Hidden Resources: Wastewater Recovery & Reuse

About the author:

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 more than 250 clients globally. He has authored over 200 articles, written several book chapters, presented more than 300 lectures in conferences around the world, and is the recipient of several patents. He also provides extensive expert witness testimony and technology training education.

He is on editorial advisory boards and technical review committees of several trade publications, and is a frequent lecturer in numerous technical conferences globally. 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. As the 2016 McEllhiney Distinguished Lecturer for the National Ground Water Research and Educational Foundation, he presented over 35 lectures throughout the world on groundwater contaminant mitigation.

Cartwright can be reached at [email protected] or through www.cartwright-consulting.com.

This planet is in the throes of climate changes never seen before with what is predicted to be devasting consequences. Drought, floods, hurricanes, crop failures, famine, and political upheaval are just some of the outcomes. Historically, specific areas of the world have always been perennially short of fresh water and the American west is just one example. But it is going to get worse! Scientists predict that not only will more areas become water-short, but the droughts will become more severe, perhaps the worst in recorded history. 

This article addresses the science behind these predictions and offers a suggestion on how additional supplies of fresh water may be accessed, with emphasis on industrial wastewater recovery and reuse. 

Data Points Regarding Climate Change 

The increase of carbon dioxide in the atmosphere is almost universally accepted as the cause of global warming. In May, 2021, scientists at the National Oceanic and Atmospheric Administration (NOAA) announced that the level of carbon dioxide in the atmosphere is the highest it has been since measurements were begun 63 years ago (1). The World Meteorological Association recently released a global analysis indicating that 2020 was one of the three hottest years on record, marking the end of the warmest decade ever recorded (2). Nineteen of the earth’s warmest years on record have occurred since 2000 (3), and NOAA has just announced that July, 2021 was the world’s hottest month ever recorded (4). 

Disasters such as the “Great Texas Freeze” ice storms in February, 2021, the nearly 10,000 California fires in 2020 that consumed 4.2 million acres and killed 33 people (3), unprecedented hurricanes and floods are just some outcomes. This climate change phenomenon is causing weather catastrophes which are likely to become the “new normal.” 

To put this in perspective, the August, 2021 United Nations Intergovernmental Panel on Climate Change (IPCC) seminal report, “Climate Change 2021,” states, “It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.” 

As more greenhouse gases (carbon dioxide and methane, among others) are released into the atmosphere, temperatures increase, causing more moisture to evaporate from land surfaces, water supplies, plants, etc. As a result of these rising temperatures, shorter winters and longer summers, the frequency of wildfires in the western U.S. has increased 400 % since 1970. 

RELATED: 2021 Western Water Crisis Hub: Drought, Water Scarcity & Water Resources in the U.S. West

Aridification & Its Impact on Water

There is little doubt that availability of fresh water on this planet is in jeopardy. U.S. scientists predict that the western states are entering the worst drought in 1,200 years which could last for 100 years (4). Some scientists say that this is not just a “megadrought,” but that we are now entering into a new climate reality – “Aridification.” Drought is temporary, aridification is permanent (5). 

The total quantity of water on this planet has remained relatively fixed for millions of years, with over 96% of it seawater. Of the tiny volume of fresh water, about 0.3% is surface water (rivers, streams, lakes) and 11% available groundwater. The rest is trapped in glaciers and ice caps or considered too deep to readily access (6). 

In the U.S., groundwater wells supply almost half of the water used by the agricultural industry and provide drinking water to over 100 million Americans. Worldwide, wells supply 40% of agricultural water used to irrigate the crops that feed billions of people. Virtually all of them are becoming depleted. Because the percolation rate to replenish these aquifers may take years, the current rate of withdrawal is not sustainable (7). One report estimates that between 1900 and 2010, the global rate of freshwater withdrawal has increased by 700% (8). 

Whereas the quantity of water has remained the same, the quality certainly has not. Humans have contaminated fresh water supplies for thousands of years. Population growth, accompanied by increased agricultural and industrial activity have exacerbated the problem. 

The drought affecting the eastern Mediterranean Levant region since 1998 may be the worst in the last 900 years (9). Las Vegas, one of the fastest-growing cities in the US, receives 90% of its water from Lake Mead, the reservoir on the Colorado River. It is currently down to 36% full. Since 2000, the water level in the lake has fallen 140 feet (10). 

Today, an estimated 20% of the world’s population is without clean water, and without drastic measures, it is expected that this number will rise to 50% by 2050. The United Nations estimates 10 million people die every year from drinking polluted water, mostly children (11). 

