Unexpected bacterial marriage

Using this contrary couple, wastewater cleaners can save hundreds of thousands of euros.

Bacteria in wastewater practically work for free. And better still, you don’t have to feed it. Just add some air to its environment and you’ve got some hungry, satisfied work horses.

The red anammox-bacterium and a bacterium from the Nitrosomonas family form a good couple. The anammox-bacterium converts nitrite into nitrogen gas, with ammonium as its energy source. The Nitrosomonas bacteria%s nitrification process produces nitrite, aided by oxygen from the ammonium. Together, both bacteria convert ammonia in wastewater%which kills fish in lakes and streams%into harmless nitrogen gas.

Until a couple of years ago, microbiologists thought the oxygen-hating Anammox bacteria and the oxygen-loving Nitrosomonas bacteria couldn’t live together in one reactor barrel. But when oxygen concentrations are very low and an excess of ammonia present, they can happily cohabitate. This discovery by a Delft microbiologist is called Canon (completely autotrophic nitrogen removal over nitrite).

Most probably, the oxygen-lovers protect the oxygen-haters. Working together, both bacteria form a flake, with the oxygen-haters in the middle. “The oxygen concentration in the flake is very low. We can’t even detect the oxygen with an electrode,” says fourth-year PhD student, Olav Sliekers. “We also pinch off the added oxygen a lot.” Because of low concentrations in the reactor, the oxygen present, which is toxic to the anammox bacterium, disappears quickly.

Sliekers: “We add exactly the amount of oxygen needed to cause a quick reaction with half of the added ammonium.” The other part remains for the second reaction. A good balance between the amounts of oxygen and ammonia is essential. Too much oxygen in relation to ammonia will introduce an unwanted guest, a guest that uses oxygen to convert nitrite into nitrate and eats, as the Dutch expression goes, the cheese of the useful bacteria’s sandwich. This phenomenon is detrimental in the water treatment process, because the ammonium pollutant is converted into a nitrate pollutant.

Sludge

Sliekers took regular samples of bacteria flakes in the barrel to determine their relations. Unique pieces of DNA, which have florescent labels, revealed the bacteria’s identity.

In experiments conducted using too much oxygen, Sliekers saw that the unwanted guest disturbed the process, although it didn’t cause irreparable damage. For a month he gave the bacteria less ammonium, after which time he increased the amount again. The process seemed robust. The aerobe and anaerobe ammonium oxidising bacteria had survived their marriage crisis; they could once again work together to demolish ammonium into a harmless nitrogen gas, making the system suitable for industrial applications. In this process, some amount of ammonium always remains, because ammonium must be present to prevent the unwanted guest from appearing again.

The Canon process is especially suitable for the wastewater that appears after sludge has fermented. This sludge%released after the sewage water is treated%is rich in organic nitrogen, which is converted into ammonium during fermenting. Moreover, this wastewater contains small amounts of carbon compounds, which, in the traditional process, serve as a food source for bacteria.

Laughing gas

The two bacteria, which can demolish ammonium in an oxygen poor environment, will begin doing their job this summer at an experimental sewage treatment plant Dokhaven (Zuid-Holland). However, the oxygen-lover and oxygen-hater won’t yet be used in one reactor. The TU has also been in involved in the development of this project.

These types of new technology are much cheaper than existing technologies, which require more aeration and that the bacteria be fed with organic carbon sources, like methanol. These traditional biological processes release harmful products like lignite and greenhouse laughing gas.

The new reaction saves money on energy bills because less oxygen needs to be added. Sliekers: “Pumping air into a ten meter high reactor is expensive, because a lot of pressure must be brought in.”

The reduction of costs compared to the traditional process is less than one euro per kilo removed nitrogen. “This seems to be less,” said Sliekers supervisor’, Professor Mike Jetter, during his inauguration at the University of Nijmegen. “But a sewage treatment plant in Holland uses 1,500 kilos of nitrogen per year. This saves **350,000 per year. Today, there are four hundred installations in Holland, so we are already **140 million richer.”

