Four Mile Creek was originally a 1.5 MGD facility. Professional Engineering Consultants, P.A. (PEC) was retained to study and design improvements to the facility to handle flows and loadings associated with the increased service area and projected growth. As a result of this study, the treatment facility was planned with the following design values:
• Average Daily Flow thru Treatment Facility.......3.0 MGD
• Peak Flow thru Treatment Facility........................6.0 MGD
• Wet Weather Flow Holding....................................6.0 MGD

The plant is capable of expansion through paralleling of components to accommodate a future average daily flow of 6.0 MGD, a peak flow of 12.0 MGD. The treatment plant process was designed to meet water quality standards as defined and anticipated by the Environmental Protection Agency (EPA) and regulated by Kansas Department of Health and Environment (KDHE). The following objectives were attained by the design team.

The facility:
• Meets the permit limitations expected within the next 10 years.
• Incorporates capacity expansion in phased approach to guide subsequent expansions.
• Provides a reliable and simply operated facility while minimizing odor.
• Maximizes the use of original facilities wherever possible.
• Minimizes capital construction cost, operational cost and staffing requirements.
• Maximizes automation and remote monitoring capabilities.
• Optimizes extraneous flow holding facilities and sludge processing and biosolids handling.

Process Design
Flows arrive at the treatment plant site, enter the plant by gravity at the main pump station which was refitted with new belts and sheaves on the three original influent pumps to increase pump operating RPM and provide the required peak pumping capacity and redundancy. Two of the pumps have variable frequency drives (VFDs). A climate-controlled electrical room was constructed above grade to house all electrical equipment for the station. Flow is then pumped into the headworks where two screening channels were retrofitted with new fine screens. Two new vortex grit removal units were constructed west of the existing building.

The biological treatment process follows the headworks and includes the new anaerobic/anoxic basins to facilitate phosphorus removal and denitrification. No additional aerobic volume was required to double plant capacity. Biological Nutrient Removal provided a solution to the capacity problems through the addition of anaerobic and anoxic zones. The structure was redesigned to accommodate a new aeration system with increased oxygenation capacity for BOD removal and nitrification.

The aerated flow enters final clarification in one of two basins. The original basin was refitted and a new larger basin was constructed to supply additional solids loading capacity, as well as to provide redundancy. The original disinfection and re-aeration systems were retained. An anoxic recycle pump station was required to return MLSS from the aeration basin back to the anoxic basin. The pumps are housed in a new building which also holds the new pumps for the RAS, WAS and scum as well as the blowers for two new aerobic sludge holding/digestion basins. Upgrades were made to the emergency power generation capacity, power distribution systems and plant control systems.

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