Central Contra Costa Sanitary District Wastewater Treatment Plant Martinez

1. INTRODUCTION

The Central Contra Costa Sanitary District (Central San) Wastewater Treatment Plant represents a critical node in the San Francisco Bay Area’s water infrastructure. Located in Martinez, California, this resource recovery facility provides wastewater treatment for approximately 500,000 residents and 3,000 businesses across a 146-square-mile service area. With a permitted Average Dry Weather Flow (ADWF) capacity of 53.8 million gallons per day (MGD) and a hydraulic peak wet weather capacity exceeding 240 MGD, the plant is engineered to handle significant seasonal flow variations typical of the region.

Distinct from many contemporary facilities that rely on anaerobic digestion, the Central San plant utilizes a specialized incineration process for solids handling, recovering energy to power plant operations. The facility is also a regional leader in water reuse, producing high-quality recycled water for industrial, commercial, and landscape irrigation use. Following extensive upgrades to its ultraviolet (UV) disinfection systems and ongoing modernization of its solids handling infrastructure, Central San continues to maintain Platinum-level compliance recognition from the National Association of Clean Water Agencies (NACWA).

2. FACILITY OVERVIEW

A. Service Area & Coverage

The District serves a diverse mix of residential, commercial, and light industrial users across central Contra Costa County. The service area encompasses the cities of Martinez, Concord, Walnut Creek, Pleasant Hill, Orinda, Moraga, Lafayette, Danville, San Ramon, and unincorporated areas. The collection system feeding the plant is massive, consisting of over 1,500 miles of sewer lines and 18 pump stations that navigate the region’s complex topography.

B. Operational Capacity

While the plant is permitted for 53.8 MGD (ADWF), current flows average approximately 32-35 MGD, indicating ample reserve capacity for dry-weather growth. However, the facility’s design is heavily influenced by wet-weather events. During severe Pacific storms, infiltration and inflow (I&I) can cause instantaneous flows to surge above 200 MGD. The plant utilizes large on-site storage basins to equalize these peaks, ensuring biological processes are not washed out during storm events.

C. Discharge & Compliance

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Treated effluent is discharged into Suisun Bay via a submerged outfall. The discharge is regulated by the San Francisco Bay Regional Water Quality Control Board. The facility operates under strict limits for conventional pollutants (BOD, TSS), pathogens, and increasingly stringent monitoring requirements for nutrients (Nitrogen and Phosphorus) as part of the broader San Francisco Bay Nutrient Watershed Permit.

3. TREATMENT PROCESS

Central San employs a conventional activated sludge process for secondary treatment, coupled with distinct solids handling via incineration and a robust tertiary treatment train for water recycling.

A. PRELIMINARY TREATMENT

Raw wastewater enters the headworks via the A-Line and M-Line interceptors. The headworks is equipped with mechanically cleaned bar screens to remove large debris (rags, plastics). Following screening, flow enters aerated grit chambers where heavier inorganic materials (sand, gravel, coffee grounds) settle out. The grit is washed, dewatered, and hauled to a landfill. Odor control at the headworks is managed via chemical scrubbers to mitigate nuisance odors for nearby residents.

B. PRIMARY TREATMENT

Flow proceeds to primary sedimentation tanks. These rectangular tanks reduce flow velocity, allowing settleable solids to drop to the bottom as primary sludge, while fats, oils, and grease (FOG) float to the surface for skimming. The primary treatment stage typically removes 50-60% of Total Suspended Solids (TSS) and 30-40% of Biochemical Oxygen Demand (BOD). The primary sludge is pumped directly to the solids conditioning system.

C. SECONDARY TREATMENT

The biological treatment utilizes a conventional Activated Sludge process. Settled wastewater (primary effluent) is mixed with Return Activated Sludge (RAS) in aeration basins.

• Aeration: The basins are oxygenated to support the microbial population that consumes dissolved organic matter.
• Clarification: The mixed liquor flows to secondary clarifiers where the biomass settles. The clear supernatant flows over weirs to disinfection.
• Nutrient Impact: While not originally designed for biological nutrient removal (BNR), the plant is optimizing operations to characterize and reduce ammonia and nitrogen discharge in anticipation of future regulatory caps.

D. TERTIARY TREATMENT (Water Recycling)

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A portion of the secondary effluent is diverted to the tertiary treatment plant. This stream undergoes:

• Coagulation/Flocculation: Chemical addition to bind remaining particles.
• Deep Bed Filtration: Passing water through granular media filters (sand/anthracite) to achieve high clarity.
• Disinfection: Intense chlorination to meet Title 22 unrestricted reuse standards.

This system produces approximately 1.5 to 2.0 MGD (seasonal peak) of recycled water for irrigation and industrial cooling towers.

E. DISINFECTION

For the main effluent stream discharged to the Bay, Central San utilizes a large-scale Ultraviolet (UV) Disinfection system. Implemented to replace gaseous chlorine (enhancing safety and eliminating chlorination byproducts), the UV system passes effluent through banks of UV lamps which alter the DNA of pathogens, rendering them unable to reproduce. The treated water is then discharged without the need for dechlorination.

F. SOLIDS HANDLING (Incineration)

Central San is unique in its use of incineration rather than digestion.

• Dewatering: Primary and Waste Activated Sludge (WAS) are blended and dewatered using centrifuges to increase solids content.
• Incineration: The dewatered sludge cake is fed into Multiple Hearth Furnaces (MHF). The furnaces operate at high temperatures (approx. 1,400°F) to combust organic material.
• Ash Handling: The resulting inert ash is collected, conditioned, and used as a soil amendment or landfill cover.
• Energy Recovery: Waste heat from the incinerator exhaust is captured in waste heat boilers to generate steam.

