Waste products from food and beverage production contain significant amounts of water, creating numerous challenges for producers.

Water adds weight, which adds to hauling costs for disposal, as well as creating an environmental impact by requiring more trips to dispose of those waste products (often known as sludge or filtrate). It also increases water usage—and the cost of water—because water that’s trapped in the filtrate could be used for various applications within your facility.

Dewatering filtrate solves many of those challenges. The question then becomes, how do you most efficiently remove water from sludge? Evoqua provides a simple answer to a complicated process: by applying pressure and friction. Essentially, squeezing the water out of the sludge.

Rotary Press Technology

Evoqua’s rotary press produces a drier cake, which yields the twin benefit of reducing the amount of waste to be disposed of, while increasing the amount of available water that may be used in another process within the facility. The net result of both of these benefits is improved efficiencies and profits.

The rotary press technology is a simple solution to a complex challenge. It operates continuously at a speed of less than 1 rpm, applying pressure and friction to squeeze water out of the filtrate. Because of its design, it requires less maintenance and less labor than some of the more traditional, and more complicated, equipment currently available on the market.

“The rotary press also uses a lot less power, a lot less wash water, and requires a lot less operator interface,” says Mike Jager, product manager, Evoqua. “It makes it easier for operators to adjust and dewater sludge.”

Here’s how the rotary press works: Sludge is fed into the rotary press and goes to a filter screen. The screen holds the solids in place while water is continuously pressed out as friction and pressure build. As the pressure differential increases, water finds its way out via the filter screens, with the solids moving to the discharge end of the system. A restrictor gate arm slows the solids to form a plug; once the plug grows large enough, it moves past the restrictor gate arm and is discharged as dry waste.

As you can see, the rotary press uses a combination of friction, pressure and time to achieve a dry cake. The efficient use of these three elements offers processors a number of benefits, and all of them ultimately add up to yield a big impact on the bottom line.

Cutting Water Usage

Processors have baseline water needs in order to manufacture the food and beverage products produced in a plant. With the cost of water rising and water scarcity being a major concern in certain parts of the country, using less water can be a significant financial savings. If a processor is not recapturing and reusing water, they’re not only paying more to haul off waste, but also having to purchase more water in the front end of the process to meet the required needs.

The first step to cutting water usage is determining not only the exact water requirements for each task in your plant, but also your waste disposal options, says Barry Reicker, Vertical Market Manager, Evoqua.

“One plant might be able to sell their high strength (waste) material, another plant might have a disposal cost,” says Reicker. “It's not a one-size-fits-all. We need investment from corporate, but we also need data and information and buy-in from all of your different plants in order to help you prioritize.”

When you have that understanding of your water needs, then you can look for opportunities to reuse water, in applications such as clean in place (CIP) systems or makeup water. These applications do not need potable water, which makes them ideal targets for reused water.

That’s where the rotary press comes in. It removes water from the sludge that can then be cleaned to the quality standard needed in order to be reused. Every gallon of water that is reused is a gallon that doesn’t need to be purchased.

The efficient rotary press features a capture rate of 98%, compared to rates in the low 90s or even 80s for traditional dewatering solutions.  That increased efficiency is significant; if a certain amount of sludge contains 1,000 gallons of water, then a press that captures 98% of that water captures 980 gallons instead of possibly 850 gallons. Multiply that times the actual amount of water used in a food or beverage plant and it adds up quickly, especially when you consider that this water can be reused more than once.

There is a cost to reusing water, of course. It has to be cleaned, and equipment and operators are needed for both recapturing the water and cleaning it. But the rotary press offers savings in that area as well, because it doesn’t need an operator constantly monitoring it. Once it’s started, it can run without supervision; if a fault is detected, it sends an alert, shuts down and performs a clean in place. Shut down and cleaning cycles can be automated and scheduled as well.

The rotary press also increases efficiency by eliminating the need for belts and bearings used in traditional presses, which are immersed in sludge during the dewatering process, and are subject to constant abrasion, resulting in maintenance and down-time.

The Evoqua rotary press requires very little maintenance. What maintenance is required can generally be performed quickly and easily on site by the operator. This includes an occasional oil change (recommended after 10,000 hours of usage). Routine maintenance on alternative systems like belt presses or centrifuges is comparatively complex, often requiring repair technicians to be sent from the vendor, or the units themselves to be sent to an authorized service center.

Cutting Weight

A gallon of water weighs roughly 8.33 lbs. If your sludge contains 1,000 gallons of water and your equipment is capturing 92% of it, you’re removing more than 7,600 lbs. of weight from your sludge before it’s hauled off. But if your equipment captures 98% of the water, that ultimately removes more than 8,100 lbs. of weight from the sludge, which means you’ve reduced the weight of the material that has to be hauled away by an additional 500 lbs!

