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:
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.
The CoagSense coagulation controller is used exclusively on municipal water treatment plants. The automatic coagulation controller from Pi is suitable for all forms of water treatment plant where the principle of coagulation is charge neutralization. These can be DAF plants, packaged water plants or more traditional coagulation flocculation plants. Water sources are typically surface water but can be any water source. The technology used in CoagSense is currently being used in many thousands of water treatment plants all over North America.
The CoagSense uses a range of sensors (including existing site sensors) that can be added to a central controller (analyzer). The controller takes the signals and manipulates them, producing 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 – For information and troubleshooting.
Coagulant Water pH – Used to control pH adjustment chemicals to maintain the correct pH for coagulation.
UV254 – On the raw water to enable the coagulant to be dosed according to the organics load of the water.
Raw Water Turbidity – On the raw water to enable the coagulant to be dosed according to the organics load of the water.
Streaming Current – On the coagulated water to enable feedback control of the coagulation process.
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.
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 ngative charges thereby enabling coagulation.
Many things affect coagulation but the most important ones are;
The most common coagulants are;
A multi-parameter analyzer from Pi attracted many customers to Beijing Anyuan’s exhibition space at the China Water Supply Conference 2021 and Pi’s representative based in
Following on from the success of numerous water treatment plants in the UK and Ireland, Pi is now beginning to offer the CoagSense coagulation controller
Working closely with a contractor, CSL, five plants in Wexford now have their coagulation process controlled by Process Instruments CoagSense coagulation controllers. Alongside Peter Houlihan
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