Amir Mahboubi, doctoral student in Resource Recovery, has recently presented a report on how an existing 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. The technology provides faster and stable production of ethanol and is better for the environment.
“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 sugar cane. However, this is controversial, since these materials have a high value as human food and animal feed”, explains Amir Mahboubi.
Ethanol production from biomass
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”, he says.
The 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. 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.
Specially designed membranes
“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”, explains Amir Mahboubi, “is to develop new membranes and modules, that are durable and specifically tailored to fit the needs of biotechnological applications.”
Membrane is a kind of filter, though with very small pores, through which different substances can selectively pass. They are used, for example, in sewage filtration, and food and drug production, to separate different substances or cells from other compounds. In the membranes that Amir Mahboubi works with, the objective is to retain large amount of yeast cells in the reactor, while enjoying high ethanol productivity.
The waste material, which the reactors are fed with, differs from sewage water, which is thin and easy to flow. 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.
This 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.
Read the report ”Reverse membrane bioreactor: Introduction to a new technology for biofuel production”.
Also read about the Swedish Center for Resource Recovery.