the environment. Carbon dioxide is a very stable molecule with a high Gibbs free energy of formation, making its conversion back into useful forms somewhat prohibitive.

Microalgae and photosynthetic bacteria are in fact some of the most efficient primary producers on Earth. As such they are frequently employed in photobioreactors (PBRs) to efficiently exploit photosynthesis, targeting metabolites that can be processed into biofuels, high-value compounds, or drugs in a carbon neutral fashion. Currently both open and closed PBR systems are under investigation, however open-pond systems, although inexpensive, can have issues stemming from poor growth control, high water losses, and contamination issues. These processes are often based on the “one-shot” use of microorganisms, as these metabolites are excreted into the growth media in which the cells proliferate. One possible alternative is the use of embedded algae through which the nutrient media is passed.

Here the medium can come into contact with the cells, yet remain in a heterogeneous phase, allowing the metabolites to be easily harvested and the cells to be reutilized. Closed systems also facilitate water management as evaporation can be minimised. Crucially, they also allow an ethically responsible attitude towards the use of genetically modified strains: such strains can be employed in PBRs based on living hybrid materials, safe in the knowledge that there is no risk to the local ecosystems.