The Global Water Recycling Situation

B. Van der Bruggen*

K.U. Leuven, Department of Chemical Engineering, Section Applied Physical Chemistry and Environmental Technology, W. de Croylaan 46, B-3001 Heverlee (Leuven), Belgium

Contents

1. Introduction 41

2. Short History of Reuse Applications 43

3. Water Recycling Today 44

4. Water Recycling in the USA 45

5. Water Recycling in Asia 52

6. Water Recycling in Europe 54

7. Water Recycling in Australia 56

8. Water Recycling in other Parts of the World 58

9. Conclusions and Further Challenges 60 References 61

1. INTRODUCTION

The awareness that water recycling is the only possible answer to the world's growing water needs is ever increasing. Governments are developing policies of incentives and/or permits to stimulate water recycling in an industrial context. Possible tools that can be deployed are: increasing taxes on wastewater discharge, requiring the development of wastewater treatment techniques that result in enhanced removal of a wide range of contaminants, and linking permits to progressive use of alternative water sources. The industry itself is working actively on water reuse projects, mainly for economic reasons, but also from the perspective of environmental responsibility. The benefits of water reuse for the industry include [1]: a supplemental and reliable water source to augment or replace existing freshwater supplies; reduction of the net amount of water consumed; and

Corresponding author. E-mail address: [email protected]

Sustainability Science and Engineering, Volume 2 ISSN 1871-2711, DOI 10.1016/S1871-2711(09)00203-7

© 2010 Elsevier B.V. All rights reserved.

reduction of wastewater generation and associated costs of wastewater treatment. Cooling water and process water recycling accounts for about 30% of all reuse applications. Because human contact is minimal or can be avoided, secondary treatment followed by disinfection is often sufficient. There is a large variation of water quality in industrial applications, with the most advanced applications requiring extensive additional treatment, but for some applications, tertiary treatment consists of only filtration and disinfection. These applications have clear and direct advantages for the industry; points of attention are monitoring and acceptance of customers, rather than technical treatment issues.

The academic community is the driver for progress and stimulates new projects by investigating feasibility on a small scale and suggesting new processes and approaches. Many examples of such studies can be found in the (recent) scientific literature for many industries [2-6]. These laboratory-scale applications have grown into large-scale projects in many cases.

The population is often ignored, because they operate on a small scale and do not have the expertise. Nevertheless, population is the one and only wastewater producer: directly through daily activities, but also indirectly by participating in the global economy, in which water (and, consequently, wastewater generation) plays a central role. More people means more freshwater, which means more wastewater: this is the real challenge for reuse. The overall water balance should remain under control, even though populations keep growing. Population growth will eventually prove to be the central water-related problem. Even more urgent than the energy issue, water scarcity will be the limitation for further growth of established economies and development of new economies. In water-stressed regions, water conflicts are already appearing, although sometimes still hidden.

At this point, it is not yet considered feasible for families to reuse own wastewater, although this is in fact common practice in the developing world, where it is often used for irrigation. Therefore, agriculture is also a stakeholder in water reuse. Irrigation seems to be a simple solution; 60% of all reuse applications are to be found here. Another 10% is used for irrigation of parks, sport fields, etc. and for groundwater recharge by percolation. Groundwater recharge requires tertiary and quaternary treatment methods for removal of organic material, micropollutants, heavy metals, and for disinfection. Agricultural applications often use lower standards, with not much attention for possible diffusion of contaminants on the land, even though aspects of crop contamination are taken into account. Water quality standards for irrigation using recycled water are feasible with relatively few extensions to existing treatment plants. Typical standards [7] for agricultural application (food crops commercially processed, surface irrigation of orchards and vineyards) are:

Monitoring includes weekly measurement of pH and BOD, daily measurement of suspended solids and coliforms, and continuous measurement of rest-Cl2. However, it is increasingly understood that more extensive tertiary and quaternary treatments are necessary in agricultural applications as well to prevent uncontrolled diffusion of contaminants such as pharmaceuticals and endocrine disruptors.

