Problem: An aging jet
aeration system led to ammonia concentrations exceeding permit requirements.
Solution: Installing a
fine-bubble diffuser aeration system improved energy- and cost-efficiency.
with a thriving agriculture industry and a growing population, the Water
Reclamation Division of Montgomery County Environmental Services (MCES)
continually searches for ways to optimize operating efficiency within its
MCES manages water and wastewater
services for the businesses and 537,602 residents spread throughout 18 cities
surrounding Dayton, Ohio. The division operates the Western Regional Water
Reclamation Facility in West Carrollton and the Eastern Regional Water
Reclamation Facility in Kettering. It also coordinates the disposal of 3018
Mg/yr (3300 ton/yr) of biosolids and regulates certain industrial waste
discharges into the collection system.
When the Western Regional Water
Reclamation Facility began having issues with its aging jet aeration
system, MCES recognized a new opportunity for optimization. The facility, which
produces 57 ML/d (15 mgd) of purified water for Montgomery County, has eight
2.27-million L (600,000-gal) side-by-side wastewater aeration tanks that use
jet aeration systems. Each of the 33-m-long (109-ft-long) × 15-m-wide
(50-ft-wide) × 5-m-deep
(15-ft-deep) open-top tanks contains jet aeration manifolds made of reinforced fiberglass.
After 35 years of
use, the fiberglass had deteriorated, rendering half of the eight tanks
inoperative. Efforts to repair cracks were unsuccessful, and the failing jet
aeration system led to inadequate oxygen supply, and, thus, effluent with ammonia
concentrations exceeding levels required by permits.
The facility had to replace the aging
system, and in September 2012, the Montgomery County Board of Commissioners
received approval for replacement.
MCES began evaluating different aeration
systems. Because aeration systems in water resource recovery facilities can
account for 50% to 70% of the energy required to operate an entire facility,
the county recognized an opportunity to save both energy and cost.
“Montgomery County recognized an
opportunity to increase their plant’s efficiency by utilizing a fine-bubble
diffused aeration system,” said Mark Livengood, water reclamation manager at
Fine-bubble diffuser aeration systems
produce smaller bubbles that have a larger surface area and a longer residence
time in the water being treated than larger bubbles. They also eliminate the
need for pumps required as part of the jet aeration system, improving
efficiency. The result is higher oxygen transfer efficiency, which lowers the
energy needed and the cost to operate the system when compared to alternative
To deliver the same mass of oxygen in
one aeration tank, for example, fine-bubble diffuser aeration systems require
48 m3/min (1700 ft3/min) of air, while jet aeration
systems require 96 m3/min (3400 ft3/min), Livengood said.
The facility purchased
the Xylem/Sanitaire® (Brown Deer, Wis.) Silver
Series Membrane Disc System that employs fine-bubble diffused aeration because
of the product’s reputation for being reliable and energy efficient, Livengood
said. Local contractor, Dugan and Meyers Construction Co. (Cincinnati),
installed the system in 3 weeks.
Prior to start-up,
Xylem sent a trained service technician to ensure the system had been installed
properly and to train operators on routine operation and maintenance
procedures. “This ensured a smooth transition … and gave the Montgomery County
plant the expertise and tools necessary to operate and maintain the plant’s new
aeration system,” Livengood said.
Operation of the new equipment began on
June 4, 2013, and within 72 hours, plant managers saw benefits. The settling
velocity of the solids greatly improved — visible in a side-by side comparison
between the jet-aeration and fine-bubble systems. In addition, the system achieved
superior ammonia removal with less air being injected into the tank, Livengood
After 3 months of successful run time,
MCES has experienced significant energy and cost savings from operating only
the fine-bubble systems. The experience resulted in the purchase of six more
membrane disc systems to replace the remaining jet aeration equipment. And with
this plan, the county expects to have additional savings when the facility is
fully converted to fine-bubble systems.
“We have identified cost savings will be
achieved by using [48 m3/min] 1700 ft3/min less air per
tank in comparison to the jet aeration system, equating to an estimated
$111,500 in annual energy savings. In addition, two 14-hp mixing pumps required
for the jet aeration system will be taken off-line, equating to an additional
$68,600 in annual energy savings,” Livengood said.
The jet aeration system, in use since
1978, provided a long service life but the increasing failure rate of the
fiberglass headers led to further risk of noncompliance.
“Our goal is 100%
compliance. The new Sanitaire/Xylem system works with our existing blowers and
motors, and we will realize a cost savings by a significant reduction in air
demand. Plus, the Xylem/Sanitaire system has been designed to allow for additional
diffusers to be added (or removed) in case our facility must meet new nutrient
Because of the smooth installation last
year, the county does not expect installation of six new systems to interfere
with normal facility operation or affect effluent compliance.
efficient aeration systems have been so successful that the Western Regional
Water Reclamation Facilityis considering reducing the number of its
fully operational tanks from eight to six. We feel confident that Montgomery
County will continue to experience reduced energy cost and increased plant
efficiency with the addition of the final six fine-bubble diffused aeration
systems,” Livengood said.