Coagulation Controller – CoagSense

Pi’s CoagSense 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.

CoagSense Coagulation Controller

CoagSense Coagulation Controller

Coagulation is affected by multiple variables associated with and individual to any one water treatment site. These include but are not limited to:

  • raw water pH, alkalinity, turbidity, organic loading, temperature
  • coagulant used
  • post coagulant pH, temperature
  • physical aspects including dosing point, mixing etc.

These variables are typically different from site to site, water source to water source, and even day to day.

Pi believes that one size does not fit all. One method of coagulation control cannot be trialled at one site and rolled out across many. Each system needs to be designed and specified for each water treatment plant and that is a service offered by Pi.

Prior to changing existing controls, it may be beneficial to install and monitor how well an existing coagulation controller is doing by installing a coagulation analyser.

The CoagSense uses a range of sensors (including existing site sensors) that can be added to a central controller (analyser). The controller then takes those signals, manipulates them and produces a signal that controls the dosing of a coagulant. These are:Flow – Used to increase or decrease the coagulant dose proportionally to the flow.

Raw Water pH – Perhaps the single most important parameter affecting coagulation, Pi uses an extremely fast responding, reliable, solid polymeric junction pH sensor to alarm if the pH moves outside a predetermined range or preferably to control the pH of raw water on a separate PID loop.

Coagulant Water pH – Used to alarm if the pH goes outside the predetermined range for optimum control.

UV254 – During periods of low turbidity and high SUVA¹, optimal organics and therefore THM removal can be achieved using feed forward control from a UVA signal.

Raw Water Turbidity – When turbidity is high, UVA sensors become swamped and no longer effectively measure organics. During these periods another basis for control is often preferable and this can potentially be turbidity.

Streaming Current – With the right water conditions and/or coagulant, streaming current feedback control can offer the simplest and most reliable coagulation control. Installed in over 5000 plants worldwide, streaming current monitors can offer a robust and cost effective solution. Understanding the relationship between pH and streaming current is essential for the successful implementation of a streaming current based coagulation controller. Streaming current measures all variables that affect charge neutralisation, a key aspect of coagulation. If not used for control, a streaming current monitor can be extremely useful as a coagulation monitor, continuously monitoring for changes in any aspect of coagulation, including changes in water chemistry, coagulant make up and the dosing region such as the pump output.

References: 1. Edzwald, J. K. & Kaminski, G. S. A simple method for plant water optimization and operation of coagulation. (American Water Works Association, 2007).

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