TALKING AERATION

CREDIT WATER ON LINE Article?| April 7, 2021

What are the most important points in this quoted article to me?

1 - Turn down capability

2- Alpha factor

3- Capital costs versus Operating Costs

6 Steps To More Holistic Wastewater Aeration Efficiency

Source:?KLa Systems

When it comes to wastewater aeration systems, experienced operators, consulting engineers, contractors, and executive decision-makers can appreciate the differences between a true workhorse and one?designed by a committee. Here are six important considerations for keeping new or upgraded designs from casting a dark shadow on aeration cost, convenience, and consistency — even when multiple parties share responsibility for different aspects of the process.

Alternatives To Total System Responsibility — In Theory And Practice

Unlike products designed, built, and sold as turnkey solutions, wastewater treatment facilities and their aeration systems are frequently a collection of individual components sourced from multiple suppliers. In theory, there’s nothing wrong with that as long as the engineering of the final system is well implemented to provide maximum efficiency. In practice, however, problems that arise can often be traced back to gaps in communication or coordination among the different specialists involved.

Individual components that go into an efficient wastewater treatment system — in-tank aerators and supports, recirculation pumps, aeration blowers, external wastewater piping, external aeration piping, and instrumentation/controls — do not operate in isolation. Each has the potential to compromise performance if the entire system is not conceived and implemented as a balanced design. That is why in the absence of assigning total system responsibility, well-coordinated communication is essential.

6 Considerations For Avoiding Compromised Aeration Efficiency

Whatever the business rationale for dividing the design and implementation among multiple suppliers or acquiring it from a single source, the physics of how the system will work in the real-world application should not be overlooked. Even if an in-tank aeration supplier does not have total system responsibility, giving them visibility into other aspects that impact oxygen transfer and operating efficiency can pay dividends in the long run. Here are six easily overlooked performance implications that should be considered for their interrelated impacts:

• Aeration Device Design.?The most efficient and easiest-to-maintain designs deliver the greatest bubble surface area with the longest path of travel to deliver the best overall oxygen exchange. Fundamental choices between diffusers vs.?jet aeration nozzles?vs.?slot injector systems?will impact?alpha factors, efficient?aeration/mixing?patterns, and maintenance requirements and should be tailored to the existing or newly specified blower system (Figure 1). Structural and material choices can also impact the efficiency and durability of the total?aeration solution.

?Jet Aerator.

• Oxygen Volume Per Horsepower.?Just because an aeration system can keep up with the worst-case total oxygen demand (TOD) of an application does not mean it is operating efficiently. Maximizing energy efficiency can involve a lot more than just choosing high-efficiency rotating equipment — including streamlining airflow, using variable frequency drives (VFDs) and high-efficiency motors, choosing aeration devices and surface-aeration patterns that optimize mass transfer when oxygen demand is at its highest, and accommodating the lowest turndown levels.
• Pump/Blower Locations.?Ideally, pumps and blowers should be mounted as close to the aeration tank as practical, to minimize piping restrictions and friction (Figure 2). Excessive distances can elevate pump/blower pressure demands by 20 to 30 percent, compromising efficiency due to pressure loss from friction within the piping. Also, pump suction intakes should not be located close to where aeration bubbles could be sucked into the pump intake.

?Keeping pipework between pumps, blowers, and treatment basins as short and straight as practical will reduce friction and minimize potential energy loss that can drive up operating costs.

• Piping Restrictions.?In addition to excessive piping lengths, restrictions related to elbows, valves, and other design features can also impact efficiency. For example, installing check valves to enable automatic transition to a backup jet or injector pump in an emergency can create up to 20 percent more pressure and demand more horsepower for every minute that the primary pump operates.
• Seasonal/Situational Operating Conditions.?Beyond treatment tank size, piping dimensions, and horsepower ratings, look for other intangibles that can impact performance reliability.
• Operating Temperature.?One important factor to consider is the operating temperature of a blower under worst-case summer conditions when oxygen demand is highest. Making sure the blower system can handle the high-temperature environment is key to reliable 24/7 operation.
• Turndown Capabilities.?Whether related to temperature, throughput volume, or treatment of waste streams with highly variable oxygen demand, the ability to fine-tune turndown capabilities in response to actual oxygen demands can make a big difference in overall energy costs.
• Maintenance Convenience.?Dry-pit pumps allow for easier maintenance access with aboveground tanks. For in-ground basins, where they are impractical to install, look for the most reliable submersible pumps and install them on a well-designed rail system for easier maintenance access.
• Capital Costs vs. Operating Costs.?Finally, don’t compare alternatives or award contracts based on the capital cost of initial design and installation alone. With the right designs, differentials in upfront capital costs can be more than offset — multiple times over — based on how they reduce 24/7 operating costs throughout the service life of the entire installation (Figure 3).

Reaping The Value Of Total System Insight

Not all aeration system projects have the luxury of a start-from-scratch design; many involve retrofitting some aspect of undersized, inefficient, or worn equipment within the structure of an existing operation.

While it is not mandatory that all components be specified, purchased, and installed by a single source, there are benefits to having the aeration technology provider take on as much scope as practical to ensure the system is reliable, flexible, and optimizes energy efficiency. When scope-of-supply responsibilities are divided, every provider should recognize how their area of contribution can impact other aspects — physically or financially. Industrial and municipal applications offer many examples of installations that required more energy or delivered less throughput than originally anticipated, due to insufficient communication or understanding of the related aspects across component categories.

Facilitating communication among all involved parties to compare crossover impacts from the earliest phases of pre-design can help in planning and delivering the most energy-efficient and cost-effective design with the most affordable balance of construction and operating costs.

FGX3 our bioaugmentation product increases the alpha factor, improves process and lowers operation cost without capital expenditure. As kWh unit costs increase the cost of dosing actually returns money to the bottom line lowering operating costs exponentially as kWh unit costs increase. I used to run modelling cost optimisation at $0.07 to $0.09 and often achieved zero cost to dosing now I'm being quoted costs of kWh between $0.25 to $0.70 as tariff protections are lost or plants operate high ours outside Triad lows. A recent exercise on a 10,000 M3/d mechanical aerator plant showed returns of $30,000 after allowing for the cost of dosing on a plant design of 1.5KgO2/kWhr. One consulting engineer was quoting an alpha factor of 0.5 for a 200,000 population head works with fine bubble diffusers; often on an example like this use of FGX3 increases the alpha factor to 0.9 what a difference this makes to the energy cost of running the variable speed blowers