Team:UiOslo Norway/Practices/Sewage

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Sewage treatment facilities

The second facility we contacted was Bekkelaget Renseanlegg, the sewage treatment facility for all of Oslo.

In total about 9500 tons of sludge is fermented in their fermentation tanks annually. The organic content of the sludge is about 75%. About 47% of the sludge content in the tanks ends up as organic residue that is not broken down; this can be used as fertilizer.

Picture 1: Waste water treatment facility in the mountain hall

There are two tanks and each of them is 4000 m³, and the fermentation process is run at 55^oC. The total annual production of biogas is about 3.500.000 m³. The biogas consists of roughly 65% methane and 35% CO₂, and is a very small quantity of other compounds (impurities) as well. The third stage of the process involves refining the biogas to bio-methane (~100% methane gas), in this process the CO₂ is removed and the pressure is set to 200 bar. CO₂ is removed by amine scrubbing using amines as an absorption-fluid for CO₂.

Picture 2: The refinery used for upgrading the biogas to pure bio-methane


Picture 3: Containers used to transport the gas.

In 2014 they delivered 1.500.000 m³ of pure methane gas as fuel for busses used for public transportation.

Picture 4: Norwegian busses running on biogas. Picture taken from Energiogklima.no

The biogas production system poses a very interesting as prospect for filter implementation. This is because the methanotrophs take up not just pure methane but also mixtures of methane with a little bit of CO₂ this is often used to culture the methanotrophs in the lab. Moreover the microorganisms in the bio-filter we are making could easily be adapted to turn methane into methanol instead of biomass. The reason this would be desirable is because methanol can be used directly as a liquid fuel, taking up a smaller volume than methane gas. The storage tanks on the buses can then be smaller, making the buses lighter and more efficient as well.

As a fuel methanol is perfectly viable and even has some characteristics that make it attractive for transportation use¹:

• It is a high-octane fuel with combustion characteristics that allow engines specifically designed for methanol fuel to match the best efficiencies of diesels while meeting current pollutant emission regulations.

• It is a safe fuel. The toxicity (mortality) is comparable to or better than gasoline.

• It also biodegrades quickly (compared to petroleum fuels) in case of a spill.

• Methanol has a lower risk of flammability compared to gasoline².

So for biogas applications the filter could be optimized for the conversion of methane into methanol instead of biomass. This could be done either by isolating the sMMO protein and using it on it’s own, if it remains stable and active, or we would change the microorganisms in the filter from E. coli that convert methane to carbohydrates to ones that only convert the methane into methanol.

The methanol could then be collected and used as fuel in itself, or it could be blended with gasoline in the same way ethanol is blended to give the gasoline a higher octane rating, making the fuel more efficient and safe.

References

1. Bromberg L. and Cheng Bodelier W.K., Methanol as an alternative transportation fuel in the US: Options for sustainable and/or energy-secure transportation. (2010).
2. U.S. Department of Energy. Alternative Fuels Data Center

iGEM UiOslo 2015 is sponsored by:

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