Brief Project Description
The North River Waste Water Treatment Plant is jointly owned by the HRRSA; members include Rockingham County, the Towns of Dayton, Mount Crawford, and Bridgewater, & the City of Harrisonburg. The existing plant has a design flow of 16.0 MGD and is capable of Biological Nutrient Removal (BNR). The existing liquid treatment processes includes an influent pump station, mechanical (fine) center-flow band screens, grit removal, four primary clarifiers with sludge/scum removal, eight bioreactors (BNR), four secondary clarifiers with Return/Waste activated sludge (RAS/WAS) anthracite effluent filtration, chlorination/dechlorination and cascade aeration prior to discharge to North River. The solids treatment process includes landfill disposal of primary screenings and grit. The biosolids facilities include: screenings and grit disposal at landfill, septage/industrial sludge receiving station, one waste activated sludge dissolve air flotation (DAF) thickener, volatile fatty acid (VFA) fermentation process to promote biological phosphorus removal, two anaerobic digesters, and a sludge dewatering belt filter press with polymer feed system. When operated, the composting facility produces Class A biosolids, which are sold to public.
Under a proposal for nutrient removal cost share, the treatment processes will be upgraded to nearly state-of-the-art nutrient removal technology (NRT) and plant hydraulic capacity will be expanded to a permitted design flow of 22.0 MGD. As part of this project, a second influent pump station and additional grit removal units (neither grant eligible) will be installed. Additional unit processes include:
- Replacement of the primary sludge pumping station
- Construction of additional biological treatment tank volume Bioreactors #9-12 (total volume =3.41 MG; anaerobic volume = 1.59 MG) and secondary anoxic tanks #1-6 (6.85 MG) for nutrient reduction. Of the new tank volume, approximately 20% is associated with nitrification/ammonia control associated with the expansion from 16 MGD to 22 MGD and 80% is anoxic (NRT). The anaerobic, anoxic and swing zones will be provided with submersible mixers to keep the mixed liquor in suspension. A fine bubble air diffused aeration system will be provided in the oxic, reaeration and swing zones of each basin. Nitrified mixed liquor from the end of the aeration stage will be recycled to the head of the primary anoxic stage with submersible propeller-type pumps.
- Two additional 160 foot diameter secondary clarifiers with center-feed energy dissipation wells
- One additional RAS/WAS Pump Station with common piping/pumps.
- Replacement of an existing RAS/WAS pump station and the mechanism associated with existing, secondary clarifiers #3 and #4 (replacement of the existing mechanisms is considered maintenance; thus, 50% eligible).
- Installation of three chemical feed systems including: supplemental carbon (acetic acid), polymer, and precipitant (ferric chloride)
- Improvements to the effluent filter pump station capacity
- Existing effluent filtration consists of eight filter cells – [each] 30 inch deep anthracite with a surface area of 840 Ft2 . A Value Engineering report (fall 2006) recommended no additional filtration (4 additional filters originally proposed) and the grantee accepted the recommendation; so the project* includes 3,360 Ft2 with a loading rate of 4.9 GPM/SF w/ recycle and 4.5 GPM/SF without recycle.
- Improvements to the disinfection contact tank and expansion of the chlorination/dechlorination chemical storage (not grant eligible)
- Retrofit of the DAF thickener to a second fermentation tank
- Construction of a multi-purpose liquid sludge storage/foreign waste handling tank (not grant eligible)
- Installation of two gravity belt thickeners in a new thickening building
- Anaerobic digestion mixing system upgrade and installation of a second sludge belt filter press
- Site work and inter-unit (yard) piping (partial grant eligibility)
- New Control Building (partial grant eligibility) with Laboratory