Call Menu

Primary Settlement Tank (PST)

The Primary Settlement or sedimentation tanks are designed to reduce the velocity of the wastewater flow, allowing heavier organic solids (called raw sludge) to settle. They are the first stage of treatment after the removal of rags and grit in the inlet works. Scrapers present in the tank move continuously along the floor of the tank to deposit the raw sludge in hoppers for removal. The scum which floats to the surface is directed by water jets or scum boards to the sludge sump. The raw, settled sludge is removed by pump or gravity feed to a sludge treatment process, either on site or via tanker to a larger processing centre. Approximately 60% of suspended solids and 35% of BOD removal efficiency can be achieved at this stage.

The supernatant will still contain relatively high levels of suspend matter which will in most cases be passed on to some form of secondary treatment process. On sites where there is no secondary treatment discharge will be straight to the local watercourse. Monitoring of the suspended solids or turbidity level in the overflowing water is an important element of process control, both as a pollution prevention tool or as a dosing control parameter.

Monitoring the sludge blanket interface level allows automatic control of the de-sludging process ensuring that pumps are only used when required. This has the added benefit of producing better quality sludge for processing in digesters, thickeners and incinerators.


For specialist advice call:

+44 (0)1726 879800

Online Enquiry

Related Measurements and Products

Sludgewatch 715

SludgeWatch 715 Sludge Blanket Detector

The SludgeWatch 715 provides a simple, low cost method of spot checking the sludge blanket level in a wide variety of settlement tanks

More Details

SludgeWatch 8200w² Monitor

The SludgeWatch 8200w² Monitor provides a reliable method of detecting the sludge blanket level in clarifiers and settlement tanks.

More Details

ASLD2200 Sludge Blanket Monitor

The ASLD2200 is a fully automatic sludge blanket level detector designed for the water and waste water industry

More Details
SludgeWatch Ultra Monitor

SludgeWatch Ultra Sludge Blanket Monitor

Highly sophisticated Sludge Blanket Monitor using an ultrasonic transducer to track the sludge blanket interface

More Details

7300w² Monitor

The core product in the WaterWatch² range - the 7300w² Monitor provides all the user interface and system configuration

More Details

SoliTechw² IL Suspended Solids and Sludge Density Sensor

Inline Sensor for Sludge Density, Suspended Solids and Turbidity Monitoring

More Details
8100 Monitor with Radio Transmitter

Sludge Blanket Detection

Detecting the presence of the Sludge Blanket at a fixed level is one of the simplest ways of carrying out this control measurement

More Details
ASLD2200 On Site

Sludge Blanket Monitoring

Continuous monitoring of the sludge/water interface or sludge blanket is central to the efficient operation of clarifiers, thickeners and settlement tanks

More Details

To speak with one of our specialist advisors, call

+44 (0)1726 879800

or complete our

Online Enquiry