By Katherine Y. Bell, Ph.D., PE, BCEE, Director of Research and Innovation, Brown and Caldwell
Changing climate is challenging the ability to meet long-term water needs, and reuse of treated wastewater provides an alternative water supply that can be more reliable than traditional raw water sources. The United States (US) has achieved numerous accomplishments toward expanding the use of reclaimed water and extending water resources for many communities. Yet, there is room for improvement in terms of the total amount of water reused, distribution of reclaimed water throughout the country and the adoption of new, higher quality uses.
With increasing interest in providing more resilient water supplies, particularly in context of environmental, social and governance (ESG) targets, industrial users are accelerating their implementation of reuse projects – using both municipal and industrial wastewater as a source of supply.
While the food and beverage industry has set the stage early in water reuse and water replenishment, other industries are seeing the benefits of greater water reuse (EPA, 2012; Cotruvo, et al., 2013). Microchip manufacturers are improving the efficiency of the processes to produce ultra-pure water (UPW) to clean silicon wafers, and the UPW to clean wafers the water is suitable for other industrial applications, such as in cooling towers and scrubbers.
Other high-tech industries, like data centers, are focusing increased attention on water reuse as part of their water-intensive operations. Data centers require cooling water to maintain continuous access to data; this practice can impact local water supplies, and this increasingly is being recognized as a risk to operations. As a result, industry leaders are adopting ambitious ESG targets with water reuse at the forefront of the conversation.
One example of this approach is the agreement that Tomorrow Water, a subsidiary of Korean firm BKT, signed in early 2022, aiming to co-locate data centers with wastewater resource recovery facilities – saving both energy and water. This approach is part of Tomorrow Water’s initiatives to make its water inputs and outputs more sustainable and affordable (Robinson, 2022).
This theme of addressing water requirements is driving rethinking of water reuse applications and shifts in industry that are shaping the ability to maximize the benefit of water reuse practices. This progress of industrial water reuse is a focus of the US Environmental Protection Agency (EPA) Water Reuse Action Plan (WRAP) (EPA, 2020) implementation, which aims to “to advance water reuse across the US” under the November 2021 Bipartisan Infrastructure Law (Sec. 50218).
One of the critical outputs of the WRAP are the Water Use Roadmaps being led by the National Alliance for Water Innovation (NAWI). This effort will help to prioritize research needs for technologies treating nontraditional source waters and desalination in the power, resource extraction, industrial, municipal and agricultural sectors.
Specifically, the Industrial Sector Roadmap addresses water use in the oil refineries, pulp and paper, primary metals, chemicals, and food and beverage industries, as well as data centers and large campuses. Recognizing that water withdrawals in this Industrial Sector are approximately 18 billion gallons per day (Rao et al., 2019; US BEA, 2017), there is a clear and increasing need for these industries to consider water reuse. NAWI’s Roadmap for the Industrial End-Use Sector (Cath, et al., 2021) establishes a framework to guide research investments to capture progress of high-priority objectives as well as the emergence of new technologies to help unlock even greater adoption of industrial water reuse across the country.
When considering treatment technologies for industrial reuse, the key objectives are to achieve a quality of reclaimed water appropriate for the intended use and that is protective of human health and the environment. These objectives can be achieved through technologies that are available today, making water reuse a cost-effective means of addressing water supply reliability as well as ESG goals. There have been literally hundreds of reuse projects implemented globally for industrial applications, and these projects, cumulatively, have demonstrated that use of ultraviolet irradiation can address both microbial and chemical treatment goals.
With respect to disinfection in industrial reuse, UV is a long-proven technology and is well suited for applications where microbiological contamination is a concern. UV can be used for inactivation of bacteria, viruses, protozoans, spores, yeast, mold and algae. These microorganisms contain genetic material (e.g., DNA and RNA) that absorb photons between 200 nm and 300 nm, which results in damage to these nucleic acids, effectively preventing reproduction of the organism. Examples of these applications include water reuse for equipment rinsing and washing, storage tank cleaning and cooling water (to prevent biofouling), to list a few.
Design of these systems depends on flow and water quality, specifically the initial anticipated concentration of microorganisms and the treatment goal, along with key water quality parameters, specifically as UV transmittance. Target UV disinfection doses typically range from 30 to 300 mJ/cm2, and these systems should be designed based on third-party validations for the appropriate application according to the National Water Research Institute UV Guidelines (2012), the US EPA UV Design Guidance Manual (2006) or ÖNORM (2001 and 2003).
UV-Advanced Oxidation Process (AOP)
As water reuse is considered for more industrial applications, the treatment focus of UV has expanded far beyond disinfection to include removal of trace chemical constituents and, in some specialized applications, removal of bulk organic carbon. Chemical constituents are amenable to treatment with removal mechanisms, direct photolysis or oxidation, depending on the properties of the target compounds. UV-AOP employs UV radiation that generates radicals via photochemical reactions with oxidants. UV in combination with hydrogen peroxide (H2O2) is one of the most extensively applied AOPs (Zhan et al., 2021). The resulting advanced oxidant radicals attack organic constituents, either transforming them into by-products or completely mineralizing them.
The efficacy of UV-AOP depends on the photon and oxidant radical scavenging capacity of the water sample (Rosenfeldt and Linden, 2007), along with the design of the reactor. Key examples of UV-AOP in industrial reuse include treatment of refractory organic compounds, including applications where chemical oxygen demand or total organic carbon must be lowered or changed for further treatment prior to reuse. These applications often are applied for side-stream treatment in the chemical, pharmaceutical, electronics, aerospace and textile industries.
Emerging UV technologies in industrial reuse
While UV and UV-AOP are established technologies deployed for industrial reuse applications, there also are ongoing efforts toward developing novel UV and UV-AOPs to keep at pace with the demand for addressing increasingly stringent treatment targets and improve overall system efficiencies. UV light-emitting diodes (LEDs) present an exciting opportunity for industry, and with ongoing research, the potential to leverage UV LEDs could help address the environmental issues associated with mercury-based UV lamps.
With respect to UV-AOP, researchers are examining the use of alternative oxidants for activating the AOP (Tian et al., 2020). Other researchers are investigating opportunities for advancing chemical-free UV-AOPs by leveraging vacuum UV (VUV, at wavelengths < 200 nm) (Kovoor, et al., 2022), where an appropriate lamp sleeve is used (Claus, 2021) to allow the second major emission line of a low-pressure mercury lamp (185 nm) to pass into the treatment stream.
The future of UV in industrial reuse is an open door, with established applications making UV a go-to technology for disinfection and chemical treatment. Looking ahead, the body of research on emerging technology in UV treatment continues to improve water quality and costs for numerous industries aiming to meet stringent treatment targets and ESG goals.
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Dr. Kati Bell is director of water strategy for Brown and Caldwell (BC), with over 25 years of experience in the water industry. She is a licensed engineer in four states and, leveraging her global water/wastewater experience of over five billion gallons per day of treatment capacity, she is responsible for leading BC’s Research and Innovation Program. The program portfolio, which includes over 100 projects, has an approximate value of $30M and reaches over 80 clients with 20 academic partnerships. The program is aligned with BC service offerings in wastewater and advanced treatment, potable reuse, digital solutions, resource recovery, aging infrastructure, and wet-weather and stormwater. Bell also leads global partnerships with strategic research partners, sets the vision for the BC Treatability Laboratory and collaborates with BCs disciplines to advance innovative solutions for clients. For more information, visit www.brownandcaldwell.com.