Reclaimed or recycled water (also called wastewater reuse or water reclamation) is the process of converting wastewater into water that can be reused for other purposes. Reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater (i.e., groundwater recharge). Reused water may also be directed toward fulfilling certain needs in residences (e.g. toilet flushing), businesses, and industry, and could even be treated to reach drinking water standards. This last option is called either “direct potable reuse” or “indirect potable” reuse, depending on the approach used. Colloquially, the term “toilet to tap” also refers to potable reuse.
Reclaiming water for reuse applications instead of using freshwater supplies can be a water-saving measure. When used water is eventually discharged back into natural water sources, it can still have benefits to ecosystems, improving streamflow, nourishing plant life and recharging aquifers, as part of the natural water cycle.
Wastewater reuse is a long-established practice used for irrigation, especially in arid countries. Reusing wastewater as part of sustainable water management allows water to remain as an alternative water source for human activities. This can reduce scarcity and alleviate pressures on groundwater and other natural water bodies.
Background
Achieving more sustainable sanitation and wastewater management will require emphasis on actions linked to resource management, such as wastewater reuse or excreta reuse that will keep valuable resources available for productive uses. This in turn supports human wellbeing and broader sustainability.
Simply stated, reclaimed water is water that is used more than one time before it passes back into the natural water cycle. Advances in wastewater treatment technology allow communities to reuse water for many different purposes. The water is treated differently depending upon the source and use of the water and how it gets delivered.
Cycled repeatedly through the planetary hydrosphere, all water on Earth is recycled water, but the terms “recycled water” or “reclaimed water” typically mean wastewater sent from a home or business through a sewer system to a wastewater treatment plant, where it is treated to a level consistent with its intended use.
The World Health Organization has recognized the following principal driving forces for wastewater reuse:
increasing water scarcity and stress,
increasing populations and related food security issues,
increasing environmental pollution from improper wastewater disposal, and
increasing recognition of the resource value of wastewater, excreta and greywater.
Water recycling and reuse is of increasing importance, not only in arid regions but also in cities and contaminated environments.
Already, the groundwater aquifers that are used by over half of the world population are being over-drafted. Reuse will continue to increase as the world’s population becomes increasingly urbanized and concentrated near coastlines, where local freshwater supplies are limited or are available only with large capital expenditure. Large quantities of freshwater can be saved by wastewater reuse and recycling, reducing environmental pollution and improving carbon footprint. Reuse can be an alternative water supply option.
Types and applications
Most of the uses of water reclamation are non potable uses such as washing cars, flushing toilets, cooling water for power plants, concrete mixing, artificial lakes, irrigation for golf courses and public parks, and for hydraulic fracturing. Where applicable, systems run a dual piping system to keep the recycled water separate from the potable water.
The main reclaimed water applications in the world are shown below:
| Categories of use | Uses |
|---|---|
| Urban uses | Irrigation of public parks, sporting facilities, private gardens, roadsides; Street cleaning; Fire protection systems; Vehicle washing; Toilet flushing; Air conditioners; Dust control. |
| Agricultural uses | Food crops not commercially processed; Food crops commercially processed; Pasture for milking animals; Fodder; Fibre; Seed crops; Ornamental flowers; Orchards; Hydroponic culture; Aquaculture; Greenhouses; Viticulture. |
| Industrial uses | Processing water; Cooling water; Recirculating cooling towers; Washdown water; Washing aggregate; Making concrete; Soil compaction; Dust control. |
| Recreational uses | Golf course irrigation; Recreational impoundments with/without public access (e.g. fishing, boating, bathing); Aesthetic impoundments without public access; Snowmaking. |
| Environmental uses | Aquifer recharge; Wetlands; Marshes; Stream augmentation; Wildlife habitat; Silviculture. |
| Potable uses | Aquifer recharge for drinking water use; Augmentation of surface drinking water supplies; Treatment until drinking water quality. |
Unplanned Indirect Potable Use has existed for a long time. Large towns on the River Thames upstream of London (Oxford, Reading, Swindon, Bracknell) discharge their treated sewage (“non-potable water”) into the Thames, which supplies water to London downstream. In the United States, the Mississippi River serves as both the destination of sewage treatment plant effluent and the source of potable water.
