Edited by: S. Venkata Mohan, Indian Institute of Chemical Technology (CSIR), India
Reviewed by: Ioannis Konstantinos Kalavrouziotis, Hellenic Open University, Greece; Antonis Zorpas, Open University of Cyprus, Cyprus
This article was submitted to Wastewater Management, a section of the journal Frontiers in Environmental Science
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From the beginning of the Bronze Age (
Water reuse is not a new technique or concept; knowledge on wastewater treatment and reuse has been accumulated along with the history of humankind. Land application of human waste is an old practice, which has undergone a number of development stages from ancient to contemporary times (Rose and Angelakis,
Water recycling from ancient to modern times is also the story of how water recycling evolved from ancient times to its decline with the development of intensified wastewater treatment methods in the late 1800s and early 1900s to its rebirth due to population growth, the development of megacities, climate change, rapid developments in technology, and the fact that the amount of fresh water in the world is finite. The information presented is intended to promote a new vision of water reuse and to highlight the important role water reuse will play in meeting future water needs, especially as the population of the world continues to grow.
For most of the 200,000 years that modern humans (
With the establishment of permanent settlements about 10,000 years ago, a new era began in which an agrarian way of life was needed to support the inhabitants of the community. Until the birth of the first advanced civilizations in the Bronze Age, the disposal of human excreta was managed in an
Facilities used for water reuse in prehistoric times
In the Indus Valley (modern-day Pakistan) similar advanced sewerage and drainage systems have been utilized dating back to
Although lost to history, it is reasonable to assume that the utilization of human waste as fertilizer evolved from observations of enhanced plant growth where animal and human wastes had been deposited either on or below the ground surface. Similar observations must have led to the use of human and animal wastes for aquaculture. As permanent settlements developed, wastewater collection systems evolved out of necessity of removing human and other accumulated wastes. Based on observations of flowing water, the first wastewater collection facilities were open channels, which evolved into channels covered with flat stones (Figure
Early in Classical times, the Ionian philosophers recognized that all fresh water in the planet is recycled and reused. Their studies, and especially those of Anaximander (
Ancient Greeks were among the first to use wastewater in agriculture (Tolle-Kastenbein,
Sewers and drains in ancient Athens used to collect and convey wastewater to central sewer:
The disposal sites for the wastes conveyed by the sewer and drainage systems were located downhill in agricultural lands. In addition, sewage and mainly the rainwater from Acropolis was led through an extensive drainage and sewerage system, to the south-east side of the hill where it was possibly reused in the workshops (Kollyropoulos et al.,
Another water reuse example comes from ancient Greece (Hellenic Ministry of Culture Archaeological Receipts Funds,
Water cisterns used for water storage and treatment:
During the Roman period (
In China and other Asian countries, agricultural use of human waste has been practiced for thousands of years. Semidry night soil (human feces and urine) was used to fertilize fields in ancient times, and the practice continues today (Khouri et al.,
In Europe during Medieval times, water technology and knowledge made little progress. During this period, the emphasis was on wars rather than on civilization. Sanitation, in the best cases, reverted to the basics, becoming very primitive in most towns. As a result, disease outbreaks were commonplace; epidemics decimated towns and villages. In Europe, during Medieval times at least 25% of the population died due to cholera, plague, and other water born diseases (Schladweiler,
Although there was turmoil in Europe during medieval times, some innovative ways to reuse water were developed and used in early Central and South America before colonization. The
Aztecs that lived in the Valley of Mexico were distributed in hundreds of towns and their capital, Tenochtitlan, is where Mexico City is today. The Valley of Mexico had, at that time, seven major lakes and 12,000 ha of wetlands placed southeast where
Sanitation practices re-emerged in the mid-nineteenth century following the great epidemics in several regions of the world. During that period, authorities recognized the need for sanitation and this led to the development of effluent disposal and reuse practices, known as sewage farms to protect public health and to control water pollution (Stanbridge,
The earliest documented application of wastewater to the land for agricultural use, occurred in what were known as “sewage farms,” first in Bunzlau (modern-day Poland), in 1531 and later in Edinburgh (Scotland) in 1650. In both locations, wastewater was used for beneficial crop production (Tzanakakis et al.,
Selected early land treatments and reuse systems.
