The goal of mechanical biological treatment of waste is also to reduce the volume of waste. This is however limited to a 30% reduction.
 
Separation of the bulky coarse fraction is the first step in the treatment chain.

Several different crusher machines and screening lines then separate the biologically treatable (organic) fraction from the fraction with the high calorific value (further processing in MSWI). Metallic components in the mixed waste are removed using a magnet. Other recoverable materials such as metal parts and wood are sent for recycling. 
 
Efficient Help from Hungry Bacteria 
The next step involves comminution, homogenisation and moistening (if necessary) of the organic fraction. This guarantees a homogeneous biological transformation.
 
Two procedures are currently available for this. One of these is aerobic digestion requiring oxygen. Special bacteria ensure a homogeneous digestion process.   The other is anaerobic digestion is without requirement of oxygen. Although more complicated from a process engineering point of view, the method has the advantage that the generated biogas can be used energetically.
 
The aerobic and anaerobic processes differ in terms of the type of ventilation, the method of conversion and the process and constructional requirements. The earth-like residual material created in the process is integrated in the refuse disposal sites.