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According to Diego Rosso (above), checking the off-gas analyzer once a week can translate into big energy savings.
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For most wastewater treatment facilities, the process of dissolving oxygen into wastewater, known as aeration, is the most energy-intensive portion of the treatment process.
By introducing air in the form of very small bubbles, fine-bubble aeration systems can increase oxygen-transfer efficiency (OTE) and save energy. Unless treatment systems are properly maintained, however, oxygen transfer can decrease and degrade system efficiency.
At the Jan. 17 Program Meeting, Diego Rosso of UCLA’s Civil and Environmental Engineering Department and Southern California Edison’s Lory Larson presented information about a new technology in wastewater treatment, an off-gas analyzer that measures oxygen-transfer efficiency.
By quantifying the levels of oxygen transferred in treated water, this instrument can determine the effectiveness of a fine-bubble aeration system.
The project is funded by the California Energy Commission (CEC) and managed by Southern California Edison. The UCLA Engineering Department has built the prototypes and provided technical support.
Aeration accounts for 40-75 percent of the energy consumed during wastewater treatment. “Fine-bubble diffusers are more energy efficient than large-bubble diffusers,” explained Larson.
“Unfortunately, the diffusers also tend to clog and this wastes energy. The solution is to clean the tank and the diffusers.”
To clean or not to clean
How often should the tank be cleaned? No one seems to know. Unless the tank is completely drained and the aeration system examined – a costly and time-consuming exercise – it’s difficult to pinpoint. So the cleaning process takes place infrequently, wasting significant amounts of electricity.
“There are no identified protocols,” Larson said, “so most plants don’t do it. They clean when they think they need to.”
By measuring the oxygen-transfer efficiency, the effectiveness of the aeration system can be monitored and an appropriate maintenance schedule can be determined.
Progress in technology
“The original prototype [of the off-gas analyzer] was large, cost about $20,000 and was difficult to operate,” said Rosso. “The current prototype is the size of a shoe box, costs $2,000 and is easy to use. You can easily save 10-30 percent of energy costs. You can save the $2,000 investment in the first month.
Rosso and Larson claim that monitoring the oxygen transfer each week can optimize efficiency while maintaining the same level of treatment. So what’s slowing down the commercialization of this device? Rosso thinks the split incentive is an important barrier.
“People who operate the equipment have no incentive for energy efficiency,” he said. “The people working downtown [in municipal offices] pay the energy bills and have the incentive to take action, but don’t know how to do it. Somehow, we need to link these two groups.”
CEE’s initiative
In many respects, the CEE Municipal Water and Wastewater Initiative was developed to help position efficiency program administrators as the link between facility operators and municipal decision-makers. Launched in 2005, CEE’s initiative sends a strong message to the water and wastewater industry (and their suppliers) that programs are organized and actively supporting energy efficiency in this sector.
At the same time, CEE’s ongoing support for the initiative provides members with the opportunity to increase program effectiveness through greater communication, coordination and development across similar North American programs. Presentations at the CEE meeting on the off-gas monitor and SCE’s pump test program (see related story) are good examples.
Members currently address water and wastewater efficiency projects through their custom programs, new construction projects and through standard offer/standard performance contract programs.
During a breakout session, members expressed interest in a number of opportunities to promote efficiency in wastewater aeration systems, including encouraging customers to clean their tanks on a regular basis (at least every 24 months); to use oxygen-transfer efficiency as an energy performance indicator and to develop guidelines for programs on aeration efficiency improvement opportunities.
Commercialization of the instrument
Finally, the group was very interested in the future availability of the off-gas analyzer technology. According to Pramod Kulkarni of the California Energy Commission, the device is scheduled for demonstrations at sites in two major utility service areas.
“The demonstrations [are expected to] validate the energy savings over a span of few months,” said Kulkarni.
Following the demonstrations, he said, the following steps will be taken:
Based on the feedback from demonstration sites, develop a final commercial product.
Ask for bids to mass manufacture the product, select manufacturers.
Utilities develop rebate programs around the energy savings.
Active promotion through industry newsletters, energy-saving forums and other venues.
“Program administrators have an important opportunity to educate their wastewater customers about oxygen-transfer efficiency as key performance indicator of their aeration systems,” said CEE Industrial Program Manager Ted Jones.
“Moving forward, the Water and Wastewater Committee plans to monitor these efforts to commercialize the technology. The next step would be to begin development of program guidelines on aeration-efficiency opportunities.”
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