Bunzlaw, Poland | 1531 | Sewage farms | ||
Edinburgh, UK |
1650 | Sewage farms | ||
Croydon-Beddington, UK | 1860 | Sewage farms | 0.25 | 17.4 |
Paris, France | 1869 | Irrigation | 0.64 | 30.3 |
Leamington, UK | 1870 | Sewage farms | 0.16 | 3.4 |
Berlin, Germany | 1874 | Sewage farms | 2.7 | N/A |
Milan, Italy | 1881 | Irrigation | 3.5 | |
Wroclaw, Poland | 1882 | Sewage farms | 0.80 | 10.6 |
Braunschweig, Germany | 1896 | Sewage farms | 4.4 | 60.0 |
Augusta, ME | 1876 | Irrigation | ||
Calumet City, MI | 1888 | Irrigation | 0.005 | |
South Framingham, MA | 1889 | Irrigation | ||
Woodland, CA | 1889 | Irrigation | 0.07 | 15.5 |
Boulder, CO | 1890 | Irrigation | ||
Fresno, CA | 1891 | Irrigation | 1.60 | 10.6 |
San Antonio, TX | 1895 | Irrigation | 1.60 | 75.7 |
Vineland, NJ | 1901 | Rapid infiltration system | 0.0026 | 3405.9 |
Ely, NV | 1908 | Irrigation | 0.16 | 6.1 |
Lubbock, TX | 1915 | Irrigation | ||
Tula (Mezquital) Valley |
1896 | Irrigation | 90.00 | |
Melbourne, Australia | 1897 | Irrigation | 4.16 | 189.3 |
In Mexico, drainage canals were built around 1890 to collect wastewater from Mexico City and to irrigate and fertilize agricultural lands in the Mezquital Valley. The scheme is now used to irrigate up to 90,000 ha of agricultural cropland and is the largest water reuse scheme in the world. An added benefit has been the recharge of groundwater in the region (Jimenez and Asano,
Since the beginning of the twenty-first century, there is renewed interest in developing urine separation systems and a number of systems have been developed and tested. However, it should be noted that the separation of urine from feces at the source is not a new development. It has been practiced for thousands of years in different regions of the world and it is varying from country to country. For example, in China the objective has been to reuse the nutrients present in human excreta for fertilizing agricultural lands. Similarly, urine was separated and collected in simple toilets as described by Antoniou et al. (
In Korea, the separation of feces and urine has been practiced for more than 600 years, during the Joseon dynasty (1392–1910). The feces and urine were used as fertilizers, to minimize the pollutant loads discharged in the environment. Different containers were used for each waste, e.g., urine jars which were usually situated nearby rooms for easier access. The collected urine and other wastes were fermented to serve as agricultural fertilizers. The different fermentation stages of urine were made possible through the use of several urine jars, which were stored in an organized method (Han and Kim,
Containers used for the storage of feces
In Danish and Swedish cities urine-separating toilets were used for hygienic reasons since the middle of nineteenth century. Their design was very similar to the toilets used today. Because most of the nutrients in household wastewater and biodegradable solid waste are present in urine, its separation contributed not only to solving hygienic problems but also to a decrease in the emission of eutrophication agents and an increase in their reuse (Antoniou et al.,
The development of modern methods of sewage treatment can be traced back to the mid nineteenth century in England and Germany. The large population in London and the limited area available for treatment in sewage farms, broad irrigation, or intermittent filtration led to renewed interest in more intensive methods of treatment before discharging the treated effluent to land and hence to freshwater bodies. Methods of treatment that were used included large septic tanks, contact beds, and trickling filters. Where sufficient land was available intermittent sand filters were also used.
The advent of twentieth century brought significant technological and scientific innovations along with a significant growth in the implementation of wastewater treatment plants (WWTPs) that could handle large volumes of wastewater for direct discharge to waterways and the ocean. These plants were adopted widely by most of the major urban centers around the globe, as they were compact and did not require large areas for treatment compared to sewage farms (Metcalf and Eddy Inc.,
The purpose of this section is to consider modern water reuse practice. Subjects considered include: (a) the importance of modern technology, (b) changing views of water reclamation and reuse; (c) water reuse applications; (d) review other non-domestic sources of wastewater for reuse; (e) understanding and quantifying unplanned potable reuse, (f) health and environmental issues; and (g) review development of water reuse criteria. Emerging trends in water reuse and future challenges in water reuse are considered in the following two sections, respectively.
