Improvements made at Seneca Wastewater Treatment Plant
Keeping the bugs in leads to cleaner water
Technology improvements are considered successful when all the bugs have been worked out. But with improvements completed recently at the Metropolitan Council’s Seneca Wastewater Treatment Plant, the bugs remain in place and are performing splendidly.
Nick Thayer, of general contractor Madsen-Johnson, installs one of the new pumps in a tunnel below the wastewater treatment tanks.
These “bugs” – as they are affectionately called – are the bacteria that consume pollutants in the wastewater treatment process. Recent improvements in this biological process at the Seneca Plant in Eagan were aimed specifically at making the bugs remove greater amounts of phosphorus before the treated wastewater (effluent) is discharged to the Minnesota River. Phosphorus is an essential element for sustaining life, but too much remaining in the effluent promotes excessive algae growth and degrades water quality.
New phosphorus removal requirements
The Seneca Plant has voluntarily removed phosphorus for a number of years, but it needed to step up those efforts to meet a new clean-water-discharge permit limit that went into effect in August 2008. The plant now can discharge no more than 1 milligram of phosphorus per liter of effluent, on an annual average.
The wastewater entering the plant typically has a phosphorus concentration of 6 to 8 mg/l, and concentrations in the effluent for the last several years have been in the 1 to 3 mg/l range. Since the improvements went online this summer, the phosphorus concentrations in the effluent averaged 0.49 mg/l in August and 0.65 mg/l in September.
“The Seneca Plant is now removing about one ton of phosphorus a day,” said Bill Moore, general manager of Metropolitan Council Environmental Services, a division of the Council. “This is a result of updated mechanical and instrumentation equipment installed at the plant, as well as some top-notch work by our staff and contractors in designing, installing, programming and operating this equipment. These and other improvements to the plant are done while we continue to treat wastewater 24 hours a day.”
Phosphorus is removed as wastewater passes through these aeration tanks.
The phosphorus-removal upgrades are part of approximately $15 million in plant improvements being completed in 2008-2009. Another major part of the work is replacing the aging disinfection system, which operates from spring through fall.
Upgrading other plant processes
The current gaseous chlorine disinfection system will be replaced this winter with a safer and more secure liquid bleach system. Liquid sodium hypochlorite will be used to kill the vast majority of pathogenic bacteria that remain in this final stage of the treatment process. Then liquid sodium bisulfite will neutralize any remaining residual chlorine in the water, which otherwise could adversely impact aquatic organisms in the river.
Other improvements include:
- Replacing some two dozen programmable logic controllers (PLCs) that control all operations in the plant. The state-of-art equipment will be the same as what was installed during a recent upgrade of the Empire Plant and will be installed in 2009 at the Blue Lake Plant. This will help operations and maintenance staff who work at multiple facilities.
- Cleaning and rehabilitating a variety of odor control systems. The work will be done during the winter when odors typically are at lower levels, and temporary carbon-filtration units will be used as needed.
- Replacing most of the plant’s heating, ventilation and air conditioning equipment, and adding sludge pumps to assure necessary redundancy in the system.