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Aeration in wastewater treatment
By Carol Brzozowski
From a horseracing track to a tilapia farm to a winery, the combination of aeration and microbes takes center stage in addressing wastewater challenges.
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| Hollywood Park uses reclaimed water to irrigate its turf. |
Right on Track at Hollywood Race Park
The combination of aeration and microbes has been a successful solution for addressing problems that had been experienced at the Hollywood Park Race Track in Inglewood, CA. There, horses are washed down every day, with the water directed to the onsite wastewater treatment plant where it is treated and pumped to a lake. From that lake, the reclaimed water is used to irrigate the turf track horses use to race. The lake is also home to many ducks, geese, and flamingos, but it also was populated by a lot of fertilizers. The bottom “looked nasty,” says David Kessinger, general foreman for plumbing with the Hollywood Park Race Track. “You could put your arm in it, pull it out, and it would be covered with little crawling bugs. The water was so nasty, it wasn’t worth using to irrigate,” he says.
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Photo: Niall Crotty
Courtesy: Creative Commons (creativecommons.org/licenses/by-sa/2.5/) |
| Tilapia are quickly gaining popularity in aquaculture farms internationally, like these fish in Debre Zeyit, Ethiopia. They are often raised in farms similar to the one below. |
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The turf track needed to be maintained because racing was being conducted on the turf track as well as the dirt track, Kessinger explains. “Our engineers were telling us we needed to get some aeration going,” he says. Kessinger explored the options and chose the AIRE-O2 Series II aeration system from Aeration Industries International Inc. in Chaska, MN. The system creates a partial vacuum under the water, dispersing air that is drawn through the shaft horizontally into the water. The rotating propeller induces a flow of atmospheric air through the air intake ports on the shaft above the water surface.
The air is drawn through the shaft, past the propeller, and exits in a high-velocity stream of high bubbles as it is diffused in the water. Kessinger used the aeration system in conjunction with a BioAmp microbe system. The system enables the horse track to produce live, active microbial culture onsite to enable “good bugs” to break down organic matter—bugs that are typically decreased in numbers due to heat, fungicides, pesticides, and compaction, among other factors.
The system mixes microbes with water and spins them for 24 hours before releasing 30 trillion microbes into the lake. “The microbes and aeration in conjunction turned the lake right around in a few months,” says Kessinger. “It’s fantastic now. The pH levels are balanced. It took care of a lot of the metal problems we were having in the water. You can see the bottom, and I hadn’t ever seen the bottom.”
The effectiveness of the combination approach initiated in January 2005 was driven home when one of the race track’s employees had stopped using the microbes for several months and the water reverted to a bad state again. The microbe treatment resumed and so did the quality of the water.
“The water is more usable now and the grass looks a lot better,” says Kessinger.
Onsite Treatment Enables a Prison’s Aquaculture Program
At the Wyoming Women’s Center, a women’s prison in Lusk, WY, intensive aeration and filtration is being applied at a tilapia farming facility.
“Two years ago, the State of Wyoming came to us looking for some opportunities in aquaculture where they could do an indoor recirculating system that would provide training for the women inmates, so when they get out of prison, they would have an opportunity to work in aquaculture,” says Jim Keeton, chief executive officer of Keeton Industries in Wellington, CO.
However, the tilapia production facility would create more wastewater, and the town of Lusk has a small wastewater treatment system not capable of taking on much more additional loading. Keeton’s plan was to use his company’s technology to treat the wastestream onsite at the prison before discharging a small amount to the Lusk wastewater system, while retaining the rest at the tilapia production facility to enhance production capabilities.
Keeton Industries came in after the aquaculture facility was constructed and conducted a rapid redesign, because it was apparent the system that had been installed was not going to work favorably. Keeton Industries built its Intensive Recirculating Aquaculture System (IRAS) for the tilapia production facility.
“There are seven modules and each module has eight round tanks that are 8 feet in diameter and 1,500 gallons,” Keeton says.
