Wastewater treatment facilities provide essential services to the communities they serve by treating polluted water and returning clean, safe water to the environment. The Rahway Valley Sewerage Authority (RVSA) was formed in 1951 to treat wastewater from municipalities in Central New Jersey. These municipalities currently include: Member Municipalities of Clark, Cranford, Garwood, Kenilworth, Mountainside, Rahway, Roselle Park, Scotch Plains, Springfield, Westfield, and Woodbridge and User Municipalities of Winfield Park, portions of Fanwood and Linden.
The RVSA is run as an autonomous agency that owns and operates a 40 million-gallon-per-day (MGD) wastewater treatment facility located in Rahway, New Jersey. The plant has primary, secondary, tertiary, and sludge treatment processes and serves more than 250,000 residents and 3,000 industrial and commercial customers within a 48.85 square-mile area. The RVSA recently completed a plant expansion that will improve service and promote a cleaner environment.
Previously, the maximum peak flow that the RVSA facilities could accommodate was 63 MGD. Due to limited trunk sewer and wet weather treatment plant capacities, the RVSA had Combined Sewer Overflows (CSOs) that were activated during extended rainfalls when this peak flow was exceeded. These CSOs were necessary to relieve street flooding and water back-up into basements within the tributary municipalities.
In 1997, the New Jersey Department of Environmental Protection (NJDEP) revised the RVSA's Discharge Permit. The revisions modified the operation of Outfalls 003 and 004 as CSOs, which had been in use as permitted Outfalls for many years during heavy rainfalls.
The RVSA worked with the NJDEP to develop a Comprehensive Strategic Plan (CSP) for addressing the NJDEP's concerns. Full realization of the CSP included implementing a Capital Improvement Program (CIP) and the following:
Significantly increase the plant's capacity from 63 MGD to accommodate wet weather flows of up to 105 MGD, by providing increased influent and effluent capabilities.
Adding sand filters, a disinfection system and other primary treatment facility enhancements to eliminate possible future violations of the permit's effluent limits.
Closing, first temporarily then permanently, Outfalls 003 and 004 in Rahway, New Jersey.
Construct a gravity relief sewer to bring the excess wet weather flow from Outfall 004 to the treatment plant.
The CSP was an eight-year plan to design and construct plant upgrades and enhancements that closed the CSOs, eliminated any effluent violations and allowed the plant to treat significantly greater flows from the Member Municipalities and commercial customers. Ultimately, the plant's upgrades and expansion increased the RVSA's daily and maximum capacities of wastewater treated, providing for a much cleaner effluent and reducing environmental pollution.
As a result of implementing the CSP, the RVSA is now compliant with current State requirements and is achieving greater operating and cost efficiencies. This enables the RVSA to continue to maintain reasonable service area rates — which are among the lowest in the State.
The upgrades have enabled the RVSA to eliminate two of the untreated CSO discharge points to the Rahway River (Outfalls 003 and 004). Also, the plant expansion and upgrades enable the RVSA to remove approximately 12.37 million pounds per year of Total Suspended Solids (TSS) and 9.06 million pounds per year of Biochemical Oxygen Demands (BOD).
The RVSA also constructed a CHP (Combined Heat Power) facility. The facility is capable of producing 6.2 MW of power. It can run on natural gas, bio-gas, or a blend of the two gasses. The Authority hopes to someday produce enough bio-gas to power the entire plant and become "net zero". Currently we produce enough gas to offset our power costs by 25%.
Everyday wastewater enters the RVSA headworks facility at flow rates from 25 MGD to 105 MGD+. The average flow is about 25- 30 MGD. The wastewater is lifted up about 45’ by five centrifugal pumps so that it can flow by gravity through the plant. In this preliminary treatment stage grit and screenings are removed. The screenings are trapped on a mechanical bar screen and then scraped off with a blade. The grit is removed through settling in an aerated grit chamber and then both grit and screenings are taken to a landfill or an incinerator for disposal. The screenings are composed of mostly floatables such as rags and plastics. The grit is composed of solids such as sand, organic and inorganic solids, egg shells and the like.
From there the wastewater goes into the primary treatment stage. Here the wastewater is spread out and slowed down so that sedimentation can occur. The mostly organic solids settle on the bottom and are scraped to a trough and pumped to the sludge concentration tank and then the solids handling facility for thickening and disposal. The grease is skimmed from the surface and pumped back to the headworks facility and blended with the grit and screenings for disposal.
The leftover liquid portion of the wastewater then flows into the aeration tanks which is the heart of the biological process in the secondary treatment stage. Here the organic solids remaining in the wastewater are consumed by microorganisms that are maintained in a liquid biomass called "mixed liquor", which has the appearance and consistency of chocolate milk and is constantly aerated by large blowers (700HP) that require the largest part of the electrical power needed to operate the RVSA. After a certain amount of time ("detention time") in the aeration tanks, the mixed liquor flows into the secondary settling tanks. Here again sedimentation occurs and the organic solids from the mixed liquor settle out and are pumped to the solids handling facility and the liquid portion of the wastewater flows out of the secondary settling tanks. Part of the settled solids is pumped back to the aeration tanks to help maintain the population of microorganisms and the rest is wasted off for thickening and blended with primary sludge for digestion. In most regional wastewater plants this is the end of treatment before disinfection. However, the RVSA utilizes a third treatment stage known as tertiary treatment.
In the tertiary treatment stage, the clarified wastewater flows by gravity from the secondary settling tanks over to the sand filters where most of any remaining solids are filtered out by dropping through the sand and then flushed back up through the sand bed and pumped back to the headworks facility and combined with the raw wastewater for processing again. The cleaned water then flows through the ultraviolet radiation process and is neutralized by passing through the high intensity light bulbs. Finally, the high quality, nearly drinking water, processed wastewater is allowed to go to the Arthur Kill River. Note that the wastewater that we have treated is now so clean that we are actually making the river cleaner every day.
Once the organic solids are removed from the wastewater in the primary and secondary treatment phases, the combined sludge is thickened in a sludge concentration tank by gravity settling. Typically the solids content is measured by percent solids. In the concentration tank the percent Total Solids (TS) the sludge is thickened, from .05%TS to 1-1.5%TS. From here it is then pumped to the Sludge Digester.
In the Sludge Digester the sludge is digested. In other words the sludge is heated, mixed and kept in suspension for about 18-30 days of detention time. During this time the volatile solids are reduced and the sludge becomes stabilized. After this digestion process, the sludge is withdrawn by pumping at a specific rate and sent to the solids handling facility for further thickening.
In the solids handling facility the sludge in mixed with polymer which is a flocculent. When flocculation occurs, many small particles are bonded together to form larger particles within the liquid that are more easily dewatered. At this point the flocculated sludge is fed into a solid bowl centrifuge which spins the sludge at a high speed and separates the water from the sludge. This produces a sludge that is about as thick as a dry mud measuring 22-24%TS. This is considered a "Class B" bio-solid. We then further dry the sludge in our Sludge Dryer. In this process the sludge is dried to 90-95%TS. Resulting in a far less volume of sludge to transport and dispose of. This can be considered a "Class A" bio-solid. From there it can be disposed of for beneficial re use in a number of ways. The sludge dryer is just that, a way to dry the sludge using indirect heat produced through natural gas, methane gas, or waste heat from the Cogen engines.