City Of Bend Water Reclamation Facility

1. INTRODUCTION

The City of Bend Water Reclamation Facility (WRF) serves as a critical infrastructure asset for Central Oregon, operating within a unique high-desert hydrological context. Unlike many municipal facilities that discharge to surface waters, the Bend WRF operates as a zero-direct-discharge facility, relying on advanced treatment, evaporation, and percolation to return treated effluent to the regional aquifer. This operational model is driven by the stringent environmental requirements of the Deschutes River Basin and the region’s volcanic geology.

Located northeast of the city limits, the facility manages wastewater for a service area population exceeding 100,000 in one of the fastest-growing municipalities in the United States. Following a comprehensive $46 million upgrade completed in 2012, the plant transitioned to an Integrated Fixed-Film Activated Sludge (IFAS) process. This technological leap allowed the utility to increase hydraulic capacity and enhance nutrient removal efficiency within the existing facility footprint, setting a benchmark for facility intensification strategies in the Pacific Northwest.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The WRF serves the City of Bend’s Urban Growth Boundary (UGB), a region characterized by rapid residential expansion and a growing commercial sector. The collection system spans over 270 miles of gravity sewer mains and includes approximately 14 major sewage lift stations required to navigate the city’s variable topography. A significant ongoing initiative is the “Septic to Sewer” program, designed to decommission thousands of private septic systems that pose a risk to groundwater quality, progressively adding these connections to the centralized treatment network.

B. Operational Capacity

The facility is designed to handle a Maximum Month Flow (MMF) of 12.5 MGD, with hydraulic peaks significantly higher to accommodate storm events, although Bend utilizes a separated storm sewer system. Current average daily flows (ADF) fluctuate between 6.5 and 7.5 MGD. The plant experiences notable seasonal variations, with lower flows during winter months and peak hydraulic loading during summer irrigation seasons and tourism spikes. Historical trends indicate a steady flow increase correlating with the city’s 3-5% annual population growth rate.

C. Discharge & Compliance

The Bend WRF operates under a Water Pollution Control Facilities (WPCF) permit issued by the Oregon Department of Environmental Quality (DEQ). The facility does not discharge directly to the Deschutes River. Instead, effluent is managed through:

• Evaporation/Percolation Ponds: The primary disposal method involves discharging secondary effluent to on-site ponds where it percolates into the volcanic substrate, recharging the local aquifer.
• Water Reuse: A portion of the flow receives tertiary treatment to meet Class A recycled water standards for irrigation of local golf courses and construction dust control.

3. TREATMENT PROCESS

The Bend WRF utilizes a sophisticated treatment train centered around the IFAS process to achieve high-level nitrogen removal and robust BOD reduction.

A. PRELIMINARY TREATMENT

Raw influent enters the headworks where it passes through mechanical bar screens (typically 6mm spacing) to remove large debris, rags, and plastics. Following screening, flow velocity is reduced in vortex grit chambers, allowing inorganic solids (sand, gravel, coffee grounds) to settle. The removed grit and screenings are washed, compacted, and disposed of at the local landfill. The headworks is fully enclosed and equipped with chemical scrubbers for odor control to mitigate nuisance for nearby developments.

B. PRIMARY TREATMENT

Wastewater flows to primary clarifiers where gravity settling removes approximately 60-70% of Total Suspended Solids (TSS) and 30-40% of Biochemical Oxygen Demand (BOD). Primary sludge is pumped to the solids handling train, while scum is skimmed from the surface. The hydraulic retention time in this stage prepares the influent carbon-to-nitrogen ratio for the biological stage.

C. SECONDARY TREATMENT (IFAS)

The core of the Bend WRF is the Integrated Fixed-Film Activated Sludge (IFAS) system. During the 2011 upgrades, the city selected IFAS technology to expand capacity without building new aeration basins.

• Configuration: The aeration basins are retrofitted with plastic media carriers retained by screens. These carriers provide high surface area for biofilm growth.
• Biological Mechanism: The system maintains two distinct biological populations: suspended growth biomass (MLSS) and fixed-film biomass on the media. This allows for a longer Solids Retention Time (SRT) for nitrifying bacteria on the media, while maintaining a lower suspended solids loading on the secondary clarifiers.
• Nutrient Removal: The process is configured for nitrification and partial denitrification to reduce ammonia and total nitrogen, essential for protecting groundwater quality.
• Clarification: Mixed liquor flows to secondary clarifiers where biomass settles. Return Activated Sludge (RAS) is recycled to the anoxic zones, and Waste Activated Sludge (WAS) is sent to thickening.

D. TERTIARY TREATMENT (Recycled Water)

A portion of the secondary effluent is diverted to the tertiary treatment train to produce Class A recycled water. This process utilizes cloth media disk filters (e.g., AquaAerobics AquaDisk or similar technology). These filters provide a physical barrier to remove remaining suspended solids and turbidity, ensuring the water meets the stringent clarity requirements for unrestricted urban irrigation.

E. DISINFECTION

The facility employs chlorination for disinfection.

• Primary Effluent Stream: Disinfected via chlorine contact chambers prior to discharge to the percolation ponds to prevent biological fouling of the infiltration surface.
• Reuse Stream: The tertiary filtered water undergoes rigorous chlorination to maintain a residual consistent with Class A requirements, ensuring pathogen inactivation before distribution to customers (predominantly the Bend Golf and Country Club).

