United Utilities targets alarms

Manchester, UK - New ammonia probes and controllers have enabled staff at United Utilities’ Macclesfield wastewater treatment works to ensure that the plant does not exceed its discharge consent. Following installation, the monitoring systems initially generated around 40 alarm texts per day (mostly night!) but significant improvements have now been implemented.

The Macclesfield WwTW is a relatively large plant treating industrial and domestic waste from a large area drawn from a network of pipes and drains that extend for hundreds of miles. Previously, however, illegal discharges from unknown sources have resulted in highly variable ammonia levels that, in April 2007, caused the plant to exceed its discharge consent.

United Utilities subsequently selected the Macclesfield site to trial a Hach Lange (HL) monitoring system that is designed to issue instantaneous alarms by SMS text message to key staff. “This site was chosen because of its strategic importance and because we were anxious to gain a higher level of understanding of the ammonia levels throughout the plant,” explains Barry Sherwood,  process controller at the Macclesfield facility. 

Initially, an ammonium probe, the ‘NH4 sc’, was installed about 50 metres downstream from the inlet with a further four probes strategically placed around the site. Each probe was connected to a HL SC1000 controller. Each controller was fitted with a SIM card so that key staff would receive text messages should an alarm condition arise. The inlet alarm was set at 45mg/l, the outlet set at 3 mg/l and the process probes were set at 25 mg/l.

“Around 40 to 50 text messages per night when the units were first installed," Sherwood reports. "However, quick and easy access to reliable data has enabled Barry to identify the sources of the peaks and he says, “It is now down to one or two text messages per day, which is great news for me, the company and my family.”

Data from the monitors is available on the Internet via a dial-up connection which is soon to be upgraded to Broadband. This has enalbed Sherwood and his team to study trends at any time from anywhere, even via a BlackBerry. Staff can, therefore, check if an alarm was the result of a temporary peak or something more serious. The alarms also help to run the plant efficiently and maintain discharge quality below consent levels.

Since the ammonia monitoring systems have been installed a number of other United Utilities staff have visited Macclesfield in order to study the results of the trial. As a result of these visits, many of them have since purchased similar systems and Sherwood believes that in the near future almost all of United Utilities’ wastewater treatment plants will employ the same probe/controller systems.