Exploring the developing technologies that aim to achieve zero-energy aeration
By Carol Brzozowski
The costs involved in running aeration for wastewater treatment can be quite energy intensive and consume more than half of the total costs. With tight budgetary concerns, investments in wastewater treatment and the subsequent maintenance costs can be daunting. So, too, can be the environmental impact in treating one challenge—wastewater—the energy it takes to do so can create another challenge: escalating costs. Thus, several companies have or are developing technologies that aim to achieve zero-energy aeration—to bring the aeration process as close as possible to utilizing “zero-(non-natural and costly) energy” sources.
Wind-Powered
One company that has done so is LAS International. LAS International manufactures two systems: Aero-Fac and Accel-o-Fac. “The concept behind our type of wastewater treatment is to provide as much of the process as we can for as little cost per treated gallon and thus any type of low energy we can use,” says Neil Whittey, chief executive officer and president of LAS.
Central to that process is wind-powered aeration equipment. The company endeavors to achieve low-energy-use wastewater treatment through Aero-Fac, which Whittey describes as “a complete wastewater treatment system composed of control systems, aeration equipment, and other facets.”
Aero-Fac utilizes single or multiple cells in series. Each cell or stage reduces biochemical oxygen demand (BOD) by 80% to 85%. Parallel trains provide for a modular approach to accommodate larger flows. Cells are about 15 feet deep and run 3:1 or 4:1 length-to-width. Cells incorporate diffuser bridge modules. Air header diffusers are supplied by low-energy, low-pressure centrifugal fan blowers cycled on and off as needed. LAS International Mark 3 wind-powered aerators and processors are used in conjunction with a diffused-air system to provide ongoing aeration and biological optimization. During light wind periods, a 0.56-kW auxiliary motor kicks in.
“Instead of using a conventional activated sludge approach, we use a purely biological (facultative biological) approach, which gives us energy advantages,” says Whittey. “We’re doing more treatment—we have no solids handling, no sludge disposal. All of that is treated within the system so 100% of the wastewater is treated in situ rather than having to remove 50% of the waste in the form of biosolids.”
Wind-powered aeration is a central factor in another LAS technology: Accel-o-Fac. The technology uses a larger land area—about 28 acres—and is engineered to depths of 4 to 20 feet. In contrast, Aero-Fac is useful for a small landmass that calls for a more compact footprint, he adds.
Whittey believes wind power—which he points out is accessible nearly anywhere in the world with so little of it needed to operate the treatment system—is more feasible than solar power. Additionally, power outages will not affect its performance. “We’ve worked on solar systems many years ago, but with day and night, you start at 50% and then you go down from there with the declination of the sun and clouds,” he says.
 |
Photo: LAS International Ltd. |
| Water treatment plants with a zero-energy setting reduce carbon footprints. |
Whittey notes that with water treatment in general—particularly in wastewater or sewage treatment—“the flow and load to a plant can vary fairly significantly, whether it’s on a day, or week, or seasonally, or over a 20-year period. One of our systems is with the Queen of England at her facility at Sandringham Estate and is also serving the Village of West Newton that she happens to own. The difficulty of that facility is that while there are only a few hundred people in the village and on the estate under normal conditions, on weekends during the summer when they have events, it can suddenly go up to 10,000 people,” says Whittey. “Most treatment plants can’t switch from a few hundred to 10,000 in literally minutes when the buses arrive,” he says. “Our system can run in a zero- or very low-energy mode, and then when the tourists show up, it suddenly reverts to a higher power mode only during those periods when it is required.”
In Scotland and also in Oregon, LAS International builds plants used by septic haulers, “which can be a very intense operation,” Whittey points out, adding that such situations call for more flexibility. Without such flexibility, energy costs can be extensively affected.
“When the septic haulers show up at a wastewater plant and want to dump an entire truckload of septic, it provides such a strong shock load that it can be very difficult to accommodate,” he says. “We can design our Aero-Fac system so that when they show up, it goes into a full-power mode and is able to operate without odors or crashing the system. Then within hours to a day or two, it reverts back to a very low-energy mode.