This is a clear and global trend that appears in industrial, agricultural, and municipal context. Water recycling applications on a large and even on a small scale today are well considered technologically and provide high-quality effluents [8]. This chapter aims at giving a tentative overview of current water recycling applications worldwide based on available information.

2. SHORT HISTORY OF REUSE APPLICATIONS

Water recycling is a hot topic today, but it was not invented in the 20th or 21st century. Agricultural applications have been practiced in Ancient Egypt and China, where wastewater was used for irrigation. And in general, it should be recognized that in fact all water is reused through the eternal water cycle. In Rome, water supply problems were solved by constructing aqueducts, which allowed a permanent influent of freshwater. Since the excess of used and unused water had to be removed, sewage was necessary as well. The extreme dilution obtained in this way resulted in remarkably few problems with the effluent quality, which was to be discharged but did not pose severe problems in surface waters to be used as water source by villages located downstream. The aqueducts fell into disuse, and since wastewater treatment systems were nonexistent in the Middle Ages, severe problems arose with surface water quality in large cities. The use of surface water was in fact no less than direct reuse of wastewater without any treatment, apart from some dilution. A typical example from the Middle Ages is London, where population growth was booming from 40,000 in the 12th century to 1,000,000 in 1666, and the Thames was used both as a sewer and for water supply. An even more difficult case was Amsterdam, where the Amstel River was dammed to prevent intrusion of the saline water of the Flevo Lake. The city's ring of canals was soon highly polluted by discharge of wastewater. It is evident that this caused epidemic of cholera and other waterborne diseases. It was not until the 16th century that measures were taken, which included prohibiting throwing of dead animals into the canals. These insights were crucial for public health, but also implied that freshwater and wastewater became two separated circuits. The "natural" link between wastewater and freshwater disappeared until the 20th century, where it was argued that in view of water scarcity and population growth, it may be more useful to restore this link, but improve purification and control. This induced the idea of water reuse, and was the starting point for many new projects and applications.

The first attempts toward water reuse were undertaken in the USA in the 1940s when chlorinated domestic wastewater was used in the steel industry [1]. However, it was not until the last quarter of the 20th century that water reuse appeared on the international agenda, at first in industrialized countries such as America and Europe. Between 1930 and 1970, the volume of reused water in Sweden increased by a factor of six. In 1951 in Japan, a program for recycling of the purified water of the Mikawashima Wastewater Treatment Plant in Tokyo started, which was to be reused as process water for a paper mill. In this case, the quality of the purified wastewater was higher than the quality of any other available water source. The fast economic growth in Japan in this period resulted in a strong competition between industry and agriculture for available water sources, which made water recycling even more important. Today, 80% of industrial process water in Japan is already reused.

3. WATER RECYCLING TODAY

Water recycling projects nowadays can be found in all parts of the world. Water recycling is particularly practiced in world regions suffering water scarcity, such as the Middle East, Australia, or southwest USA, or in regions with severe restrictions on disposal of treated wastewater effluents, such as Florida, coastal or inland areas of France and Italy, and densely populated European countries such as the UK and Germany [9]. In China, the average fraction of reused water in 1989 (in 82 important cities) was 56%, with a maximum of 93% [1]. However, a recent survey on municipal wastewater reclamation [10] mainly identified large water reuse projects in Japan (over 1800), the USA (over 800), the EU (over 200), and Australia (over 450). In the Mediterranean and Middle East area, around 100 sites were identified, whereas 50 sites were found in Latin America and 20 in sub-Saharan Africa. Large parts of Asia were not included in the survey. In particular in China, it can be assumed that many water reclamation sites can be identified, based on the numbers given above. Small projects, defined as below 0.5Mm3/y reclaimed water for unrestricted use or 2.5Mm3/y for restricted use, were also not included in this survey. This limitation may possibly influence the results in terms of fields of application, since it is known that large-scale projects are mostly used for landscape and agricultural irrigation, whereas small-scale projects often have urban, recreational, or environmental uses [10]. This is important, for example in the case of Japan where many relatively small-scale projects can be found [11], in contrast to the USA where water reclamation is mainly dominated by medium- to large-scale projects [10]. The total volume of reused water in the USA at the time of this study was estimated at 6.5 million cubic meters per day.

