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Wastewater membrane technology shows promise in cellulosic ethanol application

In Sweden, a new technology that can be used in reactors for the production of bioethanol has been designed and developed in a doctoral project at the University of Borås. Amir Mahboubi, a doctoral student in Resource Recovery, has recently presented a report on how an existing membrane technology for wastewater treatment now can be used in a completely different field– the production of bioethanol from waste, such as residues from agriculture and forestry.

In Sweden, a new technology that can be used in reactors for the production of bioethanol has been designed and developed in a doctoral project at the University of Borås. Amir Mahboubi, a doctoral student in Resource Recovery, has recently presented a report on how an existing membrane technology for wastewater treatment now can be used in a completely different field– the production of bioethanol from residues from agriculture and forestry (photo courtesy Solveig Klug).

The biofuels industry has long been seeking a solution for how the processes used today can be adapted, in an efficient and environmentally sustainable manner, to manage cellulosic waste and waste with different contaminants.

The production of biofuels has so far been limited to the choice of raw materials, process costs and what volumes can be achieved. The first generation bioethanol is mainly produced from starch and sugar, for example from corn and sugarcane. However, this is controversial, since these materials have a high value as human food and animal feed, said Amir Mahboubi.

The second-generation bioethanol is produced from biomass, for example, residues from agriculture and forestry – renewable materials that are widely available, cheap and not regarded as food.

These materials, however, contain different types of sugars, which affects the fermentation process, they are tougher to degrade and contain impurities that inhibit the fermentation process in the conversion to bioethanol. It makes it a challenge to get an efficient process that is sustainable on an industrial scale explained Amir Mahboubi.

Specially designed membranes

One problem in today’s processes is that the waste to be converted into ethanol, the yeast cells and unwanted bacteria are together in the reactor. In continuous fermentation when the ethanol is pumped out, the yeast cells are also flushed out. And unwanted bacteria can take over and interfere with the fermentation process.

We have come up with technical solutions to achieve higher productivity compared to the methods used in the industry today. With these solutions, different biodegradable raw materials can be fermented easier, faster and in a more stable way. The biggest challenge is to develop new membranes and modules, that are durable and specifically tailored to fit the needs of biotechnological applications, said Amir Mahboubi.

The reverse membrane technology and results are presented in the report “Reverse membrane bioreactor: Introduction to a new technology for biofuel production” and published in the journal Biotechnology Advances. The waste material, which the reactors are fed with, differs from sewage water, which is thin and flows easily. In the case of sewage water, it is easy to separate unwanted substances by passing the sewage through membranes.

The waste material used in bioethanol production, on the other hand, is treated to a thick slurry full of large particles. These particles can quickly block the pores in the membranes, which must then be chemically cleaned or replaced. It also means that unwanted bacteria cannot be flushed out at the required rate, and these can then compete with the yeast cells.

In other words, the new technology helps the favourable microorganisms to thrive on the feed and produce ethanol.

The research project is being conducted in collaboration with the Flemish Institute for Technological Research (VITO NV), Belgium, specialized in membrane and membrane module development and processes.

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