Some important technological developments that have brought about the renewed interest in wastewater reclamation include: the availability of reliable microfiltration, ultra filtration, and reverse osmosis membranes; the use of ozone coupled with biological filtration, low, medium, and high energy UV disinfection; high energy UV advanced oxidation. These treatment processes, can now be used to remove acute toxicity (e.g., microorganisms) and chronic toxicity (e.g., chemical constituents). Further, because multiple treatment processes are now available for any given constituent, the multiple barrier concept, which involves the use of redundant treatment processes or other activities, in parallel or series, is applied to reduce the risk from a given constituent (e.g., pathogenic microorganisms). In addition, instrumentation and monitoring equipment have also contributed to the reliability of advanced water treatment facilities.
Many things have changed in the water reclamation and reuse field in the contemporary period (1900 AD-present), but especially so during the last three decades. One of the most relevant changes is the recognition of the importance of reclaimed water in an integrated water resources management plan. Reclaimed water has become a new, additional, alternative, reliable water supply source right at the doorstep of metropolis for numerous uses in the diverse environment. This approach has even been recognized by the United Nations through the World Water Development Report 2017 (UNESCO,
Historically, agricultural irrigation has been and continues to be the largest use of untreated wastewater. Early on, direct irrigation was used. Sewage farms were developed as the quantity of wastewater increased. Subsequently, more intense forms of wastewater treatment were developed to deal with the ever-increasing quantities of wastewater to protect the environment. With the intensification of wastewater treatment processes, the quality of the effluent improved, which made reclaimed water suitable for a greater variety of agricultural applications. The development of more restrictive effluent discharge standards in the United States has led to further improvement in effluent quality, making the use of reclaimed water suitable for a variety of different applications. Health protection, as discussed subsequently, initially centered on microbiological quality, has expanded to a wider and more comprehensive view of chemical quality, particularly in association to “emerging” contaminants which are of key importance for potable reuse.
The principal water reuse categories are summarized in Table
Water reuse categories, typical applications, and major constrains and concerns.
Agricultural irrigation | Crop irrigation; commercial nurseries | Seasonal demand, need for winter storage |
Landscape irrigation | Parks; freeway medians, golf courses | Point of use often far away from the point of water reclamation |
Industrial recycling and reuse | Cooling water, boiler feed water, process water, high quality water for electronics manufacture | Constant demand, but site specific |
Recreational and environmental uses | Lakes and ponds, streamflow augmentation, snow production for skiing and snow melting in cities | Site specific |
Non-potable urban uses | Fire protection; toilet flushing; car washing; street cleaning; water for cooling | Requirement for dual piping systems; limited demand, cost |
Groundwater recharge | Groundwater replenishment; seawater intrusion barrier | Requires suitable aquifer or reservoir between the points of water reclamation and reuse |
Unplanned potable reuse | The addition of treated or untreated wastewater to drinking water sources such as rivers, lakes, or groundwater aquifers (see discussion in following section) | Uncontrolled by existing regulations, variable effluent quality, variable available dilution |
Planned potable reuse, indirect and direct | Augmentation of drinking water supplies (see discussion in following section) | Availability of environmental buffer, health, risk issues, cost of engineered storage buffers, social acceptance, existing drinking water regulations are inadequate |
To address religious concerns in some Islamic countries, Fatwas (legal ruling on an issue of religious importance) have been issued in Saudi Arabia, Oman, and in the UAE (CLIS,
