Biological Treatment Approach

A more profound look on biological wastewater process basics


The mechanical pretreatment of the raw wastewater represents the first stage of the process in all biological wastewater treatment. Coarse contaminants and undissolved organic substances are removed by sieves, coarse filters or by settling. Depending on the quality of the wastewater, the following pre-treatment processes can be used:

  • Equipments : Screening / Strainer / Sand & Grease Removal Chamber
  • Concrete structures : Primary Settler / Digester Settler / 3-Pit-chamber


Pretreatment facilities are not part of the standard PMT portfolio, but we can assist in the selectoin and design in most cases. The process used largely determines the choice and design of the subsequent biological purification stage.

Biological Treatment

Microorganisms degrade the bilogical pollution represented by C and N present in the wastewater without any addition of chemicals.

PMT technologies are exclusively fixed film processes, where the bacteria develp on a media. These process are the optimum to achieve high water quality standards with an easy operation and a great resilience to load variations.

In the case of Ecodisc, bacteria develop on the rotating biodiscs, forming a biological surface layer called biofilm. These bacteria absorb oxygen from the air as they emerge, and absorb the soluble pollution when immerged in the wastewater. Following the absorbtion of the dissolved carbon and nitrogen compounds, the bacteria multiply and their colony grow on the surface layer of biodiscs. The rotation of the discs is used to control the friction forces on the biofilm and avoid any clogging. This gives a remarkable advantage to Ecodisk systems because they can adjust automatically to pollution load variations and be operated with very little maintenance. The excess and dead bacteria are detached from the surface layer by gravity and seperated as sludge from the system by secondary clarifier.

In the case of the Ecosim and the MBBR Pack, bacteria develop on moving biofilm carriers. In the Ecosim, oxygen is made available to the bacteria when the media are brought in the air by the rotation of a drum in which they are enclosed.

In the MBBR Pack, oxygen is injected directly in the bottom of the tank through fine diffusers.

Secondary Clarification

The sludge generated during the main biological step will be seperated in the secondary clarification. PMT provides two related technologies for clarification step; lamella separators or drum filters in combination with our Ecodisk.

Thanks to their simple, robust and efficient design, our DLE lamella separators are to operate. The short settling distances and the compact design provide large settling areas in really small volumes.

For more agressive design approaches, PMT has developed the EcodiskTM Filter, a standard product with the usage of HydrotechTM drum filter pannels.