September/October 2010

System Integration

Whitecourt receives superior drinking water

Water treatment plant upgrades system with new microfiltration treatment, PLC control systems, electrical, instrumentation

FAST FORWARD

  • The water treatment plant upgrade was a two-stage, multi-year project spanning from 2002 to 2009; staging upgrades was key to project success.
  • Stage 1 required the construction of a new distribution pump house to replace the high lift pumps in the water treatment plant.
  • Commissioned in April 2009, the water treatment plant now has capacity of approximately 18 ML/day.
 
By Wally Ingham

The Town of Whitecourt's Water Treatment Plant (WTP) was originally commissioned in 1980 as a conventional treatment system to provide a capacity of approximately 6 megalitres (ML)/day. Its treatment process included rapid mixing and coagulation, a solids contact clarifier, three dual media rapid sand filters, post chlorination, and fluoridation.

white1In late 2002, the Town of Whitecourt selected Stantec Consulting Ltd. to perform a detailed audit of the WTP, which subsequently identified concerns related to:

  • WTP's capacity of approximately 6 ML/day being unable to meet the Town's current and future potable water demands
  • Insufficient total clarifier detention time, mixing and flocculation, and recirculation rates, resulting in non-filterable turbidity carry over to the rapid sand filters at flows greater than 6 ML/day
  • Insufficient chlorine contact time, primarily due to a lack of circulation through the adjacent potable water reservoir
  • With raw water Giardia concentrations regularly exceeding 100 cysts/100 L, requiring a Giardia reduction credit greater than 5.0-Log (based on Alberta Environment's 1996 standards and guidelines), the WTP's 2.5-Log Giardia reduction credit was determined to be insufficient

Following the detailed audit, Stantec was further commissioned to determine how the WTP could be cost effectively upgraded as it had reached its capacity and did not meet current standards for contact time and Giardia reduction. As a result, the Town of Whitecourt became the first in Alberta, Canada to install microfiltration pressure membranes.

The WTP upgrade became a two-stage, multi-year project spanning from 2002 to 2009. Stage 1 involved baffling the adjacent potable water reservoir and construction of a new distribution pump house to take advantage of the new baffling arrangement. In addition, Pall Corporation Microza MF pressure membranes were installed in parallel with the existing conventional treatment process, providing the redundancy required for the Stage 2 upgrades to proceed.

Since commissioning, in 2005, the Pall Corporation pressure membrane system has performed exceptionally well and has been granted a 4.0-Log Giardia and Cryptosporidium reduction credit from Alberta Environment and tripled the WTP output without expanding the plant's footprint.

Stage 2 consisted of pre-treatment upgrades involving the conversion of the existing filter chambers and re-carbonation channel to provide three stages of flocculation, and adding Lamella inclined plate settler packs into the existing clarifier. Commissioned in April 2009, the WTP now has capacity of approximately 18 ML/day, even when raw water turbidities are as high as 1,500 nephelometric turbidity units (NTU).

Electrical, instrumentation, controls updating

Stage 1 required the construction of a new distribution pump house to replace the high lift pumps in the WTP following the potable water reservoir baffling. The new pump house is designed for four 125 horsepower vertical centrifugal pumps (two variable speed and two fixed speed). Currently, only one variable speed pump and one fixed speed pump is installed. To meet the utility company's harmonic requirements, an 18-pulse Variable Frequency Drive (VFD) from Allen-Bradley (A-B) was supplied for the variable speed pump. The VFD was also supplied with a bypass fixed speed starter in case the VFD developed problems. Of the two pumps installed, only one pump is allowed to run at any time with the variable speed pump always the lead pump.

The new pump house is equipped with A-B ControlLogix PLC with touchscreen HMI for monitoring and local control of the pumps and communicates back to the WTP via Ethernet link. Pump house instrumentation includes ultrasonic level, monitoring of the pump well, discharge flow by magnetic flowmeter, and discharge pressure. The pumping scheme is the basic pressure on/flow off, with the VFD pump always the lead. The fixed speed pump is equipped with a hydraulic actuated pump control valve to prevent starting and stopping surges.

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The pump house has a secondary purpose, which is to keep the existing Hilltop reservoir full. The Hilltop reservoir used obsolete Quindar tone shift telemetry units over dedicated leased telephone lines to the WTP to control the old high lift pumps. During Stage 1, the Quindar was replaced with A-B MicroLogix PLC and phone lines redirected to the new pump house. During periods of low flow, and acceptable Hilltop reservoir level, all distribution pumps are shutdown and the Town of Whitecourt is supplied water from the Hilltop reservoir.

At the WTP, instrumentation and control upgrades for Stage 1 were provided primarily by Pall Corporation in the form of a main A-B ControlLogix PLC and remote drops for each filter rack and CIP system. Pall Corporation also provided the main operator HMI station in the WTP office, remote programming modem, and Ethernet router. This allowed the WTP to monitor the new pump house PLC and for Pall to have the ability to provide remote troubleshooting and programming upgrade services.

