There is little doubt that human activity is responsible for our current climate crisis. An October 2021 Cornell University study of 88,125 peer-reviewed scientific papers on the subject found that 99.9% of those studies supported this conclusion.1
The release of greenhouse gases into the atmosphere is resulting in rising temperatures across the planet. A significant contributor to this is carbon dioxide gas accumulating in the atmosphere. Concentrations of carbon dioxide are the highest since measurements were initiated in 1958.2 2020 was one of the three hottest years on record3 and July 2021 was the hottest month ever recorded on this earth (so far).4 Lakes in the Northern Hemisphere are warming six times faster than at any time in the last 100 years.5
An outcome of all this warming is that humidity is decreasing and evaporation of water from all surfaces increasing. The additional moisture in the atmosphere is linked to an increase of weather-related catastrophes: drought, wildfires, hurricanes, tornados, floods, etc. No wildfire in recorded history had burned from one side of the Sierra Nevada Mountain range to the other; in 2021, it happened twice.6
These increasing temperatures and evaporation rates, coupled with a rapidly growing population, have exacerbated freshwater scarcity for agricultural, commercial, industrial and residential applications.
The World Resources Institute projects a 56% shortfall of fresh water within a decade. And in areas such as the western U.S., prone to water shortages, droughts are expected to get much worse. Experts predict that they will be the worst in recorded history, and last for 100 years. To describe these megadroughts, some are using the term “Aridification.”
Looking forward, we should expect severely limited freshwater supplies in the face of increasing demand.
Industrial wastewater
In developed countries, industry can consume as much as 60% of available freshwater supplies, and most is simply discharged after use. Accordingly, industrial wastewater is significantly underutilized, and yet represents an immense source of both reusable water and possibly valuable components (recoverable “contaminants” in the wastewater). In industry, fresh water is used for many purposes, such as rinsing, cleaning, product manufacturing and other processes. This article addresses methods to treat the wastewater to generate a quality of water that can be reused within the facility and also processes to recover valuable components from the removed contaminants.
In September 2020, a survey of companies with annual revenues exceeding $1 billion revealed that most plan to “better manage” their water within the next two years.14 Some have gone so far as to declare that they will become “water positive,” meaning that more high-quality water will leave the facility than enters it. This includes water conservation and leakage prevention as well as wastewater recovery and reuse.
Resource recovery opportunities
Treating wastewater provides an opportunity for more than just recovering water. While these streams must be treated to remove contaminants that could affect human and environmental health, some may provide valuable, recoverable assets, such as nutrients, high value metals and embedded energy. In certain situations, it may be possible to recover thermal and pumping energy. Additionally, valuable components can be "fractionated" and isolated for reuse, while also recovering the treated water. This concept of “resource recovery” (specifically, multi-resource co-recovery, as wastewater treatment is reimagined as water resource recovery) is detailed in a number of articles, including “There’s Gold in Them Thar Waters”7 and “We Should Expect More out of our Sewage Sludge.”8
The chart below illustrates several classifications of water-borne contaminants and examples of recoverable products.
The value of these waste-to-resource products can be substantial. The nutrients nitrogen and phosphorus are worth approximately $31/ton, metals are $480/ton (with gold and silver alone accounting for $103/ton), and energy is $50/ton.8 Li et al. estimated that a municipal wastewater treatment facility could transform pollutants into profits with an annual return of millions of dollars from the electricity, fertilizer and clean water resources generated.9 Moreover, the economic potential of metals recovery from the biosolids alone was estimated at $13 million per year for a community of 1 million people.
Several metals, such as iridium, silver, platinum and gold, may be present at higher abundance in wastewater biosolids relative to average soil in the earth’s upper continental crust.10 Importantly, some of these elements present in wastewater are also energy critical (gallium, palladium, silver, and iridium).8 Such elements are critical to new energy-related technologies, such that shortages could significantly inhibit largescale deployment or effective production, transmittance, storage or conservation of energy.11
Other wastewater constituents, such as phosphorus, are agriculturally critical. Largescale food production relies on fertilizer, which is produced using phosphorus mined from non-renewable reserves, with estimates for depletion ranging widely from decades to centuries. Moreover, reserves are geographically concentrated, with most phosphorus being supplied by just six countries around the world.12 As an industrially and economically important, non-energy raw material for which there is a supply risk, phosphorus is on the European Commission’s list of critical raw materials.
