CASE STUDY:
Fosston, Minnesota
City Expands Existing Electromedia® System for Iron and Manganese Removal
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City Utilizes Leading Edge Controls for Water Filtration Operation

Background

“Where the Prairie Meets the Pines.” This is the city slogan for Fosston, Minnesota. It instantly conjures images of a tranquil, natural rolling landscape for this northwest Minnesota town of 1500 residents. Surrounded by farmland and with two wildlife refuges nearby, picturesque scenery abounds. It is here that computer and PLC technology have been optimized. This progressive, rural community networked their telemetry and plant controls to their full advantage for day to day operational cost savings, ease of system support, and simplicity in the automatic, unattended operation of their filtration system for arsenic, iron, and manganese removal with advanced, integrated controls.

The treatment facility is designed to treat well water on demand to fill a storage tank on the opposite side of the city from the wells through the filter plant. Chlorine is used for oxidation of the objectionable constituents and to maintain disinfection in the distribution system. The addition of the filter plant, backwash water reclaim system, chemical feed upgrades, and system controls were added on to the existing well house in this project that was constructed using Minnesota State Revolving Funds.

VPN Controls

The original plant control concept included modem access for the PLC systems, hardwired connections between the filter controls and the telemetry system, an autodialer for alarms with its own phone line, a dedicated telephone line for signal from the water tower for level, and a plant telephone. This would have involved six phone line connections. During the progression of the project, the control system was modified. The dedicated line was kept, one phone line remained in service for the autodialer, with DSL service added for the telemetry computer at the treatment plant. The monthly phone bill was significantly reduced. The system telemetry computer and filter control panel are connected via an ethernet connection that is built around a virtual private network (VPN). The ethernet communications eliminated the hardwired connections between the two control systems. On-line real-time assistance for either the telemetry or filter control panel can be provided from anywhere there is an internet connection. In the best cases, the remote connection to the controls is viewed at DSL speeds. (Phone line modem connections run at baud rates of 19,200 or about five times slower.) The collaborative effort of the design engineer, the filtration equipment supplier, the telemetry supplier, and the end user developed this simple system.

The VPN set up also allows the water department personnel remote access to telemetry and plant controls with a PC access program. Either from city hall or from a water department laptop, operators or management are able to respond to alarms from the autodialer more quickly than driving across town to the plant.

The operator interface screens of the filter control panel have been mirrored onto the telemetry system. This integration of software between the filter system controls supplier and the telemetry supplier benefits the client with a seamless set of familiar displays at all access points. This access allows for resetting of alarms remotely. Operators can change operational setpoint for flows of the well pumps and backwash reclaim pump.

Demand

Water demand in Fosston does not see much seasonal change. There are some local industries that use large water volumes through the winter, but use significantly less in the summer. So, as household demand goes up in summer time for filling pools, watering lawns and gardens, washing cars, etc, the industrial demand drops. To meet these system demands, the operation of the plant and well is based on level setpoints in the water storage tower. There is a start and stop level. A secondary start level, at a lower setpoint than the first, increases the well flow through the plant. This higher flow is maintained until the tower is filled. This prevents falling behind in storage on peak demand days.

In addition to operational setpoints, several pages are available for trending of process levels, water levels, pump operations, and pump run times. Data may be displayed for the current day, prior day, and totals.

Plant Design

The plant design by KBM, Inc. of Grand Forks, North Dakota also utilizes variable frequency drives for well pumps, allowing for flow ranges of 200 to 700 gallons per minute (gpm) from three deep wells, as selected by the plant operator and controlled by the filter system PLC. The chemical feed systems adjust automatically to the flow conditions. With automatic controls of the well pumps and chemical feed, the operation of both is optimized, reducing operating costs and minimizing operator responsibilities for day to day plant functions. This leaves more time for distribution system maintenance and upkeep, and response to consumer needs.

Backwash

Water from the four minute backwash and one minute purge (filter to waste) cycles of each filter is sent to the reclaim tanks. After a settling period, where the iron and manganese treatment residuals settle out, the supernatant is blended with the well water at the headworks of the treatment plant. The recycling pump is also controlled by a variable frequency drive to ensure to maintain the reclaim flow at ten percent of total flow when the filter is in operation. More than ninety nine percent of the water used for backwash and purge is recycled.

Conclusion

Iron, manganese, and arsenic in the raw water is as high as 2.0, 1.0, and 0.013 mg/L, respectively. Utilizing Filtronics Electromedia I filtration system, the treated water from the facility is usually less than 0.015 mg/L with many non-detectable results for iron and manganese. Arsenic is reduced to below detection limits.

While there is a straightforward, simplicity to life in the northern plains, Fosston’s Water Department has utilized technology in the concept, design, and execution of the control system of their water plant that many larger utilities have yet to utilize. As a result, it has reduced day-to-day operating costs, simplified system support and enabled the automatic, unattended operation of its filtration system.