Among the objectives for water recycling, various fields of application can be distinguished. Bixio et al. [10] identified five categories, i.e., (1) agricultural irrigation, (2) urban, recreational, and environmental uses, including aquifer recharge, (3) process water for industry, (4) direct and indirect potable water production, and (5) combinations of these categories. In what follows, an overview of water recycling projects throughout the world will be given, with a slightly different approach, based on the driving force for implementation of water recycling projects. This includes water scarcity and drinking water supply, irrigation using reclaimed water, source protection, overpopulation, and environmental protection. In the different parts of the world that will be discussed, examples of these driving forces can be found. Finally, some of the remaining challenges will be highlighted.

4. WATER RECYCLING IN THE USA

In the USA, water recycling projects can be found for various purposes, ranging from irrigation and gray water supply to indirect potable reuse projects. Logically, the southern states are the most active in this area, with California and Florida being the most notable forerunners. In California, the use of reclaimed wastewater for the irrigation of corn, barley, lucerne, cotton, and pastures began in Bakersfield in 1912, followed by other projects in the 1920s [12]. In 1970, water reclamation was formally encouraged in the California State Water Code (Asano, 1998). Public health laws were progressively developed, leading to the publication of the so-called Purple Book [13], which is a collection of guidelines, rules, and standards that was later used elsewhere as a basis for regulations. Currently, wastewater recycling projects in California are booming, with ca. 600 GL of recycled water being used across over 4800 locations from 234 wastewater treatment plants [12]. An overview of different uses of recycled water in California is given in Fig. 1. The largest volumes are used for agricultural and landscape irrigation; other applications (industrial reuse, groundwater recharge, seawater barrier, recreation and wildlife, and others) use smaller volumes. In Los Angeles County, reclaimed secondary treated wastewater, followed by dual media filtration and chlorination, is supplied to the Whittier Narrows Groundwater Basin after surface spreading, since 1962, leading to ca. 23% of the potable water being indirectly recycled water [12].

The Irvine Ranch Water District has had separate water lines since the late 1960s to provide raw water and reclaimed water for irrigation [12]. Since 1991, recycled water has been used for high-rise buildings; ca. 20% of the water supply is now reclaimed water.

In the West Basin Municipal Water District and Orange County Water District, reverse osmosis is used to purify secondary treated wastewater; the treated water is injected into coastal aquifers to mitigate salt water intrusion from the ocean. This has been practiced since the 1950s in the West Basin Municipal Water District, and since 1976 in the Orange County Water District. The latter is an example of wastewater recycling in view of source protection; 75% of the water in Orange County comes from groundwater sources; the remaining 25% is imported from Colorado River. Because an

□ Agricultural irrigation

□ Landscape irrigation

□ Industrial use

□ Groundwater recharge

□ Seawater barrier

□ Recreational impoundment

□ Wildlife habitat

□ Geysers and energy production

□ Agricultural irrigation

□ Landscape irrigation

□ Industrial use

□ Groundwater recharge

□ Seawater barrier

□ Recreational impoundment

□ Wildlife habitat

□ Geysers and energy production

Figure 1 Relative volumes of recycled water used in California for different purposes.

increase in the volume of imported water is not to be expected, and the population growth will lead to more water demand but also to more wastewater generation, wastewater recycling by injection into groundwater layers was a logical option to enhance the capacity of these layers. More extraction without recharge would lead to intrusion of saline water from the ocean; recharge protects the groundwater supplies and at the same time increases the volume that can be extracted.

