Tertiary treatment

After secondary treatment and final clarification, tertiary treatment is used to further improve effluent quality and have a targeted removal of specific substances. Residual suspended solids can be reduced by filtration, which can be combined with upstream dosing of chemicals to precipitate dissolved substances such as phosphate. Partial disinfection with UV radiation or dosing of chemical disinfectants can be used to reduce microbial contamination in the effluent. Residual organic micro-pollutants can be eliminated by oxidation, adsorption, or membrane filtration. Efficient tertiary treatment relies on a good operation of the upstream stages to limit energy and chemical demand for treatment.


Microscreen (Drum+Discfilter)

Microscreen technology (drum- or disc-filter) employs woven cloth filter elements installed on the periphery of a drum or disc structure, and utilises an inside-out flow pattern. The filter works by gravity with a few cm of water pressure gradient and is robustly designed with few moving parts to ensure long life and low maintenance costs.

Water to be treated flows by gravity into the filter via the centre drum. The media mounted on the partially-submerged drum separates solids from the water. The filtered water flows through the media into the collection tank. Once solids have accumulated on the filter and a critical head loss is achieved, the media is cleaned by a counter-current backwash system. The filters are in continuous operation even during backwash and high solids events.

Coagulants and flocculants can be added upstream the filter unit in order to improve the filterability of the particles. The dose and type of chemicals applied also have an impact on the pollutant removal efficiencies that can be achieved in the microscreens. Such a feature allows for precise particle removal up to the values required by the user by careful control of the chemical dose (mg-chemical added/TSS to be removed).


This technology was not part of the POWERSTEP project.

Sand filter

This technology was not part of the POWERSTEP project.