Cees Buisman ~ Full interview

Professor in biologically sustainable technology and scientific director of Wetsus

1.  What in your view are the most urgent problems in the field of waste water?

When you look at waste water, with the European Water Framework Directive at the back of our minds, then there are four substances in the removal of which the Netherlands will probably invest: phosphate (a nutrient), nitrogen (a nutrient), copper (poisonous compound) and sink (poisonous compound). At the moment the waste water contains numerous active biological substances that we cannot remove properly, because they are present at a very low level. Since the 70s we in the Netherlands have been able to remove the nutrients that cause growth of algae, and now the poisonous compounds are the problem. That`s going to be a huge problem. Because slowly it becomes clear what the influence of these compounds is on nature. It is very stealthy and dangerous and we don´t even have the technologies to handle this.

2.  Can you give some examples of the effects on nature?

Other countries are behind what we have done in Western Europe. The most important thing to do with waste water is remove the oxygen demanding compounds. If you don´t, the surface water will lose its oxygen and everything in it dies. There are many countries around the world that don´t even remove these compounds. The next step is removal of the nutrients. If you don´t do this, it will lead to growth of different small organisms, as we like to call ‘green soup’. That soup will decompose and all the oxygen will be removed from the water. This is caused by nitrogen and phosphate and on hot days even in the Netherlands that soup arises in the water. That means we did not remove the compounds sufficiently. The new European Water Framework Directive tells us to do more. After that, you have to remove the poisonous compounds from the water, including zinc and copper. These compounds are not poisonous directly, but accumulate slowly. Copper originates from water pipes and zinc from products like shampoo, zinc roof tops and galvanized crash barriers.

3.  What solutions do you see for these problems?

For the oxygen demanding compounds there already are different solutions, such as biological water purifications, aerobic as well as anaerobic. New solutions keep coming up, small as well as large scale and with and without membranes. Nitrogen is being removed biologically from waste water as well. The result is nitrogen gas, that in its turn will be converted to nitrogen. Factories have taken this nitrogen from the air before by using a lot of energy. We are now trying to win back the nitrogen from waste water as ammonium instead of nitrogen gas, to use as fertilizer. This could save a lot of energy.

You cannot decompose phosphate. We can pile it up biologically or chemically in sludge. This sludge can be burnt and that costs a lot of money. Phosphate is a mineral that is extracted from mines and people think we will be short of phosphate in 70 years time. So there is also a lot of attention paid to the reuse of that mineral. The problem is that waste water only contains very small amounts of phosphate.

Zinc and copper can be precipitated in sludge or it can be burnt. The rest in the waste water must be processed through filtration, absorption or precipitation techniques. Researchers don´t know yet what is the most economical way to do this.

4.  Can all these problems be solved by developing new technological innovations, in your view?

Yes, I am convinced. The problem is specifically the compounds that are present at very low levels. The question is whether we improve the existing water purification systems step by step, so that we can remove all other compounds after the oxygen demanding compounds, or do we have to work on a totally new concept that will purify the water all at once?

5.  Are there any biotechnological solutions for these problems?

The technology to remove oxygen demanding compounds and nitrogen is biotechnological. Sometimes biotechnological solutions are being used for phosphate. But not for all the other compounds, those that bacteria cannot use. To remove these compounds we have to come up with chemical or physical solutions. Or maybe another solution that we don´t know yet. But we don´t use genetically modified (GM) bacteria. Because there already are a lot of bacteria in waste water, it is difficult to keep GM bacteria in a closed system. I wonder if they can compete with existing bacteria. Furthermore, you have to apply for permits to do these kinds of experiments. And it is unclear what the use of GM bacteria means for the sludge you make.

So far, I have never heard of or seen a project that uses GM bacteria for water purification. Not even for the compounds that are so hard to remove from water. The most important problem is that there are huge amounts of water with very small concentrations of compounds like zinc. Bacteriological purification is not very effective in such cases. That is why we use electrochemical treatments for these compounds.

6.  What are the differences between developing and developed countries (in terms of both problems and opportunities)?

Until recently it was common in the Netherlands to dump the sewage water in the North Sea unpurified. This is still normal in less rich countries, but also in countries bordering the Mediterranean Sea. Purification usually is only available to rich countries. In countries where sweet water is limited , laws increasingly demand that it cannot be dumped at sea anymore. In these countries, sewage water is increasingly purified and reused.

7.  One of the Millennium Development Goals is to reduce by half the proportion of people without sustainable access to safe drinking water. How can we achieve this?

In my view, the water and sewage system we have in the Netherlands is very expensive. Other European countries are less able to develop such a system. I don´t think we can provide the rest of the world with this engineered way of providing clean drinking water. We need a more process engineered approach. Considering a person needs only a few liters of clean water a day, we should develop a method that can provide clean water locally. If you don´t use pipes, you will not develop so much waste water as we do in the Netherlands. One way to do this is to extract water from the air by cooling the air. That is relatively expensive, but if you need only a few liters a day, it is cheaper than constructing pipes. There already exist such systems driven by small wind turbines, thus providing sustainably produced and safe water.

8.  In your view, what will the field of water purification look like in 20 years time?

We will have developed techniques for the removal of zinc and copper in 20 years time. Furthermore especially the Netherlands will play a role in developing chemical, physical, biological and membrane techniques. The rest of the world wants to provide a engineered solution for drinking water provision, with for example water pipes, but in the Netherlands we are looking for process engineered solutions. This can lead to more small scale solutions than is usual. At Wetsus, a centre of excellence for sustainable water technology based in the Netherlands, we are for example researching how faeces can be collected with vacuum toilets. It is much more efficient to remove nitrogen, phosphate and energy from concentrated faeces and besides we don´t use drinking water to flush. Furthermore it is not necessary to use drinking water of high quality for washing etcetera. We can also use water with lower quality. Especially in countries without an extensive infrastructure and in dry areas we must look for these kinds of solutions.

9.  Which statement/question/dilemma would you like to put to the readers of this interview?

Do we improve the existing water purification systems step by step, so that we can remove all other compounds after removing the oxygen demanding compounds, or do we have to work on a totally new concept that will purify the water all at once?