The initial "Water Factory 21'' plant consisted of a complex system of physicochemical processes. The influent was secondary effluent treated with activated sludge. The total capacity of the plant was 57,000 m3/day. The first step of the process was a combined flocculation and softening by addition of CaO (350-400 mg/L). The pH increases to 11, so that in addition to CaCO3, heavy metals also precipitate. In this way, the concentrations of heavy metals are immediately below the standards for drinking water. Only during periods of high influent concentrations, exceeding values were observed for cadmium and chromium. Flocculation with polymeric flocculants removes suspended solids, leading to a reduction of 90% in turbidity and a chemical oxygen demand (COD) removal of 50%. There is also a disinfection effect: for coliforms and viruses, a removal of ca. 98% is obtained. Further treatment consisted of filtration and activated carbon adsorption, followed by reverse osmosis on a partial stream.

The process scheme for "Water Factory 21'' was recently modernized into the Groundwater Replenishment System; in the new process scheme Fig. 2) precipitation, filtration, and activated carbon adsorption is replaced by microfiltration. The permeate from microfiltration contains less suspended solids and less microorganisms, which reduces problems in the reverse osmosis units. Pretreatment prior to microfiltration consists of sieving (opening 1 mm) to remove particles, and the addition of sodium hypochlorite for disinfection. The microfiltration unit is a hollow fiber module with an outside-in flow direction. A light vacuum at the permeate side of the membranes is applied to provide the necessary driving force. Cleaning of the microfiltration membranes is done by a combined air-water backwash, and a chemical cleaning (e.g., base combined with surfactants). A buffer tank decouples flows in the microfiltration and reverse osmosis units. In the reverse osmosis unit, ca. 90% of salts is removed, to a level of 100mg/l, along with removal of organic solutes. The permeate yield is about 85%. Sodium hexametaphosfate is added as a scaling inhibitor, and chlorine is dosed to avoid biofouling. Sulfuric acid is dosed to obtain a pH of 5.5 in order to avoid scaling. There are three steps with in total 42 membrane modules. Each module consists of six spiral wound composite

Sieve

Microfiltration

Buffer tank

Sieve

Microfiltration

Buffer tank

To wastewater treatment plant

RO rinse water

To wastewater treatment plant

To injection

Reverse osmosis

Gas stripper

RO rinse water

Reverse osmosis

Concentrate to ocean

Sulfuric acid

Scaling inhibitor

Figure 2 Water reclamation in the Orange County Water District's Groundwater Replenishment System.

polyamide membranes and is 7 m long, 8 in. in diameter. The feed water flows first in parallel through the first step, which consists of 24 modules. The concentrate from this step goes to the second step, consisting of 12 modules; the concentrate from the second step goes to the six remaining modules in the third step. The concentrate (ca. 15%) is discharged into the ocean. The permeate is further treated by UV disinfection and air stripping to remove CO2 (due to addition of sulfuric acid); CaO is added for stabilization. Water Factory 21 has led to regulations to govern future indirect potable reuse projects involving groundwater recharge by the California Department of Health Services, which include:

• no more than 20% of injected water should return to the potable system over 5 years;

• no more than 50% of surface spread water should return to the potable system over 5 years;

• reclaimed water should remain underground for 12 months for direct injection;

• reclaimed water should remain underground for 6 months for surface spreading;

• the only feasible reclamation technologies are reverse osmosis and carbon adsorption.

Water Factory 21 and the Groundwater Replenishment System is a successful project well known over the entire world and may induce other wastewater recycling projects as well. However, the experience in San

Diego is the other side of the medal: after establishing a water recycling demonstration facility in 1983 using a sequence of processes quite similar to what was used in Water Factory 21, it tried to establish a 80ML/day plant for groundwater recharge, and this was a failure due to strong opposition from San Diego citizens. The "toilet-to-tap" cartoons that were shown (which in fact suggested that no treatment at all was applied to the wastewater) provoked such a strong reaction that eventually the plan was shelved.

