More climate-friendly wastewater treatment

Better treatment of waste water will release fewer greenhouse gases, says Mark van Loosdrecht, professor of Environmental Biotechnology, who is researching how to reduce N20 levels in the air. 

‘N2O is a party drug, did you know that?’ says Mark van Loosdrecht, professor of Environmental Biotechnology, halfway through the interview, with a smile. ‘It is also called laughing gas, and used for filling whipped cream canisters, for example.’ The gas may seem fairly innocent – for extra fun at parties – but in fact nitrous oxide, or N2O, is a greenhouse gas that is 320 times as strong as CO2. Therefore, even small amounts escaping into the atmosphere can have serious effects.

Consequently, if we want to help stop climate change, we need to focus not just on reducing carbon dioxide emissions, but also on reducing the amount of laughing gas released into the atmosphere. This is what Van Loosdrecht is working on. According to Van Loosdrecht, 7% of global warming is due to N2O. And, of all the greenhouse gases emitted during the wastewater treatment process, up to 80% can be N2O.

So, how does it work? Wastewater contains high levels of nitrogen compounds such as nitrates (NO3) and ammonia (NH3), and these need to be removed. Laughing gas (N2O) is released in the process, but in which processes exactly? The answer to this question is very complex, was the conclusion of PhD research she performed back in 2010. ‘We are therefore taking this to the next level, focusing on bacteria in the lab,’ says Van Loosdrecht. ‘The problem now is that N2O can be produced by two groups of bacteria. The first converts ammonia into nitrate, and the second nitrate into nitrogen gas (N2).’ Nitrogen gas is of course completely harmless, as it makes up 80% of the air we breathe.

Van Loosdrecht is trying to use the bacteria in his lab to establish under which conditions N2O is produced. For that reason he is involved in NORA, a four-year European research programme studying greenhouse gas emissions. He is also working together with a guest researcher from Spain who applies the micro-biological knowledge to the water treatment process, to see whether laughing gas emissions are actually reduced in practice.

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