G. PROCESS CONTROL

The facility utilizes a distributed SCADA system for real-time monitoring of flows, dissolved oxygen levels, UV transmittance, and furnace temperatures. A fully accredited on-site laboratory conducts daily compliance testing and process control analysis.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant

The treatment plant occupies a large industrial footprint north of Highway 4. The site includes the Household Hazardous Waste (HHW) Collection Facility, which serves the entire county, diverting toxic chemicals from the sewer system.

B. Energy Systems & Cogeneration

Central San is an energy-intensive facility, but it employs significant self-generation. The steam generated from the Multiple Hearth Furnaces drives a steam turbine generator (cogeneration). This system provides a significant portion of the plant’s electrical demand. Additionally, the District has installed solar arrays on facility rooftops and buffer lands to offset purchased power.

C. Odor Control

Given the proximity to residential zones and Highway 4, odor control is paramount. The District utilizes a combination of chemical wet scrubbers (using hypochlorite and caustic) and activated carbon vessels to treat foul air extracted from the headworks, primary clarifiers, and solids handling buildings.

5. RECENT UPGRADES & MAJOR PROJECTS

Steam Blower Replacement Project – $15 Million (Est.) (2021-2023)

• Scope: Replacement of aging steam-driven aeration blowers with new, high-efficiency units.
• Driver: Energy efficiency and aging infrastructure reliability.
• Tech Highlights: The project integrated the new blowers with the existing waste-heat steam system, optimizing the balance between aeration demand and power generation.

Solids Handling Improvements – Multi-Phase

• Scope: Rehabilitation of the Multiple Hearth Furnaces, upgrades to the wet scrubbers for air emissions compliance, and modernization of ash handling systems.
• Driver: Compliance with Bay Area Air Quality Management District (BAAQMD) regulations and extending the useful life of the incineration assets.

Seismic Retrofit Program

• Scope: Structural reinforcement of critical process tanks, control buildings, and pipe galleries.
• Driver: California seismic code updates and critical infrastructure resilience.
• Status: Ongoing implementation across various plant sectors.

Upcoming: Nutrient Optimization & Refinery Water Exchange

Central San is currently in planning/pilot phases for nutrient reduction strategies to meet anticipated SF Bay nutrient limits. Additionally, the District is exploring a major “Refinery Recycled Water Exchange” project, which would drastically increase recycled water production to serve nearby refineries, offsetting potable water use.

6. REGULATORY COMPLIANCE

A. Permit Requirements

Central San operates under NPDES Permit No. CA0037648. Key parameters include:

• CBOD: 25 mg/L (Monthly Average)
• TSS: 30 mg/L (Monthly Average)
• Enterococcus: Strict limits for protection of water contact recreation.
• Acute Toxicity: 90% survival (median).

B. Air Quality Compliance

Unlike most WWTPs, Central San must adhere to rigorous Title V Air Quality permits due to the incinerators. This involves Continuous Emissions Monitoring Systems (CEMS) for NOx, SOx, CO, and particulate matter.

C. Environmental Stewardship

The District has received the NACWA “Platinum” Peak Performance Award for achieving over 20 consecutive years of 100% compliance with NPDES permit limits, a testament to the reliability of their operations despite the complex mechanical systems involved.

7. CHALLENGES & FUTURE PLANNING

A. Nutrient Management

The San Francisco Bay is exhibiting signs of nutrient enrichment. Regulators are moving toward imposing load caps on Nitrogen. Central San’s incineration process produces a nitrogen-rich side stream (scrubber water) that returns to the headworks. Managing this internal load while planning for potential biological nutrient removal (BNR) upgrades is a primary engineering challenge.

B. Aging Infrastructure

With major components dating back to the 1940s and 1970s, asset management is critical. The District maintains a comprehensive 10-year Capital Improvement Plan (CIP) focused on the rehabilitation of the collection system (preventing I&I) and the refurbishment of mechanical plant systems.

C. Emerging Contaminants (PFAS)

Like all utilities, Central San is monitoring regulatory developments regarding PFAS. The incineration process is being evaluated for its fate and transport of PFAS compounds (whether they are destroyed at high heat or remain in ash/air emissions).

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FAQ SECTION

Technical Questions

Q: Why does Central San use incineration instead of digestion?
A: When the solids handling facility was expanded in the 1970s, incineration was chosen to maximize volume reduction and recover energy. The furnaces reduce sludge volume by 90% (to sterile ash) and generate steam for power, reducing reliance on the grid.

Q: Does the plant perform Biological Nutrient Removal (BNR)?
A: The plant currently operates as a conventional activated sludge plant primarily for BOD/TSS removal. However, process optimization is underway to reduce ammonia, and master planning is in progress for full nutrient removal upgrades mandated by future regulation.

Q: What is the discharge limit for chlorine residual?
A: Because the plant uses UV disinfection for its main effluent, there is no chlorine residual in the discharge, eliminating the need for dechlorination chemicals (like sodium bisulfite) for the bay discharge.

Public Interest Questions

Q: Is the white plume rising from the plant smoke?
A: No. The visible white plume, especially seen on cold mornings, is primarily water vapor (steam) from the wet scrubbers used to clean the furnace exhaust. It is heavily monitored to ensure it meets air quality standards.

Q: Can I get recycled water for my garden?
A: Yes. Central San operates a Residential Recycled Water Fill Station where residents can fill containers with treated recycled water for landscape irrigation at no cost.