Mint pH Control

Jan. 22, 2014
The Royal Mint improves pH control & compliance in water effluent

About the author: Garry Tabor is sales manager, Europe, for Analytical Technology Inc (ATI). Andy Dargue is technical director for Integrated Effluent Solutions Ltd. Graham Hartry is environmental manager, Blank Processing Department, for Royal Mint. ATI can be reached at [email protected] or 610.917.0991.


The Royal Mint has an established reputation as the manufacturer of coins and blanks for both domestic and global markets. Based in Llantrisant near Cardiff, its main business consists of the production of U.K. circulating coins; the manufacture, marketing and distribution of U.K. and overseas collector coins and medals; the manufacture of official medals; and the sale of coin-based jewelry and collectables. The Royal Mint is a U.K. governmental organization. Its primary responsibility lies with the provision of U.K. coinage; however, it also has an international reputation for the manufacture of high-quality coins and blanks for more than 100 countries worldwide.

The Royal Mint is committed to improving its manufacturing processes to ensure minimal impact on the environment. Like all manufacturing plants, water effluents from the Royal Mint are strictly regulated by the Environment Agency and by local authorities through consent to discharge. In order to comply with these regulations, the Royal Mint operates effluent monitoring systems that can cope with the large amount of fouling that can occur within sensing tanks. The company recently worked with Integrated Effluent Solutions (IES) to improve its pH control by installing Analytical Technology Inc.’s (ATI) Q45P pH/ORP monitor.

pH Control Challenges

Effluents originating from metals finishing plants in the UK are strictly controlled by the Pollution Prevention and Control (PPC) regulations. PPC is a system that has been put in place by the Environment Agency to ensure that manufacturers adopt an integrated approach to pollution control. Companies in the U.K. discharging effluents to a public sewer require a current and valid consent to discharge under the PPC regulations. The sewerage operator, which often is the company supplying water to the site, awards this discharge consent to the organization.

By issuing the discharge consent, regulatory bodies aim to eliminate potentially hazardous substances, including heavy metals and acidic and alkaline materials found in trade effluents. Because these substances can contain qualities that make their treatment difficult or complex, it is essential that their discharge into public sewers be regulated. The consent to discharge specifies various parameters including the maximum daily discharge volume, metal loading, chemical oxygen demand, pH, temperature and suspended solids concentration. 

In order to comply with these regulations, the Royal Mint has traditionally used precipitation plants with hydroxide dosing to adjust the pH value of its effluents. Due to the nature of the metals being manufactured, however, the effluent in the pH sensor tank is extremely glutinous, meaning that pH probes and electrodes require cleaning a minimum of once per shift. As a result of this sensor fouling, the pH readings can be less reliable, which is exacerbated by the poor response time of the electrodes. pH control also can be poor and often requires operator input to ensure regulatory compliance. 

The Royal Mint recently began to seek an alternative pH system in order to improve the quality of its effluents and to better comply with Environment Agency regulations. The organization also required a system that would eliminate the need for everyday cleaning and operator maintenance, and improve efficiency in a cost-effective way.

Effective pH Control

In order to improve its pH control, the Royal Mint looked to IES, a company with a background in effluent treatment. 

The Royal Mint worked with IES to review its existing pH systems and to improve the pH control and efficiency of the effluent plants. Conventional pH/ORP sensors have an open reference system, meaning that the reference element and electrolyte are in contract with the process. This allows chemicals to diffuse into the reference chamber and alter the reference system. As the reference junction becomes contaminated, the reference potential shifts. The chemicals then can attack the reference wire, meaning that the sensor cannot function. When these problems occur, cleaning and calibration cycles increase and the sensors fail more frequently, resulting in decreased efficiency and increased costs.

To overcome these problems, IES provided a solution using proportional hydroxide dosing and the implementation of Auto-Clean pH controllers from ATI, a U.S.- and U.K.-based supplier of gas and water monitors for use in a wide range of applications.

To meet the specific requirements of the Royal Mint, IES selected ATI’s Q45P pH/ORP monitor. The Q45P system is designed for use in industrial and municipal applications and contains sensors specifically engineered to function normally in applications where conventional sensors typically fail.

The differential pH/ORP sensors in the Q45P monitor 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 to ensure measurement reliability and maximum sensor lifetime. The type of glass used in the 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.

The monitor selected for the Royal Mint application contains an auto-clean option, which is designed to extend cleaning intervals on pH and ORP sensors in applications with high levels of solids contamination. The auto-clean Q45P system uses an integral high-pressure air supply to automatically remove contaminants from the face of the sensor. Featuring a time controller that the operator can increase or decrease depending on water quality, the monitor automatically places outputs in a “hold” condition during cleaning to prevent false readings or alarms. This auto-clean option prolongs the life of the pH electrode and ensures that the sensor measures the pH of the effluent rather than a crust built up on the electrode.

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

Achieving Productivity & Compliance 

Since installing the Q45P monitor, the Royal Mint has experienced significant benefits in terms of increased productivity, reduced costs and regulatory compliance. By using the auto-clean Q45P monitor, the Royal Mint can ensure that it achieves compliance with consent to discharge regulations while eliminating the need for regular and costly sensor cleaning. 

To meet the particular circumstances of the Royal Mint, the pH controller’s auto-clean air wash function operates every two hours. As a result, the monitors can operate for six months or more without any maintenance. This has led to greatly reduced operator intervention as well as a marked improvement in the pH control of the plant. The application of this technology also has enabled the Royal Mint to eliminate costly replacement of pH electrodes.

Ensuring compliance with environmental regulations is important. By supplying the ATI Q45P auto-clean monitor, IES has provided the Royal Mint with a standalone solution to pH control challenges, enabling it to reduce operator intervention while improving effluent control. 

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