Urban reuse
Unrestricted: The use of reclaimed water for non-potable applications in municipal settings, where public access is not restricted.
Restricted: The use of reclaimed water for non-potable applications in municipal settings, where public access is controlled or restricted by physical or institutional barriers, such as fencing, advisory signage, or temporal access restriction.
Agricultural reuse
There are benefits of using recycled water for irrigation, including the lower cost compared to some other sources and consistency of supply regardless of season, climatic conditions and associated water restrictions. When reclaimed water is used for irrigation in agriculture, the nutrient (nitrogen and phosphorus) content of the treated wastewater has the benefit of acting as a fertilizer. This can make the reuse of excreta contained in sewage attractive.
The irrigation water can be used in different ways on different crops:
Food crops to be eaten raw: crops which are intended for human consumption to be eaten raw or unprocessed.
Processed food crops: crops which are intended for human consumption not to be eaten raw but after treatment process (i.e. cooked, industrially processed).
Non-food crops: crops which are not intended for human consumption (e.g. pastures, forage, fiber, ornamental, seed, forest and turf crops).
In developing countries, agriculture is increasingly using untreated wastewater for irrigation – often in an unsafe manner. Cities provide lucrative markets for fresh produce, so are attractive to farmers. However, because agriculture has to compete for increasingly scarce water resources with industry and municipal users, there is often no alternative for farmers but to use water polluted with urban waste directly to water their crops.
There can be significant health hazards related to using untreated wastewater in agriculture. Wastewater from cities can contain a mixture of chemical and biological pollutants. In low-income countries, there are often high levels of pathogens from excreta. In emerging nations, where industrial development is outpacing environmental regulation, there are increasing risks from inorganic and organic chemicals. The World Health Organization, in collaboration with the Food and Agriculture Organization of the United Nations (FAO) and the United Nations Environmental Program (UNEP), has developed guidelines for safe use of wastewater in 2006. These guidelines advocate a ‘multiple-barrier’ approach wastewater use, for example by encouraging farmers to adopt various risk-reducing behaviours. These include ceasing irrigation a few days before harvesting to allow pathogens to die off in the sunlight, applying water carefully so it does not contaminate leaves likely to be eaten raw, cleaning vegetables with disinfectant or allowing fecal sludge used in farming to dry before being used as a human manure.
Environmental reuse
The use of reclaimed water to create, enhance, sustain, or augment water bodies including wetlands, aquatic habitats, or stream flow is called “environmental reuse”. For example, constructed wetlands fed by wastewater provide both wastewater treatment and habitats for flora and fauna.
Industrial reuse
The use of reclaimed water to recharge aquifers that are not used as a potable water source.
Planned potable reuse
Planned potable reuse is publicly acknowledged as an intentional project to recycle water for drinking water. There are two ways in which potable water can be delivered for reuse – “Indirect Potable Reuse” (IPR) and “Direct Potable Reuse”. Both these forms of reuse are described below, and commonly involve a more formal public process and public consultation program than is the case with de facto or unacknowledged reuse. In ‘indirect’ potable reuse applications, the reclaimed wastewater is used directly or mixed with other sources.
Direct potable reuse is also called “toilet to tap”.
Some water agencies reuse highly treated effluent from municipal wastewater or resource recovery plants as a reliable, drought proof source of drinking water. By using advanced purification processes, they produce water that meets all applicable drinking water standards. System reliability and frequent monitoring and testing are imperative to them meeting stringent controls.
The water needs of a community, water sources, public health regulations, costs, and the types of water infrastructure in place, such as distribution systems, man-made reservoirs, or natural groundwater basins, determine if and how reclaimed water can be part of the drinking water supply. Some communities reuse water to replenish groundwater basins. Others put it into surface water reservoirs. In these instances the reclaimed water is blended with other water supplies and/or sits in storage for a certain amount of time before it is drawn out and gets treated again at a water treatment or distribution system. In some communities, the reused water is put directly into pipelines that go to a water treatment plant or distribution system.
