What you need to know about water purification

“Did you go to the toilet today?” Merle de Kreuk, Professor of Environmental Technology at the faculty of Civil Engineering and Geosciences, knows how to give lively speeches. “This is one of the two questions with which I always start my presentations,” she said during her inaugural speech. “And the second is what went through your mind when you flushed the toilet? Not much probably. And that is a good thing. Water authorities do their best to treat the sewage without us noticing.”

How different this is compared to the sewage treatment in many mega cities in developing countries, which is one of De Kreuk’s research topics. She is working on projects in Delhi and Jakarta, where smaller, local systems are being developed and installed close to the source of the sewage.

“What you see here is an open sewer,” says the Professor pointing at a slide depicting a brownish stream just outside dwellings in India. “When you throw a rock in the river, methane gas bubbles up for minutes.”

Putting biogas and fertilisers to immediate use

De Kreuk believes it is a bad idea to just export huge purification plants to emerging mega-cities in Asia or other parts of the world. “We’ve learned from experience that things often go wrong once the foreign construction firms leave. Small, compact systems in the middle of a city have much more potential. You can put the purified water, the resulting biogas and the fertilisers (such as nitrogen and phosphor) extracted to immediate local use.”

The key however, to tackle the issues in the long run, is education, De Kreuk says. “The problem is that studying water treatment is not that popular in India. Young people prefer to study aerospace engineering. That is a cultural thing. It needs to change.”

De Kreuk performed her PhD research at the department of Biotechnology in the group of Professor Mark van Loosdrecht. She worked on the now much renowned aerobic granular sludge technology, Nereda. The first application in the Netherlands was officially opened in May 2012. “When that first plant opened I was so happy, I couldn’t get the grin off my face.”

‘I try to link the world of biotechnology to civil engineering’

In 2011 she started working for the section Sanitary Engineering, where she focuses on municipal and industrial wastewater treatment systems and anaerobic processes. “I try to link the world of biotechnology to civil engineering, as well as the fundamental research to industrial applications,” she says. “The main topics are hydrolysis processes in anaerobic treatment and aerobic and anaerobic granule formation processes.”

An exciting new development in her field which she highlighted during her inauguration speech was the use of MRI. How does the process of pellet formation start precisely, and what happens to the solid particles floating in the waste water? “Using MRI, we can now visualise the structure of the granules inside the sludge right down to the millimetre.”

De Kreuk hopes to find ways of extracting more resources and energy from waste water. This would not only be sustainable, but it would also improve the quality of the processing itself. “Phosphate mines have been nearly exhausted, but we still need phosphate as a fertiliser to increase food production throughout the world. Extracting it from waste water means you will have recycled a valuable resource, which also would no longer cause issues later in the processing chain.”

The same applies to biogas. “If you convert as much sludge as possible into biogas, not only do you have a great source of energy, but the remaining sludge is much easier to process too. At the moment, bacteria only digest 40% of the organic substances inside the sludge. That percentage could be increased if we had a better understanding of the digestion processes.”