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Wastewater Treatment Facility

Construction of the Wastewater Treatment Facility was bid at $1,383,378 by Lantz Construction of Broadway, VA, and completed on time for $1,316,608 without using any of the Contingency Funds allocated for the project.  Construction financing was provided by Virginia Revolving Loan Fund, and at the completion of construction, a loan was acquired from the Rural Utilities Service for long term financing.

The system is similar to the Amelia County system also provided by Kruger, Inc.  The plant is located across the street (187 feet) from residences that have reported no problems from noise or odors.  They say the plant "is a good neighbor."

The Town operates under VPDES Permit No. VA0023825, has 770 sewer connection, and uses a gravity sewage collection system.  Prior to the new system being installed, the Town had difficulty meeting VPDES Permit requirements for TSS and BODs, and was believed to be passing toxics through the treatment process.  The permit for a new plant set BODs and TSS limits at 30 mg/l daily on a monthly average.  Since putting the new system on line in March of 1998, both TSS and BODs have been in single digits and toxicity studies have shown 100% viability of Fathead minnows and Daphnia in 100% strength effluent.

THEORY OF OPERATION

The Wastewater Treatment Facility for the Town of Shenandoah is designed as 0.4-MGD (400,000 Gallons Per Day) Double Ditch system using Phased Isolation Ditch technology, a biological process in which bacteria use the waste material as food, reducing the bulk and concentration of waste products.  That is, two ditch units work sequentially, first one is active in aerating and mixing the microbes and the wastewater, then passive in clarifying the effluent.  The other ditch works at opposite times; aerating and mixing while the other is clarifying, and clarifying while the other is aerating.  Sludge is withdrawn to an aerobic digester, then placed on drying beds and removed to a landfill.  The liquid effluent is removed via a variable height weir through chlorine contact chambers and to the outfall.

DESCRIPTION

Wastewater from the Town of Shenandoah is collected by a piped collection system throughout the Town and piped to the wastewater treatment facility through a series of gravity sewers.  The Phased Isolation Ditch is controlled by a Programmable Logic Controller (PLC) having a modem, which can transit and receive data to and from the manufacturer or consultant for analysis.  If needed, the data can be used to fine tune the treatnment works operation and the PLC can then be reprogrammed, all from a remote location.  The PLC receives leveland Dissolved Oxygen data from sensors in the ditches and uses that data to control the aerator rotor speed and outfall weir positions.  It also directs the schedule of the sequencing.

At the Wastewater Treatment Facility, the flow is directed through the primary treatment, consisting of a grit chamber and an Envirex Series 100 Bar Screen.  After the Bar Screen, the flow is piped into the wet well of the Primary Pump Station.

From the Primary Pump Station, the flow is pumped by one of three installed pumps to the Ditch Inlet Box, where the flow is directed into one or the other of the two ditches.  The ditches have shrouded aerators, shielded to reduce noise, aerosol odors, and conserve heat.

The effluent from the ditches is then piped to two Chlorine Contact Chambers (CCC), where it is disinfected by gas chlorine solution.  From the CCC, the flow is piped to the effluent weir box to be measured prior to discharge to the river.  Typically the effluent is clear enough to withstandvisual comparison with distilled water.

Sludge from the ditches is withdrawn to the Sludge Pump Station, where it is pumped to the aerobic digester.  Aspirating aerators in the digester maintain aerobic conditions, create virtually no noise, conserve heat, and have no aerosol odors.  Supernatant from the digester is piped back to the Force Main upstream of the Ditch Inlet Box.  The digested sludge is piped into the Sludge Drying Beds, dewatered, dried, and hauled to the landfill.  Liquid effluent from the Sludge Drying Beds is piped back to the headworks.