Automatic water main flushing reduces costs and improves water quality

Most water distribution systems have areas where there are pipelines that may not have sufficient demands to keep the detention time short enough to maintain minimum disinfectant residuals. Long-term low disinfectant residual conditions within a water pipeline not only encourage biofilm growth, they also increase demand for disinfectant. This makes it more difficult for operators to maintain desired minimum disinfectant residual levels in the distribution system.

A recognized solution to this water quality problem within distribution systems is periodic flushing of the pipelines. This process allows for the turnover of water in the line, flushing the water that has a low disinfectant residual and the biofilm from the inside surface of the pipe.

In an effort to spend less time manually flushing hydrants and focus more time on repairing leaks to reduce non-revenue water loss, one small rural town started investigating automatic flushing systems. Its 150 km of un-looped distribution pipe had historical water losses of up to 30%. A small operations team was responsible for monitoring two water plants, reading 700 meters, repairing leaks and maintaining water quality.

Automatic water main flushing systems

Unidirectional flushing is a traditional method used to manually flush water lines for biofilm removal and water quality maintenance. Since its introduction almost 20 years ago, automatic flushing has developed into a widely accepted and preferred alternative. Automatic flushing minimizes disinfectant residuals in water distribution systems by flushing at predetermined and programmed events.

With this approach, smaller volumes of water can be used on a more frequent basis to maintain minimum disinfectant residual levels and reduce biofilm growth. This, in turn, results in a reduced disinfectant demand within the pipeline which allows for extended detention times prior to the loss of disinfectant residual. Implementation of automatic flushing also results in lower water use per flush event. Therefore, water utilities use less resources, thus lowering operational costs associated with the maintenance of a flushing program.

The solution

After careful investigation and analysis, the town purchased and installed two Hydro-Guard® HG-1 Basic/S flushing systems from Mueller Company. This model provides economical, programmable and automatic flushing capabilities with either a 25 or 50 mm controlled flow diaphragm valve. It can be used for virtually any line size application in warm climates. A cold climate model is also available.

The Hydro-Guard has a removable multi-event handheld programmer that can be programmed to flush a water line multiple times a day, up to seven days a week, with flush durations from one minute to four hours. All key system management components are located above ground for ease of access. The HG-1 model also features oversized vents for energy dissipation, to minimize erosion during discharge.

Rather than spending valuable man-hours manually flushing the system during the day, operations staff has programmed the units to flush between 2:00 and 3:00 a.m. while residents are sleeping. After installing the Hydro-Guard units, water losses dropped from 30% to between 3% and 8%.

Since the units allow precise control of the amount of flushed water, chlorine usage has dropped. Previously, three chlorine cylinders were used every month, at $400 per cylinder; now, three cylinders last seven to eight months. This is a $8,000 per year saving. Also, the town has seen a dramatic improvement in water quality, evidenced by fewer customer complaints.

Deron N. Austin, PE is with Mueller Company. This article appears in ES&E’s November/December 2015 issue.