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Control solution for wastewater treatment project

05 November 2013

Southern Water's largest ever capital project includes a new wastewater treatment works (WWTW) and sludge recycling centre, two pumping stations, 11km of sewer tunnel and a 2.5km long sea outfall. The newly completed works is able to treat 95 million litres of wastewater generated each day in the area.

The treatment works came on stream in late 2012 and via the new sewer tunnel, links with both an old network and a long sea outfall.

A duty/standby SCADA system and four thin client workstations are housed in the central control room. The SCADA/PLC system runs all aspects of the WWTW, including wastewater and sludge processing, odour control and HVAC.

The SCADA system also includes an additional five operator stations mounted on motor control centres dotted around the site, all of which can be used to control the entire system including equipment up to 7km away. The remote sites are each fitted with at least one Mitsubishi Electric HMI, but these are configured to allow only local control, rather that providing access to the whole system.

The system extracts air to maintain the negative pressure and passes it through a series of acid and hypocaustic scrubbers. Several carbon filters ensure that no foul smells escape. The rate of extraction has been calculated and set so that the internal negative pressure is always kept constant.

The lowest point of the system houses a flushing chamber. From this point the wastewater flows by gravity through the town. From here, PLC controlled fixed speed pumps are used to lift the wastewater through a 40m shaft and then travel by gravity to a second pumping station located where it is raised 30m to then flow up to the highest point in the system. All subsequent areas are gravity fed. The first two set of pumps are fitted with softstarts, while the others use variable speed drives.

The key reason Mitsubishi PLCs were specified is due to their ease of setup and use and their ability to seamlessly integrate with products from other manufacturers. The the main communications network is Profibus, with which the PLCs and HMIs are compatible.
(formerly Enpure’s Principal Systems Engineer) sees the out-of-the-box usability of the Mitsubishi The design of the HMIs used throughout the project is based on ergonomic principles to provide intuitive ease of use and to allow greater integration of functions within the control system.


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