Energy-Saving Waste Water Treatment With I.WET

"Rain and gray water, which is not recycled by the household, flows into the “energy alley“ – a green strip with plants that thrive on moisture. They stand with their roots in the water, absorb the remaining nutrients and even have ideal growing conditions" (Fraunhofer ISI)

German scientists from the Fraunhofer Institute for Systems and Innovation Research (ISI) from Karlsruhe presented an energy-saving waste water treatment concept for urban areas at IFAT trade fair 2016. It will be installed in the following three years in the German city of Lünen.

Renovation cycles of water pipes can take a very long time up to 70 years for municipal sewage systems or 30 years for baths in apartments. These long periods are an advantage on the one hand but a disadvantage on the other hand. The rigid system is not very flexible.

An integrated water energy transition concept, called i.WET, has been prepared in the joint project “Paths Of Transition For Water Infrastructure Systems TWIST ++”. It demonstrates with real scenarios how to integrate little by little a modern and intelligent water supply and energy-saving waste water treatment in urban environments.

The module-based implementation is flexible, takes account of renovation cycles of present systems, and “combines new water and wastewater technologies intelligently”. I.WET gives answers to three important challenges of the German water infrastructure – the turnaround in energy policy, the climate change and the demographic change.

The separate disposal of gray and black water (less and highly polluted water) is the central issue of specific measures for buildings, canal systems and sewage treatment plants within i.WET. In practice this means one pipe for water from shower and wash basins and another pipe for toilets, washing machines and dishwashers.  For instance, a German citizen uses an average of about 110 liters of water every day. “Up to 50 percent of this water is required for showers and baths. This water is good for reuse – such as for flushing the toilet,“ says Dr.-Ing. Thomas Hillenbrand, scientist at the Fraunhofer Institute ISI in Karlsruhe.

Water which is not reused flows into the “energy alley“. This is a roadside green verge with water-loving plants whose roots are standing in the water. This is an ideal growing condition because they can absorb the remaining nutrients of the grey water. In the long run, vacuum dewatering will keep the sewers operable.

“The result is biomass, the cities are greener and the threat of flooding is reduced – due to the water tank under the plants. One square meter per inhabitant is sufficient. In the long term, such a system can be operated more favorably than the current standard sewer system,“ Hillenbrand explains.

Energy-Saving waste water treatment i.WET realized within the next three years

Consequently, sewage water treatment plants will only receive highly polluted water. It can be used straight for the production of methane in a biogas plant. In this way, the energy demand of the treatment plant decreases considerably.

The findings of i.WET will be realized within a project in the German city of Lünen with about 85,000 inhabitants. “Time is on our side. The respective renovation cycles are expiring,“ Hillenbrand reports. Realization is expected within the next three years.