Florida, the fourth most populous state in the USA, has the second most water recycling projects after California. Out of 64 counties, ten have over 80% reuse [12], but highly populated counties such as Miami-Dade have only about 5-6%. The average is ca. 39%. In comparison to California, less reclaimed water is used for agricultural irrigation (19% vs. 47%), but much more for landscape irrigation (44% vs. 21%). Furthermore, more water is used for industrial purposes (15% vs. 5%), whereas groundwater recharge is similar (16% vs. 15%). Some of the most prominent water recycling projects in Florida include [12]; Mantovani et al., 2001):

• the CONSERV II project, in which groundwater is recharged by recycled water in Orange County and Orlando and subsequently used for irrigation of 11500 acres of citrus, eight nurseries, a tree farm, and a fernery;

• a 700 ha farm using recycled water (70 ML/day) in Tallahassee (discussed in more detail below);

• the dual distribution system in St Petersburg (discussed in more detail below);

• a 1240-acre wetland in Orlando for recreational purposes, using 5.1 MGD of recycled water from Ironbridge Sewage Treatment Plant;

• groundwater recharge into the Floridian Aquifer in Gainesville using 7.1 MGD of recycled water from the Kanapaha Sewage Treatment Plant;

• the Walt Disney World Resort Complex where recycled water from Reedy Creek Utilities is used for five golf courses, highway medians, a water park, and a tree park (horticulture);

• the Apricot project ("A Prototype Realistic Innovative Community of Today") in Altamonte Springs, comprising a dual water supply system throughout the city with recycled water being used for household irrigation and car washing, which can also be used for vegetable growing if the produce is peeled, cooked, or thermally processed before consumption;

• energy applications: Curtis Stanton Energy Center and Tampa's McKay Bay Refuse-to-Energy Centre.

Tallahassee is a city with 130,000 inhabitants, having a moderate climate with rainy summers and mild, rainy winters (Viessman & Hammer, 2005).

The average rainfall is 1500 mm. Urban wastewater contains mainly organic pollutants; no industrial wastewaters are mixed with the urban wastewater. Previously, the effluents were discharged in surface water after secondary treatment. This caused eutrophication on a large scale. Therefore, it was decided to stop discharges to surface water and instead use the wastewater for irrigation. A first plant (Thomas P. Smith Wastewater Treatment Facility) has a capacity of 104,000 m3/day and treats ca. 53,000 m3/day (average). A second plant (Lake Bradford Road Wastewater Treatment Plant) has a capacity of 17,000m3/day and treats 11,000m3/day (average). For the largest plant, the BOD, total nitrogen, and fecal coliforms are on average 5 mg/L, 12mg/L, and 4 per 100 mL. For the smaller plant, this would be 8 mg/L, 25 mg/L, and 18 per 100 mL. The effluent is collected and stored in four stabilization ponds with a total volume of 45,500 m3 Fig. 3a). From there, the effluent is further pumped to the irrigation site, where a pond is available with a capacity of 530,000 m3 (incl. emergency basins). The effluent irrigates a total surface area of ca. 1000 ha, organized in "irrigation circles'' Fig. 3b. A typical irrigation circle has a surface area of 54 ha; irrigation occurs from a central pivot. Because the crops are organized

Figure 3 Wastewater recycling in Tallahassee, Florida (Viesmann & Hammer, 2005): (a) storage ponds, (b) irrigation circle with a radius of 400 m, (c) center pivot sprinkling bermuda grass, (d) irrigation tower.

in circles, the fields can be irrigated with a single system. Sprinkling occurs through a circulating pipeline with a total length of 400 m Fig. 3c and d, supported by braces, truss angles, rods, and rotating wheels. Half of the total surface area is used for bermuda grass used on the spot as animal feed (cows). Cows graze on the fenced parts of the irrigation circles; between the fences, the rotating supports for the pipeline are moving.

