TECHNICAL BULLETIN 158 | Energy Smart Designs
It is common knowledge in wastewater treatment plants that the energy consumption of the plant is highly concentrated in the aerobic treatment process. Most plants would find that the aeration system consumes as much as 50% – 70% of the energy of the entire plant! This is an area which gives great opportunities for design optimization and opportunities for major gains in the system economics over life of the project.
Historically the systems for aeration in wastewater treatment plants have migrated from initial systems that were coarse bubble diffusers to higher efficiency diffuser selections. Coarse bubble diffusers were excellent in terms of reliability and overall system performance, but were a major energy drain (cost) in the facility budget.
Starting in about 1920 it was discovered that ceramic fine bubble diffusers could give excellent energy efficiency, but ended up with difficulties in operation and maintenance. Ceramic units were very high efficiency when new, but media fouling deteriorated performance and created maintenance difficulties.
Diffuser systems continued to evolve with medium bubble membrane diffusers developed in the period from 1970 to 1980. Medium bubble oxygen transfer efficiency was less than fine bubble but better than coarse bubble while maintaining superior system reliability.
Fine bubble membrane diffusers were then developed which gave maximum oxygen transfer efficiency. The advanced technology membrane diffuser systems provided that efficiency as a very reliable technology. Fine bubble diffuser systems today have been developed which give both efficiency and reliability, and have assumed the bulk of the wastewater treatment aeration activities throughout the industry and globally.
The overall migration from coarse bubble to fine bubble diffusers has been driven by the substantial energy conservation opportunities. Energy consumption was dramatically reduced with the latest technology in aeration vs. coarse bubble diffusers. Aeration systems today typically operate at 40% – 50% of the original coarse bubble diffuser energy requirements. This is a huge benefit in the total cost of plant operations.
One major factor must be recognized: The design of an aeration system for maximum performance now is primarily controlled with optimum configuration and application of the fine bubble diffusers! The diffuser design and the type of diffuser (tube, disc, panel etc.) is not as critical as the fact that it is a fine bubble diffuser and properly applied! This is an item that is frequently overlooked in the industry as people tend to promote they have the highest efficiency diffuser! This product performance is generally no greater efficiency than many fine bubble devices properly applied; however, there are ways you can apply fine bubble systems to get much greater efficiency than typically used in the industry. High density fine bubble systems and using fine bubble products are now becoming more popular, but in a high-density (lot of diffusers) and low air flux rate per square meter of the membrane surface to obtain efficiency gains of 15% to 30%! Application of the proper fine bubble diffusers in the proper configuration and proper airflow rate per diffuser is critical to the lowest long-term operational cost of the plant.
With that background information, we now review specific ways to drop energy consumption in waste treatment facilities. There are a number of ways to manage this energy conservation using today’s technology! Today’s technology recognizes that the energy consumption is an integrated solution considering the diffuser system is properly applied as described above, new high-efficiency blowers such as turbo or screw type which can have a major impact on the energy reductions, and of course the use of high-efficiency motors to drive this electrical equipment.
How much of an energy savings is available to properly engineer systems to peak performance levels above the traditional fine bubble diffusers currently installed today?
These are major questions and a critical decision point for proper design of any wastewater treatment system. Until those questions are clearly enunciated, it is impossible to optimize the design of the aeration system for lowest cost of ownership over the life of the project.
An example of some tools that are available and how important they can be in the energy conservation can be outlined below:
Assume traditional fine bubble diffusers systems in operation with the efficiency of 5.5% – 6.5% per meter. This is fairly traditional in the industry and results in reasonable efficiency and performance of the diffuser system, but is far from the optimum solution or the lowest total cost of ownership. Utilizing today’s technology will allow major energy savings and they can be implemented by the following procedures:
- Implementing fine bubble diffuser system designs with proper distribution and proper application of those diffusers can easily save over 20% of the energy in the plant! Net energy utilization for the system is now about 80% of what it was originally.
- New high-efficiency blower systems are available in the industry which offer an additional 15% or more in energy savings when properly applied! This 15% energy savings with the high-efficiency blowers is additive to diffuser savings in #1 above. High efficiency blowers combined with the 20% energy savings that we calculated with the diffuser design upgrade in item #1 has reduced energy consumption to only 68% of the original or typical fine bubble diffusers operating energy levels!
- Utilizing high-efficiency motors can save an additional 5% or so energy credit. Using that 5% energy savings from high-efficiency motor designs means net energy use by the optimized wastewater treatment plant design will be only 64.6% of the values when starting with a typical current design of 6.5% per meter!
This combined 35.4% energy savings is huge in the overall treatment plant cost of ownership economics and will dwarf the capital cost aspects of an aeration system that is installed using today’s technology.
EDI encourages customers and design engineers to take advantage of the Diffuser Aeration technology currently available. We recognize acceptance and use of high-efficiency blowers and high-efficiency motors is fairly common. Proper application of a premium aeration system can also save over 20% of the energy vs. the traditional designs in the industry! This 20% savings by proper application and installation of Advanced Technology aeration systems is equal to the total combined energy savings available from high efficiency blower technology plus the high-efficiency motors. High efficiency blowers and high efficiency motors are currently well accepted as engineering design factors but optimum diffuser design seems to get lost in many applications. EDI welcomes the opportunity to offer diffuser optimization solutions that incorporate and integrate the blowers, motors and the diffusers for best value and lowest total cost of ownership on any system.
The savings itemized above covers only the direct energy consumption. Proper instrumentation that paces the energy consumption or the oxygen supply to the needs of the system can save an additional 20% of the energy.
It becomes clear the total energy consumption can be reduced in many wastewater treatment plants to about 50% of the energy levels currently being expended, even when they have reasonable fine bubble diffuser systems currently installed. If the current plant aeration system is less than the traditional fine bubble diffuser system efficiency, (i.e., coarse or damaged diffuser systems) available savings can be as much as 2/3 of the energy previously used in a facility!
Please contact your EDI representative for overall evaluation and ways to reduce energy consumption in your wastewater treatment facility.