Hidden Resources: Wastewater Recovery and Reuse | WWD

2021-11-29 03:10:08 By : Ms. hongyuan ellen

Overview of wastewater recovery and reuse, technology selection and optimization considerations

This planet is in the throes of unprecedented climate change, which is expected to have devastating consequences. Droughts, floods, hurricanes, crop failures, famines and political turmoil are just some of them. Historically, certain areas of the world have been short of fresh water for a long time. The western United States is just an example. But the situation will get worse! Scientists predict that not only will more areas be short of water, but the drought will become more severe, which may be the worst on record. 

This article explains the science behind these predictions and makes recommendations on how to obtain additional fresh water supplies, with a focus on the recovery and reuse of industrial wastewater. 

The increase in carbon dioxide in the atmosphere is almost universally believed to be the cause of global warming. In May 2021, scientists from the National Oceanic and Atmospheric Administration (NOAA) announced that the carbon dioxide content in the atmosphere was the highest level since the measurement began 63 years ago (1). The World Meteorological Association recently released a global analysis showing that 2020 is one of the three hottest years on record, marking the end of the hottest decade on record (2). 19 of the hottest years on earth on record occurred after 2000 (3), and NOAA has just announced that July 2021 is the hottest month on record in the world (4). 

Disasters such as the "Texas Frozen" ice storm in February 2021, and nearly 10,000 California fires in 2020 that destroyed 4.2 million acres of land and killed 33 people (3). Unprecedented hurricanes and floods are just some of them. This climate change phenomenon is triggering a weather disaster that may become the "new normal". 

In order to put this in perspective, the groundbreaking report "Climate Change 2021" of the United Nations Intergovernmental Panel on Climate Change (IPCC) in August 2021 stated that "human influences warm the atmosphere, oceans, and land. This is unambiguous. The atmosphere, ocean, cryosphere and biosphere have undergone extensive and rapid changes." 

As more greenhouse gases (carbon dioxide, methane, etc.) are released into the atmosphere, the temperature rises, causing more water to evaporate from the ground, water sources, plants, etc. Because of these increases in temperatures, shorter winters and longer summers, the frequency of wildfires in the western United States has increased by 400% since 1970. 

Related: 2021 West Water Crisis Center: Drought, Water Scarcity, and Water Resources in the Western United States

There is no doubt that the supply of fresh water on this planet is in danger. American scientists predict that the western states will enter the worst drought in 1,200 years, which may last for 100 years (4). Some scientists say that this is not just an "extraordinary drought", but that we are now entering a new climate reality-"aridification." Drought is temporary, drought is permanent (5). 

For millions of years, the total amount of water on this planet has remained relatively constant, with more than 96% of it being sea water. Of the very small amount of fresh water, approximately 0.3% is surface water (river, stream, lake) and 11% of usable groundwater. The rest are trapped in glaciers and ice sheets, or considered too deep to be easily accessible (6). 

In the United States, groundwater wells supply nearly half of agricultural water and provide drinking water to more than 100 million Americans. Around the world, wells provide 40% of agricultural water used to irrigate crops that provide food for billions of people. Almost all of these are being used up. Because it may take years to replenish the permeability of these aquifers, the current rate of extraction is not sustainable (7). A report estimated that from 1900 to 2010, the global freshwater extraction rate increased by 700% (8). 

Although the amount of water remains the same, the quality is definitely not. For thousands of years, humans have been polluting freshwater supplies. Population growth, accompanied by increased agricultural and industrial activities, has exacerbated this problem. 

The drought that has affected the Levant in the eastern Mediterranean since 1998 may be the worst in the past 900 years (9). Las Vegas is one of the fastest growing cities in the United States, with 90% of its water coming from Lake Mead, a reservoir on the Colorado River. It has now fallen to 36%. Since 2000, the water level in the lake has dropped 140 feet (10 feet). 

