Water and Computing: A Tour of Headingley Water Treatment Works Followed by a talk on Telemetry

Date/Time:
Tuesday 15 April 2008

Speaker:
Dr Simon Earl, Site Manager and Ed Lawson, Telemetry Architecture Manager

Description:

This year’s April visit was held at Yorkshire Water’s Headingley Water Treatment Works. The evening included a tour of the site by the site manager, Dr Simon Earl, and a talk by Telemetry Architecture Manager, Ed Lawson.

Background

Headingley Water Treatment Works was completed in 1996 as a replacement for the old slow sand filtration works on the opposite side of Otley Road, Far Headingley in Leeds. The site is now able to produce a maximum of 120 million litres of water per day (roughly equivalent to 48 Olympic size swimming pools).

The works is supplied from the Washburn Valley Reservoirs and the River Ouse; water quality problems to be overcome include high levels of colour, iron, pesticides and algae. The water is treated by a complex three stage process consisting of flocculation and flotation, filtration through a sand bed treatment with ozone and filtration through a carbon filter bed.

The Treatment Works

Dr Earl started the evening by leading a guided tour around each stage of the treatment works, pointing out where Telemetry is used at various stages along the way. The tour started at the works inlet, which is gravity fed from source. The water then enters the flash mixers, where it is mixed with hydrated lime for pH adjustment and metal compounds for coagulation.

From the flash mixers, the water travels forward through the flocculators. These are tanks with very slow stirrers designed to improve the size of the floc particles formed by the reaction between the chemical coagulant, the colouring matter and turbidity present in the water (how cloudy the liquid is).

The flocculated water passes forward into the dissolved air flotation tanks. In these tanks the incoming water receives jets of water supersaturated with air. The fine air bubbles rise to the surface of the tank, attaching themselves to floc particles as they rise. This brings the floc to the surface as a floating sludge. Brushes travelling on the surface of the water move the sludge across the tank and over a weir at the outlet end of the tank.

The sludge produced moves under gravity to a pump well and is disposed of to sewer. The water from the dissolved air flotation tanks enters the first stage filters after receiving a dose of lime slurry to render the pH of the water neutral. The water gravitates through a bed of sand supported on gravel to remove any remaining suspended solids.

The filters run for 30 hours and then they are cleaned. The cleaning procedure, known as backwashing, involves draining the water down almost to sand level, disturbing the sand bed with compressed air, then passing water up through the sand to remove the accumulated solids which are sent to the sewers.

The choice of second stage of treatment depends upon the blend of raw water. If the blend contains a high proportion of Ouse water then Pesticide removal will be the process used. If the blend is predominantly Washburn and thus contains manganese then the manganese removal filters would be used.

After the second stage filters, the water receives a top up dose of sodium hypochlorite for disinfection of the water and then the water is held for 1 hour in a contact tank to stabilise before being distributed to supply the Low Level areas of Leeds.

The Control Room

After the Treatment Works, the tour moved on to the Control Room, where Telemetry Field Engineer Paul Flavell showed the telemetry in action. Paul demonstrated the SCADA system (Supervisory Control And Data Acquisition), which is used to monitor the various stages of the works. SCADA allows the engineers at the site (or remotely from home!) to view a high level representation of the works in image form, or to drill down into each stage to gain more detail such as the level or flow into a particular tank, or the amount of chemicals being dosed.

Telemetry Talk

The tour then returned to the meeting room where Ed Lawson gave a talk on the use of Telemetry in Yorkshire Water. Ed started by giving an idea of just how big Yorkshire Water is by telling us that it has 86 water treatment works, 600 waste water treatment works, and over 60,000km of clean and waste water networks.

Telemetry stats soon followed, which included the fact that Telemetry monitor over 103,000 “points” across Yorkshire, using 60,000 instruments to return over 2 million trend values a day. Ed then went on to talk about the various systems Yorkshire Water use in conjunction with the Telemetry devices, including RTS (Regional Telemetry System), which the Telemetry Team has an SLA with the business for an uptime of 99.8%, 24 x 7.

RTS receives signals from Telemetry devices when they are in an “alarm state”, such as tanks being too full or pressure being too high. These alarms are constantly monitored in the ROCC (Regional Operation and Control Centre) in Bradford so that they can be reacted to straight away. Ed then explained how the business also uses these readings within complex reporting tools so that YW can plan for the future.

Conclusion

The tour from inlet to actually sending the water down to the inhabitants of Leeds City Centre showed just how complex the process of treating water is, and how Telemetry is becoming increasingly essential to ensuring Yorkshire Water completes the process in a safe and efficient manner.