Conserving Processing Water Requires a Systems Approach

Water is life. Despite the Earth’s abundance of water, only 0.3% is accessible to humans. More than 2 billion people live in water-stressed regions, with over two-thirds experiencing severe water scarcity at least one month of the year. When combined with extreme weather events, a global pandemic, and poor water management, concerns over water scarcity are further exacerbated. A third of the U.S. population experienced drought conditions at least on a moderate level during the summer of 2020 alone.

Economic growth, consumption behaviors, population increases, and an urgent need for feeding a growing population drive significant demand for water, among other finite resources. Since the 1980s, global water use has been steadily increasing by 1% annually. The United Nations Water Development Report estimates that by 2050, demand will be up to 30% above the current level. The highest global water consumption is due to agriculture (i.e., irrigation, livestock, and aquaculture) and industrial uses, accounting for 69% and 19% of the annual withdrawals, respectively. The agriculture sector has been addressing water issues by capitalizing on recent advancements in precision agriculture, remote sensing, and implementation of various water-saving practices involving drip irrigation, dry farming, conservation tillage, irrigation scheduling, naturally drought-tolerant crops, and more. Rising food demand entails an increased need for resource efficiency at both the agricultural production level and at the remaining stages of the food value chain, including food processing, packaging, and transportation.

Such a systems approach is even more urgent for regions such as Europe and North America where the water use in industry is higher than use for agricultural practices. The food processing industry in the United States is the third most water-intensive sector with an estimated 1.4 billion liters of wastewater generated annually, following the chemical and refinery industries. High-quality water requirements such as potable or demineralized water set the food industry apart from other industrial applications. Water is utilized as an essential ingredient for formulations, as a heat and mass transfer medium, for cleaning, and for boiler feed. The microbial quality of water is of utmost importance, with about 70% being used for sanitation and 20% as a primary ingredient. Even for the beverage industry, ingredient water generally accounts for only 20%–30% of total water use. Hence, the majority of the water is discharged as effluent with high impurities, biochemical oxygen demand (BOD), and chemical oxygen demand. Technology-based regulations have varying local and federal requirements along with uncertainties for water quality and wastewater treatment. Technological opportunities exist in reducing and reclaiming water in food processing operations. However, when the strict food safety standards, quality requirements, and high variability of foods are combined, meeting the sustainable development goals for water conservation practices goes beyond the efficiency and minimum regulatory requirements and must encompass a systems approach.

Reduce, Reuse, Recycle

There are several improvements available to increase water use efficiency involving behavioral changes, monitoring water use, determining fit for purpose, and process equipment modifications. For vegetable processing, one option is to replace traditional blanchers with modified steam blanchers with better heating and insulation. The principles of fast blanching and cleaning are based on achieving forced convection with venturi nozzles (e.g., a controlled screw blancher by EIMA Engineering), heat and hold, and rotary drum types (e.g., the agitating Clean-Flow in Place system from Lyco Manufacturing). Dry caustic peeling can reduce the water requirement but generate high BOD wastewater. Water-efficient alternative methods such as infrared peeling and ohmic peeling should be evaluated against cost, energy use, and yield.

Another water-efficient method is disinfection via ozone thanks to its high oxidizing capacity. Ozone applications have been in use for a wide variety of operations ranging from fresh produce, seafood, confectionery, and cereals to cleanroom applications in food processing. Companies such as Ozone Safe Food Technologies, Ozone Solutions, and Absolute Ozone offer commercial ozone generators for food and beverage applications.

Wastewater from direct use in food processes requires treatment before reuse in the processing plant as irrigation water or as a direct food ingredient. Waterborne microbial and chemical quality risks associated with water reuse determine the feasibility of reuse applications. The water quality, regulatory, and operational difficulty benefits are weighed against the costs throughout the lifecycle of the wastewater treatment system. In many instances, low costs of water may fail to justify the investment. However, incentivizing less water use with added tax benefits or penalizing wastewater discharge motivates the industry for implementation of reuse and recycling technology.

Corporations have begun to implement large projects as part of their sustainability commitments. For example, Kraft Heinz achieved 86 million gallons of water saving in 2019 as a result of installing an effluent recycling effort by cooling vacuum seals by a dissolved air floatation treatment process. Nestlé reduced its water withdrawals by 31% from 2010 to 2019 by implementing wastewater recycling and reduction practices. Unit operations for treatment can be based on various physical, pressure-driven membrane, biological, and chemical principles, including sedimentation, stabilization, reverse osmosis (RO), ultrafiltration (UF), anaerobic and aerobic digestion, and ozone disinfection.