Today, it is estimated that 20% of the world's population does not have clean water. If strict measures are not taken, this number is expected to rise to 50% by 2050. The United Nations estimates that 10 million people die every year from drinking contaminated water, most of them children (11). 

In the United States, 39% of fresh water is used for energy production; agriculture uses 40%, and manufacturing uses another 11%. These three sectors are now estimated to use 300 billion gallons per day (10). As a resident of arguably the most "water-consuming" country in the world, Americans use an average of 100 gallons of drinking water a day, twice the average consumption of Europeans (10). 

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

We can save. Residents have succeeded in adopting a number of measures to save water, and water consumption per capita in parts of the southwest has dropped by 40%. Federal regulations in the United States have led to low-flush toilets, low-flow shower heads, and other water-saving measures. 

We can increase rainwater collection. The collection and consumption of rainwater has been implemented for centuries. Generally speaking, rainwater from roofs and other elevated surfaces is relatively clean, but it does contain particles, gases and microorganisms from the air and bird and animal manure, leaves and other surface debris. 

Residential rainwater harvesting is becoming more and more popular, using rainwater buckets to collect water for landscape irrigation. In commercial and industrial applications, rainwater is used for cooling towers, toilet flushing, and other non-potable water uses. Rainwater can be collected and used; however, it is more polluted than rainwater, which limits its application. 

Grey water is generally defined as wastewater from sinks, bathtubs, showers, and other water-using equipment other than toilets and garbage disposers (these are considered sources of black water) in houses (usually households). 

Although grey water may contain a variety of suspended solids, dissolved organics, and salts, the stream is usually diluted and can be used for landscape irrigation without treatment. With minimal treatment, grey water can be reused in many non-potable water applications in buildings. The National Sanitation Foundation (NSF) is developing comprehensive testing and performance standards (NSF/ANSI 350) for residential and commercial applications. One disadvantage of gray water collection is that it requires dedicated pipes, so it is usually used in renovations or new buildings. 

Wastewater recycling and reuse represents the greatest untapped potential for solving fresh water quality and availability issues, both now and in the future. The two main sources of these supplies are municipal and industrial. 

Great progress has been made in urban sewage treatment. The current typical representative is the Groundwater Recharge System (GWRS) located in Orange County, California. As a joint venture between the water supply area and the sewage area, it currently produces 100 million gallons (mgd) of drinking water per day from secondary treated municipal wastewater. The final treated water is pumped into the injection well to minimize the intrusion of seawater into the freshwater aquifer. 

GWRS provides drinkable high-quality water to approximately 850,000 residents and is the world's largest advanced water purification system for drinking water reuse (13). It can be said that the biggest challenge in building this system is to convince residents that drinking treated sewage is acceptable. 

Now, many regions around the world are carrying out a large number of activities in the recovery of drinking water from urban wastewater, using technologies such as membranes and advanced oxidation processes. 

A characteristic of urban sewage is that the types and concentrations of pollutants are within a relatively narrow range, regardless of location. Therefore, the choice of processing technology and system design has proven to be straightforward and requires minimal pilot testing. 

On the other hand, the treatment and reuse of industrial wastewater is more challenging. Because the manufacturing industry is so diversified, few wastewater streams are even close to each other in terms of the types and/or concentrations of pollutants. Therefore, each application requires a large number of pilot tests to develop the best technology suite and overall system design. 

Three incentives to promote the recycling and reuse of industrial wastewater. 

This may prevent the expansion of the factory and even lead to a complete cessation of operations. For those places suffering from drought conditions, unless substantial restoration and reuse measures are taken, this may be the future. 

An ongoing investigation by the U.S. Environmental Protection Agency and state pollution control agencies is identifying new hazardous chemicals. Wastewater streams that were previously discharged to public treatment plants (POTW) may now have to be treated as hazardous waste. It is possible to remove only harmful contaminants and reuse the remaining stream. 