“You might be paying heavy surcharges on cake that weighs too much because of the volume of water in it that is being hauled to the landfill, and then you could potentially be paying surcharges on your effluent discharge to the wastewater treatment plant,” says Jager. “As you can see, there are a lot of costs to take into account. It’s important to understand how clean you want your water and how light you want your waste. This is one of the main reasons why we started our complimentary sludge analysis, to help better understand your wastewater.”

Cutting the weight also has an impact on the number of trucks you need, as well as the environmental impact of those hauling runs. Although it’s not a perfectly linear relationship, the number of trucks drops off as the amount of solids captured increases; 18 trucks required at 5% of solids captured can turn into 10 trucks needed at 25%. Cutting the number of truckloads needed in half will yield significant financial savings, while also providing a significant reduction in the amount of pollutants being put in the air by reducing the number of trucks hauling away waste.

“If you're replacing a belt press, it can be as much as 30% to 40% less,” in terms of the numbers of trucks needed, says Jager. “If you're replacing the wet hauling where you don't have a good dewatering system at all, you're talking about going from two, three trucks a day to one a month. It's phenomenal the amount that you're going to save in those instances.”

The Right Tool For The Job

The rotary press is designed for use in applications involving organic waste, including those you would find in food and beverage facilities. It is available in multiple sizes, with different screen diameters, filtration areas and hydraulic flows. The number of channels ranges from 1-4 per press.

That flexibility and modular design offers food and beverage processors a number of options when it comes to installing and using a rotary press system. Because it is a “set it and forget it” operation, adding more channels or even more presses doesn’t require an equivalent investment in operators or maintenance personnel. If any of the components do need replacing, they can be removed and replaced with standard tools in as little as 30 to 60 minutes. If the composition of the sludge changes dramatically, then the press will need to be adjusted in order to meet the new requirements, but otherwise it generally runs unattended.

“If  you're suddenly feeding the system something that won't work with the polymer settings that are being applied, it'll just notify you and go into a five-minute clean-in-place state, and then sit and wait for you to come and clear the fault,” says Jager.

Compare that to a belt press system, which not only requires thousands of gallons of water per day to be cleaned, but is also prone to issues if the input changes, including sludge escaping from the edges and sides of the system, creating a costly mess for processors. With a belt press maintenance is also generally more complicated and time consuming to operate, even if everything is running efficiently.

Most importantly, there’s a significant performance difference between the rotary press and a belt press.

“Your cake is going to be about 25%, drier compared to a belt press,” says Jager. “The amount of dryness depends on the application and exactly what the sludge contains. But application to application, we're running about 25% drier, so that's 25% less volume by weight that goes to a landfill.”

As discussed earlier, that performance difference matters when it comes to cutting water waste and your reuse initiatives. The cleaner the water coming out of the press, the less work—and expense—needed to make it reusable. While water may not need to be potable to be reused in an application like clean-in-place, it does need to meet a certain standard. One critical piece of that is being able to remove fine particulate that build up over time, creating problems with piping and equipment as that build-up continues to grow.

“Some may think that you can just bring back whatever you want to the head of your system and it's not going to affect downstream equipment, but that's just not true,” says Jager. “The cleaner the water you can have as an input, the easier it is on all of your equipment and the operation in its entirety.”

The Bottom Line

Water and waste disposal are major expenses for food and beverage processors, while also having a major environmental impact. Being able to maximize how much water you can get out of your sludge lessens both the financial and environmental impact on your business.

There are already numerous options for processors who want to dewater their sludge. But what sets the rotary press apart is its ability to offer high-performance dewatering with a simplified plug and play installation, and an energy-efficient, and less-labor-intensive operation. The continuous low-speed operation reduces wear and tear on parts, the energy needed to operate the press and the amount of operator oversight necessary.

Integration into control systems and the ability to schedule shutdowns and cleaning also helps with facilitating ease of use. Ultimately, the rotary press technology gives its operators time back in their busy schedule to focus on what matters most. If an operator is needed, a built-in alarm alerts the operator while the press automatically performs a clean-in-place, enabling the operator to focus on other activities unless needed. All of these features can add up to big savings for processors, impacting the business’s bottom line, both financially and environmentally.

The flexibility of the press is an important consideration that is sometimes understated. Due to its expandability and ease of operations, processors can scale up their dewatering capacity without the requirement to overhaul infrastructure or invest in new staff. If the increased demand in dewatering is temporary or seasonal, you also have the opportunity to rent a rotary press as needed, in order to buy you time for when a more permanent solution is available.

“Whether you're a big or a small processing plant, you're going to get the same great dewatering out of the rotary press technology,” says Jager, because reducing processing costs, increasing uptime and making the job easier to do are benefits that help everyone.