Solving Complications with Filamentous Sludge

Filamentous Sludge

Wastewater treatment is vital for human health, as well as for preservation and protection of the environment from the spread of contamination and water-borne diseases.

It is a common practice that wastewater treatment plants work based on the activated sludge principle. Activated sludge is created by organisms that flocculate and clump together to form a flake-like structure surrounding the suspended organic material they feed on. Therefore, larger masses settle out of the water and produce an active pool of microbes.

Biological floc comprises of fungi and bacteria, among others. As for bacteria, it covers around 95% of the total microbial mass and is vital for deprivation of organic substances in wastewater treatment process.

Complications with Filamentous Sludge

As stated, approximately 95% of the active sludge has bacteria. Filamentous bacteria are the usual component of the activated sludge biomass. Furthermore, filamentous bacteria form in a long thread like strands that do not split from each other but grow in a form of strings which enables these to link with each other.

As a result, Primozone has a formation of the mesh, which is the most essential part of the floc formation. Another significant aspect of filamentous bacteria is that it causes separation of fluid. Simply put, filamentous bacteria act as a spine for floc foundation and settling.

Filamentous bacteria have higher surface area and volume compared to conventional floc, also it is slow to settle. Under particular conditions, these bacteria can grow excessively, which will cause issues with sludge settling thereby decreasing the efficiency of the wastewater treatment plant. Wide-ranging research is continuing to be able to establish what causes a widespread growth of a certain type of filamentous bacteria. It was observed that season changes and difference in ambient temperature could be one of the reasons of the plentiful growth of filamentous bacteria.

An augmented development of filamentous microorganisms can result in various unwanted effects, one of them is - Floating Sludge. Floating sludge is inclined to float on the surface because of the growth of filamentous organisms, among others. The cell surface of certain filamentous bacteria adsorbs air and nitrogen gas bubbles that cause the sludge to swim upwards. Floating sludge should be eradicated quickly, not only because it can cause the development of foam in the septic tanks of anaerobic sludge treatment but it can also cause “sludge escape” resulting in loss of biological mass required to perform the core treatment.

Primozone Ozone Solution for Reduction of Filamentous Bacteria

Taking into account that this time of the year can cause unrestrained growth of filamentous bacteria, Primozone wanted to share their experience and solution for the effective reduction of filamentous bacteria with Primozone ozone solution.

Ozone is an extremely strong oxidant and as a result it is an effective method for wastewater. In the treatment of sludge containing filaments Primozone ozone solution improved the settling features of the sludge without any negative effect on the main nitrification process.

Öresundsverket WWTP, opted for Primozone plant and managed to successfully solve the challenge of filamentous sludge and simultaneously boost capacity on water throughput.

The Primozone SM900 is a full ozone plant placed in a small container. In the case of Öresundsverket WWTP, the plant was equipped with a reaction tank and a dissolution system. The benefit of the container solution is the prospect of placing it near the activated sludge, without the need for new building.

The pilot project resulted in a sludge volume index that was greatly decreased, while the biological process was not impacted.


This information has been sourced, reviewed and adapted from materials provided by Primozone.

For more information on this source, please visit Primozone​.


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