Quaker Oats Uses Skimmer To
Reduce Wastewater BOD
Disposal Costs Approach $250,000 Annually
 The Quaker Oats plant in Peterborough, Ontario, Canada produces
some seven million cases of Harvest Crunch® cereal and cake mixes annually. In the
process, residue from the conveyors, dryers and other processing equipment ends up on the
floor. Periodic equipment washdowns add water to the solid and liquid residue, which
contains edible fats, starches and sugars. During house-cleaning operations, this liquid
slurry flows into wastewater collection channels below the floors, and through a pipe that
carries it to settling tanks in the basement of the 6-story plant. Since the wastewater
flow can cover a wide range of rates, two settling tanks are needed to accommodate large
surges.
[In 1993] Quaker was treating this waste stream by simply suctioning off
floating oil and solids from behind weirs on top of the settling tanks. Below the surface,
water was decanted into a line leading to Peterborough's sanitary sewer system.
Although simple, this treatment process was scarcely cost effective. A
major expense associated with disposal of the semi-solid residue was the cost to have it
hauled away and discarded in a landfill. This cost ran into six figures annually. Then
officials from the Peterborough waste treatment plant told Quaker that the BOD content of
their wastewater stream was excessive. In particular, oil levels exceeded the 15 ppm
guidelines, which resulted in a sewer tax of $127,000 (Canadian). With total disposal
costs adding up to more than one-quarter million dollars annually, Quaker began looking
for better alternatives.
Lower BOD = Lower Disposal Cost
Quaker's Plant Engineering Department was assigned the task of
developing a lower cost disposal method for this waste stream. The need to separate water,
oil and solids was clear. The challenge was to select equipment that was cost effective in
terms of both original cost and operating expense, which did not create major maintenance
problems itself.
The plan that ultimately developed was to install 100-mesh (150
micrometer) screens to remove solids upstream of heated settling tanks, and install
oil/water separation equipment in the tanks themselves. Heating the tanks helps promote
faster separation of oil from the water. Both screening and skimming contribute to lower
BOD, and this arrangement minimizes problems caused by solids fouling the separation
equipment. Although a number of separation technologies could work, the one finally
selected was belt skimming, because of its simplicity and cost effectiveness.
Quaker's subsequent search for a suitable separator led to Abanaki
Corporation, a Chagrin Falls, Ohio firm that makes belt skimming equipment. Abanaki
manufacturers the Oil Boss®, which utilizes 304 stainless steel construction and removes
up to 20 gallons of oil per hour. To handle the large influx of oil during Quaker's
house-cleaning operations, two skimmers were installed in each settling tank.By using two
tanks, there is a backup if one system is taken out of service for maintenance. The total
cost to add screening and skimming equipment to both tanks was about $17,000 (Canadian).
Operation of the System
Each settling tank allows enough quiescent time for thorough separation
of oil and water. This is important because the Abanaki unit has a continuously moving
belt that relies on free-floating (not emulsified) oil to work effectively. The difference
in surface tension between water and oil is what imparts oleophilic properties to the
stainless steel belt, which means it has more affinity for oil than water.
The stainless steel belt operates on a motor and pulley system that
pulls it through the contaminated water surface where it picks up oil and fats. The
fractional horsepower gear motor is totally enclosed and fan cooled. Various voltage
options are available, as well as Food Grade Service options.
After traveling over the head pulley, the belt passes through tandem
wiper blades where oil is scraped off both sides of the belt and discharged into a
container. The tail pulley has flanges that allow it to roll freely on the inside of the
belt without becoming dislodged. It requires no bearings and does not need to be fastened
to the tank. A tether and cage assembly prevents the tail pulley from being dislodged and
lost in the tank. Belt length is customized to make sure it stays in contact with the
fluid surface at its lowest possible level.
Quaker approved the Abanaki unit because of its reputation for high
reliability, low maintenance, and minimal operator involvement, which allows unattended
operation. The only routine maintenance required is to clean and adjust wiper blade
assemblies every 2 or 3 days, a job that takes only a few minutes. Occasionally, a
skimming belt may need to be replaced. Other features that attracted Quaker's attention
were:
- low volume of water pickup
- ability to handle fluctuating fluid levels
- small mounting area
- easy installation
- capability of lifting skimmed material up to 100 feet without a pump
Fast Payback
Shortly after installation of its new separation equipment, Quaker's
wastewater stream was tested by the city of Peterborough and found to contain less than 3
ppm oil. This resulted in the plant's tax bill being reduced to $48,000, a savings of
$79,000 (Canadian) annually. Although sewer taxes subsequently went up for everyone in
Peterborough, Quaker still enjoys substantial savings.
Equally important, Quaker's disposal costs for solids and oil have been
virtually eliminated. By recovering edible oil with low water content, it can be mixed
with the separated solids and sold to a bakery salvage company. With minimal processing,
this mixture can be sold as swine feed. The price paid by the salvage company more than
pays for the cost of shipping the residue to them, and there are no landfill costs.
After three years of experience with the Abanaki Oil Boss, Quaker has
concluded that belt skimmer technology is the best one for the Peterborough plant.
Skimmers with drum, disk, mop, and tube configurations might have worked, but they did not
seem to offer as many advantages as a belt skimmer. Although other oil/water separation
technologies are effective, including coalescing, membrane separation, and various
chemical treatments, most are more complex and more expensive than skimming. Also, some of
these methods do not easily handle the volume of oil that skimming does. The
bottom line: belt skimming is a cost effective way to lower oil concentration to
only a few parts per million.
Published in Pollution Engineering, Spring
International Issue,
Learn more about Oil Boss.
See other case studies.
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