Modern technologies such as reverse osmosis and ultraviolet disinfection are commonly used when reclaimed water will be mixed with the drinking water supply.
Indirect potable reuse
Indirect potable reuse (IPR) means the water is delivered to the consumer indirectly. After it is purified, the reused water blends with other supplies and/or sits a while in some sort of storage, man-made or natural, before it gets delivered to a pipeline that leads to a water treatment plant or distribution system. That storage could be a groundwater basin or a surface water reservoir.
Some municipalities are using and others are investigating Indirect Potable Reuse (IPR) of reclaimed water. For example, reclaimed water may be pumped into (subsurface recharge) or percolated down to (surface recharge) groundwater aquifers, pumped out, treated again, and finally used as drinking water. This technique may also be referred to as groundwater recharging. This includes slow processes of further multiple purification steps via the layers of earth/sand (absorption) and microflora in the soil (biodegradation).
IPR or even unplanned potable use of reclaimed wastewater is used in many countries, where the latter is discharged into groundwater to hold back saline intrusion in coastal aquifers. IPR has generally included some type of environmental buffer, but conditions in certain areas have created an urgent need for more direct alternatives.
Direct potable reuse
Direct potable reuse means the reused water is put directly into pipelines that go to a water treatment plant or distribution system. Direct potable reuse may occur with or without “engineered storage” such as underground or above ground tanks.
In a Direct Potable Reuse (DPR) scheme, water is put directly into pipelines that go to a water treatment plant or distribution system. Direct potable reuse may occur with or without “engineered storage” such as underground or above ground tanks. In other words, DPR is the introduction of reclaimed water derived from urban wastewater after extensive treatment and monitoring to assure that strict water quality requirements are met at all times, directly into a municipal water supply system.
Indirect Potable Reuse (IPR)
IPR occurs through the augmentation of drinking water supplies with urban wastewater treated to a level suitable for IPR followed by an environmental buffer (e.g. rivers, dams, aquifers, etc.) that precedes drinking water treatment. In this case, urban wastewater passes through a series of treatment steps that encompasses membrane filtration and separation processes (e.g. MF, UF and RO), followed by an advanced chemical oxidation process (e.g. UV, UV+H2O2, ozone).
Reuse in space
Wastewater reclamation can be especially important in relation to human spaceflight. In 1998, NASA announced it had built a human waste reclamation bioreactor designed for use in the International Space Station and a manned Mars mission. Human urine and feces are input into one end of the reactor and pure oxygen, pure water, and compost (humanure) are output from the other end. The soil could be used for growing vegetables, and the bioreactor also produces electricity.
Aboard the International Space Station, astronauts have been able to drink recycled urine due to the introduction of the ECLSS system. The system costs $250 million and has been working since May 2009. The system recycles wastewater and urine back into potable water used for drinking, food preparation, and oxygen generation. This cuts back on the need for resupplying the space station so often.
Benefits
Water/wastewater reuse, as an alternative water source, can provide significant economic, social and environmental benefits, which are key motivators for implementing such reuse programmes. Specifically, in agriculture, irrigation with wastewater may contribute to improve production yields, reduce the ecological footprint and promote socioeconomic benefits. These benefits include:
Increased water availability
Drinking water substitution – keep drinking water for drinking and reclaimed water for non-drinking use (i.e. industry, cleaning, irrigation, domestic uses, toilet flushing, etc.)
Reduced over-abstraction of surface and groundwater
Reduced energy consumption associated with production, treatment, and distribution of water compared to using deep groundwater resources, water importation or desalination
Reduced nutrient loads to receiving waters (i.e. rivers, canals and other surface water resources)
Reduced manufacturing costs of using high quality reclaimed water
Increased agricultural production (i.e. crop yields)
Reduced application of fertilizers (i.e. conservation of nutrients, reducing the need for artificial fertilizer (e.g. soil nutrition by the nutrients existing in the treated effluents))
Enhanced environmental protection by restoration of streams, wetlands and ponds
Increased employment and local economy (e.g. tourism, agriculture).
