WQIF - Proctors Creek WWTP

 

 Project Grant Amount Grant Percentage
Chesterfield County - Proctors Creek WWTP
$15,919,554
35
 Revolving Loan Fund Project DEQ Regional Area Public Review Period Ends
No
Piedmont Regional Office, Richmond
11/11/08

Brief Project Description

Grantee: ChesterfieldCounty (Proctors Creek)

Grant:  #440-S-08-20

ChesterfieldCounty’s Proctors Creek WWTP currently provides tertiary treatment and biological nutrient removal (BNR) for a permitted design flow of 27.0 MGD. The existing WWTP consists of: screening, grit removal, communition, flow equalization, primary sedimentation, activated sludge with BNR mode up to 21.5 MGD (nitrification with seasonal denitrification only at flows from 21.5 - 27 MGD), backup chemical phosphorus removal, effluent filtration, chlorination, dechlorination, and post-aeration. Sludge is anaerobically digested and land applied.

                                                                                          
Under new nutrient discharge control regulations for the Chesapeake Bay and its tributaries, the County received a combined, “bubbled” waste load allocation for nitrogen and phosphorus for its two treatment plants discharging within the James watershed. 
 
As described in a Preliminary Engineering Report (PER) revised in September 2007, the County will upgrade the existing secondary treatment/BNR process to an enhanced nutrient removal system designed to achieve a 5.0 mg/l annual average nitrogen concentration. 
 
This project consists of various facilities included in the PER which are intended to achieve nutrient compliance. Nutrient reduction technology (NRT) processes being funded for nitrogen removal are described as follows:
 
Headworks and Primary Treatment Areas: Fine screens are proposed in the plant upgrade. The screens provide protection to the Integrated Fixed Film Activated Sludge (IFAS) system and will also improve downstream processes (such as clarification and sludge handling). Due to lower maintenance requirements and owner preference, fine drum screens - installed upstream of the primary clarifiers – are anticipated for the final design.  Influent flow to the screen facilities will be pumped from the existing pump station; but, a building will be required to house the drum screens and screenings handling equipment.
 
Secondary Treatment: The existing plant includes two process trains - commonly referred to as East and West sides – and relies on a 66:34 flow split. The secondary treatment facilities and upgrades for a 4-stage activated sludge, biological nutrient removal process includes the following:
 
West Aeration Basins: The platforms and mechanical mixers will be replaced with a diffused aeration grid. A baffle wall will be placed in the initial chamber of each basin to provide aerobic and anoxic cells. The IFAS system will operate using an initial anoxic zone, followed by aerobic conditions, a second anoxic zone, and then a small aeration zone at the end. The first anoxic zone will receive a recycle of nitrates from the tail-end of the first aerobic section, as well as the influent and the RAS flows. Mixers will be installed in the anoxic zones. The first aerobic compartment will contain the suspended IFAS media and retention screens. The existing aeration grid will require modification to maintain the media screen which keeps the media from traveling forward and to supply air via ceramic, fine bubble diffusers for the increased biological activity.    The second anoxic zone receives the forward flow and the supplemental carbon, associated with denitrification.
 
EastAerationBasin: Nitrified recycle (NRCY) pumping currently is provided for each basin. The NRCY flows must be redirected to the first anoxic zones as part of this project, requiring reconfiguration of the existing piping. The IFAS system will operate using an initial anoxic zone, followed by aerobic conditions, a second anoxic zone, and then a small aeration zone at the end. The first anoxic zone would receive a recycle of nitrates from the tail-end of the first aerobic section, as well as the influent and the RAS flows. Mixers will be installed in the anoxic zones. The first aerobic compartment will contain the suspended IFAS media and retention screens. The existing aeration grid will require modification to maintain the media screen which keeps the media from traveling forward and to supply air via fine bubble, membrane diffusers for the increased biological activity.    The second anoxic zone receives the forward flow and the supplemental carbon, associated with denitrification. In addition to modifying the aeration grid, the existing baffles will require alterations and additional work is also required in these tanks to structurally brace the walls. Lastly, dewatering of individual basins was not included in the original design, so new pumps will be located at the end of each aerobic zone.
 
Current Blowers: are not all operational for the proposed modifications. Replacement of the blowers will allow/incorporate piping and sizing adjustments; thereby, making a natural division between the two sides of the Proctors Creek plant.
 
Clarifiers: The secondary clarifiers perform well and no modification is proposed. Use of an IFAS system may reduce the solids load to the clarifiers, as many of the solids will be attached growth. 
 
Chemical Feed Systems:   Carbon for denitrification will require chemical storage/feed and final design will identify the carbon source(s) for use. While methanol is the traditional chemical, the facility will be constructed so other formulations (acetic acid or sugar solutions) may be used.
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Virginia Department of
Environmental Quality
P.O. Box 1105
Richmond, VA 23218
(804) 698-4000


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