Brief Project Description
The existing Craigsville Wastewater Treatment Plant (WWTP), governed by a Virginia Pollution Abatement (“no-discharge”) permit, has a permitted design flow of 0.25 MGD, which provides secondary equivalent treatment via separate bar screen and Imhoff configurations located in the Town and at the Augusta Correctional Center. Flow is then conveyed via force main to the existing treatment plant site where parallel facultative lagoons and chlorine disinfection further treat the wastewater before spray field irrigation.
The Town intends to expand the design flow to 0.435 MGD and convert to a surface water discharge regulated under a VPDES permit. The discharge will be permitted with very stringent limitations for conventional parameters due to anti-degradation, local water quality impacts, and (to a lesser extent) compliance with nutrient discharge control regulations. A Preliminary Engineering Report (PER) for the expansion was submitted to DEQ along with a series of amendments (most recently dated: February 2008) to address changing situations. Two alternative biological processes (sequential batch reactor (SBR) and membrane bioreactor) were evaluated for the new facility. Based on the capital and annual cost comparisons along with expected treatment performance, the engineer recommended the new WWTP utilize a parallel train SBR process followed by disk filtration, ultrafiltration, chemical addition, and disinfection.
This project consists of various facilities included in the PER which are intended to achieve nutrient discharge compliance. Processes being installed, and their grant eligibility as Nutrient Reduction Technology (NRT), are described as follows.
Preliminary Treatment (not grant eligible): New pumping and screening of raw wastewater.
- The biological process (partially grant eligible) will consist of dual 236,000 gallon SBRs with an integral 72,530 gallon post-equalization tank. Two duty blowers and one standby positive displacement blower will be provided to supply diffused air to the basins. One mixer will also be installed in each SBR tank.
- Effluent Polishing Filters (grant eligible): Two disk cloth media filters in steel tanks mounted on a concrete pad with a hydraulic loading rate of 2.81 GPM @ average flow.
- Ultra-filtration (grant eligible): Further filtration of the effluent will be accomplished by parallel membrane tanks with two membrane modules per tank.
- Ultraviolet Disinfection and Post-Aeration (not grant eligible)
- Solids Handling and Dewatering (partially grant eligible): The solids handling process will include two new aerobic digester tanks integral to the SBR structure and a centrifuge.
- Chemical Feed (grant eligible): Bulk chemical storage and feed facilities are proposed for alum to precipitate phosphorus, magnesium hydroxide for alkalinity control, and supplemental carbon for denitrification.
- Electrical System Improvements (partially grant eligible): The wastewater treatment plant will include a new onsite standby generator and switchgear building, in the event electrical service is disrupted.
- Distributed Control System (partially grant eligible): A new plant-wide distributed control system will be provided to improve treatment plant automation and control.