Design considerations
Distribution
Nonpotable reclaimed water is often distributed with a dual piping network that keeps reclaimed water pipes completely separate from potable water pipes.
In many cities using reclaimed water, it is now in such demand that consumers are only allowed to use it on assigned days. Some cities that previously offered unlimited reclaimed water at a flat rate are now beginning to charge citizens by the amount they use.
Treatment processes
For many types of reuse applications wastewater must pass through numerous sewage treatment process steps before it can be used. Steps might include screening, primary settling, biological treatment, tertiary treatment (for example reverse osmosis), and disinfection.
There are several technologies used to treat wastewater for reuse. A combination of these technologies can meet strict treatment standards and make sure that the processed water is hygienically safe, meaning free from bacteria and viruses. The following are some of the typical technologies: Ozonation, ultrafiltration, aerobic treatment (membrane bioreactor), forward osmosis, reverse osmosis, advanced oxidation.
Wastewater is generally treated to only secondary level treatment when used for irrigation.
A pump station distributes reclaimed water to users around the city. This may include golf courses, agricultural uses, cooling towers, or in land fills.
Alternative options
Rather than treating wastewater for reuse purposes, other options can achieve similar effects of freshwater savings:
Greywater reuse systems – at a household level, treated or untreated greywater may be used for flush toilets or to water the garden.
Rainwater harvesting and stormwater recovery- Urban design systems which incorporate rainwater harvesting and reduce runoff are known as Water Sensitive Urban Design (WSUD) in Australia, Low Impact Development (LID) in the United States and Sustainable urban drainage systems (SUDS) in the United Kingdom.
Seawater desalination – an energy-intensive process where salt and other minerals are removed from seawater to produce potable water for drinking and irrigation, typically through membrane filtration (reverse-osmosis), and steam-distillation.
Costs
The cost of reclaimed water exceeds that of potable water in many regions of the world, where a fresh water supply is plentiful. However, reclaimed water is usually sold to citizens at a cheaper rate to encourage its use. As fresh water supplies become limited from distribution costs, increased population demands, or climate change reducing sources, the cost ratios will evolve also. The evaluation of reclaimed water needs to consider the entire water supply system, as it may bring important value of flexibility into the overall system
Reclaimed water systems usually require a dual piping network, often with additional storage tanks, which adds to the costs of the system.
Barriers to implementation
Full-scale implementation and operation of water reuse schemes still face regulatory, economic, social and institutional challenges.
Economic viability of water reuse schemes.
Costs of water quality monitoring and identification of contaminants. Difficulties in contaminant identification may include the separation of inorganic and organic pollutants, microorganisms, Colloids, and others.
Full cost recovery from water reuse schemes – lack of financial water pricing systems comparable to already subsidized conventional treatment plants.
Health aspects
Reclaimed water is considered safe when appropriately used. Reclaimed water planned for use in recharging aquifers or augmenting surface water receives adequate and reliable treatment before mixing with naturally occurring water and undergoing natural restoration processes. Some of this water eventually becomes part of drinking water supplies.
A water quality study published in 2009 compared the water quality differences of reclaimed/recycled water, surface water, and groundwater. Results indicate that reclaimed water, surface water, and groundwater are more similar than dissimilar with regard to constituents. The researchers tested for 244 representative constituents typically found in water. When detected, most constituents were in the parts per billion and parts per trillion range. DEET (a bug repellant), and caffeine were found in all water types and virtually in all samples. Triclosan (in anti-bacterial soap & toothpaste) was found in all water types, but detected in higher levels (parts per trillion) in reclaimed water than in surface or groundwater. Very few hormones/steroids were detected in samples, and when detected were at very low levels. Haloacetic acids (a disinfection by-product) were found in all types of samples, even groundwater. The largest difference between reclaimed water and the other waters appears to be that reclaimed water has been disinfected and thus has disinfection by-products (due to chlorine use).