The primary goal of the farm is not what it produces (cattle, corn, soybeans), but rather the safe discharge of wastewater. The farm's success is a side effect, although welcome. Groundwater is at a depth of 3-6 m; because the soil mainly consists of fine sand, groundwater is supplemented by irrigation water. Therefore, a monitoring program was set up to measure nitrate concentrations on site and around; it was found that on site some places have a slightly increased nitrate concentration, but this is not visible at the site's boundaries at a depth of 40 m.

St. Petersburg is located on a peninsula between Tampa Bay and the Golf of Mexico. No groundwater is available; drinking water is extracted from sources up to 100 km away from the city (Wiessman & Hammer, 2005). The population increase resulted in an increased competition for the use ofwater, so that water management became a very important matter. Meanwhile, already in 1972 legal regulations for the effluent discharged to Tampa Bay came into force. Enhanced purification was required, with a standard for BOD of 5 mg/L, suspended solids 5 mg/L, total nitrogen 3 mg/L, and phosphorus 1 mg/L. It was decided to extend the existing secondary treatment with sand filtration and extended chlorination (with increased contact time, ca. 40min based on average daily flow) in view of unlimited use for landscape irrigation and urban reuse. The plant started in 1978 and discharges to Tampa Bay stopped in 1987. The total wastewater purification capacity of St. Petersburg is about 260,000 m3/day, distributed over four sites. After storage in a reservoir, the water is distributed through pipe network. During wet periods, when not much water is used for landscape irrigation, the excess effluent is injected into a saline water body at a depth of 300 m. Water exceeding the standards is injected here as well.

Standards for the effluent are conform the legislation of Florida, and include: 20 mg/L BOD as yearly average, 5 mg/L suspended solids in any sample (daily sampling), fecal coliforms below detection limit in 75% of the samples during a 30-day period (daily sampling), and no sample above 25 per 100 mL; minimum chlorine residual of 1 mg/L after 15min contact time at peak hourly flow. The four plants meet these standards; for residual chlorine, a value of4 mg/L is used, much higher than required. Problems so far are related to the chloride concentration of the effluent. If this is too high, damage to plants is observed. Therefore, effluent with a chloride concentration above 600 mg/L is rejected. The distribution system has 9000 points of use; 95% of these are for residential use. The other applications are parks, schools, and golf courses. The pressure on the distribution system is sufficiently high, allowing the hydrants to provide secondary fire service.

Economic advantages in this case are limited cost of tertiary wastewater treatment (in this case, less than required for discharge in surface water) and the possibility to use water containing organic material at low cost. However, the most important advantage is the fact that no new investments in the drinking water network were required. The population of St. Petersburg and the commercial activity have constantly increased since 1970, yet drinking water consumption remains at a stable level. The reason for this is that a part of the consumption is replaced by recycled water. The price of recycled water for residential use was $0.30 per 1000 gal (3785 m3), or $11 per month for unlimited use. This shows that prices are very low compared to drinking water.

In various other states in the USA, recycling projects can be found as well:

• In Virginia: the UOSA or Upper Occoquan Sewage Authority, using wastewater as a source of indirect potable supply to the 40 GL Occoquan Reservoir starting from 1978, providing water for up to one million people in Northern Virginia. Typically, 15% of the water in the reservoir is reclaimed water [12].

• In Nevada, the Las Vegas Water District traditionally uses water from Lake Meed (Hoover Dam), but due to increased demand, the production volumes could only be met by recycling 180GL/year from the sewage treatment plant back to the lake [14];

• In Louisiana, bill H.B. 2016, issued in 2003, mandates a reclaimed water program to be used for irrigation at parks, cemeteries, golf courses, and highway landscaped areas.

