Treatment plants not only provide clean water, they also contain a great deal of energy. They consume a lot of electricity. However, most or all of this electricity, plus heat, can be recovered from the sewage gas that is produced in the sewage sludge. The Dülmen treatment plant run by the Lippeverband water board in the Münsterland region of North Rhine-Westphalia offers good conditions for this: the plant not only treats the wastewater produced by around 50,000 residents as well as industrial waste water from Dülmen, but also the sewage sludge from 15 smaller association plants in the area that do not have their own sludge treatment facilities.
Previously, two combined heat and power plants in Dülmen generated electricity and heat from the sewage sludge in Dülmen. They have now been replaced by the Lippeverband board with two MicroTurbines from VTA. This technology, which originated in the US space programme, is as innovative as it is fascinating: all rotating parts move without lubricant on an ‘air bearing’, and at speeds of up to 96,000 (!) revolutions per minute.
In Dülmen speed was also called for in other respects too because according to the German EEG Act, which governs the feeding of electricity from renewable energy sources into the grid, payment is also required for feeding electricity used by the company itself into its own grid. However, for plants that have been renewed or expanded by the cut-off date of 31 December 2017, there is a transitional arrangement that reduces this levy by 80%. In the case of the Dülmen treatment plant, this is equivalent to a cost benefit of around 40,000 euros per year!
Race against time
Installation of the turbines therefore became a race against time. Working together with the team at the treatment plant, VTA also achieved this goal: on 9 December 2017, the two MicroTurbines at the Dülmen treatment plant started operation.
The Lippeverband water board counts 155 municipalities and companies as members – so there is still potential for clean energy generation from sewage sludge using MicroTurbines.