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Photo: Aeration Industries International |
| In the future, aeration systems will be able to utilize hydroponics to take nutrients out of the water to increase onsite wastewater treatment. |
“We also have another line that’s called a hatchery. It has an entire series of semi-square tanks used to advance the fingerlings, which are raised to about 20 grams before being sent to the production tanks. We are always rotating through those seven different lines of tanks.”
Keeton says the system works by filtering the ammonia, the nitrites, the biological oxygen demand (BOD), and the organic loading, with the water sent back to the tank. “There may be 5% to 10% of the entire system volume that overflows each day, but this water is so good that when it goes out, it may have a BOD of 10 to 20 milligrams per liter,” he says. “It’s worth noting the average sewage treatment plant outfall has 250 to 500 milligrams per liter of BOD.
“We’re actually diluting the system and probably improving the sewage treatment plant. The quality is good enough where it will actually improve the treatment system by dilution,” Keeton adds. “The water has very low BOD, ammonia, solids, and a high oxygen level when discharged to the sewer system. There are aeration components throughout the system as well as oxygen injection.”
The solid waste from the system is taken into drying beds outside. While the solids for now are being captured, future plans call for the utilization of some of the solids through hydroponics to take up nutrients and increase onsite wastewater treatment while discharging less to the municipal wastewater system, says Keeton. The hydroponics system would be utilized to grow vegetables.
“We can take a side stream off of the sumps in the back and pump it through the hydroponics beds and then back to the tanks so almost everything is removed,” says Keeton.
The sludge and solid waste comes from the fish tank water.
“The water is recirculating at all times, and when it comes back from the tanks after it has gone through and the fish are respirating and you are putting a lot of feed into the tanks, the fish are excreting feces and ammonia,” says Keeton.
The water comes out of the tanks and goes down a main line and through a rotary drum filter, which removes 90% of the solids and takes out much of the BOD, notes Keeton. Next, the water with the dissolved ammonia is sent through biofiltration. The ammonia filter works 24 hours a day. The water goes through a high-surface-area medium, which removes the ammonia and converts it to nitrates, Keeton says. Then, the water is reaerated and ready to go back to the tanks. “There might be 10 to 15 milligrams per liter of ammonia coming in, and it comes out of the biological filter at less than 1 milligram,” says Keeton.
All of the tanks are aerated with diffuse air to maintain an oxygen level for the fish, says Keeton. “When they get to high densities—as high as a half a pound per gallon of water—then we go to onsite oxygen production,” he says. “We have machines that produce oxygen from ambient air. After the water goes through the biofiltration, we inject the oxygen in line and it goes back to the tanks.
“It’s coming in at 4 or 5 milligrams per liter and going back at 20 or 30, so it’s very high. We use an inline oxygen injection and also low-level ozone to clean up the very fine particles in the water.”
The entire system is backed up by generators. “We have a very intensive system,” says Keeton. “We have redundant systems like pumps and a system that monitors the water flow, the oxygen flow, the pumps, the electricity in the building, and the tank temperatures. You can call in and it will talk to you and tell you what the conditions are in all of the systems. If anything goes out of whack, there are relays that dial the phone up if the water starts to drop, if the water flow quits, or if something quits in one of the lines.”
Keeton says the system processes about 10,000 gallons a day, with about 50 to 100 pounds of sludge produced. The facility Keeton Industries designed will enable the women’s prison to produce 100,000 pounds of tilapia each year. Because the Lusk wastewater treatment system was so small, Keeton had to meet with Wyoming Department of Environmental Quality officials to prove to them the system his company was constructing would discharge treated waste from the aquaculture facility so as to not overload the facility. Otherwise, Lusk would have to rebuild its wastewater treatment plant to accommodate the tilapia production farm, Keeton notes.
