It’s all good, clean water

Dr Michael Strahand explains how United Utilities - which looks after the water needs of the North-west - needed the right piece of equipment to ensure that it has peace of mind when it comes to monitoring the use of chlorine in its processes.

UNITED UTILITIES (UU) owns and operates the water network in the North-west. It supplies 2,000Ml of water every day to about 2.9M households and business premises through a network of about 40,000km of water mains, 1,444km of aqueduct and 100-plus water- treatment works.

In order to supply clean and safe drinking water, UU follows a regime of testing to ensure it complies with the standards set by the government.

UU works with several manufacturers to develop process instrumentation, across a range of categories, including flow measurement, chlorine, pH, colour, turbidity, level measurement, dissolved oxygen, mixed-liquor suspended solids and ammonia.

In 2006, UU appointed Analytical Technology to supply its Q45H chlorine monitor. The Q45H measures both chlorine and pH simultaneously.

Legally enforceable

The quality of drinking water in England and Wales is the subject of legally enforceable standards derived from the European Directive and UK legislation.

Defra deals with all aspects of water policy in England, and the assessment of water quality is based on information received regularly from water companies.

Chlorine is used throughout the water industry as the primary method of water disinfection, but the levels of chlorine are strictly regulated.

UU monitors the quality of water as it leaves the water treatment works and service reservoirs – to make sure that standards are being met – and also measures the quality of drinking water as it reaches customers. Water samples are taken from addresses selected at random within certain zones.

These samples are tested at UU’s laboratories, and the results are compared with required quality standards. All test results are then recorded on the Drinking Water Register.

Monitoring the level of chlorine in drinking water is of high priority to UU, as proof of disinfection and control in the water supply.

Chlorine residual monitoring is required in drinking water systems, as well as in hygienic- use systems, and measurements must be conducted on site.

The water industry has historically relied on open-cell amperometric monitors, or a variation on open-cell amperometric technology, with buffer delivery systems, for examining the levels of chlorine in the disinfection process. It is estimated that the cost to the water industry of operating an amperometric monitor with buffer could exceed £20M a year.

While effective, many amperometric monitor designs are based on engineering technology that dates back 40 years or more, and there are a number of associated problems. These include excessive costs, maintenance requirements, high rates of component failure, and environmental and health and safety issues associated with the storage, handling and disposal of buffering reagents.

Many water companies, such as UU, are now looking for methods of measuring free chlorine residuals without the need for chemical buffering. Acetate and phosphate buffers are expensive and environmentally unfriendly. Buffer delivery systems are maintenance intensive and have fairly costly consumables.

Chlorine monitors

UU required chlorine monitors for measurement in potable water – to be used at varying stages during the water treatment process. The company devised a framework agreement extending for five years. UU appointed Analytical Technology as preferred supplier of chlorine monitors for about 100 of its sites.

The contract had been put out to competitive tender and Analytical Technology scored the highest number of points against a list of criteria that covered commercial, support, and technical requirements.

Unlike on-line colorimetric, and most amperometric monitors, the Q45H uses a membrane-covered polarographic sensor, with an enhanced response at high pH, that does not require costly chemical reagents.

The membrane protects the measuring electrodes, eliminating the need for electrode-cleaning systems.

The Q45H is available in two versions: a chlorine monitor for drinking and cooling water systems, and a combined chlorine monitor ideally suited for chloraminated drinking water. The combined chlorine system can also be used in wastewater effluents, where sufficient ammonia is present prior to chlorination to result in a predominantly monochloramine residual.

The monitors and service provided by Analytical Technology, says UU, have

surpassed its expectations.

In 2007 Analytical Technology was presented with UU’s Best Instrument Supplier award.

UU’s operational equipment suppliers are monitored each quarter for quality and

performance. Analytical Technology was recognised for promptness of design approval, quotation reply and programme delivery.

Analytical Technology offers customer service and during the installation at UU training of key staff at the utility was initiated, arranged and provided by them.

UU’s Lorraine Morton and John Davis confirm that Analytical Technology’s products have demonstrated an ability to monitor chlorine levels effectively, with little maintenance intervention, under a range of process conditions. UU says it has a legal and moral duty to maintain the high standards of water quality expected of a nationally acclaimed water company. The company works hard to ensure that compliance with government water-quality standards is second nature – and that the standards are exceeded whenever possible.

Analytical Technology’s range of Q45H monitors provides chlorine measurements that are as stable and active as traditionally buffered monitors, while removing the need for costly chemical reagents, the company says.

It goes on to say that the sensor contained in the Q45H Residual Chlorine Monitor has a response time of up to ten times higher than that of conventional sensors. This enables the monitor to provide reagent-free chlorine measurements for most water pH values.

For applications with variable pH values, the Analytical Technology monitor has an optional pH compensation feature to eliminate free-chlorine error caused by process pH drift.

When the correct sensor is used, there is an extended response to chlorine at high pH levels, allowing pH correction to be employed over a much wider range.

Dr Michael Strahand is general manager, Europe at Analytical Technology.

T: 01457 832800

Action inspires action. Stay ahead of the curve with sustainability and energy newsletters from edie