New methods for better purification of wastewater

Mar 05, 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, 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 , 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 to 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 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 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 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 ."

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.

Explore further: Spain defends Canaries oil drilling plan

More information: The thesis was successfully defended on 3 February 2012.

add to favorites email to friend print save as pdf

Related Stories

Eutrophication makes toxic cyanobacteria more toxic

Dec 06, 2010

Continued eutrophication of the Baltic Sea, combined with an ever thinner ozone layer, is favouring the toxic cyanobacterium Nodularia spumigena, reveals research from the University of Gothenburg, Sweden ...

Plant nutrients from wastewater

Sep 07, 2010

Nitrogen, phosphorous and potassium -- there are valuable nutrients contained in wastewater. Unfortunately, these essential nutrients are lost in conventional wastewater treatment plants. This is the reason why researchers ...

Recommended for you

UN climate talks shuffle to a close in Bonn

50 minutes ago

Concern was high at a perceived lack of urgency as UN climate negotiations shuffled towards a close in Bonn on Saturday with just 14 months left to finalise a new, global pact.

Study shows no lead pollution in oilsands region

Oct 24, 2014

New research from a world-renowned soil and water expert at the University of Alberta reveals that there's no atmospheric lead pollution in Alberta's oilsands region—a finding that contradicts current scientific ...

User comments : 0