Saving water is a tricky proposition for food and beverage processors worldwide. Water is critical to the food and beverage production process, with quality and quantity varying depending on where the plant is located and what it is essentially producing. The availability of clean, fresh water, its cost - and the implication production has on water conservation from a wastewater treatment perspective, plays a major role in defining what good water stewardship means.
For early adopters, much of the low hanging fruit has already been accomplished by means of eliminating egregious offenders, like once through cooling water or adding a brine recovery RO. For those who have already optimized their water to product ratio, advanced wastewater treatment facilitating direct discharge or re-use will be needed to push the envelope further. However, with thousands of food plants in North America, not everyone has had the opportunity to do so. Many food processors, both small and large, do not have dedicated water resources in house. Even so, these same facilities can still make significant gains towards their sustainability goals, without the need for large capital investments.
“We often see opportunities for immediate gains by optimizing the primary water treatment systems,” says Barry Reicker, Vertical Market Manager for Evoqua. “Reverse Osmosis (RO) has become generally accepted as a best practice in feedwater treatment, but depending on the source of supply water an RO can often only be 75 or 85% efficient, meaning only 75 out of 100 gallons fed to your primary RO will reach production. A simple brine recovery RO can increase that to 95%+ with relatively little capital demand. We often see similar opportunity with utility water applications where improving the water quality fed to boilers increases their efficiency and longevity, and inexpensive filtration of cooling tower water increases the number of cycles achievable before blowdown.”
If you’ve already picked that low-hanging fruit on the production side then odds are you are better than most. While water conservation is the intended purpose, consideration should also be given to how less water used per unit of product often translates to higher strength wastewater at the back of the plant. Just by producing a primary food product, we demonstrate the inherent tradeoff between the ingredients used and the final product.
Slogging Through Sludge
Water and wastewater costs are an inescapable reality for the food processing industry that sustains us.
“Despite having been around for as long as industrial food processing itself, organic wastewater treatment is sadly still largely misunderstood,” says Reicker. “We have a tremendous number of food and beverage processors from coast to coast that deliver us everything from pasta to potato chips to fruit juice, and we need them all. In North America, and throughout the modern world, we have often taken this fact for granted. Unexpected changes to our day-to-day lives have highlighted the importance of our trusted food processing industry and distribution system.”
That said, for an industry we largely rely on to feed our families, opinions on wastewater best practices are as varied as the end products found in every fridge in America. While true, that analogy is often best observed in the design of the treatment plant itself. Meat processors typically have high levels of fat, oils and grease (FOG) and other suspended solids (TSS) while soft drink processors often have soluble biological oxygen demand (BOD) in the form of sugar. Potato processors are responsible for the familiar french fry at our favorite restaurant, but regularly deal with silt, sand and inert solids in their wastewater. While distilleries are beginning to transition away from drying their stillage, to digesting it in an anaerobic reactor to produce valuable biogas instead.
Wastewater treatment best practices then often depend on both what you are making and your local discharge limits. Though that may seem simple, there is often more than one right answer, meaning there is often a tradeoff between what offers the most inexpensive path to compliance today vs. the lowest cost of ownership to meet future production expansion and re-use goals.
“While the industry at large continues to transition from viewing wastewater treatment as a necessary evil towards it being a value-added component of their production process, the most commonly overlooked and underestimated cost of wastewater treatment is sludge handling,” says Mike Jager, Product Manager for Evoqua. “We regularly see business underestimate both the number of trucks and the cost per load required to haul high-strength waste or biological sludge offsite.”
Many food processors assume the cost of hauling will be consistent when making purchase decisions but the reality is that hauling costs can vary significantly day to day. Dewatering any material intended to be hauled offsite is a relatively low-cost investment that pays dividends every day traffic is reduced. Transportation is expensive, so the less water in those trucks the more efficient the cost of disposal is.
“You might be paying heavy surcharges on cake that weighs too much because of the water in it going to the landfill. You might also be getting hit with surcharges on your effluent discharge to the wastewater treatment plant,” says Jager. “So, there's a lot of costs to take into account as to how clean you want your water and how light you want your waste.”
Reducing hauling costs isn’t the only reason to dewater solids. That water can also be cleaned and reused, opening up a new avenue of sustainability and efficiency. By capturing water from production byproducts and cleaning it to the point that it can be reused, processors cut down on the total amount of water they use and the amount they pay to have their waste streams hauled away.
Water reused this way can be used in a number of different applications, but, of course, the quality of reused water needed will affect the cost of cleaning it. If processors want to be able to reuse water in their process, it will need to meet the same quality requirements as incoming water. That requires more extensive cleaning, and often times it still makes more sense to pass that water along to the municipality for cleaning and rebuy it instead of cleaning the water to that level of quality on site.
But there are other parts of the process where a lower quality of water is needed, including first and second rinse clean-in-place (CIP). Boilers and cooling towers are often logical destinations to re-use water too. When food processors can clean the water onsite and reuse it for less than it would cost to have the municipality treat it, it’s a win-win situation for both industry and our environment.
“We want to get the water out of the waste so it's not going into a landfill or it's not being contaminated further,” says Jager. “If we're talking clean-in-place, the filtrate coming out of our units is clean enough to use as first or second rinse. Dewatering any high strength material not only reduces the cost of disposal but also opens up re-use opportunities where the water is given back to the processors to have another beneficial use."
“Applications such as cleaning, washdowns, boilers and cooling towers are ideal for reused water,” says Reicker. Water can be recaptured from a variety of sources including waste, treated to the desired quality if not already and used to immediately displace the freshwater demand on the environment. Every gallon of water that is re-used not only reduces cost and increases production efficiency but also alleviates the downstream demand of the POTW (publicly owned treatment works).
When wastewater can be sent to the local municipal treatment system, industry is often afforded flexibility in their wastewater treatment philosophy. But, discharge limits are becoming increasingly restrictive. Dewatering and a deliberate wastewater treatment design that recovers value from high-strength organic waste is often preferred if not necessary.
“Discharge limits are getting tighter,” Reicker says. “Many industrial food processors are used to having limits on COD (chemical oxygen demand) or BOD but are now coming to terms with their first nutrient discharge limits. Many others have been subject to nutrient limits for a long time but are now faced with increasingly lower thresholds as the EPA continues to limit the nutrient load of POTW themselves. In some areas, particularly on the West Coast, TDS (total dissolved solids) has also emerged as a parameter of concern. Regardless of where you are located you can be confident that the expectations for wastewater treatment are only growing.”
The Business Case for Reclaiming Wastewater
Combine environmental regulations with cost considerations, sustainability goals and—in some areas—water scarcity, and the case for reusing wastewater becomes clear.
CIP (clean in place), washdowns, boilers and cooling towers lend themselves to just that. While wastewater treatment to a food contact standard is generally easily achievable, utility applications generally represent the best return on investment. Anaerobic digestion is becoming increasingly popular as the primary treatment step, due to its low operating cost and inherent biogas production that can be used back in the plant. With anaerobic digestion as the primary treatment process, re-use systems can be “right-sized” to meet the re-use demand, further increasing the circular water efficiency.
As is the case with sustainability efforts in general, an evaluation of what processors are currently doing and what they hope to achieve is required before jumping into reusing wastewater.
“With the proper processes and equipment in place, the savings in both the water used and the waste disposed of can be substantial,” says Jager.