Many consumer-oriented manufacturers want to use the positive image that promotes the fact that they save water and/or reuse wastewater. Consumers are gradually becoming aware of and paying attention to issues such as climate change, water shortages, and microplastic pollution. 

When choosing a treatment technology, we must take a step back and determine the types of pollutants that must be removed. Waterborne contaminants can be classified as shown in the table below.

Dirt, clay, colloidal materials, sludge, dust, insoluble metal oxides and hydroxides

Trihalomethanes, synthetic organic chemicals, humic acid, fulvic acid

Heavy metals, silica, arsenic, nitrate, chloride, carbonate

Bacteria, viruses, protozoan cysts, fungi, algae, molds, yeast cells

Hydrogen sulfide, methane, radon, carbon dioxide

Contaminated water sources that cannot meet the requirements of almost any application without treatment. There are countless technologies available on the market, and they are becoming more and more stable. The challenge is to invest cost and time to determine the most effective technology and develop the best system design. 

For the following five treatment technology tables, the boxes marked with "X" indicate that the technology can effectively treat the pollutants in the column. The cell marked with "—" means it is invalid. Finally, the cells marked "L" indicate that the technology has limited effectiveness under certain conditions.

Although it is impossible to remove all contaminants from the water supply, it can be very close to the best technology. The initial challenge of industrial wastewater treatment is to conduct a complete water analysis of the flow. 

If it changes over time, it is recommended to analyze the "worst case" sample. Then, a decision must be made regarding the use of the treated water. This will determine the quality requirements of this supply. 

Are there any regulatory issues that need to be resolved? What are the practical issues (space, storage, plumbing, drainage, etc.)? Can the field staff take the next step and identify the most likely technical candidates? Generally speaking, the category of pollutants to be removed will guide engineers to process candidates. 

For example, if the goal is to reduce suspended solids, technical options may include screens, filters (filter elements, beds, etc.), dissolved air flotation (DAF), microfiltration, and so on. 

If the goal is to dissolve organic matter, things will become more complicated. If the organic matter is biodegradable, there are many opportunities to use bacteria to break down most of the organic matter and combine it with membrane bioreactor (MBR) technology to recover the treated water. If the organic matter is stubborn (anti-biodegradation), the choice is usually to use activated carbon products or special resin adsorption, or use advanced oxidation process (AOP) destruction, such as a combination of ozone, ultraviolet light, hydrogen peroxide, Fenton reagent, etc. Membrane processes, ultrafiltration, are often used to concentrate these contaminants. 

For the removal of dissolved ionic (salt) pollutants, the most common choice is reverse osmosis (RO) or nanofiltration, which are two of the four cross-flow pressure-driven membrane separation technologies. Although these processes are driven by pressure, there is also a set of technologies that use electricity as the driving force. These include electrodialysis and capacitive deionization. Some specific adsorption resins are also used for the removal of certain ionic pollutants. 

Microbial reduction poses special challenges in water treatment/recycling. The acceptable concentrations of these pollutants are usually regulated by health-related regulations. Microbial inactivation technology is usually in the form of chemical (chlorine, ozone, etc.) or high-energy radiation (such as ultraviolet light). Since all microorganisms are actually suspended solids (albeit very small), membrane technology can be used to separate them from the treated water without deactivating them. It is important to know that it is almost impossible to make the treated water source completely free of bacteria to re-grow. 

The gas is usually removed by activated carbon adsorption, scrubbing (medium or special membrane), vacuum or chemical treatment. For brevity, they are not included in the above table.

Sewage treatment systems are always composed of different components, especially the "three Ps": pretreatment, primary and polishing. Each component contains one or more technologies that are selected to accomplish a specific task. Pretreatment usually aims to protect the primary treatment technology from contamination (scaling, chemical attack, etc.). The primary treatment performs the main treatment functions and produces the final treated water quality. 

Post-processing usually includes storage and distribution components, and includes techniques to maintain the quality produced by the primary processing technology. 

