New Montevallo facility reaps cost savings, minimizes environmental impact
In May 2012, the City of Montevallo, Ala., was named an "Alabama Community of Excellence" (ACE)—only 25 Alabama cities have received that recognition. The criteria for the award include commercial business development, education enhancement, health and human services and quality of life.
When Montevallo does anything, it appears, it tries to do it right. In addition to winning the prestigious ACE award, the city's water and sewer board recently completed construction of a refurbished wastewater treatment plant that is designed to enhance cost-effective operation and environmental responsibility.
Montevallo, which has a population of approximately 6,300, is located in the geographic center of the state of Alabama, about 35 miles due south of Birmingham. Serving the population's water and wastewater needs is the Montevallo Water Works & Sewer Board, which owns and operates the Montevallo Wastewater Treatment Plant. In 2005, the board recognized that the existing treatment facility, which was constructed in 1962, was nearing the end of its useful life, and the flow into the plant was approaching the hydraulic capacity of the treatment units. Additionally, since the plant’s construction, the Alabama Department of Environmental Management had issued more stringent discharge permit limits for all treatment plants discharging into tributaries of the Cahaba River. As a result, the board retained InSite Engineering of nearby Hoover, Ala., to plan, design and administer the construction of the necessary improvements to the plant.
The required improvements included a new influent pumping station, a grit removal facility, a dual-basin sequencing batch reactor (SBR) treatment process, a post-equalization basin, chemical injection and mixing facilities, filtration, disinfection, blowers, sludge dewatering facilities, an administration building and laboratory and the conversion of existing facilities into sludge digesters and thickeners.
Environmentally friendly design
The new treatment plant would have a capacity to treat 950,000 gal per day (3.59 million liters) and a short-term surge of up to nearly 3 million gpd (11.35 million liters) to serve 1,600 wastewater customers. In addition, the board asked InSite to incorporate environmentally friendly and cost-effective features into the design wherever possible. InSite worked closely with equipment manufacturers to find equipment that met both of these requirements. These technologies include:
• A grit-removal system with no moving parts or electrical energy consumption.
• Solids dewatering facilities that are estimated to reduce the number of loads of sludge hauled from the plant by 81 percent and provide an operational cost savings in excess of $80,000 per year.
• SBR technology utilizing dissolved oxygen probes and variable speed blowers that are estimated to use 20 percent less energy than similar systems without these features.
• An ultraviolet disinfection system to replace the original gas chlorination disinfection system. The selected system uses low-pressure microwave technology, which is estimated to use 90 percent less energy than similar alternative technologies while accomplishing the same level of disinfection.
• A re-use water system that will allow the board to utilize treated filtered plant effluent for the nonpotable water needs at the plant.
Combined, all of these technologies were estimated to generate an annual energy and operational cost savings to the Board of more than $250,000 when compared to similar alternative technologies while achieving the same levels of treatment and disinfection.
Innovative microwave UV technology
After considering other disinfection systems—including conventional low pressure/high intensity UV, closed vessel technology and on-site generation of sodium hypochlorite—the board selected the MicroDynamics microwave UV disinfection technology from Severn Trent Services. One MicroDynamics system with four OCS 660 units was installed in December 2011.
The MicroDynamics technology uses microwaves to energize low-pressure, high-output electrodeless lamps to a maximum UVC output of 254 nm. With electrodeless lamps, there are no electrical connections that can fail, corrode or leak, which dramatically increases system efficiency and lamp life when compared with traditional UV lamps. And because the electrodeless lamps have no underwater wires, safety concerns that are inherent with the repair of corroded electrodes or wiring are eliminated.
The MicroDynamics system is a modular, open-channel system with UV output that is independent of ambient water temperatures, making it less susceptible to rising temperatures during periods of low flow. In addition, because the lamps can operate in air, the system does not require them to be submerged in the channel, thus reducing concerns regarding precise water level control and damage to the system due to unexpected loss of flow.
MicroDynamics systems also feature MicroPace, a flow-pacing technology that can match UV dosage to operating conditions in real time to save energy. The system activates and deactivates modules as needed based on an external flow meter signal. The modules offer quick restarts and unlimited starts and stops, thus providing a more finely tuned flow pace than is possible with traditional systems, thereby saving money on electricity costs.
The microwave UV system does not require chemical addition to clean its quartz sleeves. Unlike other low-pressure, high-output UV systems whose lamps run at more than 200°F (93°C), the MicroDynamics quartz sleeves are kept at 115°F (46°C), making these systems less susceptible to foulants baking on the sleeves. Therefore, a chemical-free wiper system is sufficient to keep the sleeves clean.
"We selected the MicroDynamics microwave UV system because it appeared the electrodeless lamps would offer longer lamp life, lower maintenance costs and more cost effective operation in the long term," said chief wastewater operator Adam Dunaway. "We also intended to apply for an American Recovery and Reinvestment Act credit by utilizing this new technology.
"The microwave UV system is operating as we anticipated. And the best part about our new disinfection system is that we are spending less maintenance time with it than with the gas chlorination system. The UV system eliminates the requirement for storing and handling of hazardous chlorine gas and sulfur dioxide, and we no longer need to maintain a USEPA risk management plan."