Middlesex County Utilities Authority Sayreville

1. INTRODUCTION

The Middlesex County Utilities Authority (MCUA) Central Wastewater Treatment Facility (CWTF) stands as one of the largest and most complex wastewater infrastructure assets on the East Coast of the United States. Located in Sayreville, New Jersey, this 147-MGD secondary treatment plant serves as the environmental backbone for the densely populated and heavily industrialized Lower Raritan River Basin. Commissioned in 1958 and operated by the MCUA, the facility is a critical component of regional water quality management, processing wastewater for nearly one million residents and hundreds of industrial clients.

The facility is distinguished not only by its sheer scale but also by its integrated approach to resource recovery. It operates in conjunction with the adjacent Middlesex County Landfill to utilize landfill gas for power generation and produces a beneficial reuse biosolids product known as “MeadowLife.” Following the devastation of Superstorm Sandy in 2012, the CWTF has become a national case study in resilient infrastructure engineering, having implemented over $100 million in flood mitigation and hardening upgrades to ensure operational continuity during extreme weather events.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The CWTF serves a highly urbanized 500-square-mile service area encompassing 25 municipalities across Middlesex, Somerset, and Union Counties. The collection system is massive, involving over 100 miles of interceptor sewers ranging from 18 to 102 inches in diameter. The influent profile is unique due to a significant industrial contribution (approximately 20% of flow), requiring robust biological treatment capabilities. The service area includes major industrial hubs, pharmaceutical manufacturers, and dense residential corridors.

B. Operational Capacity

The plant is designed for an average daily flow of 147 million gallons per day (MGD), with a peak hydraulic capacity of approximately 350 MGD to handle wet weather flows. Historically, the plant operates near 100-110 MGD on average, providing adequate reserve capacity for regional growth. The facility relies on the Main Pump Station (MPS)—one of the largest of its kind globally—capable of lifting the entire influent flow 65 feet into the headworks.

C. Discharge & Compliance

Treated effluent is discharged into the Raritan Bay via a 4.5-mile long dispersion outfall system. The discharge is regulated under the New Jersey Pollutant Discharge Elimination System (NJPDES). Due to the ecological sensitivity of the Raritan Bay and its connectivity to the Atlantic Ocean, the facility must adhere to strict secondary treatment standards for BOD, TSS, and pH, while monitoring for toxicity to protect marine life.

3. TREATMENT PROCESS

The MCUA Central Wastewater Treatment Facility utilizes a High Purity Oxygen (HPO) activated sludge process, a technology selected for its ability to handle high organic loading and industrial shock loads within a smaller physical footprint than conventional aeration.

A. Preliminary Treatment

Raw wastewater enters the facility at the Main Pump Station. Preliminary treatment occurs at the headworks, consisting of mechanically cleaned bar screens to remove large debris, rags, and plastics. Following screening, flow passes through aerated grit chambers where inorganic solids (sand, gravel, cinders) settle out. The removed screenings and grit are dewatered and disposed of at the adjacent landfill. Odor control at the headworks is critical and managed via chemical scrubbers.

B. Primary Treatment

The screened wastewater flows into primary sedimentation tanks. These large rectangular clarifiers reduce the velocity of the wastewater, allowing settleable solids to drop to the bottom as primary sludge and floatables (grease/oil) to rise to the surface for skimming. The primary treatment stage typically removes 50-60% of Suspended Solids and 30-35% of BOD. The primary sludge is pumped to gravity thickeners for processing.

C. Secondary Treatment (High Purity Oxygen)

The biological heart of the CWTF is the UNOX High Purity Oxygen (HPO) system. Unlike conventional systems that use ambient air (21% oxygen), this system utilizes cryogenic oxygen generation plants on-site to inject 90%+ pure oxygen into covered aeration basins.

• Reactor Configuration: The basins are covered to maintain high oxygen partial pressure, significantly increasing the oxygen transfer rate.
• Benefits: The HPO process supports a higher mixed liquor suspended solids (MLSS) concentration, allowing the plant to treat high-strength industrial waste effectively and preventing the growth of filamentous bacteria that cause bulking sludge.
• Secondary Clarification: Mixed liquor flows to final clarifiers where biological floc settles. Return Activated Sludge (RAS) is recycled to the HPO tanks, while Waste Activated Sludge (WAS) is sent to thickening.

D. Disinfection

The clarified effluent undergoes disinfection using sodium hypochlorite (liquid chlorine) in contact tanks to eliminate pathogenic bacteria. Prior to discharge into the Raritan Bay, the effluent is dechlorinated using sodium bisulfite to ensure residual chlorine levels do not harm marine aquatic life.

E. Solids Handling & Biosolids Production

MCUA operates a sophisticated solids handling facility:

• Thickening: Primary sludge is gravity thickened, while WAS is thickened via dissolved air flotation (DAF) or gravity belt thickeners.
• Anaerobic Digestion: Thickened sludge is pumped to anaerobic digesters. These heated tanks stabilize the sludge, reduce volatile solids, and produce methane-rich biogas used for on-site power generation.
• Dewatering: Digested sludge is dewatered using high-solids centrifuges.
• Drying: The dewatered cake is processed in indirect thermal dryers. This creates a Class A Biosolid product marketed as “MeadowLife,” an alkaline-stabilized fertilizer used for land application and soil amendment, diverting massive tonnage from landfills.

