Microalgae waste has been used by researchers to make asphalt and successfully replace petroleum-based substances in the process.
Researchers in France have proved the viability of bio-asphalt by demonstrating its close similarity to the asphalt currently used to pave roads.
To make the bio-asphalt scientists at labs based in Nantes and Orléans used a hydrothermal liquefaction process – pressurised water – to transform the microalgae residue into a black, viscous substance that closely resembles petroleum-derived asphalt. The process achieved a conversion efficiency of 55 per cent.
Trials are now taking place to analyse the material’s behaviour over time, as well as cost considerations to evaluate its potential for large scale production, which means the road-building industry, mostly reliant on petroleum, could soon see microalgae waste used to make asphalt.
Microalgae have been used traditionally in cosmetic dyes and food supplements, but in recent years there has been a shift towards refining microalgae to produce biofuel, now seen as an alternative to petroleum. The move could lead to more cost-effective processes and other microalgae products becoming available.
Other types of bio-asphalt that have been developed use oils from agriculture or from the paper industry, mixed with resins to improve their visco-elastic properties. But, as opposed to these resources, which are used in the food or manufacturing industry, microalgae are a promising alternative to petroleum products without competing for other uses.