The first step in wastewater treatment is usually a physical pretreatment.

The following biological treatment is the main efficient technology to degrade the majority of organic compounds, parts of the nutrients and to decrease the level of microbiological pollution. The most developed techniques at the level of urban treatment plants are intensive biological processes (removal of organics and nitrogen). Their principle is to enforce and concentrate the natural phenomena of organic and nutrient removal in a small space. They are especially appropriate and effective for high concentrated domestic wastewater and blackwater.

The following technologies are some examples of those used for an intensive treatment:

• Activated sludge plant / Sequencing batch reactor (SBR)

• Trickling filter

• Rotating biological contactors

• Anaerobic treatment systems

On the other hand there are extensive treatment techniques available which are less intensive processes close to nature, use very little energy and often much more space.

• Constructed wetlands (soil filter)

• Natural lagoon, stabilisation pond

• Slow sand filtration