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Pilot study at activated sludge plant shows that ozonation of filamentous sludge is very effective

At Öresundsverket WWTP in Helsingborg, Sweden, they have problems with filamentous sludge during springtime, as do many other activated sludge plants. With ozonation of the return sludge flow Öresundsverket has drastically reduced the amount of filamentous sludge and significantly increased the quality of the water – and this without any negative impact on the nitrification or the biological phosphorus separation.


In the line that was treated with ozone there is almost no foam or sludge on the surface compared with the untreated pools

Ozone is a very strong oxidant and therefore a very good method for treating wastewater. In the treatment of sludge containing filaments the ozone breaks up the filaments and improves the settling characteristics of the sludge, without any negative effect on the important nitrification process.

Pilot projects

To find out more about ozonation of filamentous bacteria and ozone’s impact on the other biological processes, NSVA chose to start with a pilot project. Öresundsverket’s activated sludge plant is optimally designed to run pilot tests as the cleaning process is divided into four completely separate treatment lines.


The pilot project gave clear results in comparison with the untreated lines. Sludge Volume Index was reduced dramatically, while the biological processes were not  affected. Marinette Hagman, who is specialist in Development & Benchmarking at NSVA is very satisfied with the results.

“In the line that was treated with ozone there is almost no foam or sludge on the surface compared with the untreated pools. Whether the problems in the digester are reduced, we cannot say anything about because sludge from all the lines is mixed before the reactor”, says Marinette Hagman. However it is reasonable to assume that these problems would disappear if all lines were treated.

SM900 Containerized ozone system

The Primozone SM900 is a complete ozone plant housed in a small container. At Öresundsverket the plant was complete with a dissolution system and a reaction tank. The container solution means that you do not need a new or existing building to install the plant. In addition, it can easily be placed close to the activated sludge process and even moved to another facility.

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