• In El Paso, Texas, the Fred Hervey Water Reclamation Plant provides water (ca. 7.6 MGD) for groundwater recharge through injection in the Hueco Bolson aquifer, and, to a lesser extent, for cooling in electricity generation and for irrigation of a golf course. This plant uses biological activated carbon, biological denitrification, lime precipitation and ozona-tion, in addition to screening and conventional primary sedimentation. Many other recycling projects can be found elsewhere in the USA and

Canada, but most of these are of a much smaller scale.

5. WATER RECYCLING IN ASIA

In Asia, Japan and Singapore are the most prominent water recyclers. Japan has a long tradition in reuse; ca. 150 GL of water is recycled annually in

Japan. Water recycling is a necessity in urban environments, where the existing potable water infrastructure is unable to cope with the increasing building density. The piping in large buildings in cities like Tokyo and Fukuoka is fit for using primarily recycling water. Furthermore, toilets have an arrangement in which the water filling the cistern can first be used for washing hands; this is a direct form of reuse. Domestic supply is available at a price 16% below that of potable water. Landscape and agricultural irrigation is much less important Fig. 4).

In Osaka, a "21st Century Master Plan'' was developed that aims to develop 30% recycling by 2013, and 100% by 2030 [12]. Since 2002, the Nagisa plant on the left bank of the Yodo River processes 115ML/day of which 10% is recycled (within the plant, for landscaping, for heat exchanging in the air conditioning system of the City General Welfare Centre, for fire mains and toilet flushing).

Yokohama has a 70,000-seat International Stadium, the largest in Japan; 5 ML/day of treated wastewater is used in the facilities as a heat source for a heat pump, for flushing toilets, for sprinklers, and for artificial streams in parks neighboring the stadium.

Elsewhere in Asia, the NEWater project in Singapore [15] is the most visible. Singapore depends for a large part on Malaysia for freshwater, because it has a very limited catchment area. This is an undesired and insecure position. Therefore, other options have been explored since the 1970s, which has led to a gradual development of the current large-scale water recycling project. Starting from secondary effluent, a multiple barrier approach is used: a dual membrane filtration step consisting of microfiltration/ultrafiltration and

□ Environmental use

□ Toilet flushing

□ Snow melting

□ Use within plants

□ Agriculture

□ Other

□ Industry

Figure 4 Relative volumes of recycled water used in Japan for different purposes.

Figure 4 Relative volumes of recycled water used in Japan for different purposes.

reverse osmosis, followed by UV disinfection. NEWater is primarily aimed at nonpotable use, for example, as process water for wafer fabrication plants (as a source for ultrapure water). This is not controversial, because the recycled water is used in an industrial context and in a sequence of further treatment processes with the final result being water without any impurities. NEWater is also used for other industries and as cooling water in air conditioning systems. Since 2003, a small flow of NEWater has been introduced to existing raw water reservoirs for indirect potable reuse. This is similar to the approach in some applications in the USA. However, in this case, it was well understood that information and education are a prerequisite for the success of the project. A Web site was developed (www.pub.gov.sg/NEWater) and an information campaign was held, which contributed to the success of this project.

Elsewhere in Southeast Asia, water is seldom reused after purification, mainly because water sources are often not scarce. Exceptions are India and Vietnam, although in most cases treatment is quite limited. This is partly also true for China, where recycling is more common, but the effluent does often not meet standards for, e.g., agricultural reuse. The situation in China, however, is rapidly improving in terms of quality and quantity.

