Streamline - Winter 2011 - (Page 29)
Woodstock Wastewater Treatment Plant Meets
Challenge of Chesapeake Bay Initiative
Source: City of Woodstock
heart of the Shenandoah Valley, the Town of Woodstock is as progressive as it is traditional. A drive through Main Street is lined with antique shops and quaint restaurants. Founded in 1752, Woodstock boasts the oldest courthouse west of the Blue Ridge Mountains, designed by Thomas Jefferson and built from native limestone in 1795. Along with being home to the Massanutten Military Academy since before the turn of the 20th century, there also exists a thriving commerce of fast food restaurants, shopping centers and hotels.
NESTLED IN THE
BY DONNA J. LAWSON, WASTEWATER TECHNICIAN II
The plant upgrade cost the Town about $33 million. Approximately $18 million was state funded and Woodstock had to borrow the remaining amount.
Woodstock resides in the Chesapeake Bay Watershed and has had to come under strict effluent limitations imposed by the Clean Water Act under the direction of the Environmental Protection Agency (EPA). Starting in 1983 with the Chesapeake Bay Agreement, the EPA imposed the even stricter standards of the Chesapeake Bay Total Maximum Daily Load (TMDL) in 2010. In 2005, the Town decided to upgrade their existing facility to be able to meet the new requirements. They selected engineering firm O’Brien and Gere to design the new facility. Construction started two years later. The Class II facility is rated for 2.0 MGD. Average daily flow is currently about 400,000 gpd. They replaced the older oxidation ditch with dual train bio-reactors and replaced the clarifier with membrane filters. The plant is classified as an ENR (Enhanced Nutrient Removal System). This involves chemical addition and filtration to remove pollutants such as phosphorus, nitrogen and sediments (TSS). The bio-reactors are monitored by a SCADA (GE) system to closely control the dissolved oxygen (DO) to provide for optimum nitrification and denitrification removal. The 2 microban bar screen at the head of the plant reduces the average incoming BOD from 250 mg/L to 100 mg/L so an external carbon source (Microglycerin) is fed to complete the denitrification cycle. Alum
is added at the end point of the bio-reactor prior to the membrane filters for phosphorus removal. Once the sludge has reached the membrane holding tank, effluent water is then filtered through the membranes (GE/Xenon 500) and is then disinfected by inline UV banks before being discharged to the North Fork of the Shenandoah River via step aeration. The membranes have a maximum filtration rate of 4,500 gpm. This is a peak production of 6.5 MGD which is more than triple the plants total capacity. The average life span of the membranes is five to seven years with a possibility of 10 years before replacement. The membranes are cleaned with citric acid 1/week and sodium hypochlorite (12.5 percent) 1/month. The UV Disinfection system has 8 tubes in each UV unit with a total of 16 tubes with a replacement cost of $800 per tube. The life span of a UV lamp is approximately a full year of run time. With two separate units in alternate use, only one side needs replacement each year. In the membrane holding tank, the sludge is either returned to the bioreactors as activated sludge or is diverted to a gravity thickener for solids removal. The plant has two Westfillia centrifuges rated at 60 gpm that typically produce solids of about 18 perecent. Shenandoah County has an ordinance prohibiting land application of biosolids, so the solids are hauled by dump truck to the local landfill.
Table of Contents for the Digital Edition of Streamline - Winter 2011
From the President
From the Executive Director
Farm Tours for Source Water Protection
Preparing Yourself for an Emergency Response
One Step Ahead: Tappahannock Wastewater Treatment Plant Upgrade
Improving Virginia Waters – VACS
Variable Frequency Drives Can Save You Money
City of Emporia Water Plant Upgrade
The Woodstock Wastewater Treatment Plant
Bird Contamination and Your Water Tank
VRWA 24th Annual Exposition Preview
Throwing My Loop
eLearning Benefi ts
Do You Know What Your VRWA Benefi ts Are?
Welcoming New Members
Board Of Directors
Index To Advertisers/Ad.Com
Streamline - Winter 2011