In the U.S., 39% of the fresh water is used for energy production; agriculture uses 40% and manufacturing another 11%. These three sectors now use an estimated 300 billion gallons per day (10). As residents of arguably the most “water-wasting” country in the world, the average American uses 100 gallons of potable water per day, easily two times the quantity of the average European (10). 

Potential Mitigation Activities

So, what can we do to access more fresh water? 

Conservation

We can conserve. A number of strategies have been successfully employed for residential water conservation, with per capita water consumption down 40% in some areas of the southwest. U.S. Federal mandates have resulted in low flush toilets, low flow shower heads and other water-savings initiatives. 

Rainwater Harvesting

We can increase rainwater harvesting. Collection and consumption of rainwater has been practiced for centuries. In general, rainwater from roofs and other elevated surfaces is relatively clean, but does contain particles, gases, and microorganisms from the air and bird and animal droppings, leaves and other debris on the surface. 

Residential rainwater harvesting is becoming increasingly popular, using rain barrels to collect water for landscape irrigation. In commercial and industrial applications, rainwater is used for cooling towers, toilet flushing and other non-potable purposes. Stormwater can be collected and used; however, it is much more contaminated than rainwater, which limits its applications. 

Greywater Reuse

Greywater is generally defined as wastewater in a premise (usually home) from sinks, bathtubs, showers, and other water-using devices except toilets and garbage disposers (these are considered sources of blackwater). 

Although greywater may contain a variety of suspended solids, dissolved organics and salts, the stream is usually dilute and can be used for landscape irrigation without treatment. With minimal treatment, greywater can be reused inside the building in many non-potable applications. National Sanitation Foundation (NSF) is developing a comprehensive testing and performance standard (NSF/ANSI 350) for residential and commercial applications. A downside of greywater collection is that it requires dedicated plumbing, so is usually incorporated during renovation or in new construction. 

Wastewater Recovery & Reuse

Wastewater recovery and reuse represents the greatest untapped potential for addressing freshwater quality and availability issues, now and in the future. The two primary sources of these supplies are municipal and industrial. 

Great strides have been made in the treatment of municipal sewage, with the current poster child being the Groundwater Replenishment System (GWRS) located in Orange County, California. A joint venture between the water and wastewater districts, it currently produces 100 million gallons per day (mgd) of potable water from secondary treated municipal sewage. The final treated water is pumped into injection wells to minimize seawater intrusion into the freshwater aquifer. 

Supplying potable quality water to approximately 850,000 residents, the GWRS is the world’s largest advanced water purification system for potable reuse (13). Arguably, the greatest challenge to the construction of this system has been convincing the residents that drinking treated sewage water is acceptable. 

There is now significant activity in recovery of potable water from municipal wastewater in many areas throughout the world, employing technologies such as membranes and advanced oxidation processes. 

A characteristic of municipal wastewater is that the kinds and concentrations of contaminants fall within a relatively narrow range regardless of location. As a result, the selection of treatment technologies and system designs has been proven, is straightforward, and minimal pilot testing is required. 

On the other hand, the treatment and reuse of industrial wastewater is much more of a challenge. Because the manufacturing industry is so diverse, it is rare that two wastewater streams are even close to each other with regard to the kinds and/or concentration of contaminants. Therefore, each application requires extensive pilot testing to develop the optimum suite of technologies and total system design. 

3 Reasons for Industrial Wastewater Recovery

There are three major incentives that drive industrial wastewater recovery and reuse. 

Lack of Available Fresh Water

This may prevent plant expansion or even result in the cessation of operations entirely. For those locations suffering under drought conditions, this may be the future unless drastic recovery and reuse measures are taken. 

Discharge Regulations

Ongoing investigations by the U.S. EPA and state pollution control agencies are resulting in the identification of new chemicals determined to be hazardous. A wastewater stream previously discharged to the Publicly Owned Treatment Works (POTW) may now have to be treated as a hazardous waste. It may be possible to remove only the hazardous contaminants and reuse the rest of the stream. 

Desire to Appear Green

Many consumer-oriented manufacturers want to take advantage of the positive image resulting from publicizing the fact that they are conserving water and/or reusing their wastewater. Consumers are slowly becoming more cognizant of and concerned about climate change, water shortages, microplastic contamination, etc. 

Selecting Appropriate Treatment Technologies

When it comes to selecting treatment technologies we must step back and identify those classes of contaminants that must be removed. It is possible to categorize water-borne contaminants as shown in the table below.