Historically, wastewater, derived from wastewater collection systems, has been the principal source reclaimed water. However, population growth and urbanization combined with limited reliable water resources have also contributed to the consideration of a wider range of potential water sources for reclamation and reuse. Other potential sources of wastewater for reclamation and reuse are identified in Table
Other potential water sources for reclamation and reuse
Blackwater | Wastewater originating from toilets and/or kitchen sources (i.e., kitchen sinks and dishwashers). |
Graywater | Wastewater collected from non-blackwater sources, such as bathroom sinks, showers, bathtubs, clothes washers, and laundry sinks. |
Wastewater (local) | Water from combined graywater and blackwater sources, which is not discharged to a collection system (e.g., wastewater from a residence served with a septic tank or seepage pit). |
Roof runoff | Precipitation from rain or snowmelt events collected directly of a roof surface that is not subject to frequent public access. |
Stormwater | Precipitation runoff from rain or snowmelt events that flows over land and/or impervious surfaces (e.g., streets, parking lots, and rooftops). Runoff from roofs with frequent public access is defined herein as stormwater. |
Condensate | Water vapor that is converted to a liquid and collected, the most common source in buildings being air conditioning, refrigeration, and steam heating. |
Shallow groundwater | Groundwater located near the ground surface in an unconfined aquifer and, therefore, subject to contamination from infiltration of surface sources. |
Foundation water | Shallow groundwater collected from drainage around building foundations or sumps. |
Blended water | Various combinations of water derived originally from blackwater, graywater, wastewater, roof runoff, stormwater, condensate, or foundation water. In many areas, ordinances do not allow the combination of roof runoff and/or stormwater with wastewater as part of the wastewater collection system due to documented concerns associated with sanitary sewer overflows and/or treatment and hydraulic capacity at the publicly owned treatment works. Blended water, however, is the purposeful aggregation of water for use as a non-potable water supply. |
It is estimated that over 80% of the world's wastewater and over 95% in some under developing countries is released to the environment without treatment. Typically, untreated wastewater is either discharged to rivers or streams where it is diluted and transported downstream or infiltrated into aquifers, where the constituents in raw wastewater can impact freshwater supplies (UNESCO,
The downstream use of a water source, for drinking water, that is subject to upstream wastewater discharges is referred to as unplanned potable reuse (also known as
In addition to discharges to rivers, numerous cases have been documented where untreated wastewater applied to land for agricultural use has resulted in unplanned recharge of groundwater aquifers, from which water is withdrawn for human consumption. Locations where such unplanned groundwater recharge has occurred include Egypt, Mexico, Peru, and Thailand. In Mexico, a large flow of wastewater from Mexico City is discharged to the arid Tula Valley (also known as the Mezquital Valley) where a total of 500,000 inhabitants are supplied water this way (Jimenez and Asano,
While there is no reliable epidemiological evidence that the use of reclaimed water for any of its applications (see Table
Health and environmental issues associated with water reclamation and reuse are related to wastewater treatment, reclaimed water quality, chemical and microbiological constituents that may be present in the reclaimed water, health risk assessment, and public perception and acceptance. Reclaimed water derived from municipal wastewater comes from a variety of sources including households, schools, offices, hospitals, and commercial and industrial facilities. Thus, untreated municipal wastewater typically contains a variety of biological and chemical constituents that may be hazardous to human health and the environment. In many developing countries, the irrigation of vegetable crops with untreated or inadequately treated wastewater is a major source of enteric diseases and other waterborne diseases. The situation is different, however, in the United States and other industrialized countries where reliable wastewater treatment and health-related water reclamation and reuse criteria and regulations dictate the feasibility and acceptability of water reuse.