Compared to municipal systems, the economic boon could be even greater for resource recovery from industrial wastewater considering the higher loads of, e.g., organics in petrochemical or food wastewater, nutrients in livestock wastewater and metals in manufacturing wastewater.9 For example, depending on the application, industrial wastewaters can contain valuable heavy metals such as mercury, copper, palladium, lanthanide, lead, cadmium, cesium and gold.13 Wastewater from mining, electroplating, electronic and jewelry manufacturing, and industrial or automotive catalyst production may contain gold or platinum-series elements. In this age of depleting natural resources, all of these “wastes” can be converted into valuable resources, one of the most important of which is a renewable supply of fresh water.
Wastewater recovery
When considering wastewater treatment, two categories present themselves: centralized and decentralized. "Centralized" is a single wastewater treatment system serving several or many end users. A municipal sewage treatment system is one such example. "Decentralized" refers to a particular facility (residence, manufacturing plant, etc.) treating its own wastewater for reuse, usually within the facility. Either type of operation can employ a range of physical, chemical and biological treatment processes designed with an explicit focus on co-recovery of value-added resources.
Treating wastewater for reuse may present significant challenges. The plant personnel responsible for making decisions and taking action are often unaware of which technologies can be used for this purpose. Also, they may have negative views such as:
- Our freshwater supply is sufficient in both quantity and quality. That may be the situation now, but as supplies diminish and become more contaminated, this could change drastically, and the cost of this water (both incoming and outgoing) will certainly continue to increase.
- A treatment system will cost too much. As more and more wastewater recovery and reuse systems are designed and installed, new and existing technologies become more widely employed and competitive in price. The recovery of valuable solute may also provide sufficient economic incentive.
- We don't have the engineering knowledge to tackle this. There are many competent consulting engineering firms and academics with expertise in designing complete treatment systems for wastewater reuse.
- Will it make a difference to our customers? As the public becomes more aware of the looming water shortages associated with climate change, manufacturers of consumer products are discovering that being able to make recovery and reuse claims has excellent public relations value. “Sustainability” has become today’s buzzword.
There are technologies that can treat virtually any wastewater stream for reuse in any application. The increasing acceptance of treated municipal sewage for drinking water provides testimony.
The "Poster Child" for this is the Groundwater Replenishment System (GWRS) located in Orange County, California. It generates over 100 million gallons per day of potable quality drinking water from secondary treated sewage. This treated water meets the potable water requirements for over 850,000 residents.
Because sewage all over the world has similar kinds and concentrations of contaminants, it is possible to design similar treatment trains for virtually any location, often without pilot testing.
On the other hand, in the industrial manufacturing sector, the wastewater from one plant is usually very different from every other plant. This "dissimilarity" of industrial wastewater streams requires a disciplined approach to designing the optimum treatment system.
For a specific application, the following approach is recommended:
- What’s in the wastewater? A complete chemical analysis of the wastewater must be obtained. Because concentrations of contaminants vary as a function of time, a "worst case" sample should be analyzed.
- Where can this treated water be used? Back in the manufacturing process? Cooling tower feed? Boiler feed? Product rinsing? Toilet flushing? Landscape irrigation? There is usually no shortage of potential applications.
- The choice of the water use(s) will determine the quality requirements of the treated water.
- Quality requirements will dictate the selection of treatment technologies. This requires an understanding of the chemistry of the specific contaminants as well as the plethora of available treatment technologies. There are usually several excellent technologies appropriate for the removal of each class of contaminants. The key is to identify the optimum technology for this particular application.
- For those skilled in wastewater treatment, it is possible to quickly narrow down the treatment technology choices most appropriate for this application. Because more than one class of contaminant will usually have to be removed, several different technologies will usually be required for the total treatment system. The selection of a specific kind or model of a technology may require initial testing, and a pilot test to establish performance parameters for the final design.
- As part of the design process, it is possible to estimate the capital and operating costs to allow the company to determine if this recovery and reuse program has sufficient merit to proceed.
