Sewage treatment plants always consume energy to filter water (around 44 watt-hours per day per person). They use three types of bacteria and energy to pump oxygen for the first type of bacteria and methanol for the second. Adding the fact that methanol is also produced through an energy-intensive process… you can pull the conclusions.
The first type of bacteria digests solid waste in “activated sludge”, converting the organic matter into methane, but leaving behind ammonium and phosphates, which must be removed from the liquid before water can be returned into a river. To work (or, better said, to have the bacteria live and do the job), the process needs to be fed with oxygen – consuming energy.
The second type of bacteria convert ammonium into nitrate. These also need oxygen to work. But it’s the third type of bacteria, the ones which convert the nitrate into nitrogen, who need methanol – these are celled “denitrifying bacteria”.
Gijs Kuenen and his colleagues from the Delft University in Holland have just developed a technique that cuts out the energy consuming processes, by eliminating the bacteria that need oxygen and methanol. They replace it with a so-called “anammox bacteria”, which are able to convert the ammonium directly into gaseous nitrogen. The anammox bacteria even produce methane, which can be used as fuel.
Not only their process is able to make savings to municipal sewage treatment plants, but it can also produce energy, and make the plants self-sufficient, because the process generates about 24 watt-hours per person per day. “This is about trying to make waste water treatment plants completely sustainable, in the sense that they could even produce energy, which is not the case in present treatment facilities,” says Kuenen.
A pilot sewage treatment plant will be opened at the Dokhaven plant in Rotterdam, Holland, working with from Radboud University Nijmegen and water purification firm Paques, based in the Dutch town of Balk.