Historically, as noted previously, water reuse evolved from observation, necessity, and opportunity. These factors remain the same for the contemporary period (1900-present). Although agricultural irrigation with low quality wastewater was practiced in some areas of Europe as well as the United States in the late 1800s, there were no significant criteria or restrictions on the practice until the early part of the twentieth century. As urban areas began to encroach on sewage farms and as the scientific basis of disease became understood more widely, concern about the health risks associated with irrigation using wastewater grew among public health officials. Public health concerns led to the establishment of regulations and/or guidelines for the use of reclaimed water for agricultural irrigation, which was the first reclaimed water application to be regulated (Paranychianakis et al.,
The timeline of water reuse criteria and regulations is shown in Table
Timeline of water reuse criteria, regulations, and standards worldwide
<1918 | Before 1918, wastewater was applied to the land for irrigation and disposal purposes in various regions since the Bronze Age, but no indices for any criteria have been found. Common sense practices probably applied as protection measures |
1918 | California State Board of Public Health set up the first water reuse regulations for the irrigation of crops consumed cooked (California State Board of Health, |
1973 | WHO releases water reuse guidelines aimed mainly for developing countries including quality thresholds (100 FC/100 mL) and treatment requirements (WHO, |
1977 | Italy regulates water reuse for irrigation describing extensive treatment processes (CITAI, |
1978 | California water reuse regulations (Title 22) provide limits for unrestricted irrigation (2.2 TC/100 mL) (State of California, |
1978 | Israel issues regulations for water reuse in irrigation defining treatment requirements, quality limits (unrestricted irrigation: 12 FC/100 mL in 80% of samples: 2.2 FC/100 mL in 50% of samples), crops and additional barriers |
1983 | State of Florida: No detectable |
1983 | Sanitation and Disease-Health Aspects of Excreta and Wastewater Management, (Feachem et al., |
1984 | State of Arizona: Standards for virus (1 virus/40 L) and Giardia (1 cyst /40 L) (US EPA, |
1985 | Water Quality for Agriculture. FAO Irrigation and Drainage Paper 29 (Rev. 1) Food and Agriculture Organization of the United Nations, Rome, Italy (FAO, |
1986 | UNDP/World Bank Report: A theoretical epidemiological model was developed for quantitative risk assessment (Shuval et al., |
1989 | WHO first revision of water reuse guidelines (unrestricted irrigation: 1,000 FC/100 mL; <1 nematode egg/L) based on the conclusions of the previous reports (WHO, |
1989 | Tunisia issues standards for water reused in irrigation based on FAO ( |
1991 | French recommendations for water reuse based on WHO guidelines (Circular no 51 of July 22, 1991, of the Ministry of Health) |
1992 | US EPA publishes guidelines for water reuse to guide states to set up their own criteria (US EPA/USAID, |
1996 | Mexico changes its standards to control wastewater discharges moving from a vision to control pollution in rivers to consider the water quality need for the next use of water, i.e., reuse. For agricultural reuse a value of 1,000 FC/mL combined with either 1 Helminth egg (HE)/L for unrestricted irrigation or 5 HE/L for restricted one were set (Jiménez, |
1999 | Revised Israel regulations: Unrestricted irrigation <1 FC/100 mL and a multi-barrier approach (Fine et al., |
1999 | Australian guidelines were published defining four microbiological qualities of recycled water corresponding to the intended uses (NHMRC, |
2000 | State of California regulations are revised to include additional applications of recycled water (State of California, |
2003 | WHO State of the Art Report on Artificial Recharge of Groundwater with Recycled Water (Aertgeerts and Angelakis, |
2003 | Revised Italian regulations for water reuse (Ministry Decree no 185/2003) |
2004 | US EPA revises its guidelines of water reuse to include IPR (US EPA, |
2005 | Cyprus issues criteria for water reuse in agriculture (Decree no 296/03.06.05) |
2006 | WHO releases its second revision of water reuse guidelines on Treated Wastewater in Agriculture: Risk analysis and management, which adopt a quantitative risk assessment methodology (WHO, |
2006 | Australian guidelines for water recycling: Managing health and environmental risks (NRMMC-EPHC, |
2006 | Portugal releases regulations for water reuse (Portuguese Standard NP 4434) |
2007 | Spain issues water reuse regulations (Royal Decree 1620/2007) |
2008 | Guidelines for Series of Standard on Water Reuse in China ( |
2010 | France sets water reuse criteria (OJFR, |
2011 | National Health and Medical Research Council and National Resource Management Ministerial Council: Australian Drinking Water Guidelines (Khan and Anderson, |
2011 | Greece issues water reuse regulations (Hellenic Ministry of Environment, Energy and Climate Change ( |
2013 | EU Commission assigns to the working group “Program of Measures” the development of a strategy for the maximization of water reuse in EU. This action may initiate the development of EU-based criteria |
2013 | ILSI publishes its criteria to reuse water in the food and beverage industry (Cotruvo et al., |
2014 | California Department of Public Health issues regulations for potable water reuse through aquifer recharge (CDPH, |
2014 | Revised French water reuse regulation (OJFR, |
2015 | ISO Standards (Guidelines for agricultural irrigation). Developed by ISO in collaboration with CEN (5 water qualities, the stringent: thermotolerance coliforms ≤ 10 /100 mL) (ISO, |
2016 | Guidelines for Integrated Water Resources Development and Management in India ( |
2017 | World Health Organization, Geneva, Potable Reuse: Guidance for Producing Safe Drinking Water (WHO, |
2018 | EU minimum water quality requirements for irrigation and aquifer recharge (Alcalde-Sanz and Gawlik, |
It is estimated that by 2050 the world population will increase by an additional 2 billion people (e.g., a city of about 145,000 every day) (Reiter,
Perhaps the most important future trend in the field of water reuse, especially in large metropolitan areas, is PR. As the name implies, PR involves the reuse of wastewater for human consumption following various treatment interventions. Today, wastewater is no longer viewed as a waste requiring disposal, but as a
When discussing PR, one of the problems is terminology. Water reuse definitions and terminology in common use in the literature and newly adopted terminology in California are reported in Table
Terminology and definitions for potable reuse.
