Is it safe?
Water is an important part of our lives. We need it to survive, but in some areas, it’s becoming increasingly scarce. In order to make sure that there is enough water for people to drink, many places are looking at creative solutions. One such solution is using recycled toilet water. The idea of this has left many people wondering if it’s safe? How is the process accomplished?
Since over 97% of Earth’s water has salt in it, it’s unfit for drinking. Of the 3% that remains, more than two-thirds is frozen in glaciers and icecaps, which leaves just 1% of all the water on our planet as freshwater. Only one one-hundredth of that 1%t is in lakes, rivers and other waterways. The rest is in aquifers beneath the surface or trapped in soil. This makes freshwater an essential commodity that most people in the developed world take for granted. Pressure on this invaluable resource is mounting significantly. With the global populations growing and thanks to the effects of climate change, the United Nations (UN) says that at least half of the planet will face water scarcity by 2030. That’s only 10 short years from now. These shortages would threaten food production and cause health crises through people’s increased exposure to unsanitary water. Since unsanitary water already kills millions each year due to waterborne diseases, such as cholera and diarrhea, this will have a considerable impact. Over the last several decades, regional and local water shortages here in the United States are becoming increasingly common. The two largest reservoirs, Lake Powell and Lake Mead, store a significant amount of water. In 2000, they were both full, but five years later they were half-empty and haven’t rebounded. This depletion worries a lot of people who are dependent upon them for water, such as the City of Las Vegas. Over 90% of the city’s water supply comes from Lake Mead, so if it goes dry that’s a couple million people who don’t have water. As the awareness level of these shortages rises, it has helped to highlight the need to find alternative resources for water. One of these innovative technologies is to used recycled wastewater. While it may sound gross, it’s not a new concept. Typically, recycled wastewater is used for irrigation and other non-drinkable uses. In fact, Israel recycles 80% of its sewage and uses much of it for irrigation. The relatively new idea is to use recycled wastewater for drinking water.
It’s important to realize that wastewater is much more than just toilet water. It’s water that comes from residences and non-residences and goes into septic or sewer systems. In your home, it’s not just your toilet, but includes water from your kitchen, bathroom sink/shower, washing machines and rain runoff. If the wastewater goes into a septic system, it’s eventually absorbed back into the ground. If it goes into a sewer system, it goes through a treatment process that removes contaminants. When the wastewater arrives at the treatment plants, large solid material is separated from the liquid by using grates or screens. Then, in a settling tank, smaller solids fall to the bottom of solution while oils rise to the surface and are skimmed off. Next, the wastewater goes to an aeration tank, where microbes feed on the waste and break it down. After the final settling step, the water is treated with ultraviolet light, chemicals (like chlorine) or other processes to kill any remaining germs. Once the entire process is complete, the water is released back into the environment. Where it ends up depends on your state’s laws and individual municipalities’ treatment plans. Often water used for consumption in one area is drawn from the same river, lake or reservoir where the treated wastewater was released upstream from another area. Many of the same steps are then repeated before the water is sent through to the public water supplies. Many cities use rivers, such as the Colorado, Mississippi and Thames, in this way. When you think of all the water that goes down the drain every time you turn on a faucet or flush the toilet, you begin to realize just how much water you use and, potentially, waste. It’s easy to see that recycled wastewater is an untapped resource that there’s a lot of, it’s cheaper than other resources and it’s a guaranteed resource. Some scientists estimate that if an average city recycled all its wastewater, it could reduce how much water it needs by 60%.
