Owensboro Municipal Utilities Wastewater Treatment Plant

1. INTRODUCTION

The Max Rhoads Wastewater Treatment Plant serves as the cornerstone of wastewater infrastructure for Owensboro and Daviess County, Kentucky. Operated by the Regional Water Resource Agency (RWRA)—an independent agency distinct from Owensboro Municipal Utilities—this facility is crucial to the protection of the Ohio River Basin. As the primary treatment facility for the region’s combined sewer system (CSS), the plant plays a pivotal role in managing both sanitary flow and wet-weather events.

With a rated design capacity of 15 million gallons per day (MGD) and a peak hydraulic capacity exceeding 30 MGD, the Max Rhoads facility utilizes advanced biological treatment processes, specifically Vertical Loop Reactors (VLR), to meet stringent Kentucky Pollutant Discharge Elimination System (KPDES) standards. In recent years, the facility has been the focal point of a massive operational overhaul, including the integration of a multi-million dollar deep tunnel system to mitigate Combined Sewer Overflows (CSOs), distinguishing it as a model for wet-weather management in the Ohio River Valley.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The RWRA system, anchored by the Max Rhoads plant, serves the City of Owensboro and unincorporated areas of Daviess County. The service area is characterized by a mix of dense urban residential zones, commercial districts, and significant industrial contributors. The collection system is complex, comprising over 500 miles of gravity sewer and force mains, supported by more than 80 pump stations. A defining characteristic of the service area is the historic downtown combined sewer system, which directs stormwater and sanitary sewage to the Max Rhoads facility.

B. Operational Capacity

The facility is designed for an average daily flow of 15.0 MGD. Current average flows typically range between 9 and 11 MGD during dry weather. However, due to the combined nature of the collection system, the plant experiences significant hydraulic peaking during precipitation events. The facility’s hydraulic profile is engineered to handle peak hourly flows of approximately 32 MGD. Flows exceeding the biological treatment capacity are managed through a sophisticated network of flow equalization basins and the newly constructed deep tunnel storage system.

C. Discharge & Compliance

Treated effluent is discharged directly into the Ohio River. The outfall is submerged to ensure rapid mixing and dilution. The facility operates under a KPDES permit administered by the Kentucky Division of Water. Strict limits are placed on Carbonaceous Biochemical Oxygen Demand (CBOD), Total Suspended Solids (TSS), Ammonia-Nitrogen, and E. coli. The plant consistently achieves high compliance rates, with removal efficiencies for BOD and TSS typically exceeding 95%.

3. TREATMENT PROCESS

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The Max Rhoads WWTP utilizes an extended aeration activated sludge process configured with Vertical Loop Reactors (VLRs), followed by UV disinfection. The treatment train is designed to handle variable loadings characteristic of a combined sewer system.

A. PRELIMINARY TREATMENT

Raw wastewater enters the headworks where it undergoes aggressive physical screening. The facility utilizes mechanical bar screens (typically 6mm or similar step-screen design) to remove rags, plastics, and large debris. Following screening, flow enters vortex grit removal chambers. These systems utilize centrifugal force to separate inorganic solids (sand, gravel, coffee grounds) from the organic waste stream. Grit is classified, washed, and dewatered before disposal to protect downstream pumps and clarifiers from abrasion.

B. BIOLOGICAL TREATMENT (Vertical Loop Reactors)

The heart of the treatment process is the Vertical Loop Reactor (VLR) system. Unlike accurate conventional aeration basins, VLRs function similarly to oxidation ditches but are “flipped” on their side, utilizing a deep tank design with upper and lower compartments.

• Aeration: Surface aerators (discs or rotors) drive oxygen into the mixed liquor and propel the flow through the loops.
• Process Control: The VLR design allows for simultaneous nitrification and denitrification by creating aerobic and anoxic zones within the loop. This configuration provides high energy efficiency and a smaller footprint compared to conventional ditches.
• DO Control: Dissolved Oxygen is monitored in real-time via SCADA to modulate aerator speeds, optimizing energy consumption.

C. SECONDARY CLARIFICATION

Mixed liquor from the VLRs flows to secondary clarifiers. These large circular tanks allow biological floc to settle out of the water column via gravity. The settled solids are collected by rotating rake arms and directed to the center hopper. A portion is returned to the head of the biological process as Return Activated Sludge (RAS) to maintain the microbial population, while excess biomass is removed as Waste Activated Sludge (WAS).

D. DISINFECTION

Historically, many plants in the region used chlorine gas. However, the Max Rhoads facility utilizes Ultraviolet (UV) disinfection. The effluent passes through channels containing banks of UV lamps. The UV light penetrates the cell walls of pathogens (bacteria and viruses), scrambling their DNA and preventing reproduction. This method eliminates the need for hazardous chemical storage and dechlorination chemicals, ensuring the effluent is safe for the aquatic life in the Ohio River.

