Union County Utilities Authority Rahway

1. INTRODUCTION

The Rahway Valley Sewerage Authority (RVSA) stands as a critical pillar of environmental infrastructure for Central New Jersey, serving a densely populated and heavily industrialized corridor. Treating an average of 26 to 28 million gallons daily (MGD) with a design capacity of 40 MGD, this facility ensures public health and environmental compliance for approximately 250,000 residents across Union and Middlesex counties.

Situated near the banks of the Arthur Kill, the plant operates under strict New Jersey Department of Environmental Protection (NJDEP) regulations. The facility is distinguished by its focus on energy self-sufficiency and resource recovery, notably featuring a cogeneration facility fueled by digester gas. Following the devastating impacts of Superstorm Sandy, the RVSA has become a regional model for climate resiliency, investing heavily in infrastructure hardening to maintain operational continuity during extreme weather events. It represents a complex integration of conventional secondary treatment with advanced solids handling and energy recovery systems.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The RVSA operates as an autonomous regional authority serving a specific watershed basin rather than a single political boundary. The collection system spans approximately 48 square miles. The member municipalities include:

• Union County: Clark, Cranford, Garwood, Kenilworth, Mountainside, Rahway, Roselle Park, Scotch Plains, Springfield, Westfield.
• Middlesex County: Woodbridge (portions thereof).

The service area is characterized by mature suburban development with significant commercial corridors and legacy industrial zones, resulting in a mixed influent profile requiring robust industrial pretreatment program (IPP) monitoring.

B. Operational Capacity

The plant is designed for an annual average flow of 40 MGD. However, the facility’s hydraulics are engineered to manage significant peaking factors:

• Current Average Daily Flow: ~26-28 MGD
• Peak Wet Weather Flow: 105 MGD

Like many historic northeastern US systems, the RVSA collection system experiences inflow and infiltration (I/I) challenges during precipitation events, necessitating the high peak flow capacity relative to average flow.

C. Discharge & Compliance

Treated effluent is discharged into the Arthur Kill, a tidal strait separating New Jersey from Staten Island, New York. This water body is part of the NY/NJ Harbor Estuary. Consequently, the facility operates under a stringent NJPDES permit that mandates careful monitoring of suspended solids, BOD, and nutrients to prevent eutrophication in the estuarine environment. The outfall structure is designed to maximize mixing within the tidal current.

Read moreBroward County North District Regional Wastewater Treatment Plant

3. TREATMENT PROCESS

The RVSA utilizes a conventional activated sludge process supplemented by advanced preliminary treatment and modern disinfection technologies.

A. Preliminary Treatment

The headworks facility is designed to protect downstream equipment from the debris common in combined or older collection systems.

• Screening: Mechanically cleaned bar screens remove large solids, rags, and plastics.
• Grit Removal: Following screening, flow enters aerated grit chambers where inorganic solids (sand, gravel) settle out. This protects the pumps and prevents volume reduction in the digesters.
• Flow Equalization: While limited, hydraulic buffering helps manage diurnal peaks before primary treatment.

B. Primary Treatment

Flow is distributed to rectangular primary clarifiers. Here, gravity settling removes approximately 30-40% of BOD and 50-60% of Total Suspended Solids (TSS). Scraper mechanisms collect primary sludge from the bottom and scum from the surface. The primary sludge is pumped directly to the gravity thickeners, a critical step for the facility’s energy recovery strategy.

C. Secondary Treatment (Activated Sludge)

The biological heart of the plant employs a conventional activated sludge process.

• Aeration Basins: The facility utilizes plug-flow aeration tanks. Air is supplied via fine-bubble diffusers to maximize oxygen transfer efficiency. The biological community (biomass) metabolizes the remaining organic matter and converts ammonia to nitrate (nitrification) depending on seasonal permit requirements.
• Secondary Clarifiers: Mixed liquor flows to final settling tanks where the biomass separates from the treated water.
• RAS/WAS: A portion of the settled biomass is returned to the aeration tanks (Return Activated Sludge – RAS) to maintain the population, while excess growth is wasted (Waste Activated Sludge – WAS) to solids handling.

