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Project reduces cost of creating biofuel from microalgae

At APP's International Algae Congress held in Amsterdam towards the end of 2008, there was a consensus that the capability to cultivate microalgae in sufficient volumes for biofuel production on a commercial basis was nearing reality. But one of the biggest pinch points that remains is how to extract the oil from the microalgae biomass in an efficient, cost effective manner. How, after all, can one extract such a small quantity of oil from each microbial algae cell?

Global Companies like Neste Oil and UOP have the ability to process and convert the algal oil within the microalgae biomass to JP-8 and other high grade fuels.

Traditional methods have been considered but these are neither efficient nor economic. These also seek to extract the oil by using external energy to break down the microbial cell walls. The amount of energy required to achieve this makes the whole process too costly.

The solution appears to come from a biomass pre-treatment technology that is used to break down biomass feed stocks prior to anaerobic digestion. The microbes in anaerobic digesters break down organic material generating biogas. The smaller the particle sizes of the feedstocks entering the digester, the more efficient the digestion process. A UK company, Eco-Solids International Ltd, has been trialling a new proprietary patent pending process called Cellruptor with utility Yorkshire Water, to enhance biogas production at one of its wastewater treatment sites.

Cellruptor effectively gives the sewage sludge being treated at the site “the bends” before the sludge enters the digester. As deep sea divers are aware, it is critical that they do not rise to the surface too quickly after a deep sea dive, otherwise the CO2 within their bodies expands too rapidly rupturing their internal organs. Cellruptor replicates these conditions within its own reactor. The CO2 that is used comes from the biogas that the digester generates.

Biogas typically contains 40% CO2 by volume. The biogas itself is mixed with the sludge under pressure prior to the digestion process and during a short residence time, the CO2 permeates through all the microbial cells. The pressure is then suddenly dropped and the carbon dioxide within the cellular material expands very rapidly. The cell walls are unable to withstand this rapid expansion and the cell structures rupture. Enhanced biogas production then results when the material is fed into the digester. Importantly, the CO2 coming out of solution is recycled back into the reactor. Thus the process uses internal expansion energy to break open the microbial structures, which provides significant advantages compared with existing external energy technologies.

Eco-Solids holds the rights to the Cellruptor technology for pre-treating biomass prior to anaerobic digestion, and has been working with the licensor in the US to develop the capability to extract algal oil from microalgae biomass. The potential of Cellruptor to do this has been recognised by General Atomics, a multibillion dollar organisation that has secured US Defence Agency funding to develop affordable algal-derived JP-8 jet fuel.

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