For those who wish to investigate the possibility of reusing wastewater in their manufacturing facilities, the following activities are recommended:

Editor's note: Detailed information on the above activities is available in the unpublished document "Wastewater Recovery and Reuse-Part 1", Peter S. Cartwright, Saudi Arabian Water Environment Association, April 2016. 

Remember, you can also recycle certain "pollutants" for reuse. This involves "fractionating" wastewater to separate and concentrate the required materials. 

Although industrial wastewater treatment requires investment of time and money, the amount of fresh water required will decrease, and as the supply of fresh water decreases, this cost will definitely increase. There are many highly qualified consulting engineering companies that can carry out testing and design activities in this field. 

The client wanted to recycle and reuse all the wastewater in the existing electrodialysis reversal system to produce drinking water for large entertainment facilities. The contaminants in this wastewater are hardness, silica, and total dissolved solids (TDS). The management hopes to return the treated water to the drinking water supply system, and almost no water leaves the facility. The water quality requirement is that the treated water meets the quality standards of the EPA Safe Drinking Water Law, with TDS less than 500mg/L, total hardness less than 100mg/L, and pH between 6-8. 

Once the wastewater analysis is recorded, the first decision is how to remove the hardness (the hardness in the feedwater is 1435 mg/L). The technical options considered are to raise the pH above 10 to precipitate insoluble calcium carbonate, or use clarification to precipitate solids, or use continuous microfiltration (MF) to dehydrate the flow using a filter press to remove most of the water. Because the latter method requires a significantly smaller footprint and higher throughput, it was chosen. The sludge produced by the filter press can be sold as high-quality calcium carbonate. The treated water (permeate) from the MF system is adjusted to a range of 6 to 8, and then sent to the reverse osmosis (RO) system to reduce TDS and silica. The permeate is returned to the drinking water system. The RO concentrate is sent to a falling film evaporator, then a crystallizer, and finally a centrifuge to produce relatively dry solids, which are then transported to a landfill. The total flow of wastewater is 58,000 gallons/day, and the total amount of solids produced is 2600 lbs/day.

This is an example of a ZLD (Zero Liquid Discharge) device in which no liquid waste water is discharged. 

The challenging water-related era is coming soon-in all areas of society. Fortunately, many highly qualified organizations are committed to helping us respond. 

For those in the manufacturing industry, realizing that “the same, the same” will no longer apply, facilities must find innovative ways to maximize water recycling. The survival of industrial facilities may depend on it. 

Peter Cartwright entered the water purification and wastewater treatment industry in 1974 and has his own consulting engineering company since 1980. He has a degree in chemical engineering from the University of Minnesota and is a registered professional engineer in the state. Cartwright has provided consulting services to more than 250 clients worldwide. He has written more than 200 articles, written many book chapters, delivered more than 300 speeches at conferences around the world, and obtained multiple patents. He also provides extensive expert witness testimony and technical training education.

He is a member of the editorial advisory board and technical review board of several trade publications, and is a frequent lecturer at numerous technical conferences around the world. Cartwright is the recipient of the Merit Award, Life Member Award and Hall of Fame Award from the Water Quality Association, and served as a technical consultant for the Canadian Water Quality Association from 2007 to 2018. As the 2016 McEllhiney National Groundwater Distinguished Lecturer Research and Education Foundation, he has delivered more than 35 lectures on groundwater pollutant mitigation around the world.

Cartwright can be contacted via [Email Protection] or via www.cartwright-consulting.com.

The Water and Waste Digest staff invites industry professionals to nominate what they consider to be the most outstanding and innovative water and wastewater projects to be recognized in the annual reference guide question. All projects must be in the design or construction stage within the past 18 months.

7 basic types of temperature measurement sensors

Flint water crisis: 7 years later

What is biological oxygen demand (BOD)?

What is sewage treatment aeration?

What is total suspended solids (TSS)? 

©2021 Scranton Gillette Communications. Copyright Site Map| Privacy Policy| Terms and Conditions