Wastewater Treatment

HPUD improvements to the wastewater treatment plant.

The Beaver Creek WWTF, is a tertiary treatment facility currently permitted for a 9 million gallons per day (MGD) discharge.  Beaver Creek is on the State 303D list as an impaired stream because of pathogens, nutrients, and siltation.  Because of the 303D listing, all mass loading limits for the plant NPDES permit are fixed at 5.4 MGD, effectively reducing all permit limits and concentrations by 40%.  Therefore, the permit limits and loadings are extremely tight for Beaver Creek WWTF. 
To accommodate these difficult discharge limits, while also continuing to serve growth and expansion in the district service area; HPUD has embarked upon an aggressive improvement and expansion plan at the plant.  The current plant configuration and description of the improvement plan follows.

Current Plant Description

The treatment plant receives sanitary domestic sewage from approximately 20,400 sewer taps.  The treatment plant receives flow from three major industrial users - Merita Bread is a bread baking operation; Weigels is operating a milk processing facility; and Travis Meats is a meat repackager.  A brief description of the current plant configuration follows.
Currently, flow enters the treatment plant through a 36-inch gravity sewer. Two lifts of screw pumps are followed by screening and grit removal. Discharge from the grit removal system is transported to the oxidation ditch through a long open channel. This channel includes flow metering and wet weather flow diversion to two lagoons that are used for flow equalization. Flow from the oxidation ditch is split between two rectangular and three circular final clarifiers. The flow is then sent to tertiary disc filters (Aquadisc) and disinfected with chlorine prior to discharge to Beaver Creek.
Sludge from the final clarifiers is wasted to three aerobic digesters. The digested sludge is thickened in a gravity thickener prior to dewatering with a 2.0-meter belt press. Solids are normally land applied, but are also sent to a Knox County composting facility when weather conditions prohibit land application of the dewatered solids.

Planned Improvements

The Beaver Creek improvements will be implemented in three phases. This phased approach will allow HPUD to address the most severe operating problem of high influent flows quickly by restoring existing lagoons for use as flow equalization basins in Phase I.  In Phase II, a state of the art Membrane Bioreactor (MBR) plant will be built along with ancillary plant improvements.  During Phase III, the existing oxidation ditch and associated processes will be improved while the Phase II plant handles incoming flows.  In summary, the phased approach will allow for significant immediate operating improvement and continuous operations during expansion and rehabilitation of the plant.

Phase I Improvements – The improvements included in this phase are removing solids from the existing lagoons, replacing broken sections of the splash apron surrounding the lagoons, adding six aerators to each lagoon which will keep solids in suspension while the lagoons contain liquid and upgrading the influent and effluent piping and adding motorized valves to the lagoons to allow more flexibility and control in using the lagoons for equalization.  This work was completed in Spring 2006 and the lagoons are currently operational.

Phase II Improvements – The improvements included in this phase are new major unit processes that include influent pumping, coarse screening, grit and grease removal, fine screening, and a new 6-MGD (maximum month flow) membrane bioreactor (MBR) Zenon treatment train.  The MBR process, in which membranes are submerged directly into the mixed liquor, will be used to produce very high quality effluent.  Additional improvements to the chlorination, dechlorination, and post-aeration processes will also be provided. These improvements will bring the plant capacity to 12 MGD (maximum month flow).  The new MBR train will operate in parallel to the existing oxidation ditch, for biological treatment.   The oxidation ditch will act as the wet weather treatment unit while the MBR will treat the majority of normal base flows (~80%).  This will increase the plant’s capacity to accommodate the anticipated future growth in HPUD’s service area. 

The design of Phase II Improvements is expected to be complete in October 2006.  Construction will require 36 months resulting in an estimated completion date of November 2009.

Phase III Improvements – Phase III Improvements include retrofitting the existing oxidation ditch with air diffusers to provide effective biologic treatment; thereby, eliminating the maintenance and operational issues with the existing rotating disk aerators.  Phase III will also increase capacity of the sludge processing train to accommodate growth.
Design of Phase III Improvements will begin after Phase II design is complete.  Construction of Phase III Improvements will only be made once Phase II Improvements are on line and flow can be diverted to the new treatment train. The estimated completion date for Phase III improvements is 2010.

Planned Improvement Summary

By making these improvements, HPUD will become the first operational full-scale membrane bioreactor plant in the State of Tennessee.   The new plant will produce near drinking water-quality effluent to protect the receiving stream, while also demonstrating to other utilities and regulators across the state that this is a viable technology for producing the best possible effluent.  HPUD plans to hold frequent training and educational seminars at the facility to increase understanding and adoption of the technology by others.  Additionally, HPUD is currently building two membrane ultrafiltration water plants to provide the best possible drinking water for its customers.  Once these projects are complete, HPUD will be the first utility in the State of Tennessee to have all membrane plant technology for both water and wastewater.

The metrics for successful implementation of this plan are summarized below:

• Increased plant hydraulic and biological capacity (12 MGD)
• Better quality effluent using best available technology for treatment
• Reduce and eliminate NPDES permit violations – ensure compliance
• Get Beaver Creek de-listed from State of TN 303D list
• Reduce and eliminate SSO’s in collection system
• Demonstrate water reuse potential in the region
  

Technology section

SCADA Improvements – HPUD is implementing a new SCADA (supervisory control and data acquisition) system.  This implementation is taking place in 3 phases.  The first phase – water booster stations, tanks, and the water plant is in operation.  The second phase – sewer lift stations is beginning implementation.  The third phase – Beaver Creek sewer plant – will take place while Phase II of the WWTP improvements are under way. 

The SCADA system will utilize state-of-the-art Allen Bradley PLCs (programmable logic controllers) and Allen Bradley RSView graphical human machine interface.  The system will continuously monitor all key process parameters and control points for pump stations, plant operations, and tanks.  The design utilizes a redundant server approach, so that each facility (sewer plant, main office, water plant) can monitor key operational parameters for other facilities.  In the event of a catastrophe, a facility (sewer plant) could actually be operated remotely from one of the other server control points, provided the communication link remained open.  This redundant approach also provides for data backup at each facility should there be an emergency or localized damage. 

The new system will allow an unprecedented level of optimization within the plant and collection system.  Key operational data can now be analyzed and trended, alarms generated to dispatch personnel to appropriate areas, and problems caught before they manifest as violations.