The technology, called tertiary recycling, used to treat wastewater and make it drinkable is a three-level system that starts with sewage and ends with excellent quality water that is safe to consume. The process is very similar to what is done to water before it’s bottled and sold at stores. The first part of the process involves microfiltration. The water flows through a series of tubes containing filters with microscopic pores. Each one of these pores is 500 times smaller than the thickness of a human hair. This means that microbes and all but the smallest solids are filtered out because they can’t pass through the tubes. Next, a process called reverse osmosis is completed. This technology is used for a wide range of water purification needs to produce everything from drinking water to cleaner car washes. It uses high pressure to force water through a plastic membrane that has pores so small even dissolved salts can’t get through. This process is usually reliable enough that all contaminants should be remove. However, as a way to ensure that the water is absolutely pure, it flows past ultraviolet lamps to sterilize it. This is actually the same technology used to treat drinking water supplies that have become contaminated, which means that it’s been around for years. Once this process is complete, the clean water can be added to the drinking water supply through two different methods. The direct potable reuse (DPR) method is when this water is sent directly back into the potable distribution system. The indirect potable reuse (IPR) method is when the clean water is blended with the water in an environmental buffer, like an aquifer or a reservoir, and then makes its way into the potable water supply through traditional collection methods. This mixing the output with groundwater is a largely unnecessary, but is used as a confidence-building measure to alleviate public fears. People who support recycling wastewater for human consumption merely want to shorten the pathway between wastewater and consumable water, which means reintroducing highly treated wastewater into water supplies without it going into a lake or river first.
One of the earliest implementations of wastewater recycling took place in Windhoek, Namibia. Their program has been in operation since 1968 when the first DPR facility opened and has helped to overcome both water shortages and water-borne diseases. More than half of the population in Sub Saharan African faces water insecurity and health risks from the water with diseases that kill over a million people each year. Data from the 1970s through now show that disease occurs at lower rates for people whose water is supplied by the Windhoek plant than through conventional treated sources. When the water from the plant has been tested, the quality is very good and, in some cases, better than the tap water in any city in the developed world.
The best-known wastewater recycler is probably Singapore. While it’s a little over half the size of Los Angeles, it has about 1.3 million more residents and only has enough water for 60% of its daily needs. In order to make up the remaining 40%, it imports the water from neighboring Malaysia. In the 1960s, the two countries signed treaties that ensured that Singapore has enough clean water for drinking, agriculture and industrial processes. Since Singapore’s economy relies heavily on exports, making sure that there is enough high-quality water to make electronics and other goods is essential. The treaties are set to expire in 2061. The treaties guarantee water supply, but not price. So, in 1998 and 2002, Malaysia proposed raising the price on the water. This made Singapore decided to pursue a new strategy. The government came up with the “Four Taps” plan. This plan makes use of Singapore’s reservoirs, water imported from Malaysia, recycled wastewater and desalinated seawater. The idea of recycling wastewater in Singapore actually began in 1974 when an experimental plant was built, but cost and reliability problems shut it down within a year. In 1998, with the first proposed rate hike on the imported water, Singapore’s Public Utilities Board (PUB) decided to reinvestigate the possibility of making clean water from sewage. Since then, there have been four new plants built that use the tertiary recycling process. These plants are referred to as NEWater plants. Reports from PUB state that the water from the NEWater plants exceeds drinking water standards set by the US Environmental Protection Agency (EPA) and the World Health Organization (WHO). This water is cleaner than the water that flows to taps in Singapore. Since it’s so clean, it’s mostly used in industrial processes that require extremely pure water. Singapore now delivers 30% of its needs through the NEWater reclamation facilities. Their goal is to grow NEWater production, increase desalination and impose regulations to encourage water conservation in efforts to become water independent by the time the treaties with Malaysia expire.
The idea of using recycled wastewater has been a hard sell in the US. There are only a few facilities around the country. In 2008, California’s Orange County Water District (OCWD) starting using a process similar to Singapore’s. Prior to that, the county had been using recycle water for non-potable use starting in the 1970s. Currently, their plant is generating as much as 265 million liters of clean water from part of the 1.3 billion gallons of wastewater generated each day, which is enough to supply about 20,000 average US households or around one-third of the county population. Since the OWCD output is mixed with the main groundwater supply, it reaches over 70% of residents. The OCWD says the water quality exceeds all state and federal drinking water standards. Due to the success of the plant in Orange County, California has put $1 billion into funding recycling wastewater and launching new initiatives in Los Angeles, San Francisco and San Diego. In 2013, after the spring that supplied Big Spring, Texas with water dried up, the town needed to find a new way to provide water to its residents. They were the first city in the US to have a facility that uses the DPR method. Five years later, it was reported that the process saves the water district about 1.7 million gallons per day. Texas as a whole is often severely affected by drought, so it’s aiming to generate 10% of all new water supplies through reclaimed water by 2060. A study done in 2012 by the National Academy of Sciences found that US coastal cities could increase their water supply by 27% if they started using treated wastewater.
