Chriwa Group - Water matters. We care.

Mechanical pretreatment

Pump sump

Mechanical pre-treatment is standard at the beginning of every wastewater treatment process and takes place in the so-called pump sump. Here, abrasive solids are removed to protect the machine technology from increased wear. The removal of fats and oils, in turn, serves to prevent unwanted build-up and deposits in tanks and machines as well as the clogging of pipelines. The following technologies are used as standard.


Coarse sieves

Coarse screens are found at the inlet to the treatment plant. With hole or mesh widths between 5 and 10 mm, coarse solids are retained from the wastewater in the inlet. The screens are mainly used to protect pumps installed downstream.


Oil separator

Since oil is less dense than water, it always floats to the surface. In the oil separator, which consists of a basin with a submersible wall or pipe, the floating oil is retained, while the denser, oil-free water below the wall/pipe can flow off and on. An automatic oil extractor continuously removes the oil floating on the surface.


Sand separator

Used to remove sand and other abrasive particles from the wastewater. Unlike the oil separator, the solids sediment in the wastewater due to their higher density. The flow velocity of the wastewater flowing to the treatment plant is slowed down to <0.5 m/s in the grit separator by abruptly increasing the cross-sectional area of the basin. The solids contained in the wastewater settle to the bottom of the grit trap and can be continuously removed either manually or automatically with a scraper or a mammoth pump.


Drum and curved screens

With mesh or hole widths of 0.5 to 2mm, drum and curved screens are used to discharge smaller solids that have not been removed by the pump sump. For high solids loads, a self-cleaning drum screen is recommended. Curved screens are cheaper, but more labour-intensive.