Historic Vineyard Turns to Modern Technology
In Napa Valley, CA, Trefethen Vineyards, a historic vineyard established in 1886 under a different name by a Scottish sea captain, produces 70,000 cases of wine a year on its 100-acre ranch. It has not always been a thriving vineyard: Over the years it fell into a state of disrepair until the Trefethen family purchased the property in 1968 and began restoration efforts. Today, the vineyard has a spot on the National Register of Historic Places as the only 19th-century, wooden, gravity-flow winery in Napa County. Like all vineyards, there’s always a challenge in treating the onsite waste.
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| Harvest time requires the heaviest aeration system use. |
“Prior to getting our aeration equipment, odors were apparently worrisome at the site during the ‘crush’ season,” notes Cheri Cohen, a spokeswoman for Aeration Industries International. “Incoming flows are at their highest usage levels from August 15 to November 1 during grape harvesting. The subsequent winemaking adds considerable biodegradable grape and solids to the system until the end of December.”
In 2001 and 2003, the winery installed the AIRE-O2 Aspirator Aerator and AIRE-O2 Triton Aerator respectively.Bubble size, hang time, and complete mixing of a basin to prevent dead spots and short circuiting are factors that affect oxygen transfer andwastewater treatment performance.
The AIRE-O2 Triton aerator disperses oxygen throughout an entire wastewater treatment basin. The aerator/mixer is an electric motor-driven propeller-type floating aerator equipped with a regenerative blower. The aerator induces the flow of air below the surface of the water, providing flow-linkage mixing in multiple-unit arrangements. Air is forced down through the shaft past the propeller and exits in a high-velocity stream of fine bubbles as it is diffused in the water. The average bubble size is 2.0 millimeters, which meets the EPA definition for fine bubble-diffused air systems, says Cohen.
Multiple units create flow-linkage and increase bubble hang time throughout a basin, allowing for more oxygen transfer/mixed liquor interface time, she adds. The Triton aeration system has the capability to be operated in a mixing-only or the “mixing plus aeration” mode using the same unit and controlled independently for complete process control in biological nutrient removal (BNR) applications, says Cohen. “This feature can save energy costs and also allows for the ‘turn-down’ of one or more units to match incoming influent flows,” she says.
Typical of vineyards, Trefethen Vineyards has two aeration ponds and a holding pond on its property. All of the production water is pumped from the winery processing area to the aeration ponds.
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Photo: Aeration Industries International |
| In this aeration system a propeller mixes the pond while a pump injects oxygen. |
“It is pumped over a separator screen, which takes all of the solid material out before it goes to the pond, and then it’s pumped out into a main pond, which has two of the large Triton aerators in it and then it gravity flows into a secondary pond, which is aerated and settled, so there’s solids settling out of two ponds,” says Richard Degarmo, the operations manager. “Then it’s pumped over into the third pond—the irrigation pond—which we use to irrigate the vineyard. We have not quite 100% recycled water at the vineyard, but very, very close.”
During the harvest time, the aeration is running 24 hours a day, notes Degarmo. “We generate the heaviest use of water at that time, and our aerators are going constantly to keep the oxygen level up for the biodegradable matter we’re trying to take care of.”
Prior to the installation of the AIRE-O2 Aspirator Aerator and the AIRE-O2 Triton Aerator, the ponds had pontoon vertical pump aerators that were switched over to the new ones as they got changed out, Degarmo says. “The ones we had before churned the water up over a platform so that it could gather oxygen and then drop back down into the pond,” he says. “With the Tritons, as the propeller is mixing the pond, another pump is injecting oxygen into the water. It’s not relying on the water to just splash on the surface to catch oxygen. We’re getting a much higher oxygen concentration at the ponds than we ever were before.”
Additionally, the aerators are more efficient than older versions, Degarmo adds.
“We were using 10-horsepower motors to drive our older aerators, and we’re now using 7.5 horsepower on one and 5 horsepower on the other. We’re using significantly less energy,” he says.
The aerators also are easier to maintain, he points out. “They’re doing the same job as before, but they’re much more efficient with the decomposition we want to do in the ponds, as well as energy-efficient, so we’re not consuming as much electricity as we were before.”
Carol Brzozowski is a journalist in Coral Springs, FL.
OW - May/June 2007 |
