In a wastewater treatment plant, aeration tanks are the most energy-intensive portion of the plant, and can account for 45 to 75 percent of the energy footprint. Because of the high consumption of energy in the aeration tanks, this area is a prime place to turn to when looking to conserve energy in your plant.
Aeration tanks use bubble diffusers to distribute oxygen within the wastewater. Fine bubble diffusers, or those that produce a large amount of very small air bubbles, first began to become popular in the 1980s, as they had a much higher efficiency than coarse bubble diffusers. Fine bubble diffusers generally feature a membrane that allows airflow to pass from the piping system on the floor of the tank through the body of the diffuser and the membrane, providing oxygen into the wastewater for treatment.
Stamford Scientific International, Inc., headquartered in Poughkeepsie, New York, has developed and patented multiple advanced membrane technologies, including our PTFE (Polytetrafluoroetyhylene) coated membranes. PTFE membranes from Stamford Scientific International (SSI) have been installed worldwide in various applications — both municipal and industrial. These membranes have become increasingly popular, as the focus on energy conservation and life-cycle costs has grown worldwide.
How Do PTFE Membranes Impact Blower Efficiency?
SSI’s patented PTFE membranes were first introduced in 2004, and feature a coating which prolongs efficiency and reduces whole-life costs. The PTFE coating not only reduces plasticizer extraction, shrinking, and membrane hardening, but also limits dynamic changes that can result from swell, such as creep. Both swell and creep dramatically change the initial shape of the membrane and can cause the membrane to stretch or even tear. As a membrane stretches out the airflow pattern is no longer even along the surface of the membrane, and this will affect the overall performance of the system. In addition, PTFE slows the rate of fouling on the surface of the membrane when compared to uncoated products. Uncoated products are more susceptible to increases in dynamic wet pressure (DWP, or head loss), due to more aggressive fouling and changes in physical properties and weight. The PTFE-coated membrane improves consistency of DWP values over the product life.
These direct benefits of the PTFE coating impact long-term power costs and the ability of a system to distribute air uniformly across the tank floor. As a membrane fouls and loses its initial shape, many plant operators find they need to increase the airflow rate of their blowers to overcome the fouling on the membrane and achieve the same oxygen transfer rates. Since PTFE membranes maintain their initial efficiency and slow the rate of fouling overtime in service, plants will not see the same increase in energy needs and consumption as they would when compared to an uncoated or untreated product.
Bubble Diffuser Upgrade Yields Energy Savings
With the increased focus on conserving energy, energy savings contracts have become increasingly popular and provide a way for plants to finance improvements. Wastewater treatment plants can finance capital improvements overtime using the projected savings in energy costs to help pay for the project.
PTFE membranes have been recognized by energy savings contractors, and have been supplied on a number of energy savings contracts to date. In 2010, SSI was chosen as a vendor for an energy savings contract with the City of Fort Worth, Texas, where 70,000 pieces of our 9-inch disc diffuser with PTFE membrane were supplied to upgrade their wastewater treatment plant.
The WWTP of the City of Fort Worth, Texas, installed 70,000 pieces of 9-inch disc diffusers with PTFE membrane coatings.
Jerry Pressley, the Operations and Maintenance supervisor at the plant, could not be more pleased with SSI’s products. He said:
“Aeration diffusers are a major part of the wastewater activated sludge process. Ours were old, and we needed to replace them. We have 13 aeration basins and over 75,000 diffusers, so we spent a lot of time looking for the right supplier for the project. We had to keep costs in mind and needed to implement the change without any interruptions to our service. We, along with our “energy savings performance contractor,” chose SSI and their PTFE diffusers because they have an excellent track record, and they focus on improving energy efficiency. Although it’s a major undertaking to replace all these diffusers, it’s an investment in the future and is much more efficient in the long run. We earn the investment back in savings in energy costs.”
PTFE Membrane Technology Boosts Plant Productivity
In addition to the energy savings experienced by upgrading the plant, the staff at the Fort Worth Village Creek Wastewater Treatment Plant also noticed an increase in the productivity of their system.
Installing PTFE-coated membranes helped avoid the costly construction of additional facilities.
“With the old system, we were really limited in the loading, particularly ammonia, from return streams that we could run through the plant,” noted Gary Lagassey, Operations Superintendent. “Our plant is very large. Anything we do costs a lot of money just because of the scale. We were facing the possibility of having to build side stream treatment facilities to keep up with the demand — and this would have been extremely expensive. But because the SSI PTFE diffusers are so effective, we didn’t need to do that project, and we’re handling more water than ever before. With the old diffusers, we were limited with the amount of MLSS (the industry term for mixed liquor suspended solids), which we could use in our process. Before, we could manage about 2,000 to 2,500 MLSS. With the new diffusers, we’ve upped that to 3,500 to 4,000 mg/L.”
“Our plant is very large. Anything we do costs a lot of money just because of the scale. We were facing the possibility of having to build side stream treatment facilities to keep up with the demand — and this would have been extremely expensive.” — Gary Lagassey, Operations Superintendent
These diffusers are unique because of a patent on the membranes that resists the accumulation of matter, which avoids the blocking of the oxygen transfer and extends the time between cleaning cycles. This is a patented process unique to SSI.
“SSI really made it a straightforward implementation for us,” Pressley continued. “We had several different projects going on at once, and they just made something that we thought could be a huge headache into a smooth, seamless process.”
To read more about the Wastewater Industry, please visit www.airbestpractices.com/industries/wastewater.