“If you have industry that works various processing during the week or seasonally throughout the year, it allows the system to run either at zero-energy or very low-energy mode or anywhere in between.”
Another benefit to the zero-energy systems is the impact to the carbon footprint, Whittey points out. In England, LAS International is involved in a number of projects where global warming is a primary concern, Whittey notes.
“England is an island where the sea level is rising slightly, and that has a very dramatic impact on whether you’ve got property or not,” he adds. “We don’t appreciate it as much here in the United States, but when your property happens to be along the coast—which a lot of it is over there—as the water goes up over the next few years, it will have an impact.
“In the United Kingdom, we understand the number-one consumer of power is the water industry. If you are using an awful lot of energy and electricity, you have a large carbon footprint. Secondly, if you are hauling sludge away from a wastewater plant on a daily basis, having to handle biosolids, you have a large carbon footprint.”
Zero-energy systems can reduce electricity to a small amount and by eliminating solids handling, and the large carbon emissions that result from trucking trips and out of facilities is eliminated as well. “It comes into focus that if you can cut back on all forms of energy- and carbon-emission impact, it’s a far more sustainable approach going into the future,” says Whittey.
Whittey says in his experience, half of the world’s wastewater plants’ operators do not conduct the minimally required manufacturer-suggested maintenance on aeration equipment. Some consultants place the number higher. “Routine service and maintenance does not get done for lack of budget, manpower, training, and time,” he says. “Not only does the equipment fail and cost more money to eventually replace it, but worse than that is during the expected lifetime of the equipment, very often it’s not running.
“If it’s not running, it causes problems with effluent quality; thus there are permit violations and related issues because communities and small industries can’t keep up with the maintenance.”
LAS International partners with the World Bank Group in South America when working on plants there, “and the premise of World Bank Group is if we’re going to grant money to these communities to improve their sanitation, it’s going to have to be sustainable technology the people can put in once and will last for many years,” says Whittey.
While grants are often available to build plants, there is seldom money to maintain them, he adds. Such cases exist here in the United States in municipal areas with budget constraints. “About 15 years ago, the EPA switched from primarily grant money to the revolving loan funds, and today, instead of getting a nearly free wastewater plant, you have to not only pay back that money, but you also must be able to maintain it and pay the operating costs,” says Whittey.
In terms of capital costs, the wind-powered Accel-o-Fac aeration units are about the same price as conventional electric surface aerators but are in some cases slightly higher, says Whittey. “However, based on electrical costs alone, the units on average will recoup all capital costs within two to six years,” he says. “Over the last 20 to 30 years, the average cost recapture period has been approximately two-and-a-half years. Some installations take longer, and some are less. But the equipment is somewhat unique in its ability to pay for itself. With energy costs increasing, this payback will become even more dramatic.”
 |
Photo: Turblex Inc. |
| The less energy used, the lower the cost. |
 |
Photo: LAS International Ltd. |
| The average aeration process in a wastewater treatment facility consumes upwards of 60% of a plant’s power footprint. |
There are many variables associated with the Aero-Fac system, but compared to standard activated sludge or extended aeration plants, Aero-Fac is typically 50% to 75% of the capital cost, Whittey says. “Over a 20-year life, it is typically only 15% of the total capital and operating cost due to annual operating cost savings,” he adds.
And while Aero-Fac is initially more expensive than surface aerators, safety features such as durability, less routine maintenance, and longer equipment life can mean fewer long-term costs, Whittey says. “Because of its robust design, it will perform more reliably over the years,” Whittey says. “Treating the water is what is key to any system—it must be able to continuously treat wastewater for many years in a truly sustainable manner. If it can also do it with a smaller carbon footprint, better yet.”
In La Pine, OR, three years ago LAS International helped address challenges with respect to the city’s treatment plant expansion. The city not only needed an increase in capacity but also needed a system to address its lagoon system’s odor problem. Its proximity to residential and business areas required the problem be immediately and extensively addressed. The existing system was converted to an Aero-Fac primary stage of treatment, followed by “accelerated” secondary and tertiary cells prior to field application. Septic tank haulers used the system, which was able to handle the increased shock load, resulting in revenues for the city.
