The results can prove very costly whenever water makes contact with the electrical controls in a wastewater treatment plant. It can be even worse in the dead of night--in the snowy grip of winter--when plant operators must rely on needed expertise and equipment located many miles away. Those factors really tested a plant’s major service supplier.
Consider the incident in January at the secondary treatment pump station within the activated sludge plant that serves 22,400 customers in the city of Zanesville, Ohio. That stage of the 13 million gal per day facility removes ammonia and biological phosphorus supplemented by the addition of ferric chloride, and disinfects with sodium hypochlorite before discharging the final effluent into the Muskingum River.
At precisely 4:38 p.m. on Jan. 5, 2010, the plant’s SCADA system sounded an alarm that an electrical failure had occurred at the building housing the wetwell for four, 135-hp Flygt submersible pumps that advance the plant flow to the secondary treatment’s trickling filters. The mechanic responding to the incident discovered a stream of clear water pouring from beneath the door of the building housing the pumps. Ted Ansel, the plant’s maintenance foreman, quickly ordered the potable water supply shut off and began assessing the situation. The resulting bypass of the plant’s primary treated flow was allowed to reach the river for the first time in 20 years.
“A 2-in. potable water line installed in 2006 for a wash station used to hose down the pumps during inspections had ruptured at a ball valve, tripped the MCC and taken out the four pump drives,” he said. “We shut down the water line and placed a call to the ITT Water & Wastewater Flygt Maintenance Center in Milford, Ohio, and then began disassembling and inspecting everything that might have been affected.”
The Flygt emergency response group, comprised of Ray Sizemore, John Gray and Scott Myers, the shop leader, headed out for the 130-mile drive with two soft start units, 8-in. hose and enough new electrical cable to connect to the existing power supply. The temporary fix would hopefully restore the pumps and stop the bypass pending permanent repairs. Unfortunately, the attempted test start of the first pump connected to power revealed the main breaker was ruined on the MCC. After gaining the necessary approvals, Myers called the Milford Center and had the remaining technician dispatched to Zanesville with two trailer-mounted, 8-in., diesel-powered pumps. The mobile setup with the 150-hp diesel-powered pumps is kept in Milford for major dewatering assignments and offered the needed capacity to temporarily restore the plant flow back through secondary treatment.
“Fortunately, the flow from primary treatment was fairly clean but the ammonia level left us out of compliance by 4:38 am,” he noted from his SCADA report. “The five-day average for BOD might have been a little high but ammonia is more critical because it is measured daily here.
“The Flygt team quickly had the trailer-mounted pumps on site and operating to restore the secondary treatment. The crew was professional and the response was great. We were down about one day and by 1:30 p.m. the afternoon of Jan. 6 we had restored the secondary treatment and ended the bypass. The plant operated with the diesel pumps for five days until electrical service and the first two pumps were brought back online.”
In the wake of the damage, the ruptured line was initially attributed to the unheated environment in the building. The ruptured ball valve was retrieved for forensic examination.
“I doubt it was caused by the temperature inside the building because we’ve had many comparable winter cold spells since we installed the potable water line,” Ansel explained. “It was probably a fluke."
The Flygt facility in Milford is part of a worldwide network of branches that provides routine and emergency response services to customers. Myers said his team typically responds to “…a couple of outages a month” to restore critical processes. Problems range from flooding situations, effluent bypasses into receiving streams or other dire issues involving crippled pumps. As with most specialists, Myers was already experienced when he joined the branch where the field personnel undergo periodic training. He has a total of 15 years in the field, with the last five years with Flygt operations of ITT Water & Wastewater.
According to Ansel, the damages had an impact on the plant's O&M budget of approximately $87,000. Without the prompt actions that were taken, the incident would have been much more costly.
Source: ITT Water & Wastewater U.S.A.