4. INFRASTRUCTURE & FACILITIES

A. Power & Energy Systems (Cogeneration)

The MCUA CWTF is a leader in energy self-sufficiency. The facility incorporates a Combined Heat and Power (CHP) system that utilizes two renewable fuel sources:

1. Digester Gas: Methane produced during the anaerobic digestion process.
2. Landfill Gas: Methane piped directly from the adjacent Middlesex County Landfill.

This gas fires combustion turbines and boilers to generate electricity and steam. The steam is critical for heating the anaerobic digesters and powering the thermal sludge dryers. This circular energy economy drastically reduces the facility’s carbon footprint and operational utility costs.

B. Odor Control

Given the plant’s size and the nature of the industrial influent, odor control is paramount. The facility utilizes a combination of chemical wet scrubbers (acid/bleach/caustic) and activated carbon adsorption systems, particularly focused on the headworks, primary clarifiers, and sludge processing buildings. Atmospheric dispersion modeling is used to monitor off-site impacts.

5. RECENT UPGRADES & MAJOR PROJECTS

Main Pump Station & Flood Mitigation Project (2014-2018)

• Context: In 2012, Superstorm Sandy caused a catastrophic storm surge that flooded the Main Pump Station (MPS), taking the plant offline and necessitating bypass pumping for months.
• Budget: ~$75 Million (Funded largely via FEMA and NJ Environmental Infrastructure Trust).
• Scope: Construction of a perimeter flood wall protecting the MPS to an elevation of 19 feet (500-year flood plus sea-level rise buffer). Replacement of giant influent pumps, motors, and electrical switchgear that were destroyed by saltwater intrusion. Installation of submersible pumps capable of operating even if the dry well is compromised.
• Result: The MPS is now one of the most resilient wastewater assets in the region, capable of withstanding extreme storm surges without loss of critical pumping capacity.

Combined Heat and Power (CHP) Modernization

• Scope: Upgrades to the cogeneration turbines and gas cleaning systems to improve efficiency in utilizing landfill and digester gas.
• Technical Highlight: Implementation of advanced gas conditioning skids (siloxane removal) to protect turbine blades and reduce maintenance intervals.

Current/Upcoming Projects

MCUA continues to invest in asset management, with planned upgrades for the cryogenic oxygen generation facility and ongoing rehabilitation of the primary settling tanks to ensure structural integrity and hydraulic efficiency.

6. REGULATORY COMPLIANCE

The facility operates under NJPDES Permit No. NJ0020141. Key compliance parameters include:

• BOD5: 85% removal minimum; monthly average limits typically < 30 mg/L.
• TSS: 85% removal minimum; monthly average limits typically < 30 mg/L.
• Disinfection: Fecal coliform limits consistent with bay discharge requirements.
• Nutrients: Monitoring of Nitrogen and Phosphorus forms to support regional watershed management plans for the Raritan Bay.

The MCUA maintains a strong compliance record, utilizing an on-site state-certified laboratory to conduct daily process control testing and permit compliance monitoring.

7. CHALLENGES & FUTURE PLANNING

Climate Resiliency

Located adjacent to the bay, the CWTF is on the front lines of climate change. While the MPS has been hardened, long-term planning involves assessing the vulnerability of the gravity outfall and low-lying clarifiers to rising sea levels, which could impact hydraulic grade lines.

Infrastructure Aging

With major structures dating back to 1958 and the 1970s, the Authority faces the challenge of rehabilitating concrete tanks and subterranean piping while maintaining continuous 24/7 operations. Asset management programs are prioritizing the rehabilitation of the grit chambers and secondary clarifier mechanisms.

8. TECHNICAL SPECIFICATIONS SUMMARY

9. FAQ SECTION

Technical Questions

1. Why does MCUA use High Purity Oxygen (HPO)?
The HPO system allows for a higher concentration of biomass (MLSS) in the aeration tanks, enabling the plant to treat high-strength industrial wastewater and shock loads more effectively within a smaller footprint compared to conventional air activated sludge.

2. How is the facility powered?
The plant utilizes a significant amount of renewable energy through its Cogeneration facility, which burns methane gas captured from the anaerobic digesters and the neighboring Middlesex County Landfill to generate electricity and steam.

3. What is the capacity of the Main Pump Station?
The Main Pump Station is designed to lift up to 350 MGD of raw wastewater, utilizing massive centrifugal pumps driven by engines and electric motors to overcome the static head required to enter the gravity-flow treatment train.

General Interest Questions

4. What is “MeadowLife”?
MeadowLife is the trade name for the dried, pelletized biosolids produced at the facility. It is a Class A biosolid product used as a fertilizer and soil conditioner, representing a sustainable alternative to landfilling waste.

5. Is the plant protected against future hurricanes?
Yes. Following Superstorm Sandy, MCUA invested heavily in flood walls, watertight doors, and elevated electrical substations to ensure the facility remains operational during severe storm surges.