OPS Thickener or Settlement Unit

OPS Thickener or Settlement Unit

The OPS high throughput, rapidly deployable thickener (also known as a settlement tank or a settlement unit). The unit provides effective removal of suspended solids from construction and soil washing wastewater. The unit has no internal plates or packing providing a low maintenance solution within a very small footprint.


The Unique OPS Thickener


The OPS thickener is unique in being able to process 120m3/h in a 3m diameter footprint. The unit is designed to remove suspended solids from construction and solids washing wastewater providing effective silt management/total suspended solids (TSS) removal.

OPS thickeners are transportable by road in a single piece making them robust easy to install and easy to operate. The small footprint enables them to be used in areas where normal settlement units cannot fit.


What is Silt?


Silt is technically fine solids which are less than 63 microns. It is very important to remove this fraction of material from:

  1. Construction Site Water – silt carried into watercourses has a detrimental impact on the ecosystem. These ecosystems are now protected by legislation.
  2. Solids Washing Waste-Water – silt builds up in wash water carrying larger and larger particles which damage pumps, sludge up tanks and block wash nozzles.
  3. Industrial Site Yard Water – silts carries contaminants into watercourses such as hydrocarbons and heavy metals. Again, the ecosystems are now protected by legislation.


How does a settlement unit without plates or packing work?


The OPS Thickener uses a contact bowl in the top section of the unit where the incoming water is contacting with polyelectrolyte. The solids gather together in floccs which then pour down the inside wall of the vessel. In the base of the vessel, they are stirred slowly by a mixer on the same shaft as the bowl mixer. Clear water exits via a manifold into an outlet cylinder where it weirs over an outlet pipe for reuse or for disposal.


Advantages of using an OPS Thickener


  • Occupies less than one 3rd of the footprint of a traditional clarifier /thickener.
  • The only energy required is a 0.75kW motor.
  • Large sludge holding capacity in the base of the unit.
  • Oil/plastics/organics can be scraped from the surface of the unit.
  • Can be installed in a single day.




The OPS thickener is currently used as a settlement unit in several different washing applications.


Road Sweepings: organics and floating trash removed from the top of the unit. Sludge removed from the base.

Oily Sand Treatment: sludge removed from the base whilst oil is removed from the top.

Glass Washing: Produces a neutral buoyancy sludge so some sludge sinks and some floats, the OPS thickener removes both sludges and recombines them before the dewatering device.


The sludge is removed using a torque instrument from the central stirrer which starts and stops the sludge pump system. Typically, the sludge would then be stored in a further mixed tank before being dewatered in a centrifuge or press.

OPS have a good understanding of water treatment chemistry; it is very important that chemicals are introduced in the right order, the right mixing and given the right contact time.

As engineering systems integrators, we combine cost efficient 'off the shelf' products with our high throughput proprietary processes. Integrated by best in class process control into a single solution individually engineered to site conditions, OPS deliver consistent performance, reliability and optimised life cycle costs.

Oil Pollution Services Ltd.
Building 52, Wrest Park Enterprise Centre,
Silsoe, Bedfordshire
MK45 4HS


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