A 2005 study titled “Irrigation of Parks, Playgrounds, and Schoolyards with Reclaimed Water” found that there had been no incidences of illness or disease from either microbial pathogens or chemicals, and the risks of using reclaimed water for irrigation are not measurably different from irrigation using potable water.
A 2012 study conducted by the National Research Council in the United States of America found that the risk of exposure to certain microbial and chemical contaminants from drinking reclaimed water does not appear to be any higher than the risk experienced in at least some current drinking water treatment systems, and may be orders of magnitude lower. This report recommends adjustments to the federal regulatory framework that could enhance public health protection for both planned and unplanned (or de facto) reuse and increase public confidence in water reuse.
Many humans associate a feeling of disgust with reclaimed water and 13% of a survey group said they would not even sip it. Nonetheless, the main health risk for potable use of reclaimed water is the potential for pharmaceutical and other household chemicals or their derivatives (Environmental persistent pharmaceutical pollutants) to persist in this water. This would be less of a concern if human excreta was kept out of sewage by using dry toilets or systems that treat blackwater separately from greywater.
To address these concerns about the source water, reclaimed water providers use multi-barrier treatment processes and constant monitoring to ensure that reclaimed water is safe and treated properly for the intended end use.
Environmental aspects
There is debate about possible health and environmental effects. To address these concerns, A Risk Assessment Study of potential health risks of recycled water and comparisons to conventional Pharmaceuticals and Personal Care Product (PPCP) exposures was conducted by the WateReuse Research Foundation. For each of four scenarios in which people come into contact with recycled water used for irrigation – children on the playground, golfers, and landscape, and agricultural workers – the findings from the study indicate that it could take anywhere from a few years to millions of years of exposure to nonpotable recycled water to reach the same exposure to PPCPs that we get in a single day through routine activities.
Using reclaimed water for non-potable uses saves potable water for drinking, since less potable water will be used for non-potable uses.
It sometimes contains higher levels of nutrients such as nitrogen, phosphorus and oxygen which may somewhat help fertilize garden and agricultural plants when used for irrigation.
The usage of water reclamation decreases the pollution sent to sensitive environments. It can also enhance wetlands, which benefits the wildlife depending on that eco-system. It also helps to stop the chances of drought as recycling of water reduces the use of fresh water supply from underground sources. For instance, The San Jose/Santa Clara Water Pollution Control Plant instituted a water recycling program to protect the San Francisco Bay area’s natural salt water marshes.
The main potential risks that are associated with reclaimed wastewater reuse for irrigation purposes, when the treatment is not adequate are the following:
contamination of the food chain with microcontaminants, pathogens (i.e. bacteria, viruses, protozoa, helminths), or antibiotic resistance determinants;
soil salinization and accumulation of various unknown constituents that might adversely affect agricultural production;
distribution of the indigenous soil microbial communities;
alteration of the physicochemical and microbiological properties of the soil and contribution to the accumulation of chemical/biological contaminants (e.g. heavy metals, chemicals (i.e. boron, nitrogen, phosphorus, chloride, sodium, pesticides/herbicides), natural chemicals (i.e. hormones), contaminants of emerging concern (CECs) (i.e. pharmaceuticals and their metabolites, personal care products, household chemicals and food additives and their transformation products), etc.) in it and subsequent uptake by plants and crops;
excessive growth of algae and vegetation in canals carrying wastewater (i.e. eutrophication);
groundwater quality degradation by the various reclaimed water contaminants, migrating and accumulating in the soil and aquifers.
Examples
Australia
When there are droughts in Australia interest in reclaimed effluent options increases. Brisbane has been seen as a leader in this trend, and other cities and towns will review the Western Corridor Recycled Water Project once completed.
While there are currently no full-scale direct potable reuse schemes operating in Australia, the Australian Antarctic Division is investigating the option of installing a potable reuse scheme at its Davis research base in Antarctica. To enhance the quality of the marine discharge from the Davis WWTP, a number of different, proven technologies have been selected to be used in the future, such as ozonation, UV disinfection, chlorine, as well as UF, activated carbon filtration and RO.