A similar situation is found in West Asia and the Middle East, where raw effluent is used for irrigation in Yemen, Syria, Lebanon, Palestine Territories, Egypt, and Iran [12]. Notable exceptions are Israel, Jordan, and Kuwait. In Jordan, 95% of the total volume of 74Mm3/year is reused, mainly (80%) for (restricted) irrigation in the Jordan Valley, after discharge to the Zerqa River and storage in the King Talal Dam. The remaining 20% is used on site as process water. In Kuwait, 25% of its agriculture and green areas are irrigated using 52Mm3/year of treated wastewater. Groundwater recharge is also practiced in Kuwait [12]. In Israel, 20% of its water supply came from recycled water already in 1994 [12]. Large projects include the Dan region where 95 GL/year from Tel Aviv is used for recharge of the coastal aquifer and for irrigation after 2 months storage. In Haifa, 32 GL/year goes to the Kishon complex, which consists of two deep stabilization reservoirs [16]. Currently, 65% of the connected sewage in Israel is reused for irrigation purposes [17]; unrestricted agricultural irrigation is envisaged for future projects as well as public park irrigation, industrial reuse, and aquifer salinity reduction.

6. WATER RECYCLING IN EUROPE

A good overview of water recycling in Europe is given by Bixio et al. (2006) as a result of the EU project AQUAREC. From this, it could be concluded that the water sector in Europe is in a transitionary phase with unique opportunities for improvement of water management, including water reuse. Nevertheless, the success of water reuse depends on many factors such as local communities and companies as well as on centralized rules and regulations; differences between EU member states often complicate the implementation of individual projects. This leads to significantly different levels of implementation in European countries. Guidelines and regulations are often not clear (enough), which results in uncertainties about what is (not) allowed. In addition, the use of recycled water is not the same in all countries (Bixio et al., 2006): in southern Europe, the primary use is agricultural irrigation (44%) and for urban or environmental applications (37%), whereas in northern Europe, the focus is more on industrial use (33%) along with urban and environmental applications (51%). However, this is only a tendency; individual countries may show large deviations from this picture, as was shown by Bixio et al. (2006). Italy is an example where regulations impede water recycling: wastewater recycling is only allowed for agricultural purposes, and on condition that an increase of crop production can be achieved by using recycled wastewater [18]. In a similar way, wastewater reuse is not developed in Poland and Hungary, where not more than a few percent of the total generated wastewater is used, mainly for (small) irrigation projects. Water recycling in the Czech Republic is also still underdeveloped, but a recent study [19] showed the potential for agricultural reuse in the Znojmo area, and, more importantly, industrial reuse as a replacement of surface water for cooling purposes.

European countries have always been very innovative, in particular countries like the Netherlands, where centuries of experience are available. The "third pipe'' system was experimented with in Utrecht, denoted as "household water,'' but this was abandoned because of cross-contamination problems. In Belgium, the recycling project carried out by the local drinking water company IWVA in Koksijde has received much attention; this project involved treatment of 2.5 GL of wastewater by microfiltration and reverse osmosis and subsequent storage ofthe treated water in an aquifer in the dunes. After a residence time of 1-2 months, the water is distributed as drinking water. No quality problems have been encountered, and customer satisfaction is high. Elsewhere in Belgium, a membrane bioreactor (MBR) is used in Schilde to provide water for unrestricted irrigation. Long-term effluent results for a broad range of water reuse parameters demonstrate the suitability of MBR to meet standards for unrestricted irrigation (Bixio et al., 2006).

In the UK, water recycling came only slowly into practice, with indirect reuse with abstraction points downstream having some proportion of treated wastewater. For example, treated wastewater is discharged into the river Chelmer, and subsequently used for recharging the Hanningfield reservoir in Essex [16]. The Millenium Dome on the bank on the river Thames in Greenwich was, in fact, the first significant recycling project in the UK. Around 500 m3/day of water, partly from the hand basins in the toilets, partly rainwater and mixed with groundwater, is recycled and used on site for toilet flushing.

In the northern part of Europe (Scandinavian countries and Germany) people have a very high environmental awareness, which translates into many small-scale projects that can be designated as "zero discharge,'' involving not only wastewater recycling but also minimization of solid waste generation and energy consumption. These "ecological villages'' are prototypes and could be seen as experiments in view of a more sustainable future society.

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Responses

  • scott
    Why is the situation reverse for suspended solid?
    2 years ago

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