Streaming Current Monitors and Streaming Current Detectors from Pi use streaming current measurement (similar to Zeta Potential) to maintain proper electrokinetic charge (ionic & colloidal) in coagulation control applications in water treatment. Effectively these coagulation analysers detect and control the level of residual coagulant. The objective is to keep this residual at a minimum while maintaining desired final water quality and process efficiency. The Streaming Current Monitor can be used as an effective feedback coagulation control tool allowing the operator to optimise the coagulation dose, effectively building a coagulation analyser.
The coagulation analyser uses streaming current measurement to maintain proper electrokinetic charge (ionic & colloidal) in the treated water. Effectively, it responds to changes in raw water characteristics (turbidity, colour, pH, etc.) and flow rates. This allows the operator, or an automated control device, to make the necessary coagulant feed adjustments in order to continuously maintain the optimum dosage. In some water treatment facilities the water chemistry is such that the coagulation analyser on its own is insufficient to properly control coagulation and in these applications the coagulation analyser (streaming current monitor) can be enhanced with UV254 measurement, turbidity measurement and pH measurement to create a multi-sensor coagulation control system.
Please contact us for advice with any coagulation control application.
The treated water sample flows into the sample cell where it is drawn into the bore during the upstroke of the piston cycle and is expelled from the bore on the piston down stroke. Particles contained in the water are temporarily immobilised on the piston and cylinder surfaces. As the water is moved back and forth by the piston, charges surrounding these particles (+ and -) are moved downstream to the electrodes. This movement of like charges causes an alternating current to be generated, defined as “streaming current.” A signal gain selector, accessed through the menu screen, is used to select the best signal amplification. The signal amplification should be set where a normal change in dosage results in a desired deviation in streaming current (normally 30 units). The displayed streaming current value (SCV) should be considered as a relative reading due to amplification of the primary signal.
- Immediate response to process changes in coagulation treatment – coagulation monitor
- Maintain high quality finished water through improved coagulation control – coagulation controller
- Reduce coagulant/polymer costs – coagulant analyser
- Automate dosing coagulant/polymer dosing using the streaming current monitor – coagulant control
- Ensure coagulation reliability – coagulant analyser
- Improve operator efficiency – coagulant analyser
- Improve filter performance and coagulation treatment – coagulation controller
- Monitor your coagulation control process – coagulation monitor
Streaming Current Monitors Standard Features
- Patented sensor design
- Quick replacement probe and piston
- Self-diagnostic sensor
- High-volume flow minimises sensor fouling
- Removes electronics from harsh environments
- Corrosion-free Nema 4x enclosure (IP65)
- Optional computer interface
- Spare probe cartridge and piston included
- Auxiliary input signals
The Streaming Current Monitor (Streaming Current Analyser) allows the cost effect control of coagulant.
- Water treatment coagulation control analyser
- Water treatment coagulation monitor
Many water treatment plants still use manual control for coagulant dosing (usually Alum or Ferric). Whilst the raw water quality is steady this is an effective method to get a coagulant dose, however when the raw water changes then manual control of the coagulant dose breaks down, particularly when plants are unmanned overnight or at the weekend. When the raw water is likely to be of proper quality in the future (e.g. a weather forecast predicts a rain event) operators often increase the coagulant dose in anticipation of a rainfall event. This can lead to poor coagulation prior to, during, and after the rainfall event (if it comes at all) and also can introduce longer term issues such as filter blinding, shorter filter run times and increased aluminium residuals (in the case of Alum).
For many plants it is possible to automate coagulant control such that a streaming current monitor can effectively increase and decrease the dose of coagulant automatically in response to changing water quality. This is particularly common in areas of low alkalinity raw water.
If you would like to learn more about how Pi might be able to help or plant manage coagulation control when plants are unmanned please contact us.
- SmartTrac PID control
- Sensor Maintenance Module (S.M.M.)
- Automatic sensor wash and chemical rinse
- Duratrac II Sensor (a heavy-duty motor and double flow capacity sensor)
- Data acquisition and web browser access (Ethernet/internet)
|Coagulation Control Using Streaming Current Monitoring (IST20)||250Kb|
|CRIUS® Remote Communications (ISB18)||250Kb|
|CRONOS® and CRIUS® Control Options (IST08)||250Kb|
|Remote Access GPRS (IST30)||250Kb|
Focus Ons are a series of short articles distributed by email providing technical information regarding instrumentation, process measurement in potable, waste, process and pool waters. If you would like to join the mailing list, please contact us.
However, did you know that…
… no single online water quality measurement stands out as always being the best to monitor or control coagulation in all situations (as there are multiple factors that can affect coagulation)?
… some of these factors, like organics, are very critical to coagulation but are not commonly measured online and so are often overlooked?
