“Wastewater is a resource”

Water-resource management is one of the areas in which you specialise. To what extent do you need to take account of climate change?
We have to address two major challenges in integrated water-resource management at present: demographic change and climate change. Due to climate change, water resources are becoming ever more scarce in areas that already are quite arid. At the same time, population figures are changing, so it will become increasingly difficult to guarantee an adequate supply of water for everyone.

Please give examples.
In Southern Africa, for instance, precipitation is becoming more variable. Torrential rains spread diseases and destroy crops, whereas long periods of drought make it harder to create sanitary conditions and supply potable water. At the same time, population growth is compounding problems of drinking water and food supply.

But populations are not growing everywhere.
Indeed, there are some areas where populations are in decline, eastern Germany for example. Infrastructures there – schools, hospitals, water supply et cetera – are still geared to serve twice as many people. In places like that, it is hardly worth keeping expensive water-treatment facilities going. At the same time, parts of eastern Germany are getting less precipitation, so land is drying up. The big question is: Can we find a single solution to both of these challenges?

Well, can you?
In the area of water supply, a rethink is necessary. The guiding principles will have to be to minimise freshwater consumption, maximise recycling, conserve energy and reduce emissions. The systems we have today are not up to those tasks. They resulted from a 19th century mind-set. Industry, agriculture and households are all supplied with expensively provided freshwater. After being used, all wastewater – regardless of the degree of contamination – is piped to some treatment facility. That facility has to remove all kinds of chemical, biological and physical contaminants from the water. As many as ten treatment stages may be necessary. Such operations require a lot of energy, a lot of chemicals and a lot of money. Moreover, they extract many substances that would serve farming purposes. In Germany, we even channel rainwater into the sewers, although it could be easily and cheaply transformed into freshwater.

What would a better water-supply system
look like?
Any new system must meet two key requirements:
– It needs to reduce freshwater consumption. Freshwater should only be used where it is urgently needed – for drinking, cooking and perhaps hygiene purposes. For other purposes, treated wastewater could be used, and more economical methods would help to reduce water consumption.
– Today's suppliers need to treat wastewater as a resource; they must recycle it as many times as possible. This calls for the creation of differentiated wastewater management and decentralised circulatory systems. For example, domestic “grey water” – wastewater from domestic showers, kitchens or washing machines, for instance – could be used in agriculture locally. No complex treatment facilities would be needed, basic cleaning with simple technology would do.

How exactly does wastewater differentiation work?
Wastewater differentiation means treating different types of wastewater separately. For example, if you separate grey water, it needs no complex treatment. If you use more sophisticated procedures like membrane technology, it can be used again as freshwater, so more freshwater becomes available. What is more, grey-water recycling is cheaper than conventional wastewater treatment, because it consumes little energy and reduces carbon emissions. In eastern Germany, membrane systems and small grey water cycles could be used to address both the problem of expensive wastewater treatment and water shortages.

Isn't it quite a challenge to separate domestic wastewater?
Yes, it is. In developing countries in particular, grey water cannot be separately collected everywhere, and certainly not in the informal settlements on the outskirts of cities. But wastewater collected from such sett­lements – that is “black water” that contains faeces and urine – can also be recycled. Processing black water to eliminate bacteria results in water with a high nitrate and phosphate content, and those nutrients are useful for farming. Such water can serve to fertilise low-phosphate soils in Africa.

Can developing countries afford the technologies needed?
Different technologies have different price tags. What all the new systems have in common, however, is quite low energy consumption. That, in itself, cuts costs. In some developing countries, conventional facilities are not in use because the power costs they would entail are too high. Apart from that, freshwater provision and transport costs can be reduced if wastewater is recycled. To give an example, the city of Stuttgart gets its water from Lake Constance and shoulders a treatment and transport bill for around five kilowatt-hours of electricity per cubic metre of water. If a local grey water cycle was set up, the energy required to supply new freshwater would go down to one or even 0.5 kilowatt hours per litre.

Why do new technologies require less energy?
During the treatment process, energy is generated by a thermal exchange in the wastewater flow or by anaerobic fermentation of the water. The energy produced is enough to meet the power requirement of the system. Such systems are basically energy-self-sufficient.

What does that mean for development cooperation and the Millennium Development Goals (MDGs)?
Water-resource management should figure more prominently in development cooperation. After all, water management is more than just resource protection. Our project in Namibia shows that new wastewater treatment methods can do more than just reduce supply shortages. They lower water-supply operating costs, energy consumption and health costs. In addition, more farmland can be irrigated, so incomes are generated and poverty goes down. In this sense, good water-resource management makes a fundamental contribution to achieving the MDGs relating to health and poverty. Development cooperation should focus much more on programmes that deliver on multiple MDGs.

What is most urgent?
We need to start at home. At present, there are no reference projects in Germany that would serve as ­shining examples. We have the technology in Germany, and the expertise for crafting new innovative solutions, but we still use conventional large-scale treatment facilities. In the ISOE Networks project, we have introduced city authorities in Essen, Chemnitz and Hamburg to new solutions based on decentralised water cycles. In this way, we hope to gradually transform the wastewater treatment systems in Germany.

But you don't work only in Germany. Where do you see the starting point for development ­cooperation?
Development agencies should cooperate more closely with researchers. Rather than clinging to conventional processing, they should focus on new approaches to treating wastewater. In future, it will become increasingly important to conserve freshwater and reduce ­energy consumption.

Questions by Franziska Baur and Eva-Maria Verfürth.