Fine-Tuned Airflow
Another company, Turblex, provides single-stage centrifugal compressor and air distribution control systems to the wastewater and utility industries in the range of 2,000 to 150,000 standard cubic feet per minute (scfm) at 4- to 30-pound force per square inch gauge (psig). Recognizing that the average aeration process in a wastewater treatment facility consumes upwards of 60% of a plant’s overall power footprint, a great deal of energy recapture is available in this area, notes Colby Mace, national sales manager for Turblex.
Turblex’s compressor unit is typically 15% to 35% more efficient than other compressor technologies across the entire operating range, he says, adding that other advantages include the widest available airflow regulating range. “This capability minimizes the number of individual compressors required and allows more exact air volumes delivered to the downstream process, thus avoiding wasted air and energy,” says Mace.
In conjunction with compressor packages, Turblex also provides air delivery and control systems. “These systems are designed to work in concert with the compressor system to deliver the minimum amount of air required for process health at the lowest-possible pressure,” says Mace.
“These systems include process-monitoring equipment such as dissolved-oxygen probes, air-flow meters and modulating valves, and pressure-sensing instruments. Minimizing air and pressure means minimizing power consumption.”
The Turblex compressor technology dates back to the late ’70s, and the company pioneered implementation of compressor and downstream air distribution control systems since the early ’90s to enhance operational flexibility, stability, and efficiency, says Mace. As such, many of the original units are still in operation today, having proven long-term reliability and robustness, he adds. Some 6,000 units are in operation worldwide in industrial process and municipal applications.
One such unit is in Springfield, MA, where a conventional activated sludge system was replaced in 1998 with a tapered aeration-activated sludge system. The older equipment—low-speed mechanical surface aerators, which consumed 60% of the plant’s power—was replaced with three 1,250-horsepower Turblex single-stage systems of 28,600 scfm each and 8.3 psig. The system also features Sanitaire Ceramic diffusers. The 67-million-gallon-per-day plant has realized a 66% reduction in aeration system power consumption with a greatly improved operating efficiency. Springfield received a $750,000 energy efficiency rebate from the Western Massachusetts Electric Co.
One of the benefits of the system is a “unique journal-bearing technology resulting in no metal-on-metal contact, minimizing maintenance and maximizing compressor life,” Mace says. “All air stream components are custom engineered for each project and application for maximum aerodynamic efficiency.”
Additionally, the compact nature of the technology minimizes “brick and mortar” expenses, he says. “These expenses are further minimized due to the air-flow flexibility of each unit, leading to the need of fewer units to meet the overall process air-flow demand,” says Mace.
Those who want to further reduce their dependence on traditional energy supplies can opt for Turblex’s engine-driven and turbine-driven options. “Many wastewater processes produce methane gas as a by-product,” Mace points out. “Depending on the available volume and quality of this gas, it can often be used to power the Turblex compressors.”
The technology has higher “first-cost” expenses compared to other systems. “However, given the concern of increasing energy costs and environmental impact of inefficient equipment, most end users evaluate equipment on a total cost of ownership [TCO] basis,” says Mace. “This approach takes into account not just the first cost of equipment but the operational costs as well.”
 |
Photo: LAS International Ltd. |
| Zero-energy aeration units can last several decades. |
The first cost of a Turblex system is often mitigated by long-term energy and operational savings. Most end users recoup the additional upfront investment in only a few years due to the dramatic decrease in power consumption provided by the Turblex system, says Mace.
The minimal maintenance required for the Turblex system is changing the inlet and oil filter elements on a routine basis. Oil quality is typically checked on a semi-annual basis. Turblex offers troubleshooting service to address issues that come up throughout the 20- to 30-year life of the equipment.
The Gravity Option
Meanwhile, another company has been working with gravity to achieve zero-energy aeration.