E. SOLIDS HANDLING

RWRA operates a robust solids handling program. Waste sludge is thickened and stabilized. The facility utilizes high-performance centrifuges for dewatering, producing a cake with 20-25% solids. The dewatered biosolids are transported to RWRA’s dedicated drying facility or land applied in accordance with EPA Class B (or Class A where applicable) regulations, supporting local agriculture through nutrient recycling.

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4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The Max Rhoads site is an industrial campus located near the Ohio River. It houses the main process tanks, the blower buildings, the solids handling complex, and the central administration/laboratory building. The site is designed with flood protection measures given its proximity to the river.

B. Energy & Controls

The facility is a major energy consumer, with aeration and pumping being the primary loads. Recent upgrades have focused on VFD (Variable Frequency Drive) installation on major pumps and aerators to match energy use with biological demand. The entire plant is monitored via a centralized SCADA system, allowing operators to visualize flows, tank levels, and dissolved oxygen concentrations from the control room or remote terminals.

C. Odor Control

Given the plant’s proximity to urban areas, odor control is a priority. The headworks building and solids handling facilities are equipped with air exchange systems routed through chemical scrubbers or activated carbon filters to neutralize hydrogen sulfide and other odorous compounds before venting to the atmosphere.

5. RECENT UPGRADES & MAJOR PROJECTS

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Permit Requirements

The facility operates under NPDES Permit KY0022713. Key parameters include:

• CBOD5: Monthly average limits typically < 25 mg/L.
• TSS: Monthly average limits typically < 30 mg/L.
• Ammonia-Nitrogen: Seasonally variable limits to protect aquatic life (stricter in summer).
• E. Coli: < 130 colonies/100ml (geometric mean) during recreation season (May-Oct).

B. Compliance History

The Max Rhoads facility has maintained a strong compliance record. The implementation of the Long Term Control Plan (LTCP) via the tunnel project effectively addressed historical issues related to wet-weather bypasses. The plant frequently receives recognition from the Kentucky Water and Wastewater Operators Association (KWWOA) for operational excellence.

7. OPERATIONAL EXCELLENCE

RWRA employs a dedicated staff of certified wastewater operators, maintenance technicians, and laboratory analysts. Operators are required to hold Class III or Class IV wastewater certifications from the Commonwealth of Kentucky. The on-site laboratory is state-certified for key compliance parameters, allowing for rapid process adjustments based on real-time data rather than waiting for external lab results.

8. CHALLENGES & FUTURE PLANNING

A. Aging Infrastructure

Like many US municipalities, Owensboro faces the challenge of maintaining aging collection lines. Infiltration and Inflow (I/I) remain a focus area, as groundwater seeping into cracked pipes reduces the effective capacity of the treatment plant.

B. Future Regulations

RWRA is monitoring potential future regulations regarding nutrient limits (Total Nitrogen and Phosphorus) for the Ohio River and the Gulf of Mexico hypoxia zone. While the VLR process provides some nutrient removal, stricter future limits could require chemical addition or tertiary filtration upgrades.

9. COMMUNITY & REGIONAL IMPACT

The Max Rhoads plant is vital to the economic development of Owensboro. By ensuring reliable sewer capacity, the region can attract water-intensive industries and support residential expansion. Furthermore, the facility’s successful management of CSOs has directly contributed to the revitalization of the Owensboro riverfront, making the Ohio River cleaner and safer for recreational use.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

• David Hawes Wastewater Treatment Plant: A second facility operated by RWRA, located in the eastern portion of the county, serving newer growth areas with separate sewer systems.
• Molfetta Pump Station: A critical large-capacity lift station managing flow from the downtown interceptors to the Max Rhoads plant.

12. FAQ SECTION

Technical Questions

Q: What is the design flow of the Max Rhoads WWTP?
A: The plant is rated for an average daily flow of 15 MGD, with hydraulic peaks manageable up to approximately 32 MGD.

Q: Does the plant use chemical disinfection?
A: No, the facility utilizes high-intensity UV light for disinfection, eliminating the safety hazards associated with chlorine gas.

Q: How does the facility handle wet weather flows?
A: Excess flows from the combined sewer system are diverted to a deep rock tunnel storage system. This stored water is pumped back to the plant for treatment once storm flows subside.

General Public Questions

Q: Who operates the wastewater plant?
A: While often confused with Owensboro Municipal Utilities (OMU), the wastewater plants are operated by the Regional Water Resource Agency (RWRA).

Q: Where does the treated water go?
A: The treated, disinfected effluent is discharged into the Ohio River.

Q: Does the plant smell?
A: The plant utilizes chemical scrubbers and other odor control technologies at key processing points (headworks and sludge processing) to minimize odors for the surrounding community.