Table 1. Contaminant Classes & Example Contaminants

There is no contaminated water supply that cannot be treated to meet virtually any application requirement. There are an endless number of technologies commercially available, with more steadily coming on-line. The challenge is to commit the cost and time to determine the most efficacious technologies and develop the optimum system design. 

For the following five tables of treatment technologies, squares marked with an “X” indicate the technology is effective at treating that column’s contaminant class. Cells marked with a “—” indicate it is not effective. Lastly, cells marked with an “L” indicate the technology will have limited effectiveness under certain conditions.

Table 2. Biological Processes & Extended Aeration

Table 3. Chemical Processes (Oxidation, Precipitation, Reduction & Coagulation)

Table 4. Electrolytic Processes & Incineration

Table 5. Physical Processes (Carbon Adsorption, Specialty Resins, Filtration)

Table 6. Membrane Processes & Thermal Processes

Considerations for Technology Choices & Optimization

While it is impossible to remove all of any contaminants from a water supply, it is possible to get very close with the optimum technologies. The initial challenge in industrial wastewater treatment is to get a complete water analysis of the stream. 

If it changes as a function of time, analyzing a “worst case” sample is advised. Then, a decision must be made as to the use of the treated water. That will determine the quality requirements of this supply. 

Are there regulatory issues that need to be addressed? What are the practical concerns (space, storage, piping, drainage, etc.)? Are the staff onsite capable of proceeding to the next step, identification of the most likely technology candidates? In general, the class of contaminants to be removed will direct the engineer to the treatment candidates. 

Suspended Solids Example

For example, if the goal is to reduce suspended solids, the technology choices could include screens, filters (cartridge, bed, etc.), dissolved air flotation (DAF), microfiltration, and many others. 

Dissolved Organics Example

If the goal is dissolved organics, things get more complicated. If the organics are biodegradable, there are many opportunities to use bacteria to break down most of the organics, combined with membrane bioreactor (MBR) technology for treated water recovery. If the organics are recalcitrant (resistant to biodegradation), the choices are usually adsorption with activated carbon products or special resins, or destruction with advanced oxidation processes (AOPs) such as combinations of ozone, ultraviolet, hydrogen peroxide, Fenton reagents, etc. The membrane process, ultrafiltration, is often used to concentrate these contaminants. 

Dissolved Ionic Example

For dissolved ionic (salts) contaminant removal, the most common choice is reverse osmosis (RO) or nanofiltration, two of the four crossflow, pressure-driven membrane separation technologies. Whereas these processes use pressure as the driving force, there is also a suite of technologies which utilize electricity as the driver. These include electrodialysis and capacitive deionization. Some specific adsorptive resins are also used for certain ionic contaminant removal. 

Microorganism Example

Microorganism reduction offers particular challenges in water treatment/recovery. The acceptable concentrations of these contaminants are usually dictated by health-related regulations. The technologies for microorganism inactivation are usually either chemical (chlorine, ozone, etc.) or a form of high energy radiation (e.g., ultraviolet). Since all microorganisms are actually suspended solids (albeit extremely small), membrane technologies can be employed to separate them from the treated water but not inactivate them. It is important to know that it is almost impossible to keep a treated water supply completely free from bacterial regrowth. 

Gases Example

Gases are most commonly removed by activated carbon adsorption, scrubbing (media or special membranes), vacuum or chemical treatment. For purposes of brevity they are not included in the above tables.

Pre-treatment, Primary Treatment & Polishing

Invariably, a wastewater treatment system will consist of separate components, particularly the “three Ps”: Pretreatment, Primary and Polishing. Each component consists of one or more technologies selected to accomplish specific tasks. Pretreatment is usually intended to protect the primary treatment technologies from contamination (fouling, chemical attack, etc.). Primary treatment performs the major treatment function and produces the final treated water quality. 

Posttreatment typically encompasses the storage and distribution components and includes technologies that maintain the quality produced by the primary treatment technologies. 

For someone wishing to investigate the possibility of wastewater reuse within their manufacturing facility, the following sequence of activities is recommended:

1. Obtain a comprehensive wastewater analysis, either “worst case” or composite sample.
2. Decide where the treated wastewater can be used. 
   1. Inside the manufacturing process? 
   2. Premise applications (toilet flushing, showers, etc.)?
   3. Cooling tower feed?
   4. Landscape irrigation, truck washing, floor scrubbing, etc.?
3. Determine quantity requirements, daily and instantaneous. 
4. Develop the minimum quality requirements of the treated water for the selected use(s). 
5. Select the technologies to evaluate. 
6. Determine the technology treatment train. 
7. Pilot test as required. 
8. Prepare a Request for Proposal for the complete system. 