“Finding the right water recovery unit operations for the specific food processing application is predicated on a complete wastewater characterization, an assessment of regulatory discharge limitations of any brine or blowdown streams,” says Mike McDonald, senior business leader with SUEZ Water Technologies & Solutions. “The major constraint here is also to assess available recovered water use points within the food processing unit operations evaluated by flow and water quality requirements.”

RO is a widely used industry standard due to its reliability and high-quality reclaimed water generation, i.e., low Total Dissolvable Solids (TDS). However, RO can be energy intensive and generate RO concentrates (i.e., brine) and high TDS outlets that can be harmful when discharged. RO membranes are also prone to fouling and deposits, which can lead to higher energy consumption and lower recovery rates. Swirltex developed a buoyancy-based membrane enabling the binding of suspended solids and oily contaminants to the aerated mixture, which is then channeled away from the membrane surface through a spinning mechanism. This technology enables filtration of high strength and oily wastewater that would otherwise cause membrane fouling. Aqua Membranes offers a new 3-D printed feed spacer, an additional mesh structure with improved geometry, to optimize flow and turbulence characteristics in spiral-wound RO systems and claims to improve energy efficiency by 20%–50%. Veolia Water Technologies offers to retrofit for moving bed biofilm reactors, including a new carrier with modified surface features to better control the biofilm thickness and reduce scaling, which is a concern for environments such as dairy processing that have a high organic load. Bioprocessing is used to convert organic substrates in wastewater into high-value byproducts such as hydrogen, methane, protein, and lipids.

Water as an Ingredient

Using recycled water as an ingredient is another option for finding use points. Consumer perceptions and acceptance play a critical role, while a business case can be created from increased interest in sustainability efforts. In 2016, Tetra Tech, Water Reuse Association, Xylem, and General Electric collaborated on a project for a Full Advanced Treatment process combining UF and RO to produce drinking water in compliance with U.S. Environmental Protection Agency standards to make craft beer from reclaimed water from Hillsborough County, Fla. A number of small brewers have developed craft beer from recycled wastewater, including the Village Brewery in Canada, a German brewer that made Reuse Brew, New Carnegie Brewery in Sweden, and Half Moon Bay Brewing and Stone Brewing in the United States. Australia’s Aqua-Botanical brand is bottled water made by recycling and mineralizing water from juice concentrate production.

The sensory and quality characteristics of reclaimed water will determine the ingredient viability for food applications. In addition, the taste, odor, and physicochemical properties of the potable water may change over time or across geographical regions. For example, New York WaterMaker eliminates regional variability in water by providing compact filtration and reconditioning of water to replicate the characteristic water parameters required in pizza and bakery products for culinary purposes.

What Awaits

As the pressure on water resources increases, food processing businesses will continue to be challenged to improve the sustainability and resource efficiency of water. The data map for water use in specific food process sites is seldom available. However, specific water use data can aid decision-makers in assessing risks associated with water scarcity and use in particular processing lines. According to the Australian government, behavioral changes, recycling water, and monitoring water consumption can reduce consumption by 25%, 30%, and 60%, respectively. Tracking water use through flow meters, leak detectors, and oxygen and conductivity sensors can enable improvements in water use.

Processors can run risk analysis on water availability for planning for targeted water-efficiency applications. For example, Aqualoso enables farmers to obtain feasibility data by generating a water security score. Similar monitoring and data-based applications can be adopted by the food processing industry.

Remote monitoring of water quality can also be required for integrated water recycling systems as assets are distributed for many medium and large-scale processors. SENTRY, part of Canada-based Island Water Technologies, offers a bio-electrochemical sensor technology and a data platform to monitor the microbial activity of the wastewater treatment systems in anaerobic, aerobic, and drinkable water systems. The company’s real-time sensing technology is based on biofilm deposition on the microbial fuel cell due to the microbial activity and thus requires low maintenance and cleaning. Such solutions can replace time-consuming wastewater stability testing while enabling biofilm testing in existing cooling tower, dosing, and disinfectant systems or in freshwater streams for in-house use.

The use of renewable energy in the food processing sector can provide additional water recovery benefits and advanced technology to be incorporated into water treatment methods. Bioeconomy as a part of the wastewater treatment by anaerobic bacteria, microalgae, and yeast is also promising but can be disadvantageous due to additional energy and further treatment needs. A systems approach with a water-energy-food nexus is essential to assess the feasibility of the emerging water conservation technologies in food processing.

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