With many cities experiencing droughts and growing populations, more and more are incorporating recycled wastewater into the water supply. For most places to have a sustainable water future this will be a necessity. The World Water Council estimates that recycled wastewater will be a normalized source of drinking water in cities across the globe within 30 years. Since much of the infrastructure and technology are already in place the transition should be physically easy. The problem is public skepticism surrounding the safety of the recycled water. Psychologists say the disgust comes from intuitive concepts of contagion and is deeply held and difficult, but not impossible, to overcome. This is where public relations are key. One group, Water Reuse, participates in education outreach. Their message is called Downstream and conveys the concept that all water is ultimately recycled. When Orange County was starting their program, it used a comprehensive PR and education campaign to ease public fears. The best ways to get past the disgust factor is perceptual cues. If someone can see sparkling fresh, clear water and it tastes great, then this helps to overcome the negative connotation. This is evidenced by a recent study from researchers at University of California, Riverside and Santa Barbara City College. They had 143 participants complete a blind taste test to get a comparison between bottled water, recycled wastewater from the tap and conventional groundwater from the tap. The results showed that more people preferred the taste of recycled waste tap water over conventional tap water and it was comparable to bottled water. There’s no question that recycled water is safe and tastes like any other drinking water. As awareness improves, the goal is to move from indirect to direct potable reuse because this would bring down energy use and costs. Also, it would avoid the counter-intuitive step of re-contaminating purified water by mixing in with groundwater.
When it comes to finding water resources, a multi-faceted approach is vital. There are options that should be used in addition to recycled wastewater. One source is rain. If a city collected all the storm-water that drains into the gutter, they could provide water for the entire city. Another option is using plants to convert salt water into fresh. While desalination is expensive, it’s effective. The main cost is energy and since that is coming down all the time, it will continue to become more affordable. Compared to the cost of desalination or imported water, energy cost of reverse osmosis has come down by 75% since the 1970s and emerging technologies may reduce it even further because improvements in membrane technology allow less pressure to be used to do the same thing. There are also new technologies that are being tested and could change the future of wastewater treatment. For instance, traditional membrane bioreactors are already used in many modern wastewater treatment plants because they shorten the conventional sewage treatment process by adding a membrane to the aeration step. This is where aerobic bacteria, those that need oxygen, break down the organic matter in wastewater. By sending the water through a membrane, settling and filtration steps are not necessary after. Instead, the water is clean enough to be discharged or used for irrigation. The new technology is an anaerobic membrane bioreactor. These bacteria that don’t need oxygen to breathe, so oxygen is not bubbled through the reactors. This would reduce treatment costs. Also, anaerobic bacteria can consume more solid waste, reducing the amount requiring costly disposal. If configured appropriately, they also release less methane than aerobic bacteria. Expanding upon this technology is something called microbial fuel cells. This means that the bacteria breaking down sewage also generates electricity. A microbial fuel cell consists of two chambers of water separated by a membrane with a wire connecting two electrodes (one on either side). In one chamber, anaerobic bacteria feed on sewage and as they break down the organic matter, they produce electrons and positively charged hydrogen atoms (protons). The electrons go to the electrode and travel across the wire, which generates an electrical current. At the same time, the protons go through the membrane into the other chamber. Once there, they combine with the electrons coming from electrode and with the oxygen in the solution to make pure water. So far, the latest prototypes are said to remove 99.9% of organic substances from wastewater while producing electricity. Unfortunately, the amount of electricity isn’t much. The eventual goal is that the devices could help power the wastewater treatment plants. Other scientists are investigating a device that uses light and electricity to clean the water. Ultraviolet light activates titanium oxide on one side of an electrode, which results in a reaction that breaks down pollutants. On the other side, electricity activates a similar reaction. The device has been found to be particularly effective against pharmaceuticals, pesticides, dyes and other molecules, which are the hardest compounds to remove when treating wastewater.
Water shortages and lack of clean water is something will be affecting every country, every society. The control of water resources is a point of friction already among countries and some experts think that issues over water rights may become a major spark for future conflicts. All of these are why the case for recycled wastewater is strong. Obviously, the safety has been established by the many projects currently operating successfully around the world. We need to continue to move forward down this path toward using more recycled wastewater in order to make sure we have enough water for our future.