Siemens joins war on Crypto

Compliance with the latest DWI regulations designed to prevent Cryptosporidium outbreaks has led North West Water to sign-up the services of Siemens Industrial Projects and Systems.

“I welcome these new controls which further protect public health against this nasty bug… the new regulations will ensure that water companies take appropriate precautions against water-borne outbreaks occurring. The DWI will implement these new regulations rigorously,” commented chief drinking water inspector Michael Rouse following the DWI’s announcement that water companies which don’t adequately treat their drinking water supplies to prevent Cryptosporidium will be liable for criminal prosecution. New regulations have since been introduced which require water companies to:

  • carry out risk assessments to identify those sites which are most at risk
  • carry out continuous sampling and daily analysis of treated water where a significant risk is found
  • treat the water to a defined standard.

In response, water companies have initiated projects to control and continuously monitor the presence of Cryptosporidium in drinking water. In one such initiative, Siemens Industrial Projects & Systems (IPS) has completed a £1.2m fast-track contract for North West Water (NWW) involving the enhancement and upgrading of instrumentation, treatment systems and controls at WTWs in Manchester, Lancashire and Cumbria. The contract was one of two let under NWW’s regional Cryptosporidium removal stage 3 Project, initiated in response to recommendations made in the Badenoch and Bouchier reports. To meet NWW’s schedule, measures had to be in place by the end of March 2000, giving Siemens IPS 30 weeks to complete the contract.

The work formed part of a £1.6Bn capital investment programme Bechtel Water is managing on behalf of NWW. Although Siemens had already worked successfully with both Bechtel and NWW, the company won the contract by competitive tender.

Work in progress

The brief included design, installation and commissioning of filter monitoring systems; extending automation of the filter backwash water system on one site and adding a new dissolved air flotation (DAF) sludge processor at another. The contract covered all mechanical and electrical (M&E) work, installation of programmable logic control (PLC) systems and improving turbidity monitoring. Work was undertaken at Piethorne, Paddy End, Sweetloves, Castle Carrock, Barley, Worsthorne, Laneshaw, Mitchell’s House and Padfield WTWs.

One of the main requirements of the contract was to update the turbidity monitoring systems at each site. Turbidity monitors give a guide to the performance of filtration systems by monitoring changes in the quality of samples taken from the filtered water. Siemens installed constant, dedicated turbidity monitoring/sampling systems at each site, usually on the raw water inlet, filtered water outlet of each primary filter, the common primary filtered water outlets and any supernatant returns to the process stream.

At Piethorne WTW, there was a need to automate the filter backwash recovery systems to provide a ‘fill-and-draw’ system to ensure all supernatant and sludge was removed from each tank before it was re-filled by subsequent washes. This ensured the separation of liquids and solids. At Castle Carrock, Siemens installed a new DAF sludge processing system, enabling the DAF and backwashwater sludges to be treated separately prior to removal from site for disposal.

Working at nine sites spread over 30 miles required good project coordination skills and the ability to select reliable sub-contractors from a wide range of disciplines in order to create focused team.

As part of the Badenoch and Bouchier reports’ recommendations, utilities were required to continuously monitor treated water for Cryptosporidium at high risk sites. A minimum standard of an average of <1 oocyst/10 l was set.

Successful completion of the first stage of NWW’s Cryptosporidium removal project led to Siemens being chosen to implement the monitoring phase, initially at three sites.

Because the DWI imposed strict regulations regarding the type and installation of sampling equipment, Siemens was faced with having to integrate DWI-specified equipment with a variety delivery systems. This meant advising on siting location, the design and installation of associated equipment and pipework and the tagging of each instrument to prevent unauthorised access.

The sampling system was programmed to extract 1,000l/d which is monitored for turbidity and passed through the Cryptosporidium filter. Each week the filter is removed and taken to a laboratory for analysis, the results of which are made available to the DWI. Since the initial contract, Siemens has been chosen to install monitoring equipment at 13 other sites and selected to tender for the remaining 38 sites.

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