Science - October 27, 2016

Smarter sewage systems

Didi de Vries

‘Why dilute pee and poop first just to fish it all out later?’ This has been the crucial question throughout the career of Grietje Zeeman, personal professor of New Sanitation. She says goodbye to the Environmental Technology chair group this month.

Photo: Sven Menschel

‘I’m only doing it because I have to; I’m not looking forward to retiring at all.’ It is with reluctance that Grietje Zeeman leaves her job as personal professor of New Sanitation at the Environmental Technology chair group on 17 October. She will carry on working a few hours a week for the LeAF Foundation as a consultant on anaerobic purification.  

After graduating in 1890, Zeeman decided she wanted to do research on anaerobic (oxygen-free) purification of household wastewater. Due to the lack of jobs in this field, however, she started out at a drinking water company in Utrecht. ‘I didn’t like that so much: too clean.’ A year later she could go back to the subject of excrement, albeit of animal origin at this point. Zeeman spent ten years at Environmental Technology studying the digestion of animal manure. ‘Only after getting my PhD in 1991 did I at last get involved in research on the treatment of household wastewater. I did that at the laboratory Environmental Technology had in Bennekom back then. For old times’ sake I sometimes still walk past it with a colleague.’

What kind of research did you do in the Bennekom lab?

‘We had an anaerobic purification plant of six cubic metres, which was directly linked with Bennekom’s water purification system. But it proved difficult to treat the diluted flow of wastewater in a sustainable way at low temperatures. That is why I took the route of new sanitation, because why dilute the pee and poop first with water from baths, showers, kitchens, sinks and rainwater, only to fish it all out later?

I would like to see toilets that only use a litre of water a day.

In 2001 we got a very big project. We installed three vacuum toilets in the lab, linked to three anaerobic purification plants. All staff were asked to record how much faeces and urine they produced and when the system was full of faeces we put up a noticeboard saying “for urine only”. Using the knowledge we gained we were able to build a pilot installation for 32 households in Sneek in 2006. That is an entirely decentralized system, with wastewater being separated at the source. So black water – from the toilet – is collected apart from grey water –  all the other household wastewater. The purification installations for black and grey water are situated in the middle of the neighbourhood. Which is great because everyone sees it. And it doesn’t stink. The concept was adopted later in a neighbourhood of 250 houses.’

Are you satisfied with the results of your research?

‘I am proud of the fact that the concept we developed here is being put into practice. In Sneek, in Venlo, in The Hague and at the NIOO in Wageningen. It is going too slowly for some people. We started in the lab in 2001 and there are now five full-scale demonstration projects. I wouldn’t call that slow at all. A sewer has been in the ground for 100 years, so you don’t dig it up lightly.’

Your project is partly about extracting nutrients from poop and urine. Is that the biggest development coming up in your field?

‘I think so. We are developing several technologies, but I don’t know yet which method is best in the end. Now we collect black water using vacuum toilets which flush with one litre of water. That means you get a much more concentrated waste flow than you get conventionally, but it is still six litres of water per person per day. What I’d really like to see is toilets that only use one litre per person per day. Then you make a highly concentrated flow that you can put in a digester. Preferably at a higher temperature so that you kill off pathogens and are left with manure to spread on the land.’

Shouldn’t we just go back to the compost toilet?

‘I think a compost toilet is a terrific system but I don’t think everyone wants to sit on it. It does not meet the comfort requirements of today. You can close the hole to the composting chamber so that you don’t see your own poop but you still have to spade out the poop. Not many people want to do that. I once spoke to a man in Germany who had a compost toilet. He said: ‘I don’t have a problem with doing it but I do wonder who will do it for me when I’m 80.’ That gives you an idea of the problem. We don’t want any contact with our own shit these days.’

Do you have any tips for researchers at the start of their careers?

‘I think the main think is to choose a subject in which you can express yourself. It is best of course if you work on a subject with which you contribute something to science or to the world. But at the same time, I do realise that is not easy. People sometimes just want to get on in the scientific world and then they are dependent on which research proposals get approved.’

What does your professorship mean to you?

‘One of the main motives for becoming a personal professor was that I wanted to be the one to award the PhDs I had supervised myself. And of course it is also the peak of my career, especially since a personal chair is based on your own achievements. Officially I am allowed to go on supervising PhDs for five years after retirement. Apparently they think you’ll have deteriorated too much after that.’

New sanitation

‘New sanitation’ is the collective term for a range of technologies which can be used to process wastewater flows separately and to extract minerals from wastewater.

Anaerobic purification is one of the methods that can be used in the new sanitation. In an oxygen-free environment, bacteria convert waste matter in wastewater into biogas and biomass. You can cook on biogas, while the biomass is suitable for use as fertilizer.

Many new sanitation systems use vacuum toilets. These are toilets that do not flush using gravity, as a regular toilet does, but using a vacuum pump that reduces the pressure in the pipes so that the toilet is emptied by suction when a valve at the bottom of it opens. This means you only need a small amount of water, enough to prevent soiling of the pot.