Biological treatment is achieved by creating an environment suitable for the survival and reproduction of various bacterial cultures and exposing them to organic substances present in the wastewater.  
The task of biological treatment is to reduce the oxygen demand exerted by the microorganisms to a level that will have no significant impact on the receiving stream. The BOD removal process is illustrated  by the following equation:

Gemwater can apply all different technologies known today :

There are several Biological systems to treat different type of waters:
Conventional Activated Sludge Process.
Sequential Batch Reactor (SBR) process is a variant of the Activated Sludge process.
  The SBR process eliminates the need for primary and secondary clarifiers.
A MBBR (Moving Bed Biofilm Reactor) or biomass reactor in mobile bed.
Intermittent  Cycle Extended Aeration System  PROCESS