Before wastewater reaches recipient waters, nutrients must be removed in order to avoid eutrophication and large algal blooms, which may result in serious damage to animal and plant life. Robert Almstrand at the University of Gothenburg, Sweden, has shown in his thesis that better removal of nitrogen from wastewater can be achieved by providing the bacteria that purify the water with alternating high and low levels of nutrients.
The emission of wastewater to oceans, lakes and rivers contributes nutrients in the form of nitrogen and phosphorus to these recipients. This causes large algal blooms, and to prevent this the wastewater must be purified in wastewater treatment plants before being released.
The removal of nitrogen is a biological process in which different groups of bacteria are used to convert the nitrogen compounds to nitrogen gas in a number of steps. The nitrogen gas is then emitted to the atmosphere. The first, and rate-limiting step is nitrification. Nitrification is carried out by bacteria that oxidize ammonia via nitrite to nitrate ions.
Robert Almstrand at the Department of Chemistry and Molecular Biology shows in his thesis that the ability of the bacteria to carry out nitrification is improved if the bacteria receive alternating high and low levels of substrate (in the form of dissolved ammonium), rather than a constant low level. This will enable the wastewater treatment plant to cope better with variations in the concentration of nitrogen in the wastewater.
"Since the composition of the wastewater varies continuously, it was important to carry out the studies in a set-up that was as similar as possible to real wastewater treatment plants. For this reason we constructed a pilot plant at Ryaverket in Gothenburg", says Robert Almstrand.
The bacteria grew in what are known as "biofilms", which are dense collections of microorganisms on surfaces. Robert Almstrand used microscopy and digital image analysi
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| Contact: Robert Almstrand robert.almstrand@cmb.gu.se 46-317-862-569 University of Gothenburg Source:Eurekalert |