From Pond to Power: Hydrogen production from microalgal biomass

To limit the global average temperature to 1.5°C above pre-industrial levels and prevent crossing catastrophic environmental tipping points, carbon dioxide removal methods are seen to be key by most climate models. There are several methods available but in most cases bioenergy with carbon capture and storage (BECCS) is seen as an important technology. However, growing crops for bioenergy comes with unwanted environmental consequences. These include habitat loss from the large land requirement, death of aquatic life due to fertilizers entering the waterways and the use of pesticides. Algae offers an alternative biomass source that, due to a higher growth rate than terrestrial plants and being grown in a contained environment, has a lower environmental impact.

However, the cost of building and running algal farms is significant, which has held back widespread use of algae for lower value products, such as fuels. To get the aforementioned benefits of this technology, the cost must be brought down to make it more financially viable. This can be achieved by optimising the process of converting the biomass into energy, so that more energy is produced per unit of biomass. For algal biomass, the moisture content is too high for conventional combustion or gasification processes. To achieve an efficient conversion, supercritical water gasification (SCWG) can be used to covert the biomass into energy rich gas containing hydrogen and methane. This process is far less researched, but also comes with the added advantage of recovering the inorganic parts of the biomass which could be recycled for algal growth. As a result, the optimisation of SCWG could be a big step towards the commercialisation of the technology.