Israel
As of 2010, Israel leads the world in the proportion of water it recycles. Israel treats 80% of its sewage (400 billion liters a year), and 100% of the sewage from the Tel Aviv metropolitan area is treated and reused as irrigation water for agriculture and public works. As of today, all the reclaimed sewage water in Israel is used for agricultural and land improvement purposes.
Namibia
An example of direct potable reuse is the case of Windhoek (Namibia, New Goreangab Water Reclamation Plant (NGWRP)), where treated wastewater has been blended with drinking water for more than 40 years. It is based on the multiple treatment barriers concept (i.e. pre-ozonation, enhanced coagulation/dissolved air flotation/rapid sand filtration, and subsequent ozone, biological activated carbon/granular activated carbon, ultrafiltration (UF), chlorination) to reduce associated risks and improve the water quality. The reclaimed wastewater nowadays represent about 14% of the city’s drinking water production.
Singapore
In Singapore reclaimed water is called NEWater and is bottled directly from an advanced water purification facility for educational and celebratory purposes. Though most of the reused water is used for high-tech industry in Singapore, a small amount is returned to reservoirs for drinking water.
At the end of 2002, the programme – successfully branded as NEWater – had garnered a 98 percent acceptance rate, with 82% of respondents indicating that they would drink the reused water directly, another 16% only when mixed with reservoir water. The produced NEWater after stabilization (addition of alkaline chemicals) is in compliance with the WHO requirements and can be piped off to its wide range of applications (e.g. reuse in industry, discharge to a drinking water reservoir). NEWater now makes up around 30% of Singapore’s total use, by 2060 Singapore’s National Water Agency plans to triple the current NEWater capacity as to meet 50% of Singapore’s future water demand.
South Africa
In South Africa, the main driver for wastewater reuse is drought conditions.
For example, in Beaufort West, South Africa’s a direct wastewater reclamation plant (WRP) for the production of drinking water was constructed in the end of 2010, as a result of acute water scarcity (production of 2,300 m3 per day). The process configuration based on multi-barrier concept and includes the following treatment processes: sand filtration, UF, two-stage RO, and permeate disinfected by ultraviolet light (UV).
U.S.
The leaders in use of reclaimed water in the U.S. are Florida and California.
In a January 2012 U.S. National Research Council report, a committee of independent experts found that expanding the reuse of municipal wastewater for irrigation, industrial uses, and drinking water augmentation could significantly increase the United States’ total available water resources.
One example is Orange County which is located in Southern California, USA, and houses a classic example in indirect potable reuse. A large-scale artificial groundwater recharge scheme exists in the area, providing a much-needed freshwater barrier to intruding seawater.
Growth prospects
Demand for the use of the wastewater recycling method is expanding rapidly around the world, with differences across countries. By 2015, the main players in water recycling estimate that the volume of recycled water will double, from 19.4 Mm3 / day recycled in 2005 to about 55 Mm3 / day in 2015. Demand growth is expected to vary geographically: very strong (40-60% growth) in areas of high water stress (Spain, Australia, Italy) or intensive urbanization (China), significant in the countries industrialized countries (around 25%).
In France, since 2015, the number of projects has increased as a result of the relaxation of the regulatory framework and the launch of an ambitious call for projects by the Rhone-Mediterranean-Corsica Water Agency which led in 2016 to financing of some forty files. At the same time, research is intensifying to gain knowledge for optimal reuse practices and to provide recommendations for regulatory change. For example, in the context of various projects in France and in Maghreb, Irstea’s scientistsstudy the environmental and health risks of the reuse of wastewater as well as the phenomena of “plugs” that are created in irrigation equipment (sedimentation, development of biofilms, deposits by precipitation of mineral salts). The social acceptability of consumers, farmers and elected officials with regard to the reuse of treated wastewater is also a subject of study.
Source from Wikipedia