Implementation of The LSP-concept in Extended Aeration

Amongst the micro-organisms found in aerobic treatment plants, mainly bacteria are
responsible for the conversion of soluble organic matter. Bacteria occur in three
different forms of growth; dispersed (free living cells), aggregate forming (as flocs in
activated sludge and as biofilm in biofilm processes) and as filamentous (as long
chains of cells in a threadlike manner). Microbes, where stalked ciliates and rotifiers
are the dominating groups, are mainly feeding on bacteria and are therefore an
important part of the micro fauna to keep the excess bio sludge at a minimum.
Nitrogen and phosphorus are essential nutrients needed in biological wastewater
treatment. The phosphorus play a vital role in the energy transfer within the cells,
while the function of nitrogen is to function as a component in the cell protein. The
effluents from pulp and paper industry are often short in these nutrients, which can
cause problems like insufficient COD reduction and poor sludge settling
characteristics.
The LSP-process is, as described in the introduction, a way to treat wastewater for
getting a high amount of dispersed bacteria in a first stage, which can be consumed
of filter feeding microbes in a second stage. It is important to keep the dispersed
bacterial stage free from microbes, which is solved by having a short retention time
(only a couple of hours). The second stage functions almost in the same way as an
ordinary activated sludge process. The principle is based on that dispersed bacteria
are easier for the microbes to consume than floc forming bacteria. This would lead to
higher consumption of bacteria and in the long run a lower production of excess
biological sludge. The disadvantage is that the LSP-process requires nutrient addition
for the first stage to function as expected. This can lead to release of nutrients in the
second stage due to the consumption of dispersed bacteria by the filter feeding
microbes.
The process for extended aeration is based on the same concept as ordinary activated
sludge, with the difference that the process for extended aeration has considerably
longer sludge age. Comparatively the normal sludge age for an extended aeration
process can vary between 25 and 50 days, while an ordinary activated sludge process
normally vary between 3 and 7 days. This means that the biological degradation
processes can go on for a longer time, which result in a increased degradation and a
decreased biological sludge production. The advantage of long sludge age is also
applied in activated sludge treatment processes with suspended carriers (biofilm) and
membrane bioreactors.
The expectation of introduce the LSP-process in extended aeration processes is to
get a wastewater treatment process that get even lower excess biological sludge than
the extended aeration process in combination with improved sludge settling
characteristics.
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