Application of SCM530 Streaming Current Detector in a Waterworks in Yulin, Guangxi

Streaming current detector is a very important online monitoring and control instrument in the coagulant dosage control of waterworks. Its main function is to realize the precision and automation of coagulant dosage, so as to improve the water quality, reduce the drug consumption, reduce the sludge amount and stabilize the operation.

This article provides a brief introduction to the application of the SCM530 current meter in a waterworks in Yulin, Guangxi.

1.Basic application principle of current streaming sensor

The Streaming current meter measures the charge movement (i.e. Streaming current) of colloidal particles in water under the action of shear force (water Streaming through the instrument detection chamber).

Colloidal particles in natural water (such as clay, organic matter, algae, etc.) are usually negatively charged and repel each other to maintain stability (colloidal stability).

The addition of positively charged coagulants (such as polyaluminum chloride PAC, aluminum sulfate, etc.) will neutralize the negative charge of the colloid, destabilize the colloid and make it easy to aggregate to form floc.

SCD indirectly reflects the charge state of colloidal particles in water (approximate Zeta potential) by measuring the Streaming current value (SC value).

When the turbidity or colloidal concentration of raw water changes, the Streaming current deviates from the set value. The SCD instrument automatically adjusts the frequency of the injection pump to increase or decrease the dosage of the agent, so that the Streaming current returns to the target range.

2.Application objectives and values of current Streaming meter in a water plant in Yulin, Guangxi

Precise control, stable water quality:

Guangxi's surface water sources (such as rivers and reservoirs) are highly seasonal and rainfall-dependent, with significant fluctuations in raw water turbidity, organic matter content, pH levels, and temperature. Traditional chemical dosing methods based on turbidity or empirical approaches struggle to respond promptly.

SCD directly reflects the core coagulation process (charge neutralization), enabling rapid detection (with short response times, typically seconds to minutes) of raw water quality changes (especially colloidal charge characteristics). This allows timely adjustment of chemical dosage to maintain coagulation efficiency near optimal levels, thereby stabilizing turbidity in sedimentation/clarification tanks, reducing filter load, and ensuring final effluent quality.

Significantly save medicine consumption:

Avoid excessive dosing caused by manual control or fixed proportion addition (this is the most common problem in the traditional method).

By maintaining optimal coagulation efficiency while keeping chemical dosing near theoretical levels, we can substantially reduce coagulant (e.g., PAC) consumption, typically achieving 10%-30% savings with significant economic benefits.

Reduce sludge production:

The reduction of the dosage of drugs directly leads to the reduction of the generation of chemical sludge, and reduces the cost and difficulty of sludge treatment and disposal.

Automate and reduce manual workload:

The SCD output signal (typically 4-20mA) can be integrated into the water plant's automation system (PLC/DCS), forming a closed-loop control system with metering pumps or control valves. This enables fully automated coagulant dosing, minimizing manual intervention and operational errors.

Handling complex raw water:

For complex raw water with high algae content, low turbidity, high organic matter, and high color, turbidity control alone is ineffective. SCD's sensitivity to colloidal charges better addresses these challenges by determining the appropriate dosage.

3.Key links and precautions for the application of current Streaming meter

Installation site ：

Best point: Usually installed after rapid mixing at the sampling point. Ensure the mixture is uniform and the reaction has just started, which can represent the true state of colloidal charge in water, while avoiding interference or damage to the probe caused by large flocs in the subsequent flocculation process.

Sampling system: A stable, continuous, and representative sampling Streaming path is required, with appropriate Streaming rate. A filter should be installed to prevent large particles from clogging the detection chamber, but ensure that the colloid charge characteristics are not changed.

Calibration and set points:

Initial calibration: On-site calibration is required after installation. The dosage under current water quality is usually determined by the beaker test, and the corresponding SC value is recorded.

Setpoint adjustment: The target SC setpoint is not fixed. When the raw water quality changes significantly (such as water source switching or seasonal changes) or there are special requirements for the effluent, the set point may need to be fine-tuned in the beaker test.

Control system：

The SCD, functioning as the core sensor, transmits its output signal to the process variable input of the controller.

The controller (PID algorithm) compares the measured value (PV) with the setpoint (SP) and calculates the control output signal (OP).

Control the output signal to drive the actuator (such as frequency converter to control the speed of metering pump and adjust the opening of the regulating valve) to change the dosage of coagulant.

Control parameters (such as PID's P, I, D values) should be properly set to ensure rapid response while avoiding oscillation.

Maintenance ：

Regular cleaning: The probe detection room is prone to scaling or pollution (especially high hardness or algae-containing water), so it needs to be cleaned regularly (the frequency depends on the water quality).

Calibration verification: Perform regular zero span checks or compare with beaker test results to ensure measurement accuracy.

Part replacement: Wear parts such as piston rings and O-rings should be replaced as needed.

The deployment of a current Streaming meter at a water treatment plant in Yulin, Guangxi, exemplifies the industry's progress toward precision, intelligent, and efficient water treatment. By directly monitoring key parameters during coagulation—particularly colloidal charge status—the system enables real-time, closed-loop, and optimized control of coagulant dosing. This evolution from "experience-driven" to "data-driven" coagulation processes significantly enhances water quality stability and operational cost-effectiveness, establishing a crucial technological foundation for smart water plants. With the deepening integration of multi-parameter fusion and AI technologies, future coagulation control will achieve even greater precision and efficiency, providing robust safeguards for safe water supply.