Till startsida
To content Read more about how we use cookies on gu.se

New methods for better purification of wastewater

News: Feb 08, 2012

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 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 N2 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 analysis to study how the bacterial colonies in the biofilms changed when exposed to different levels of nutrients.

“Different species of bacteria are promoted or inhibited to different extents by changes in their habitat”, he says. “These properties are reflected in their positions in the biofilm, and so we developed new methods to analyse these in detail. The new methods are very flexible and can be used to analyse pretty much any type of biofilms.”

Furthermore, Robert discovered that groups of bacteria that are normally considered to be the same species (Nitrosomonas oligotropha) were affected differently by the changes. It is, thus, important to understand the diversity within species of nitrifying bacteria, in order to improve the removal of nitrogen.

The thesis “Biofilms in Nitrogen Removal – Bacterial Population Dynamics and Spatial Distribution” was successfully defended on 3 February 2012 at the University of Gothenburg. Supervisor: Malte Hermansson

Link to the thesis: http://hdl.handle.net/2077/28022

Robert Almstrand, Department of Chemistry and Molecular Biology, University of Gothenburg
Tel.: +46 31 786 2569
Mobile: +46 73 525 2187

Figure legend, image 1:
Robert Almstrand. Photo: Ann Svensson

Figure legend, image 2:
An image of a nitrifying biofilm taken in a confocal microscope showing how different bacterial populations can be distinguished with the aid of species-specific labelling (in situ fluorescence hybridisation). Photo: Robert Almstrand

Author: robert.karlsson@gu.se
Telephone: +46 31 786 9871

031-786 9871

Page Manager: Katleen Burm|Last update: 1/2/2012

The University of Gothenburg uses cookies to provide you with the best possible user experience. By continuing on this website, you approve of our use of cookies.  What are cookies?