The downstream use of surface water as source of drinking water that is subject to upstream wastewater discharges (e.g., also referred to as unplanned PR or indirect PR). Although common in many parts of the country, |
|
Direct PR (DPR) | There are two forms of DPR. In the first form, advanced treated water (ATW) is introduced into the raw water supply upstream of drinking water treatment facility. In the second form, finished drinking water from a AWTF permitted as a drinking water treatment facility is introduced directly into a potable water supply distribution system. |
Indirect PR (IPR) | The introduction of advanced treated water into an environmental buffer such as a groundwater aquifer or a water body before being withdrawn for potable purposes (see also |
Direct PR (DPR) | The planned introduction of recycled water either directly into a public water system or into a raw water supply immediately upstream of a water treatment plant. |
Raw water augmentation (RWA) | The planned placement of recycled water into a system of pipelines or aqueducts that deliver raw water to a drinking water treatment plant that provides water to a public water system |
Treated drinking water augmentation (TDWA) | The planned placement of recycled water into the water distribution system of a public water system, as defined in Section 116275 of the Health and Safety Code. |
IPR for groundwater recharge (IPRGR) | The planned use of recycled water for replenishment of a groundwater basin or an aquifer that has been designated as a source of water supply for a public water system |
Reservoir water augmentation (ReWA) | The planned placement of recycled water into a raw surface water reservoir used as a source of domestic drinking water supply for a public water system, as defined in Section 116275 of the Health and Safety Code, or into a constructed system conveying water to such a reservoir. |
Pictorial view of alternative forms of PR:
In DPR (see Figure
Representative examples of successful potable reuse projects
Orange County Water District Ground Water Replenishment System (GWRS), California | IPRGR | Currently, GWRS, in operation since 2008, is the largest water reclamation facility of its kind in the world employing the latest advanced treatment technologies. Purified water from an advanced treatment process is infiltrated into the groundwater aquifer by means of spreading basins. Blended purified water and groundwater serves as a water supply source for Orange County, California. |
Singapore NEWater | ReWA | Based on the success of a demonstration program, NEWater was first introduced into surface water reservoirs in 2003. Currently, surface water augmentation with NEWater is about 5 percent. The original plan called for a greater percentage, but industrial demand for high quality recycled water increased, reducing demand for potable water. |
Upper Occoquan Sewage Authority | ReWA | Since 1978, water from a full-scale reclamation facility has been discharged to the Occoquan Reservoir. The reservoir is the major water source for more than 1.4 million people in Northern Virginia. |
Big Spring, Texas | RWA | Filtered secondary effluent is treated with advanced treatment. The advanced treated water is blended with raw water in a transmission line. The blended water is treated in a water treatment plant before distribution. |
City of Windhoek, Namibia | TDWA | Since 1968, highly-treated reclaimed water has been added to the drinking water supply system. The blending of reclaimed water with potable water takes place directly in the pipeline that feeds its potable water distribution network. |
The principal concerns with PR are related to public health. More specifically, acute toxicity related to pathogenic microorganisms (i.e., enteric virus,
In most wastewater collection and treatment systems, wastewater is transported through the collection sewers to a centralized WWTP at the downstream end of the collection system near to the point of dispersal to the environment. Because centralized WWTPs are generally arranged to route wastewater to these remote locations for treatment, water reuse in urban areas is often limited by the lack of dual distribution systems (Tchobanoglous et al.,
An alternative to the conventional approach of transporting reclaimed water from a central WWTP is the concept of decentralized (satellite) treatment at upstream locations with localized reuse and/or the recovery of wastewater solids. A pictorial view of an IWM system is illustrated in Figure
Schematic view of an integrated wastewater management system (adapted from Gikas and Tchobanoglous,
Another trend in the environmental engineering and water resources field is the use of the term
