Although the city of Mandeville, La., is a small community, the city's administration realized the efficiency and potential of green technology back in 1989 when biological wastewater treatment was considered innovative compared to mechanical treatment processes. The city has long embraced a green philosophy befitting its scenic natural surroundings. Now that two decades have passed, their once deemed pioneering ultraviolet (UV) disinfection system is old and outdated with high maintenance and costly replacements. The city of Mandeville went on a search for an environmentally friendly system that reduced their maintenance frequency and cost.
Project Background
Just 30 miles north of New Orleans, the Mandeville Wastewater Treatment Plant serves a small city with a little more than 12,000 residents. Residents and visitors appreciate the variety of tree-lined bicycle and pedestrian pathways, fishing piers and boating areas, Lake Pontchartrain, and its surrounding estuaries, including Big Branch Marsh National Wildlife Refuge. To stay in line with their green philosophy, officials knew they had to replace their outdated UV disinfection system that became gallingly expensive due to the increased frequency of required maintenance. Such concerns included breakage of quartz sleeves and bulbs, and fouling of the lamp sleeves. Moisture inside the sleeves caused receptacle plugs and ground fault circuit interrupters to overheat and fail. While the plant remained in compliance, the city of Mandeville decided to replace the UV system with a less costly, greener technology.
"Finding a UV system that was self-cleaning and low maintenance was an important consideration for us," said David deGeneres, the city's director of public works. "Ease of maintenance was important, too. With the plant's first UV system, we had to change the sleeve and the bulb on each unit, which increased the potential for a lamp failure."
It was important for the city of Mandeville to find a system that was not only better for the environment, but also easier to maintain, in return producing significant cost savings. That is why De Nora Water Technologies' MicroDynamics microwave UV disinfection technology was chosen to replace the existing UV disinfection system at Mandeville’s Wastewater Treatment Plant. MicroDynamics technology uses microwaves to energize low-pressure, high-output electrodeless lamps to maximize a UVC output at 254 nm. Suitable for municipal or industrial water and wastewater applications MicroDynamics systems are available in modular, open-channel and closed-vessel system designs.
Pilot Testing the MicroDynamics Technology
Eight MicroDynamics Series OCS 660 modules were installed—two trains of four each. Unlike traditional UV disinfection systems, MicroDynamics uses electrodeless lamps; there are no electrical connections to fail, corrode or leak, which dramatically increases system efficiency and lamp life when compared to traditional UV lamps. Because electrodeless lamps have no wires under water, safety concerns inherent with the repair of possibly 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 lamps 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. The microwave UV system does not require chemical addition to clean the quartz sleeves. Unlike other low-pressure, high-output UV systems whose lamps run more than 200˚F (93˚C), the MicroDynamics quartz sleeve is kept at 115˚F (46˚C), making the lamps less susceptible to foulants baking on the sleeves. Therefore, a chemical-free wiper system is sufficient to keep the sleeves clean, making the system greener than traditional UV lamps.
Full-Scale Operation
The Mandeville Wastewater Plant has seen significant cost savings since the instillation of the MicroDynamics system. The system eliminated the eight man-hours per week spent cleaning the old system's UV bulbs. In addition, the new system put an end to spending more than $100,000 per year on bulb and sleeve replacement. Since the MicroDynamics system allows for bulbs to be removed without taking them out of the water, Mandeville Wastewater Treatment Plant employees are relieved of the maintenance hassle the old UV system was causing them.
After more than a year of operation, the Mandeville plant is achieving fecal coliform discharge levels of less than 2 MPN/100mL, compared to permit levels of less than 200 MPN/100mL.
"All in all, I feel the public works department provides good quality service at a minimal cost to our residents," deGeneres said. "And by embracing green technologies, we are able to enhance the native wildlife and vegetation of our valuable wetlands."