Newton Industrial Group’s Newton Gravity Aerator depends on gravity as the driving force of aeration, reducing energy requirements by 50%. It works as such: The target body of liquid is pumped to an inlet reservoir at a head of between 0.5 and 0.7 meters (1.64 feet to 2.30 feet) and requires just enough energy to do that. If the supply has this head, then the process requires zero energy. Sustainable energy sources can include solar panels or wind turbines. Liquid flows over a curve and down a vertical column, imparting turbulence and capturing air on its outer surface. When the flowing liquid reaches the target liquid, the entrained air creates gas bubbles. A bubbly column consisting of an air/water mix is created that rises up the column. This rise is due to the bubbly column being lighter than the target liquid. The gas bubbles descend slowly with the faster-moving liquid down the column. The bubbles continuously change shape with their descent. Their changing shape and slow descent allow the gas bubbles to release around 90% of their oxygen to the liquid. After descending more than 4 feet, the water has obtained more than 90% of all oxygen available. The highly oxygenated liquid can be either released to the target liquid or directed to any other point in the tank. The bubbles then flow to the surface but do not enhance the oxygen transfer as they have already given up their oxygen.
The system requires a lower capital-equipment cost than other types of aeration and has minimal maintenance as there are no sensitive membranes or venturi that could be blocked. Only the pump need be maintained, company officials point out. Additionally, there is no need for a compressor and thus no need for soundproofing.
The Newton Gravity Aerator is being installed for wastewater treatment at United Utilities and for the treatment of disused minewaters at United Kingdom Coal Authority sites. Among its applications, the Newton Gravity Aerator can aerate effluent in wastewater treatment plants to support microbes and their beneficial effluent breakdown; oxygenate water in paper mills, food processing plants, and breweries before discharge; oxygenate water flowing from mines no longer used to assist with ochre removal; oxygenate fish-farm water to help support fish and plant life; remove odors from docks and canals; assist in the ozonation of water by mixing other gases with liquids; treat leachate from landfill sites; and aerate reservoirs to reduce algae bloom.
“Zero-energy aeration is possible with our aerator when there is an available head between input and output,” says John Haworth, director of the Newton Industrial Group. “We need 0.5-meter head for every pass through the aerator. This situation is more likely to occur in fish farms and mine-water reclamation than in wastewater treatment.
“In wastewater treatment, the aim is to reduce the energy consumption dramatically compared to current technologies,” he adds. “We are still in the research and development phase.”
Results at United Utilities have been mixed, Haworth points out, adding that his company is “revisiting the core science behind the aerator. It is an exciting new technology, but as with most radically new technologies, it has its teething problems,” he notes. “I would hope that within six months we are in a position for more large-scale trials.”
Ask Whittey why sustainable technologies in wastewater aeration are not more common, and he replies that these are times when simple solutions are overlooked in favor of more technology. “We can have technology simply run amuck where we say we have to do everything mechanically,” Whittey says.
Whittey references an article in a European magazine on sustainable engineering that illustrates how in the past, the thrust of engineering was to build; sustainable engineering means to fix something without having to build something else. The article—based on an interview with Charles Ainger, a visiting professor of sustainable development at Cambridge University—includes a mention of the Errol wastewater treatment plant in Scotland. The plant—Europe’s first aerated facultative sewerage treatment plant—was cited as “an excellent example of innovative, sustainable wastewater treatment” and “is among the world’s most eco-friendly treatment facilities.” Among the benefits cited: The wind-powered system meant a 15% to 50% reduction in energy use over a mechanical system.
“It is a thrust of our company to get nature to do most of the work, even though the footprint is going to be a little bit larger,” says Whittey. “Sometimes I think within this industry we lose sight of what the job is—that this is a tax and we’re all spending money cleaning up sewage—and we think that because we’re spending taxpayers’ money it doesn’t matter. It does.
“It’s diversion of money for energy, manpower, equipment, and everything else that could be better spent on other things just by employing sophisticated technology by using as much of the natural process as you can conceivably use and optimizing these natural processes. This approach may not make as much money, but we’re never worried about running out of sewage plants in this world.”
Carol Brzozowski is a journalist in Coral Springs, FL.
OW - January/February 2008
|
