Brief Project Description
The existing Luray STP was most recently upgraded in 1990 with a design capacity of 1.60 MGD, which provides treatment capability for the Town of Luray and a portion of Page County. No increase in the treatment plant capacity is proposed as part of the upgrade which is the subject of this Agreement. A two-stage Modified Ludzack-Ettinger (MLE) activated sludge process followed by tertiary filtration has been determined to be the most reliable and cost effective means for complying with the nutrient removal objectives for the facility, which are based on annual average effluent concentrations of 4.0 mg/L for total nitrogen and 0.30 mg/L for total phosphorus. The major treatment system modifications and new treatment system components which will be provided under this upgrade are as follows.
The two existing oxidation ditch activated sludge basins will be modified to operate in series as a MLE biological nitrogen removal process. Oxidation ditch #1 will normally operate as a first stage Anoxic Reactor #1 to achieve carbonaceous BOD removal and removal of nitrate nitrogen contained in mixed liquor recycled by pumping from oxidation ditch #2 which will operate as a second stage Aerobic Nitrification Reactor #2.
A new jet aeration system will be installed in each oxidation ditch to provide mixing and aeration. The new jet aeration (submerged air diffusion) system will provide increased oxygen transfer capability and reduce surface cooling of wastewater during the winter operating months.
A new nitrate recycle pump station will be installed to recirculate nitrate nitrogen in the mixed liquor from oxidation ditch #2 back into oxidation ditch #1.
The two existing 50 foot diameter secondary clarifiers will be upgraded to improve volume and efficiency by increasing the liquid depth of each and replacing the clarifier mechanisms with new rapid sludge suction removal mechanisms.
A new 70 foot diameter secondary clarifier with new return activated sludge pump station will be installed to provide additional clarification necessary to reduce effluent suspended solids in the clarified effluent.
Fifteen new continuous backwash, upflow effluent filters will be installed to provide for final polishing and denitrification of clarified effluent prior to disinfection. Supplemental carbon addition will be necessary to provide a food source for the growth of denitrifying bacteria on the filter media. To assure adequate mixing, a carbon storage and feed system will dose into the clarifier effluent upstream of the filtration system.
Total phosphorus (TP) removal will be achieved by chemical precipitation in the secondary clarifiers and by filtration of solids in the new tertiary filters. New chemical storage and feed equipment will be incorporated, with multi-point dosage of a coagulant solution into a new flocculation tank upstream of the secondary clarifiers and another new flocculation tank upstream of the proposed tertiary filtration system.
Additional ancillary equipment (including instrumentation and controls) will be provided to have a complete and operational enhanced nutrient removal system.