8- Why are retrievable & fixed grid fine bubble aeration systems superior over mechanical aeration systems?
Better system control on biological activity and oxygen control to the loading entering the basin. A diffused
air system can provide higher oxygen transfer capacity / time period and over a wider system oxygen uptake
range / system turn down
Energy conservation is important in today’s world. Fine bubble membrane diffusers are 30-60% more energy
efficient per HP provided / have a 2 to 3 x higher SAE [lb. O 2 /hr/hpwire] than mechanical aeration systems. Especially with variable loading to the plant.
Redundancy of diffuser design vs mechanical design. A diffuser system can be provided with multiple levels of redundancy for system operations staff vs a mechanical system that has limited redundancy.
9- What design compensation should an engineering firm provide into our design for the diurnal curve?
Older mechanical aeration systems become oxygen deficient as they achieve loading capacity limits.
For most plants, the load is entered into the plant in 16 hours vs the 24 hours in a day.
Therefore, the amount of oxygen available for the biological system should be designed on 16 hours and not 24 hours.
A system design based on average plant loading/h per 24 hours will become oxygen deficient from mid-morning to late afternoon (diurnal peak loading hours) starting at or greater than 75% actual loading vs. planed max. capacity.
A system design based on average plant loading/h per 16 hours will provide sufficient plant capacity regardless of the time of day
10- What additional parameters to the following should be incorporated regarding process design for a new
WWTP facility? Yr. 1 to yr. 20+ Projected per capita loading, residential diurnal patterns, & safety factors?
The planning process should also focus on:
≥ 6:1 system turn down of the aeration basin and all of its aggregates – 8:1 recommended – especially of the fine bubble aeration diffusers & blower system
nutrient loading driven process control scheme – OxyProcess TM
Separation of oxygen uptake / aeration from mixing energy for suspended solids
11- What additional parameters to the following should be incorporated regarding process design for a new
WWTP facility? Current & future permits, System redundancy, Capital cost savings, O&M cost savings?
The planning process should also focus on:
The discussion of NPDES permit; physical space allowed; flood plain concerns, design flow, current flow, number of trains, retrievable or fixed grid, future permit requirements, BNR or just ammonia removal, TN, TP limits, environmental conditions (weather, etc.).
However, in general, we find most clients like the single or two train design with all retrievable design which saves capital and O&M money while increasing the redundancy of the wwtp.
12- What should the minimum recommended turn down range of a blower & aeration system be? What is it based on?
Based on nutrient loading, hydraulic flow, temperature patterns:
13- How does temperature affect the wastewater treatment plant performance / the activated sludge process? What physics apply?
Ambient air and water temperatures influence the oxygen solubility in water [mg/l]
& the oxygen concentration [ppm] in ambient air.
I.e. @ sea level:
Dissolved O2 in water: 9.2 mg/l @ 20o C; 7.4 mg/l @ 30o C
O2 Concentration in ambient air: 20.3 ppm @ 23o C; 19.9 ppm @ 30.5o C
14- How does temperature affect the wastewater treatment plant performance / the activated sludge process? What are the practical WWT
The O 2 yield of the i.e. blower per m 3 [ft 3 ], or a mechanical aerator system and the capacity of dissolved O 2 in water will decrease with increasing temperatures. Potential violation to discharge permit limits.
15- How do prolonged summers and elevated temperatures effect the wastewater treatment plant performance, the activated sludge
process, & effluent water quality?
The plant may become oxygen deficient reducing its nutrient removal capacity, effluent water quality will decrease, discharge permits limits potentially will not be met.
Short term: The OxyPOD TM system
Long term: Increase system turn down capabilities, OxyProcess TM
16- Can the fine bubble diffuser system of circular or rectangular basin with a basin diameter or width > 20’
to 35’ [6m to 10.5m] be made retrieval?
Yes, OxyLift TM has no retrievability limitation by basin geometry
17- What is the minimum, the recommended, & the maximum possible diffuser floor coverage (aera effective
diffuser membrane / aeration basin footprint?
The minimum is 3%
Recommended 7 % or greater
The maximum possible warries form diffuser type of with a disc diffuser system has the lowest maximum. A diffuser floor coverage of > 40 % can only be achieved with the OxyStrip TM & Dual-Air-Control TM diffuser systems.
18- What is the minimum required mixing energy of a fine bubble aeration system to prevent settling out of suspended solid – complete mix without supplemental mechanical mixing?
Min. Air Mixing req.: 2.0 to 3.0 Nm 3 /h per m 2 of tank bottom area
Min. Air Mixing req.: 0.12 to 0.18 SCFM/ft 2 of tank bottom area
The higher airflow / tank bottom value is needed for shallower tanks
19- What is the minimum required mixing energy of a coarse bubble aeration systems i.e. in digester or sludge holding tank applications to prevent settling out of suspended solid? What is the difference in req. blower
capacity / power consumption of coarse bubble vs fine bubble mixing systems?
20.0 to 30.0 SCFM / 1,000 ft 3 of liquid - subject to tank depth & TSS levels
115 to 170 Nm 3 /h / 100m 3 of liquid - subject to tank depth & TSS levels
Coase bubble mixing requires up to 2.5 higher blower capacity and energy consumption than fine bubble mixing
Fine bubble mixing offers non clog protection as added benefit
JAEGER offers check valve options for its coarse bubble systems as well