F. SOLIDS HANDLING

Solids processing is a major energy recovery component of the plant:

• Thickening: Primary sludge and WAS are thickened (often via gravity belt thickeners or rotary drums) to reduce hydraulic volume.
• Anaerobic Digestion: Thickened sludge is stabilized in mesophilic anaerobic digesters. This process breaks down volatile solids and produces methane-rich biogas.
• Dewatering: Digested biosolids are dewatered using belt filter presses to achieve a cake solid concentration suitable for transport.
• Disposal: The resulting Class B biosolids are land-applied at the city’s “Outback” site or permitted agricultural lands, recycling nutrients back into the soil (agronomic application).

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The facility occupies a substantial footprint north of the city near the Bend Municipal Airport. The site includes the main treatment process buildings, an administration/laboratory complex, maintenance shops, and extensive acreage dedicated to the evaporation/percolation pond system. The percolation ponds are rotated in service to allow for drying and scarification, maintaining infiltration rates.

B. Energy Systems & Cogeneration

The Bend WRF is a leader in energy recovery. The facility utilizes a Combined Heat and Power (CHP) system. Biogas produced in the anaerobic digesters is scrubbed and fed into cogeneration engines. These engines generate electricity to offset grid consumption and produce waste heat, which is captured via heat exchangers to maintain the temperature of the digesters and heat facility buildings during Central Oregon’s cold winters.

C. Odor Control

Given the proximity to expanding residential zones, odor control is paramount. The facility utilizes biofilters—beds of organic media (wood chips/bark) that facilitate the biological oxidation of odorous compounds like hydrogen sulfide. Key sources of odor, including the headworks and solids handling building, are maintained under negative pressure with foul air routed to these biofiltration units.

5. RECENT UPGRADES & MAJOR PROJECTS

Ongoing Capital Improvements (2020-2025)

The City continues to invest in the facility through its Capital Improvement Plan (CIP). Recent and current projects include:

• Collection System Master Plan Implementation: Addressing the “Septic to Sewer” transition, requiring strategic upgrades to lift stations feeding the plant.
• Aging Infrastructure Replacement: Rehabilitation of the original 1980s-era clarifier mechanisms and structural concrete repairs.
• Headworks Improvements: Enhancements to screening capture and grit removal efficiency to protect downstream IFAS media and membranes.
• Scada & Automation: Migration to updated Rockwell/Allen-Bradley platforms for enhanced remote monitoring and data logging.

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

A. Groundwater Protection

Operating under an Oregon DEQ WPCF permit, the primary compliance objective is the protection of the Deschutes Basin aquifer. The permit stipulates strict limits on Total Nitrogen (TN) discharge to prevent nitrate contamination of the groundwater, which eventually communicates with surface waters. The IFAS system is specifically tuned to maximize denitrification (conversion of nitrate to nitrogen gas) to meet these agronomic loading rates.

B. Recycled Water Quality

The Class A reuse permit requires continuous monitoring of turbidity (typically < 2 NTU) and chlorine residual. The facility maintains a robust compliance record, providing safe irrigation water that offsets potable water demand during the arid summer months.

7. CHALLENGES & FUTURE PLANNING

A. The Growth Curve

Bend’s population growth presents a continuous hydraulic loading challenge. The “Septic to Sewer” program, while environmentally necessary, accelerates the rate at which flow reaches the plant. Future planning involves evaluating the ultimate build-out capacity of the percolation ponds, which are geologically constrained.

B. Emerging Contaminants

Like all modern WRFs, Bend is monitoring regulatory developments regarding PFAS (Per- and Polyfluoroalkyl Substances). As a facility discharging to groundwater, the fate and transport of these persistent chemicals are of future regulatory concern.

C. Water Resiliency

The City’s “One Water” approach aims to maximize the use of recycled water. Future master plans evaluate expanding the distribution network for Class A water to additional golf courses, parks, and potential industrial users to further reduce groundwater withdrawal.

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FREQUENTLY ASKED QUESTIONS

Technical Questions

Q: Why was IFAS selected over MBR for the upgrade?
A: IFAS was selected primarily for its ability to retrofit into existing aeration basins, significantly increasing capacity and nitrification performance without the high civil costs of building new basins or the high energy consumption associated with Membrane Bioreactors (MBR).

Q: Does the facility discharge to the Deschutes River?
A: No. The facility is a zero-discharge plant regarding surface waters. All effluent is disposed of via evaporation, percolation into the groundwater table, or beneficial reuse.

Q: What is the target Total Nitrogen limit?
A: While specific permit limits vary by season and flow, the process is designed to reduce nitrogen to levels safe for groundwater recharge, typically targeting effluent Nitrate-N well below the drinking water standard of 10 mg/L.

General Interest

Q: Does the plant smell?
A: The City employs advanced biofiltration systems to scrub foul air from the headworks and solids handling areas. While wastewater treatment inherently involves odors, these systems capture 99% of odorous compounds.

Q: Where does the recycled water go?
A: The Class A recycled water is currently pumped to the Bend Golf and Country Club for irrigation and is also available at a fill station for construction trucks to use for dust control.