Rigid water pipes, fit for the future

Water infrastructures -- such as pipes, sewers or water storages -- are rigid systems. They are renewed according to certain renovation cycles. This can take up to 70 years for municipal sewage systems and up to 30 years for baths in rental apartments. "That has to be considered when creating concepts for the future of the water infrastructure," says Dr.-Ing. Thomas Hillenbrand, scientist at the Fraunhofer Institute for Systems and Innovation Research ISI in Karlsruhe.

Modernise existing water infrastructures

In the joint project "Paths Of Transition For Water Infrastructure Systems TWIST ++" the institute developed the integrated water energy transition concept i.WET. By means of real scenarios, the concept shows how a modern and intelligent water supply and watewater management can be implemented step by step in urban areas. It takes the renovation cycles of existing systems into account, can be flexibly implemented in modular form, and combines new water and wastewater technologies intelligently. i.WET includes solutions for three major challenges of water infrastructure in Germany: demographic change, climate change and energy policy. In Lünen, a city of 90,000 people in Westphalia, the results of i.WET are to be implemented in a pilot project over the next few years. The scientists are presenting the concept at IFAT, the International Trade Fair for Environmental Technologies, from May 30th to June 03rd in Munich (Hall A5, Booth 217/316).

i.WET envisages specific measures for buildings, sewer systems and wastewater treatment plants. The decisive point is the separation of less and more heavily contaminated wastewater already in the household (gray/black water). In buildings, the researchers want to install separate pipes for water from showers, wash basins, sinks on the one hand, and the rest of the waste water from toilets, washing machines and dishwashers on the other hand. Approximately 110 liters of water per day are consumed in households in Germany. "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," Hillenbrand explains.

Energy alley as green water treatment

The water, which is not recycled in 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 have ideal growing conditions. "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 says. The scientists want to initially keep the sewers operable through regular surge irrigation with recycled water from households and, in the long term, replace them with vacuum dewatering.

Then, only highly-concentrated wastewater will reach the wastewater treatment plant. It can be routed directly into the biogas plant, in order to recover methane, thus reducing the energy demand for wastewater treatment. "The energy gain is significant. We can also recover nitrogen and phosphorus," says Hillenbrand.

Pilot project in Westphalia

In Lünen, it is intended for a housing association to incorporate the separate pipes for gray and black water in the buildings of the model district. The wastewater disposal rehabilitates the sewage system. "Time is on our side. The respective renovation cycles are expiring," Hillenbrand reports. The measures should be implemented within the next three years.