Case Study

Project Profile: WWTP Scottsburg, Indiana Replaces A Chlorine Feed System With Closed Vessel ETS-UV Disinfection Systems

SCOTTSBURG INDIANA

CUSTOMER PROFILE

​The City of Scottsburg is located in Indiana between Louisville, Cincinnati, and Indianapolis.  Scottsburg maintains a healthy balance between commercial, industrial and residential community with a celebrated history and bright future. Scottsburg has put a large emphasis on "quality of life" and it shows in their beautiful parks and lively downtown square.

THE CHALLENGE

The Scottsburg Indiana WWTP had been using a chlorine feed system. The common trend for an upgrade to UV disinfection is to retrofit chlorine contact basins with open channel disinfection. Unlike chlorine treatment, no storage or risk of handling or transportation of This configuration of placing UV lamps in an open channel has historically been the industry standard. Even yet today, when new plants are constructed, the norm is to install open channel UV systems because they are familiar to engineers and operators. These open, gravity flow channels suffer from many disadvantages; poor hydraulic mixing, very large footprint, expensive to build, difficult to maintain and are vulnerable to fluctuation in flow rate.

Discharged wastewater from communities often becomes drinking and recreational water for downstream communities. Chlorine can react with naturally occurring compounds in the water to produce disinfection by-products (DBP’s). DBP’s have shown evidence to be a human carcinogen. Unlike chlorine, with UV disinfection, there is no transportation, storage or the risk of handling of toxic or corrosive materials. In addition, microorganisms, such as Cryptosporidium and Giardia, are exhibiting a growing tolerance to chlorine. Removing these dangers supports public health, nature and aquatic species.

THE SOLUTION

The City selected a more efficient approach by containing the waste stream in a pipe to disinfect the water within a closed vessel. Closed vessel ETS-UV™ disinfection systems are easy to install within existing pipework and new construction does not require the large footprint of concrete channels. Disinfection into a closed pipe will ensure optimized hydraulics and prevent the operator for exposure to the wastewater and UV light.

ETS-UV systems are designed by utilizing Computational Fluid Dynamics (CFD) modeling to design and optimize how the systems will perform. More importantly, this allows systems to be designed to deliver the highest performance for the least power and headloss.

Two ETS-UV SW-835-14 systems were chosen. The UV chamber is fabricated from 316L stainless steel and contains an automated wiper to keep the quartz free from fouling. The chamber also features an access hatch which makes routine maintenance much easier and convenient for operators. Each chamber contains medium pressure lamps, which can be removed with effluent in the chamber. The lamps use a Twist-Lok lamp connector for a safe and easy connection. Municipal plants like Scottsburg that only disinfect seasonally can often achieve a two year lamp life.

DESIGN ADVANTAGES

PLUG & PLAY CONNECTION
Single ended lamps utilize a twist lock plug connection that automatically centers the lamp.  No tools are required.  This is safer for operators and maintenance crews as the UV light and electricity are isolated with a water tight connection.

ENERGY EFFICIENT MOTOR
Low voltage, 24V motor leads to safer, smaller and less expensive wiper option without impacting performance or cleaning capabilities.

NO PROBLEMATIC LIMIT SWITCHES
Optical counter used to stop wiping mechanism before reaching the chamber ends.  Similar technology used in elevators to signal flow levels.

ONE PIECE WIPER RING
Viton wiper rings fit directly onto the stainless steel yoke.  This design reduces components while not impacting performance and cleaning capabilities.

PRODUCT DESIGN AND CONTINUOUS IMPROVEMENT

We believe that good design should make products safe, understandable, innovative and useful. Through the continued relationship of service, we examine wear throughout the product lifecycle and rely on Field Service Technician feedback on product improvement.  We also utilize a variety of design tools that provide emulation of system performance. This has led to many of the innovative features that have been a source of advantage. 

  • Emulate the performance of UV systems by using advanced software tools
  • Use Finite Element Analysis (FEA) to understand how the UV chambers will become stressed under hydraulic pressure
  • Predict weakness in design with Computational Fluid Dynamics (CFD)

COMMON ISSUES WITH OPEN CHANNEL UV DISINFECTION

Open Channel System
Dead Zones

Dead Zones or spaces can be formed within the channel, which leads to short circuiting and untreated water.

Poor hydraulics

Erratic or reduced inactivation performance caused by poor hydraulics, density currents can be created that cause incoming wastewater to flow along the top or bottom of the lamp banks, resulting in short circuits and poor disinfection. Often the entry and exit conditions are inappropriate; these lead to the formation of eddy currents that create uneven velocity profiles which lead to short circuits.

Debris recovered from an open channel system
Under sized channel width and depth

This can create very high velocities and can reduce the residence time required for adequate UV dose delivery.  This can be made worse if the open channel is designed for average dry weather flows and not peak wet weather flows, at which time the head loss will affect upstream processes and can breach the channel walls. 

Large open water surfaces

This can lead to fly and mosquito nuisance and cause corrosion of electrical  components due to the elevated humidity.  Operators can lose tools that are dropped into the water.  Sunlight causes algae to grow and stimulates an enzyme that can repair DNA damage caused by the UV system.  This phenomenon is called photorepair. Inhalation risk for operators from aerosols containing pathogenic  organisms is poorly understood.

Caution signs required for open channel
Level control is vital, but fragile

The level of the fluid in the channel must be carefully controlled.  This can be achieved by a sliding gate mechanism; however, these are prone to blocking.  Counter weighted gate systems require frequent hinge lubrication and often struggle to meet height tolerances. 

Safety considerations

UV light will burn exposed skin in seconds, causing erythema (sunburn). Burns to the inside of the eyeball, sometimes called arc eye or welding flash, are extremely painful and can lead to retinal lesions, cataracts and yellowing of the lens on prolonged exposure.