In the next decade, a number of issues and challenges will need to be resolved to optimize water reclamation and reuse. Important issues include (a) how to couple advanced wastewater treatment facilities with seawater desalination facilities, (b) the development of more effective techniques and methods incorporating risk assessment to assess human and environmental health effects of wastewater constituents, and (c) the development of appropriate water reclamation and reuse regulations, applicable to many different situations, that both help to promote reuse as well as regulate it. Further, based on recent studies it was found that users of recycled water are mainly interested in the quality rather than in the origin of water (Paranychianakis et al.,
In megacities, located on or near coastal areas, the opportunity to couple advanced wastewater treatment facilities with seawater desalination facilities will offer additional opportunities for PR. Operationally, the effluent from the advanced treatment facility would be combined with desalinated water and treated in a membrane type water treatment plant permitted as a drinking water plant. Because both water sources are of high quality, the combined flow would be easy to treat. The advantage this scheme offers is that drinking water could be used locally, thus avoiding the need for environmental buffers (e.g., groundwater or surface water) and long pipelines to deliver dilution water.
Another approach that has been used is to integrate seawater desalination and advanced wastewater treatment facilities to produce high quality water for industrial uses. Typically, brine from the advanced wastewater treatment facility is blended with seawater and desalinated. Use of water produced in this integrated approach increases the amount of water available for potable and other uses. In Japan, as well as Singapore, high quality water from advanced wastewater treatment facilities is used in industrial applications.
An integrated approach is needed that combines risk assessment and risk management of water related diseases as well as health effects of chemicals and unknowns. The WHO provided a framework for the development of health-based criteria for water- and sanitation related microbial hazards as well as illness resulting from water related exposure to toxic chemicals (Fewtrell and Bartram,
Although a large variety of water reuse criteria exists there is little standardization throughout the world. Efforts for more consistency among different international regulations and/or guidelines related to water quality should be fostered. At the same time, efforts should be made to align legislation produced to protect the environment in a way which allows effective water reuse. For the sake of integrated water management and to gain public understanding and acceptance, water reuse criteria should be part of a set of consistent water regulations applying to all forms of water reuse.
What is needed is the development of comprehensive, flexible, and efficient regulatory framework based on a realistic risk assessment. In some cases (e.g., EU-Mediterranean States), the existing national regulations for recycled water need to be updated considering new knowledge to address in a realistic way the potential risks arising from pathogens and trace organics to encourage water reuse by avoiding unnecessarily restrictive regulations (Paranychianakis et al.,
Starting from the historical tradition of land disposal and irrigation, water reuse has evolved into a myriad of applications, with PR representing one of the last frontiers. As in historical times, the modern practice of water reuse has evolved through observation, necessity, and opportunity. The development of megacities has rendered the traditional concept and use of a single WWTP for all wastewater untenable; also, limiting reuse applications. Decentralization is a necessity which is inevitable. However, with decentralization will come many more opportunities for local water reuse. New technologies that are now being implemented as well as those under development will usher in a new day in conventional and advanced wastewater treatment. Combining advanced treated water with desalinated water will be an attractive option in megacities. New scientific breakthroughs will lead to enhanced understanding of the significance of criteria found in both water and wastewater and their significance to human health. New regulations will be needed to reflect this enhanced biological and chemical understanding. To meet future water resource management and water reuse challenges effectively, cities must embrace the
All of the authors contributed collaboratively to the preparation of the final version of the manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
A portion of the material presented in this paper was presented in the 2nd IWA Regional Symposium on World's Water Resources: Past, Present and Future, held on 22–24 March, 2017 in Çesme-Izmir, Turkey.
Critical and constructive comments offered by John. Anderson, Afton Water, 1 Cumbora Cct, Berowra, NSW 2081, Australia and Dr. Valentina Lazarova, SUEZ Environment, 78230 Le Pecq, France are gratefully acknowledged.