Brief Project Description
The Clarke County Sanitation Authority (CCSA) owns and operates the Boyce Wastewater Treatment Plant, which has a current design flow of 0.050 MGD. The discharge is to Roseville Run, a tributary to the Potomac River basin. Under new nutrient discharge control regulations for the Chesapeake Bay and its tributaries, the facility must address total nitrogen and total phosphorus in the discharge as part of the expansion to 0.099 MGD.
Based on a present worth comparison of Nutrient Reduction Technology (NRT) options, the Membrane Bioreactor (MBR) system was ultimately selected due to cost-effectiveness and additional considerations regarding existing site constraints and future expandability. Grant eligible facilities included in the Project are described as follows:
Preliminary Treatment: New Influent rotating drum screen and screw type conveyor. Fine Screening is partially eligible for grant funding.
Flow Equalization (partially grant eligible): As part of this project an existing clear well will be converted to an equalization structure to reduce the forward flow and reduce the size of downstream biological/membrane units.
Secondary Treatment (partially grant eligible): The bioreactor basins (BRB) will convert the existing activated sludge package plant to a 3 stage configuration for NRT treatment. Each parallel treatment train will include: (1) primary anoxic zone for denitrification; (2) aerobic zone for nitrification; and (3) secondary anoxic zone for denitrification. Respectively, the volumes [in gallons]for each zone are: 4,440, 19,390, and 6,060; thus, 35.1% of the reactor volume is anoxic (grant eligible). Two parallel membrane filtration reactors – each including one 3,610 gallon tank and 34 filter modules – will follow the bioreactor.
The aeration system consists of three variable speed blowers that provide low pressure air to the fine bubble air diffuser system. There are two recycle streams in the biological treatment system: Nitrified Recycle (NRCY) and return activated sludge (RAS). The NRCY will be pumped by submersible pumps installed directly in the primary anoxic zone and RAS will be returned by gravity from the MBR to the head of the aerobic zone.
Membrane Filtration (partially grant eligible): Two parallel MBR trains – each including one 3,610 gallon tank and 34 filter modules – will follow the bioreactor. The project will include installation of two cassettes – each initially including 34 modules (each module contains 340 ft2 of membrane fiber); therefore, one cassette will initially include 11,560 ft2 of membrane area. Each cassette is ultimately capable of holding 48 modules.
The Membrane Filtration System will rely on two air blowers to agitate the membrane fibers and remove accumulated solids from the fibers; 3 permeate pumps are also provided.
Solids Train (partially grant eligible): Two parallel tanks with diffused aeration are provided for solids digestion. Dewatering will be accomplished dual rotary fan sludge presses, sludge feed pumps, and a polymer feed system.
Chemical Feed Systems: A new methanol storage and feed system will be installed to provide supplemental carbon to the denitrification process; chemical storage and feed for phosphorus reduction is also included in this project.