'Methane Emissions From Drinking Water Purification Can Be Reduced By 50%'

It is becoming increasingly difficult to produce sufficient drinking water, and this process also releases large amounts of the harmful greenhouse gas methane. For his PhD thesis, microbiologist Alje Boersma researched how we can purify drinking water more efficiently and found ways to reduce methane emissions by 50%. He will defend his research at Radboud University on 10 June.

The Netherlands produces around 70% of its drinking water from groundwater. These water sources are under increasing pressure, while demand for drinking water is rising. For his research, Boersma looked at ways to improve the drinking water production process. 'Most drinking water is purified by sand: water is passed through a sand filter – a large tank filled with 2.5 metres of sand – where all kinds of microbiological and chemical processes clean the sand. We have been using this system for 100 years, but we don't really know why it works.' This knowledge is useful if you want to improve the process, especially since filtering doesn't always work.

Manganese
The microbiologist conducted different experiments and looked at what happens exactly in sand filters. ‘Manganese, a type of metal, is particularly difficult to remove from water. My research shows that manganese is mainly removed by bacteria and not by a chemical process, as was long thought.’ Now we know this, we can help those bacteria, so that they do their job even better. ‘Running the water through copper pipes, for example, can help; it is believed that bacteria remove manganese more effectively with a little extra copper.’ This leads to better filters that last longer and are more efficient.

Dry filters
Boersma also looked at methane emissions during drinking water production. Methane must be removed from drinking water, which is currently done by pumping large amounts of air in the water. This causes methane to evaporate. ‘But you don't want that: huge amounts of methane are being blown into the air this way, which contributes significantly to global warming.’

The researcher therefore experimented with a closed dry filter: large steel cylinders filled with sand onto which water is sprayed. Methane is still released, but it can be removed biologically by bacteria that eat the methane and convert it into carbon dioxide: still a greenhouse gas, but much less harmful than methane. Boersma: ‘We saw that 50% of the methane was removed biologically, which reduced greenhouse gas emissions by 50%. That's a huge difference.’

As far as Boersma is concerned, all drinking water should be purified in this way: ‘The water from these dry filters is of good quality, so this seems like a good solution to me.’