The filter block assets at Langham WTW, some of which dated back to 1931 when it was constructed, were showing their age and in need of investment. Some investment was already yielding tangible benefits through the greatly improved performance of the backwashing process and the works as a whole.

In 2013, a contract was awarded to IWS, following a competitive bid process, to undertake the remaining upgrade works. This, in brief, consisted of a complete refurbishment of filter 5 (which had been out of service for some years following a catastrophic failure of the under drains), new backwash pumps, new MCCs and ICA panel, new actuated outlet valves, backwash valves and additional launders fitted in the external filter shells.

The electrical automation of the washing process was installed with additional equipment highlighted below:

• The replacement of the instem and pump starters with new local starters, incorporating new inverter drives and new Allen Bradley PLC complete with new control software
• Installation of two new Ideal backwash pumpsets and flow meters including the associated isolation valves, non-return valves and pipework
• Installation and commission of a new nozzle and lateral under-drainage system in filter No 5, together with new air pipework and media
• Installation of a new second launder, a new inlet channel and modifications to the existing baffle wall

The works required the modification of the existing lauder channels so dual lauders could be installed to increase the wash rate. In addition to dual lauders being installed the old mechanical valves were removed and electrical automated valves were installed to regulate the flow through the filters by ultrasonic monitoring equipment.

Benefits Delivered

The successful completion of the work ensured an increase of the backwash rate to a maximum of 35 m/h. This increase improved the expansion of the media during washing. The close working relationships that developed between the contractor, the investment delivery team and the production team at Langham WTW was also a significant contributing factor in the success of this project.

“The success of this project was partly down to a detailed contract and the right choice of contractor to deliver it. The expertise of IWS and their key suppliers, was invaluable, especially given the demanding programme and the risks and constraints that had to be managed during the construction phase”