Coagulation Controller – CoagSense

What’s the best way to control coagulation on a water treatment plant? The answer is that it depends on the water, the type of plant and the coagulant used. Pi’s CoagSense automatic coagulation controller is an integrated controller that accepts multiple inputs from appropriate parameters including pH, flow, temperature, UV254, turbidity and streaming current. From these measured parameters, the CoagSense outputs a flow proportional coagulation control signal that can go to a site SCADA or direct to control a coagulant dosing pump.

Coagulation is affected by lots of different variables like:

  • Raw water pH and alkalinity, turbidity, organic loading, and temp.
  • The type of coagulant used
  • Post coagulant pH, temperature
  • Physical aspects of the plant including mixing etc.

In the past most coagulant control has been dosed automatically with the setpoint determined manually by looking at the variables and sometimes by using lab methods such as jar testing. There are two main problems with this approach. The first is that when the main goal of coagulation was to remove turbidity, operators eyeballing the water and changing the dose was a good method of determining the dose of coagulant required. Now that the focus is on enhanced coagulation and the removal of organics that are often not visible to the naked eye.

This method of manually determining the coagulant dose is no longer providing operators with the outcomes that they need. In addition the consequence of under dosing coagulant is often more severe than the consequence of overdosing coagulant. For this reason the tendency is for operators to add more coagulant than is required leading to shorter filter run times and more sludge to dispose of. This overdosing of coagulant is typically approximately 30%. The implementation of automatic coagulation control will typically save money (often giving a ROI of months rather than years) while improving water quality and plant outcomes.

CoagSense Application QuestionnaireTechnical Note519kB
Coagulation Control Using Streaming Current MonitoringTechnical Note842kB
PID ControlTechnical Note710kB


Coagulation is the process by which suspended and dissolved solids clump together which is necessary to remove them.

Flocculation is the process of the coagulated solids clumping togetehr to make large aggregations or “flocc”.

A coagulant is a chemical, added to water that enables coagulation. Typically a charged metal salt such as Ferric or Alum or PACl.

A flocculant is a chemical added to water to enable flocculation, typically a charged organic chemical.

Charge neutralization is when solids are held in suspension in water by the negative surface charges. Charge neutralization happens when a positively charged coagulant is added to neutralize the negative charges thereby enabling coagulation.

Many things affect coagulation but the most important ones are;

  • pH
  • Coagulant charge
  • Temperature
  • Suspended solids
  • Dissolved organics
  • Mixing of the coagulant



The most common coagulants are;

  • Ferric – Iron Chloride
  • Alum – Aluminum Sulphate
  • PACl – Polyaluminum Chloride

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