Biotechnologists have arranged a good marriage between

oxide-hating and oxide-loving bacterium. Their favourite food: wastewater full of ammonia. Using this contrary couple, wastewater cleaners can save hundreds of thousands of euros.

Bacteria in wastewater practically work for free. And better still, you don’t have to feed it. Just add some air to its environment and you’ve got some hungry, satisfied work horses.

The red anammox-bacterium and a bacterium from the Nitrosomonas family form a good couple. The anammox-bacterium converts nitrite into nitrogen gas, with ammonium as its energy source. The Nitrosomonas bacteria%s nitrification process produces nitrite, aided by oxygen from the ammonium. Together, both bacteria convert ammonia in wastewater%which kills fish in lakes and streams%into harmless nitrogen gas.

Until a couple of years ago, microbiologists thought the oxygen-hating Anammox bacteria and the oxygen-loving Nitrosomonas bacteria couldn’t live together in one reactor barrel. But when oxygen concentrations are very low and an excess of ammonia present, they can happily cohabitate. This discovery by a Delft microbiologist is called Canon (completely autotrophic nitrogen removal over nitrite).

Most probably, the oxygen-lovers protect the oxygen-haters. Working together, both bacteria form a flake, with the oxygen-haters in the middle. “The oxygen concentration in the flake is very low. We can’t even detect the oxygen with an electrode,” says fourth-year PhD student, Olav Sliekers. “We also pinch off the added oxygen a lot.” Because of low concentrations in the reactor, the oxygen present, which is toxic to the anammox bacterium, disappears quickly.

Sliekers: “We add exactly the amount of oxygen needed to cause a quick reaction with half of the added ammonium.” The other part remains for the second reaction. A good balance between the amounts of oxygen and ammonia is essential. Too much oxygen in relation to ammonia will introduce an unwanted guest, a guest that uses oxygen to convert nitrite into nitrate and eats, as the Dutch expression goes, the cheese of the useful bacteria’s sandwich. This phenomenon is detrimental in the water treatment process, because the ammonium pollutant is converted into a nitrate pollutant.

Sludge

Sliekers took regular samples of bacteria flakes in the barrel to determine their relations. Unique pieces of DNA, which have florescent labels, revealed the bacteria’s identity.

In experiments conducted using too much oxygen, Sliekers saw that the unwanted guest disturbed the process, although it didn’t cause irreparable damage. For a month he gave the bacteria less ammonium, after which time he increased the amount again. The process seemed robust. The aerobe and anaerobe ammonium oxidising bacteria had survived their marriage crisis; they could once again work together to demolish ammonium into a harmless nitrogen gas, making the system suitable for industrial applications. In this process, some amount of ammonium always remains, because ammonium must be present to prevent the unwanted guest from appearing again.

The Canon process is especially suitable for the wastewater that appears after sludge has fermented. This sludge%released after the sewage water is treated%is rich in organic nitrogen, which is converted into ammonium during fermenting. Moreover, this wastewater contains small amounts of carbon compounds, which, in the traditional process, serve as a food source for bacteria.

Laughing gas

The two bacteria, which can demolish ammonium in an oxygen poor environment, will begin doing their job this summer at an experimental sewage treatment plant Dokhaven (Zuid-Holland). However, the oxygen-lover and oxygen-hater won’t yet be used in one reactor. The TU has also been in involved in the development of this project.

These types of new technology are much cheaper than existing technologies, which require more aeration and that the bacteria be fed with organic carbon sources, like methanol. These traditional biological processes release harmful products like lignite and greenhouse laughing gas.

The new reaction saves money on energy bills because less oxygen needs to be added. Sliekers: “Pumping air into a ten meter high reactor is expensive, because a lot of pressure must be brought in.”

The reduction of costs compared to the traditional process is less than one euro per kilo removed nitrogen. “This seems to be less,” said Sliekers supervisor’, Professor Mike Jetter, during his inauguration at the University of Nijmegen. “But a sewage treatment plant in Holland uses 1,500 kilos of nitrogen per year. This saves **350,000 per year. Today, there are four hundred installations in Holland, so we are already **140 million richer.”