D. Disinfection

Historically a chlorination facility, RVSA upgraded to Ultraviolet (UV) Disinfection. This modernization eliminated the safety risks associated with storing bulk chlorine gas and the potential for chlorinated byproducts in the effluent. The UV system inactivates pathogens by disrupting their DNA before the water is discharged to the Arthur Kill.

E. Solids Handling & Energy Recovery

The solids handling train is the facility’s most technically complex sector:

• Thickening: Primary sludge and WAS are thickened to reduce hydraulic load on the digesters.
• Anaerobic Digestion: Thickened sludge undergoes mesophilic anaerobic digestion. This process reduces volatile solids and produces methane-rich biogas.
• Cogeneration (CHP): The produced biogas is cleaned and utilized in on-site cogeneration engines. These engines generate electricity to power plant operations and heat to maintain digester temperatures, significantly offsetting energy costs.
• Dewatering & Drying: Digested sludge is dewatered using centrifuges. The facility has historically operated sludge drying technology to produce a Class A beneficial reuse product, reducing the mass of material requiring off-site disposal.

4. INFRASTRUCTURE & FACILITIES

A. Energy Systems

The RVSA has been a pioneer in the region regarding waste-to-energy implementation. The facility’s Cogeneration Plant allows it to utilize the methane produced during anaerobic digestion. By combusting this renewable fuel source, the plant generates a significant portion of its electrical demand and captures waste heat for process heating loops. Natural gas supplements the system when biogas production fluctuates.

B. Odor Control

Given the facility’s proximity to residential zones in Rahway and Woodbridge, odor control is a primary operational mandate. The plant utilizes a combination of chemical scrubbers (wet scrubbers) and biofilters, particularly focused on the headworks, primary clarifiers, and sludge processing buildings. Negative pressure is maintained in critical buildings to prevent fugitive emissions.

C. Resiliency

Following Hurricane Sandy in 2012, which caused significant surge flooding in the Arthur Kill region, RVSA invested heavily in resiliency. Critical electrical switchgear was elevated, and flood walls/barriers were reinforced to protect the facility against a 500-year flood event plus sea-level rise projections.

5. RECENT UPGRADES & MAJOR PROJECTS

6. REGULATORY COMPLIANCE

A. Permit Requirements

The facility operates under NJPDES Permit No. NJ0024643. Key parameters include:

• CBOD5: Strict removal percentages (85% minimum) and mass loading limits.
• TSS: 30 mg/L average monthly limit (typical for secondary treatment).
• pH: 6.0 – 9.0 Standard Units.
• Pathogens: Enterococcus monitoring consistent with saline water discharge.
• Nutrients: Nitrogen monitoring is critical due to the impaired status of the NY/NJ Harbor.

B. Industrial Pretreatment

RVSA manages a Delegated Industrial Pretreatment Program. Because the service area includes significant pharmaceutical, chemical, and manufacturing industries, the authority monitors significant industrial users (SIUs) to prevent the discharge of substances that could inhibit biological treatment or pass through to the Arthur Kill.

7. TECHNICAL SPECIFICATIONS SUMMARY

8. FAQ SECTION

Technical Questions

1. Does RVSA accept trucked waste?
Specific policies on trucked waste (septage or greywater) vary based on current capacity and operational status. Engineers or haulers must contact the Authority directly for current permits and tipping fees.

2. How does the plant handle wet weather flows?
The plant is capable of handling up to 105 MGD. During extreme events, flow equalization strategies and maximized primary treatment throughput are utilized to ensure all discharged water receives treatment and disinfection.

3. What is the solids retention time (SRT) for the biological process?
While variable based on season, the plant generally operates a standard activated sludge SRT suitable for BOD removal and seasonal nitrification.

General Questions

4. Does the plant smell?
Wastewater treatment inherently generates odors, but RVSA utilizes extensive odor control scrubbers and covers. Occasional odors may occur during maintenance of the scrubbers or extreme weather conditions.

5. Who pays for the facility?
The Authority is funded through user fees collected by the member municipalities. It does not have direct taxing authority over residents but bills the towns based on flow volume.