… Process Instruments controllers can monitor multiple parameters simultaneously including charge (streaming current), organics (UV254), pH, flow rate and turbidity to provide a complete overview of water characteristics minute by minute?
What is Coagulation Control?
The aim of water treatment is to remove soluble (e.g. organics) and insoluble (e.g.colloidal particulate) contaminants. These contaminants often carry an anionic charge which keeps them in suspension or in the soluble phase. Coagulants are added to neutralise the charge of colloidal particles and to also “complex” with organic molecules which ultimately results in their precipitation. Reducing the charge of the particles and precipitating the organics means they will no longer be able to remain in a stabilized suspension. Once the repulsive charge component is removed these contaminants will naturally start to clump together due to attraction forces called Van Der Waals forces. The removal of these contaminants is aided by the formation of chemical floc (resulting from the hydrolisation of the coagulant) that both enmeshes and sweeps up the smaller agglomerations so they can be removed more easily by sedimentation or floatation.
If the coagulant dosing is too high, the unnecessary additional coagulant can cause increased amounts of sludge to be generated, shorter filter run times, aluminum carry over, and other unwanted side effects.
This situation is made considerably more complex because the amount of coagulant required and the effectiveness of coagulation can vary greatly throughout the day or even hour by hour due to changes in turbidity, pH, temperature or the levels of natural organic material (NOM) of the incoming water.
What happens to the raw water entering a plant during a rainfall event?
The obvious answer is that incoming water gets more turbid and the coagulant dose goes up. Turbidity is used as an online measurement of water quality in virtually all WTP’s and also when jar tests are carried out, however turbidity is not the only water quality parameter that is changing. There are other factors which are critical to coagulation that are likely to be changing at the same time:
- Depending on the nature of the river the pH can change which in turn can increase or decrease coagulation efficiency. Each coagulant has an optimum pH range where it can achieve the highest efficiency in terms of turbidity and organics removal. Thus, changes in pH can have a considerable impact on coagulation and filtration performance, and resulting turbidity and DBP reduction.
- The alkalinity of the water can change. If this drops below around 10ppm then effective coagulation cannot occur because the hydrolysis reaction that is essential for coagulation cannot occur. This situation can only be rectified by adding alkalinity.
- The level of dissolved organics (NOM) can change. Unless monitored with appropriate instrumentation (preferably online), initial changes in organics often go unseen and under-treated as a result. The actual demand on a coagulant from organics can in some cases appear before an increase in turbidity is seen and can also remain elevated after the turbidity has returned to normal. Lack of proper instrumentation to monitor changes in organics as they occur leads to a reduced removal efficiency of NOM which can lead to the formation of Trihalomethanes and other unwanted disinfection by products.
So what is the best measurement to optimise and control coagulation?
The answer is that no one single water quality measurement provides the complete picture on its own. As has been discussed here, there are multiple factors that need to be taken into account and ideally monitored on a continuous and online basis in order to most effectively control coagulation. Expecting a single measurement parameter to be effective is simply not very practical because different water treatment plants all have different raw waters, which each have different challenges to overcome when controlling their coagulation dosing. This means that for any system to be most effective it needs to be flexible and modular, allowing different parameters to be measured based on what is needed at different water treatments plants, which depends greatly on the individual characteristics of the raw water. Even if a particular water treatment plant doesn’t currently face an issue like DBP formation due to elevated levels of organics, we have lots of examples where water quality has changed in unpredictable ways for a good many WTP’s. So, having a flexible, modular, and well rounded approach to online coagulation control, versus a single measurement approach, makes the most obvious sense.
The solution to this problem?
Not a ‘one size fits all’ product but a modular, customisable system designed to be flexible enough for all applications.
How we design your individual coagulation monitoring/control system.
At the heart of Pi’s coagulation monitoring/control systems are Pi’s controllers (CRONOS® and CRIUS®). Depending on the individual requirements of the application the system is designed around one of these controllers.
- First we will ask you for details about your particular application and water treatment challenges and from this discuss the parameters you may wish to monitor. These parameters will include one or more of the following: pH, Temperature, Conductivity, Streaming Current, UV254 and turbidity.
- We will then discuss what control and communication requirements you might need. How many dosing pumps, alarms or signal outputs are needed? Is flow pacing going to be required? Does the system run continuously or only certain hours of the day? Do you require remote access or integration with telemetry systems? If your SCADA will be handling control, then what sort of communication protocol is needed to get the measurement data integrated?
- Finally we will discuss the ideal system installation to get the most reliable performance out of your online coagulation control system.
Once this process is complete you will have a custom designed system, created by you, specifically for your needs with all the necessary features for effective control and no unnecessary extras. You will also have a system that can be easily expanded upon should it prove necessary at a later time, or as budgets allow.
Process Instruments Coagulation Controllers – truly bespoke systems.