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In the Swiss municipality of Engelberg, the local wastewater treatment plant has been using a rather unusual source of energy since the end of October to heat its office building and at the same time produce electricity. According to the Luzerner Zeitung (Lucerne Newspaper), around 2,000 liters of whey from the nearby dairy are processed every day instead of fossil fuel oil. This last building block of the now one hundred percent self-sufficiency in electricity and heat shows how a random synergy effect can also lead to a green energy balance in the commercial sector. For the first time, this new approach eliminates the need for the wastewater treatment plant to purchase fuel oil in the last quarter of the year. However, a cost saving is not associated with this because of the expenses, although at least on the part of the dairy there are lower transport distances and expenses for waste disposal.

The high-energy whey is fermented for at least 25 days in a special septic tank along with solids in the wastewater at an ambient temperature of minimally 33 °C. During this process, methane gas is produced, which is then burned in the cogeneration plant of the cleaning plant. The resulting heat heats the entire building including the septic tank, while a downstream generator produces additional electricity. In combination with a photovoltaic system and a small hydropower plant, their energy requirement is covered in this way for the entire year. The plant’s own consumption amounts to 450,000 kWh. A surplus of another 120,000 kWh is fed into the power grid.

A group led by Prof. Lars Angenent is researching the reuse of sour whey at the University of Tübingen as well. The waste material is converted into oil by microorganisms in a purely biological process and can then be used to produce fuels for aircraft.