Survey of Available Information on U.S. Manufacturing Wastewater and Energy Requirements for Reuse
Manufacturing represents a significant portion of the U.S. economy, making up 12 percent of gross domestic product (GDP) and one quarter of energy consumption, directly employing 12 million people, and selling products valued at nearly $6 trillion in 2016 (DOE 2016). Manufacturing also demands an estimated 6 percent of U.S. water intake, around three quarters of which are self-supplied (Rao et al. 2015). At the same time, water is a critical component of many manufacturing processes, with manufacturing water demand globally expected to increase by 400 percent between 2000 and 2050, more than any other sector (OECD 2012). However, its valuation does not accurately reflect the vital role water plays in manufacturing. In addition, little robust information exists on the amount of water used by different manufacturing subsectors, the manner in which water is used at manufacturing plants, and the costs of pumping and treating or buying water of sufficient quality and quantity, as well as the associated physical, regulatory, and reputational risks.1 In a changing world with increasing constraints on water availability and quality, on-site reuse has the potential to alleviate watershed impacts of manufacturing by reducing the use of water sourced from the watershed. In addition, it may offer substantive benefits to manufacturing facilities, such as reducing risk and increasing resilience via decreasing reliance on outside water resources. Some cost savings may also result; however, a fuller accounting of risks, costs, and benefits is precluded by the current poor understanding of the many and varied constituents of manufacturing effluent, as well as the complexity and heterogeneity of treatment trains. Water is a critical input to manufacturing, and the water-energy nexus also deserves closer attention in the industrial context in order to deepen our understanding of the choices manufacturers face in terms of resource use. Manufacturing plants see interdependencies between water and energy. In some instances, conserving energy also saves water (e.g., returning condensate from industrial steam systems); in others, instituting water efficiency measures may require additional energy. On-site manufacturing water reuse requires energy for treating effluent to a standard suitable for reuse, but outside of a number of case studies reviewed in this paper, there is a paucity of published information on the energy-related implications of such reuse. In addition, the magnitude of this additional energy use depends upon where system boundaries are drawn. This report seeks to inform an improved understanding of the energy tradeoff associated with manufacturing water reuse in the United States, in part by developing an analytical framework for understanding when this tradeoff for reuse is beneficial. In order to apply this approach, existing literature and publicly available information on typical contaminants in industrial effluent and available treatment technologies are reviewed and summarized. An existing case study is then discussed in light of how the analytical framework could be applied if sufficient data were available. We conclude that the shortcomings of the available data severely restrict our ability to apply this framework. These limitations are highlighted with the intent of providing the broader research community information on where data gaps need to be filled. Finally, note that this report complements a recently published journal article by the same authors (Fuchs and Rao 2021); this longer report can be viewed as a supplement to that work. In the interest of providing sufficient context to understand the information contained in this report, it is necessary to include some figures, equations, and text from the journal article here.