Editor’s Note: Detailed information on the above activities is available from the unpublished document, “Wastewater Recovery & Reuse – Part 1,” Peter S. Cartwright, Saudi Arabia Water Environment Association, April, 2016. 

Recovering Contaminants for Reuse

Keep in mind that it is also possible to recover a particular “contaminant” for reuse. This involves “fractionating” the wastewater to isolate and concentrate the desired material. 

Although industrial wastewater treatment requires an investment in time and money, less freshwater will be required, and as freshwater supplies diminish, this cost is certain to increase. There are many very qualified consulting engineering firms capable of performing the testing and design activities in this area. 

Wastewater Reuse & Recovery Case Study

A client wanted to recover and reuse all of the wastewater from an existing electrodialysis reversal system producing potable water for a large recreational facility. The contaminants of concern in this wastewater are hardness, silica, and total dissolved solids(TDS), and management wanted the treated water to be returned to the potable water supply and for virtually no water to leave the facility. The water quality requirements were that the treated water meet the EPA Safe Drinking Water Act quality standards, that the TDS be less than 500 mg/L, total hardness less than 100 mg/L, and that the pH be between 6 and 8. 

Once the wastewater analysis was documented, the first decision was how to remove the hardness (1435 mg/L in the feedwater). The technology choices considered were to raise the pH above 10 to precipitate the insoluble calcium carbonate and either use clarification to let the solids settle out or continuous microfiltration (MF) to dewater the stream with a filter press to remove most of the water. Because the latter approach required a significantly smaller footprint and had a higher throughput, it was selected. The sludge produced by the filter press could be sold as high-quality calcium carbonate. The treated water (permeate) from the MF system is pH-adjusted to within a range of 6 to 8 and then fed into a reverse osmosis (RO) system to lower the TDS and silica. This permeate is returned to the potable water system. The RO concentrate is fed to a falling film evaporator followed by a crystallizer and finally a centrifuge to generate relatively dry solids which are hauled to a landfill. The total flow of wastewater is 58,000 gpd and a total of 2600 lbs/day of solids are generated.

This is an example of a ZLD (zero liquid discharge) installation wherein no liquid wastewater is discharged. 

Conclusions 

Challenging water related times are ahead – in all sectors of society. Fortunately, many very qualified organizations are committed to helping us cope. 

For those in the manufacturing sector, realize that “same old, same old” will no longer work and facilities must look for innovative approaches to maximize water recovery. The very survival of industrial facilities may depend on it. 

References 

1. Bernstein, Sharon, June 7, 2021. Carbon dioxide in the air at highest level since measurements began. Reuters.com. (Environment). 
2. Vestal, Shawn, June 6, 2021. Ins, The Spokesman-Review, Spokane, Wash. 
3. Hochman, David, et al, June, 2021. Climate Change, A Practical Guide. AARP.ORG/Bulletin.
4. July was Earth’s hottest month on record: NOAA. August 13, 2021. Science Daily. www.sciencedaily.com/releases/2021/08/210813164802.htm. 
5. Lohan, Tara, August 7, 2021. ‘Megadrought’ and ‘Aridification’- Understanding the New Language of a Warming World – The Revelator. https://therevalator.org/megadrought ardification-climate/ 
6. Shiklomanov, Igor, 1993, World fresh water resources, Water in Crisis. Oxford University Press.
7. Perrone, Debra, et al, May 10, 2021. Water wells are at risk of going dry in the US and worldwide. The Conversation. https://theconversation.com/water-wlls-are-at-risk-of-going-dry-in-the-us-and-worldwide-160147. 
8. Valuing Water, The United Nations World Water Development Report 2021, page 12. 
9. The Facts About Climate Change and Drought. June 15, 2016. The Climate Reality Project. 
10. Sommer, Lauren, June 9, 2021. The Drought In The Western U.S. Is Getting Bad. Climate Change Is Making It Worse. NPR News. 
11. Magill, Bobby, et al, July 12, 2021. It’s Not Just Water Supply: Drought Harms Water Quality Too. https://bloomberglaw.com/environment-and-energy/its-not-just-water-supply-drought harms-water-quality-too. 
12. Cartwright, Peter S., April 24, 2018. Crossflow Technologies for Wastewater Treatment. AFS Filtcon 2018, Conference & Exposition. 
13. Groundwater Replenishment System. www.ocwd.com/gwrs/.