Wastewater Treatment in Grain and Food Processors- Case Study
For grain processors, removing suspended solids such us fats, grease, grit, contaminants and leftover process materials from liquids is necessary to comply with regulations like the EPA`s Clean Water Act. which sets wastewater standards for industry and national water quality criteria for pollutants in surface waters. To remain compliant, processors often use clarificrs, also known as settling tanks or settlers.
Clarifiers are designed to continuously remove the solids that accumulate due to sedimentation, the separation of suspended solids from a liquid by gravity. Concentrated impurities are discharged from the bottom of the tank while scum particles float to the surface of the liquid and are typically removed with strainers.
Although clarifiers are common, there are substantial limitations when conditions are unpredictable. The problem for wastewater treatment is that no fluid processing or filtration system remains static. Treatment conditions continually change due to variable factors such as pressure, particle size, solids loading and even the presence of sticky biologicals.
"The flow rate and volume of suspended solids in the fluid changes depending on production demands and the equipment used as well as the time of day, day of the week and seasonal factors," says Robert Presser, Vice President of Acme Engineering Prod Inc. a North American manufacturer of industrial self-cleaning strainers. The company is an ISO 9001:2015 certified manufacturer of environmental controls and systems with integrated mechanical, electrical and electronic capabilities.
Fortunately, a separation technology designed to tolerate variability - automatic scraper strainers - is being used after clarifiers and before further processing when reliable, economic, low-maintenance water treatment is necessary. These self-cleaning scrapers filter out both tiny particles and larger debris, utilising a blade and brush that work together to keep all straining surfaces fully effective and free of obstruction.
The technology assures reliable straining that facilitates regulatory compliance. The approach also virtually eliminates manual maintenance as well as equipment clogging and fouling issues with downstream water treatment processes such as membrane filtration, reverse osmosis or zone disinfection.
Claritier Challenges
Since (he clarificrs used by food and grain processors rely on gravity to clear suspended solids from wastewater, the natural separation process can take a very long rime to occur. Plocculants are also often added to facilitate the agglomeration and settling of suspended particles out of the wastewater, however, the amount of flocculant must change. In addition, the "size` of the solid particulate is also continually changing, which makes balancing the process more difficult.
Large clarifiers must be regularly emptied of wastewater and washed down as well. This requires replacing a significant volume of water or other processing fluid at great expense.
Unpredictable factors such as algae blooms can further compromise traditional treatment. Food processors must periodically clean algae and other undesirable materials from the weirs, baffles and troughs of clarifiers/settling tanks.
"Algae can grow at a surprisingly fast rate, particularly in summer, until it impairs tank function. If an algae bloom flows over the top of the settling tanks, you cannot let it compromise the downstream equipment. When food processors use a high-pressure hose to wash down the rims of the settling tank, this releases a substantial amount of algae and contaminants that must be captured." says Presser.
With wastewater, typical automatic backwash strainers are particularly challenged by sticky biologicals like algae, which can harbour other contaminants like scum, grease, sludge and foam. The accumulation can continually shrink the usable open area of the strainer until it is no longer effective and must be cleaned.
"Algae can adhere to the screen and create a "cake` that the backwash arm cannot remove since it decreases pressure and suction. It is ironic that you need a relatively good open area on the clean side of your screen for backwash units to function." says Presser.
Backwash design also relies on a substantial amount of constant pressure, which can compromise reliability if not always available. "Backwash units do not operate well in backwash mode below 30 PSI. To compensate, some utilise complex, pressure-inducing tactics, but these do not always resolve the issue." says Presser.
Additionally, conventional backwash units are not designed to effectively remove larger or irregularly shaped solids.
"Oversized solids that are larger than the gap between the screen and the backwash arm does not tit within cleaning mechanism, so remain in the vessel and must be removed manually."
Today, automatic scraper strainers like Acme`s are designed to tolerate surprises while meeting water treatment requirements. The company`s motorised units is designed to continually remove both very large and very small, suspended solids from wastewater. Cleaning is accomplished by a spring-loaded blade and brush system, managed by a full automatic control system.