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A SLC 505 was installed in the WTP's existing relay panel to provide minimum interfacing to the old controls required to remain under Stage 1. In addition to the instrumentation supplied by Pall Corporation, the WTP's old Foxboro influent magmeter was replaced with a current Rosemount unit, which could provide a 4 to 20 mA signal to Pall PLC; and all Healy Ruff float level units were replaced with ultrasonic level monitors using the existing standpipes. The remaining WTP pneumatic instrumentation was left in place until the Stage 2 upgrade.

The WTP 600 Volt electrical service was upgraded to accommodate the new pressure membrane and Clean-In-Place (CIP) systems; fortunately the original designers had provided for future upgrading, which resulted in minimal WTP downtime. The existing 30-year-old motor control center (MCC) was retained with only the old high lift pumps being decommissioned due to the construction of the new pump house. To accommodate the new pumps, air compressors, CIP heaters, etc., supplied by Pall Corporation, a new A-B MCC, with DeviceNet, was provided with VFDs, starters, and breakers. All of the new electrical and control equipment were all networked together using DeviceNet resulting in reduced installation material, labor, and commissioning time.

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Stage 2 of the WTP upgrade was when the fun began. All the existing pneumatic filter controls, filter consol, old relay logic, old annunciators, and decommissioned pumps were removed. Additional I/O was added to the SLC 505 in the old control panel to replace the old relay logic. The existing MCC was required to remain in place, but with removal of old starters and rearranging remaining starters, there was sufficient space to install six new small VFDs, specially fabricated with DeviceNet interface, to fit the old MCC for Stage 2 flocculator and chemical feed pump additions. In addition, DeviceNet interfaces were added to select existing starters such as the clarifier rake drive, allowing control through the new Pall Corporation PLC/HMI control system. Finally, the old annunciator alarm and status light boxes in the WTP's office were removed with all alarms and statuses switched over to the HMI. Arrangements were made with Pall Corporation and their programmers to provide the additional PLC programming and HM
I development required for the final WTP configuration.

A Stage 3 had been planned, whereby the river water intake pump house PLC would be upgraded to match the WTP PLCs once Stage 2 was completed. This upgrade was moved ahead and added into Stage 2 and consisted of replacing an obsolete GE PLC with A-B ControlLogix, with a local control panel touchscreen HMI communicating back to the WTP via Ethernet using an existing direct buried multi-pair instrument cable.

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Issues, challenges

At the beginning of Stage 1, renovations to the existing WTP, to prepare for the Pall Corporation pressure membranes, it was found the fluorescent light fixtures contained PCBs requiring total fixture replacement.

During commissioning and initial operation of the new reservoir pump house, the variable speed pump was found to have a vibration, of course just at the optimal operating speed. Despite numerous efforts and investigations, the pump vendor could not eliminate the vibration. The solution was therefore to program out the speed range of the vibration in the VFD. In spite of this, the pump operates well.

During Stage 2 commissioning of the communication link between the WTP and the raw water pump house, the link worked fine, but the A-B Ethernet module could not be configured to transfer the data between the two ControlNet PLCs. The solution to this apparent protocol incompatibility (signal conversion from RS232 to Ethernet) is still being investigated with A-B.

Overall, the project was a huge success, and the WTP currently has upgraded electrical, instrumentation, control, and SCADA systems. The operators currently have the capability to centrally monitor their entire system from the WTP. As an additional benefit, Pall Corporation included a dial-in modem in the main PLC, which has proved to be a big asset in assisting the plant to refine its treatment and operating systems by remotely troubleshooting and modifying the PLC operating program.

The major success of the Whitecourt WTP has resulted in additional contracts for microfiltration upgrades at other WTP's of the same vintage throughout Alberta.

ABOUT THE AUTHOR

Wally Ingham, P.E., is a senior electrical instrumentation engineer for Stantec Consulting Ltd. His e-mail is wally.ingham@stantec.com.

RESOURCES

 

 

Microfiltration for potable water treatment

Microfiltration water treatment systems are specifically designed to produce drinking water that meets today's stringent standards. The systems use a uniquely designed hollow fiber membrane that is mounted in enclosed modules or open frames to filter out solids and particulate matter from surface and ground water sources for potable water use.

Membrane filtration is a pressure (or vacuum) driven process that uses a semi-permeable (porous) membrane to separate particulate matter from soluble components in the carrier fluid, such as water. Microfiltration membranes act much like a very fine sieve to retain particulate matter, while water and its soluble components pass through the membrane as filtered water. The retained solids are concentrated around the fibres until they are backwashed and discharged as a waste stream from the membrane system.

Typical pore sizes range from 0.02 to 0.1 microns in size. Combined with the integrity of the sealing mechanism, virtually all of the fine matter, such as silica, bacteria, and parasite cysts, can be removed from the water being treated. Typical treated water quality from microfiltration systems meet the new standards requesting turbidity of <0.1 NTU, and also provide a physical barrier to pathogens such as Cryptosporidium and Giardia.

One of the key benefits of the microfiltration systems is the consistent quality they can produce, even when subjected to varying feed water qualities. The hollow fiber membranes are highly permeable, resulting in high water production rates, and consequently require a smaller building footprint than conventional filtration processes.

In addition, with the updated controls and instrumentation systems, system monitoring can now be carried out on-line, to provide WTP operators with technical support for troubleshooting and optimization that is only a phone call away.

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