Improving pH Control and Compliance in Industrial Effluents

Industrial effluents from UK metal finishing plants, like the Royal Mint, are tightly regulated under the Pollution Prevention and Control (PPC) regulations and the Water Industry Act 1991. Discharging trade effluent without consent is a criminal offense, and strict controls are in place to protect public health, the environment and sewer systems. Discharge consents aim to eliminate hazardous substances, including heavy metals and acidic or alkaline materials from wastewater.

Challenges with Existing pH Control System

The consent to discharge specifies various parameters including the maximum daily discharge volume, metal loading, chemical oxygen demand, pH, temperature and suspended solid concentration. In order to comply with these regulations, The Royal Mint traditionally used precipitation plants with Hydroxide dosing to adjust the pH value of its effluents. However, due to the nature of the metals being manufactured, the effluent in the manufacturer's pH sensor tank is extremely glutinous, meaning that the existing pH probes and electrodes required cleaning a minimum of once per shift. As a result of this sensor fouling, the pH readings were less reliable, which was exacerbated by the poor response time of the electrodes. Operator input was often required for regulatory compliance, as the pH control was very poor.

“When looking into improving our pH systems, we found that most sensors required cleaning either manually or by installing a separate cleaning system,” said Graham Hartry, Environmental Manager (Blank Processing) at The Royal Mint.

The Royal Mint sought an alternative pH system in order to improve the quality of its effluents to better comply with regulations, eliminate the need for everyday cleaning and maintenance, and improve efficiencies.

Review and Audit of Existing Systems

Working alongside independent effluent treatment specialists, The Royal Mint reviewed and audited the existing systems of their effluent plants. As part of this process, they realized that their conventional pH/ORP sensors had an open reference system, meaning that the element and electrolyte were in contact with the process. This allowed chemicals to diffuse into the reference chamber and alter the reference system.

As the reference junction becomes contaminated, the potential shifts, chemicals attack the reference wire and the sensor cannot function. Not only did this result in an increase in cleaning and calibration cycles but there was also increased sensor failure frequency, resulting in decreased efficiency and raised costs.

Upgraded pH and ORP Monitoring Solution

To overcome the challenges of the existing monitoring system, a new solution was implemented, incorporating proportional hydroxide dosing, pH water quality monitors, and the Q-Blast AutoClean system from Badger Meter.

The updated system featured Q46P pH monitors and Q46R ORP monitors from the BlueEdge suite of solutions. These advanced sensors are designed for use in industrial and municipal applications and are specifically engineered to function in environments where conventional sensors often fail.

The differential pH/ORP sensors in the Q46P and Q46R monitors consist of a sealed reference system with a second glass pH electrode as the reference element in the sensors. The glass reference system protects the sensor from chemical poisons such as sulfide, cyanide, chlorine and bisulfite, which can destroy conventional pH sensors. Sensor electrodes can be user-specified for measurement reliability and maximum sensor lifetime. The type of glass used in these pH electrodes can be selected for optimal performance and the metal electrode for ORP measurement can be platinum or gold, depending on the chemical makeup of the process solution.

Reduced Maintenance and Increased Optimization

The Q46P and Q46R monitors selected for The Royal Mint feature an AutoClean function, reducing manual cleaning frequency for this environment with high levels of solids contamination. The system uses high-pressure air to clear contaminants from the face of the sensor. With an adjustable time controller that can be increased or decreased depending on water quality, this system allows minimal downtime by placing outputs in a ‘Hold’ state during cleaning to prevent false readings or alarms. This extends sensor life, maintains accurate pH readings and prevents crust buildup.

In order to accurately monitor pH levels in effluents, the pH monitor installed at The Royal Mint was directly linked to the digital dosing pump, so that the volume of hydroxide added is proportional to the pH signal from the pH controller.

“With the Q46P AutoClean monitor, we now have a stand-alone solution to control pH challenges, enabling us to reduce operator intervention at the same time as improving effluent control," added Hartry.

Results

Since installing the Q46P and Q46R monitors, The Royal Mint has experienced improved productivity, cost savings, and enhanced regulatory compliance. The AutoClean feature has significantly reduced maintenance needs by eliminating frequent sensor cleaning, while the pH controller’s AutoClean function operates every two hours, allowing the system to run for up to six months without intervention. As a result, pH control has improved, operator involvement has decreased, and costly electrode replacements have been eliminated, maintaining consistent effluent quality and meeting discharge regulations.