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 listed above 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 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.
References: 1. Edzwald, J. K. & Kaminski, G. S. A simple method for plant water optimisation and operation of coagulation. (American Water Works Association, 2007).
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.
Provides remote controller access over local area networks such as those belonging to a certain organization or location.
Provides remote controller access over mobile networks.
Provides Modbus communication and remote controller access over LAN.
Provides Modbus communication and remote controller access over RS-458 networks.
The CoagSense is able to take in outputs from other site instruments potentially saving money
Provides data logging for investigation and troubleshooting purposes.
Offers the ability to manipulate process variables such as pressure, speed, temperature, flow and others.
The CoagSense allows for the direct control of the dosing pumps for pH correction and coagulant addition.
Allows you to gather and analyze real-time data via the use of SCADA systems.
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
Scottish Water has recently updated their Approved Instrument List and Process Instruments (UK) Ltd. (Pi) has been selected as the sole supplier for Coagulation Controllers.
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