Conclusion
As underscored by an old Bob Dylan ballad, “The Times They Are a-Changin,’” we can no longer expect to maintain the old status quo. Climate change won’t let us. Industrial wastewater on-site treatment will enable us to recover valuable components, while regenerating a critical resource. It will require a significant commitment, but our children and grandchildren will thank us for it.
References
1. Lynas M, Houlton BZ, Perry S. Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature. Environ Res Lett. 2021;16(11). doi:10.1088/1748-9326/ac2966
2. NOAA. Carbon dioxide peaks near 420 parts per million at Mauna Loa observatory. NOAA Research News. Published 2021. https://research.noaa.gov/article/ArtMID/587/ArticleID/2764/Coronavirusresponse-barely-slows-rising-carbon-dioxide
3. Zhongming Z, Linong L, Xiaona Y, Wangqiang Z, Wei L. 2020 was one of three warmest years on record. Glob S&T Dev Trend Anal Platf Resour Environ. Published online 2021. http://resp.llas.ac.cn/C666/handle/2XK7JSWQ/311053
4. NOAA. July 2021 was the warmest July on record for the globe; global land surface was also record warm. Assessing the Global Climate in July 2021. Published 2021. https://www.ncei.noaa.gov/news/global-climate-202107
5. Sharma S, Richardson DC, Woolway RI, et al. Loss of Ice Cover, Shifting Phenology, and More Extreme Events in Northern Hemisphere Lakes. J Geophys Res Biogeosciences. 2021;126(10):1-12. doi:10.1029/2021JG006348
6. Wigglesworth A, Smith H. ‘Unprecedented’ Caldor, Dixie fires are the first to burn from one side of the Sierra to the other. Los Angeles Times. https://www.latimes.com/california/story/2021-08-31/caldor-and-dixie-fires-firstburn-from-one-side-of-sierra-to-the-other. Published 2021.
7. Mayer BK. There’s gold in them thar waters. Water Cond Purif Int. Published online 2021. https://wcponline.com/2021/12/15/theres-gold-in-them-thar-waters/
8. Peccia J, Westerhoff P. We should expect more from our sewage sludge. Environ Sci Technol. 2015;49:8271-8276. doi:10.1021/acs.est.5b01931
9. Li W-W, Yu H-Q, Rittmann BE. Reuse water pollutants. Nature. 2015;528:29-31.
10. Westerhoff P, Lee S, Yang Y, et al. Characterization, recovery opportunities, and valuation of metals in municipal sludges from U.S. wastewater treatment plants nationwide. Environ Sci Technol. 2015;49:9479−9488. doi:10.1021/es505329q
11. APS, MRS. Energy Critical Elements: Securing Materials for Emerging Technologies.
12. Mayer BK, Baker LA, Boyer TH, et al. Total value of phosphorus recovery. Environ Sci Technol. 2016;50:6606-6620. doi:10.1021/acs.est.6b01239
13. Rongwong W, Goh K. Resource recovery from industrial wastewaters by hydrophobic membrane contactors: A review. J Environ Chem Eng. 2020;8(5):104242. doi:10.1016/j.jece.2020.104242
14. piperepair.com.uk. Water Positive – what does it mean and how can it be done? Published 2020. https://piperepair.co.uk/2020/09/23/water-positive-what-does-itmean-and-how-can-it-be-done/
Dr. Brooke K. Mayer is an Associate Professor in the Department of Civil, Construction and Environmental Engineering in the Opus College of Engineering at Marquette University. She holds Master of Science and doctorate degrees in Civil Engineering with an emphasis in environmental engineering from Arizona State University. Her research interests focus on physicochemical water/wastewater treatment processes
Peter Cartwright entered the water purification and wastewater treatment industry in 1974 and has had his own consulting engineering firm since 1980. He has a degree in Chemical Engineering from the University of Minnesota and is a registered Professional Engineer in that state. Cartwright has provided consulting services to clients worldwide. He has authored over 300 articles, written several book chapters, presented more than 300 lectures in global conferences, and is the recipient of several patents. He also provides extensive expert witness testimony and technology training education. Cartwright is a recipient of the Award of Merit, Lifetime Member Award and Hall of Fame Award from the Water Quality Association and was the Technical Consultant for the Canadian Water Quality Association from 2007 until 2018.
