To meet the new Department of Natural Resources discharge limits, the city of Harrisonville, Missouri, set out to upgrade its wastewater treatment plant.
When the city of Harrisonville, Mo., set out to upgrade its wastewater treatment plant in 2007, the focus was on meeting new Department of Natural Resources (DNR) discharge limits and improving peak flow handling.
Thanks to some innovative design techniques, when construction was completed on the plant in September 2011 the city began reaping a bonus from the improvements — significant cost savings as a result of reduced energy consumption. Burns & McDonnell provided planning, design and construction administration for the project.
The upgraded plant fulfilled the city's initial objectives by meeting new permit requirements, including effluent ammonia limits and new wet weather peak flow management rules. The revised wet weather management rules precluded the city from bypassing the treatment process and discharging wet weather peak flows from an on-site storage basin. The improvements increased wet weather peak flow treatment plant capacity from 4.5 million gallons a day (MGD) to 8 MGD, mitigating reliance on the peak flow storage basin.
But it was a new aeration basin using fine bubble diffusers instead of coarse diffusers, along with revised treatment process operations, that enabled the plant to run more efficiently and produce cost savings.
"Biomass solids represent the waste consumption power of the treatment process. By balancing the biomass solids with incoming waste, or food, the treatment process runs more efficiently, and power consumption is reduced," says Jeff Barnard, environmental section manager in the Burns & McDonnell Water Group. "Further, with fewer biomass solids under aeration, the liquid being aerated was less concentrated, which also resulted in reduced power consumption due to increased oxygen transfer efficiency."
Eric Patterson, assistant director of public works for Harrisonville, says the new method of operation has decreased mixed liquor suspended solids (MLSS) from around 7,000 milligrams per liter (mg/L) to 2,500 mg/L. MLSS is the concentration of suspended solids in an aeration tank during wastewater treatment.
"It wasn't the way our plant was used to operating. We had to make adjustments, but our operators have been carrying the lower level for a year and a half now and have had no significant issues," he says.
It's Adding Up
The new aeration basin and modified treatment process, combined with an additional tank and new blowers that are cycled at the aerobic digesters, have saved the city $4,000 to $5,000 a month.
"We started this project with the goal of meeting the new DNR regulations and increasing our capacity to handle heavy flows during storms," Patterson says. "The reduction in energy costs was not part of our original plan. That was an added benefit. We're pleased with the results."
Cost savings will be passed on to the city's fund for water and sanitary sewer projects.
Construction on the wastewater treatment plant also included a new code-compliant administrative building, and space has been allocated for expansion, positioning the plant for handling future effluent limits, including those involving nutrients and disinfection.
The upgraded plant provides capacity to meet the city's needs as it grows, up to a population of 20,000, double its current size.
For more information, contact Jeff Barnard, 816-822-3834.