The principle of operation of the sand trap is to retain and discharge sand from raw sewage pre-cleaned on inlet
screens. Mineral particles are separated by gravity, and waste water with only dissolved pollutants is processed for
further treatment, which may further be subjected to chemical treatment in the case of industrial sewage, or biological
treatment in the case of municipal sewage. Separators create a space in which the mixture introduced through the inlet
shaft at the top of the body calms its flow, which enables mineral particles fall to the bottom by gravity. The key to
successful separation is to achieve a dynamic equilibrium between the falling speed of the particle and the speed with
which it flows along the trough. A special partition helps in this, preventing both the sand from flowing back into the
inlet stage and the outflow of sewage in the outlet stage. The precipitated particles are evacuated from the inside of
the sand trap by means of a screw conveyor which, thanks to gravity drainage, effectively separates the sand from the
liquid remaining in it.
An interesting option for the further treatment of the sand after the sand trap is the WPP sand washer, in which the
sand is introduced into a wide funnel directly from the sand trap. The solution is based on an intensive swirling
movement inside the scrubber with a forced agitator and simultaneous multiple supply of clean water or treated
wastewater with periodic blowing of air from the compressor. Multiple rinsing of the sand pulp with clean water removes
organic particles, allowing the desired sand purity to be obtained. The process is fully automatic, the wash- water with
organic matter is discharged to the sewage system, and the washed sand can be disposed to landfill.
The offered mechanical devices are characterized by a simple but effective design that guarantees effective separation
of water from the mineral fraction. Sand separators can be additionally equipped with scrapers for the removal of
floating material on the surface of the trough and with systems for blowing the sand pulp with air. In combination with
a drum screen, it is possible to create a small technological line, sufficient to operate a facility that does not
require biological treatment with low production of wastewater, which can be effectively mechanically cleaned and
prepared for evacuation by sewerage or sewage transport.
