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Master's student Janet Eustasie (on the right) and researcher Anders Malmquist are operating a biogas plant that transforms KTH's lunch leftovers to electricity and heat. (Photo: Christer Gummeson)

KTH's lunches become sustainable energy

Published Jun 19, 2012

The leftovers of your lunch that you leave on your plate are now being transformed into biogas at a research facility at the edge of the wood on Brinellvägen on KTH's campus. The experiment may become a first stage in having food waste from restaurants and kitchens at KTH being transformed into electricity and heat.

A meeting is arranged at the edge of the forest on Brinellvägen by Janet Eustasie where the mobile biogas plant is demonstrated; it has been borrowed from the Swedish Institute of Agricultural and Environmental Engineering.  She spends two hours a day here, despite the fact that it is quite possible to operate the plant remotely.

“We have been able to make use of the plant for three weeks and the learning experience has been very interesting. The project also forms the conclusion of my Master’s thesis,” says Janet Eustasie, who carried out her KTH Master's degree at a distance in her home country of Mauritius. She is now finalising her work on site at the Department of Energy Technology.

The idea is that a similar facility will be made permanent in order to transform today's food waste from KTH's restaurants and staff kitchens into biogas. The on-loan biogas plant is mobile, fully automatic and state-of-the-art and would cost around SEK 4.5 million to buy.

But the facility that KTH may receive should not cost more than ten per cent of that amount to manufacture and ship to Sweden, according to Janet Eustasie.

“We are looking at solutions that uses established technology where the facility is built of fibreglass. We are in contact with both Indian and Chinese manufacturers and are investigating whether they can build in accordance with Swedish legal requirements and regulations.”

Ten cubic meters of biogas per day

This is the second week which the biogas plant is in place. When it is fully operational, it will be able to produce up to ten cubic metres of biogas per day. The start was delayed a few days however, as it was difficult to get hold of adequately sorted food waste.

Janet Eustasie points to the container where the waste is stored, and it is a delightful mixture of paper, plastic bags and food waste. Every fourth day, she therefore has to put on her protective overall and manually sort through the remains of food waste and broken aluminium packagings for example.

“A very important issue is that the sorting of the waste must take place at source if this is to work well. But at the same time, it is a problem which we think will be resolved through more stringent legal requirements with regard to the sorting of waste. We need waste that is 75-80 per cent organic in order for the facility to operate without manual sorting.”

The waste is ground down in a large mill and then mixed with the correct amount of water to make a thick soup. When the plant is being used to the full, it will produce 200 litres of soup waste per day, consisting of about 100 kilos of food waste with the rest being water. The soup is heated to 55 degrees before it is led into an anaerobic digestion tank.

“The residual waste will be used as fertilizer, so it must not contain harmful bacteria. We will however not be conducting this experiment as far as to produce fertiliser.”

The gas is fed into large balloon-like sacks which are then transported.  The incineration plant is still not in place, so much of the gas goes up in smoke via the flare bleeder on the roof.

“It takes 21 days on average to complete the entire process, but it is possible to obtain biogas after only a few hours.”

The bio-energy is used by KTH

The gas that is produced consists of up to 70 per cent methane and can be used both for the production of heat and electricity, primarily for KTH's own needs.

When a permanent facility is in place, Janet Eustasie will have returned to her home university in Mauritius.  Her goal is to develop the technology in order to equip farms in her home country with biogas facilities. We can use the manure from pigs and cows to make electricity and the residual waste can be used as fertilizer in the fields.

“Many of the farms are isolated and lack electricity. Making biogas from manure is however not as effective as making it from food waste. That is why food waste will become more valuable in the future.”

Janet Eustasie is returning to Mauritius at the end of June after having spent the last five months at KTH.

“Most of the time, the education comprised of distance tuition, thanks to a collaboration that was established as early as 2007 between KTH and the University of Mauritius. There have been three years of student exchanges and I really do hope that it continues,” she says.

Janet Eustasie’s degree project forms a part of the Explore Polygeneration project which aims to create the conditions for a more sustainable society. The aim is the optimisation of existing, renewable energy sources and to offer a variety of concurrent energy services such as electricity, heat, cooling and clean drinking water. The project forms a part of the major European initiative EIT KIC InnoEnergy.

For more information, see , or contact the project manager Anders Malmquist, Department of Energy Technology, 070 590 60 21, , or Janet Eustasie, 070-443 78 72,

Text: Magnus Trogen