Keywords

Introduction

Continuing economic growth, urbanization, and globalization have caused overconsumption of resources like water, energy, and food, especially in cities (Rees 1992). Scientists have been warning of the consequences for about half a century (Meadows et al. 1972). This pattern of overconsumption of natural resources has caused dangerous alteration to the climate (IPCC 2014). Despite the apparent risks associated with climate change, demand for these resources continues to rise worldwide (OECD 2012): global water demand is expected to exceed supply by 40% within 20 years (UNEP 2014), global energy demand will grow by 40% by 2030 (IEA 2009), and food demand is expected to increase by 60% by 2050 (WBCSD 2014). Further, this pattern of development has served 0.7% of the world population in amassing 45.2% of global wealth (Credit Suisse 2015), while billions of people live in dire poverty and lack basic services. Rapidly transforming cities particularly in developing economies are often already facing serious water-related public health risks resulting from inadequate access to safe drinking water and inadequate management of wastewater with concomitant environmental challenges, as local governments often lack the capacity to develop adequate water infrastructures in accord with the pace of urban growth. These issues are being exacerbated by climate change-induced water scarcity and planning uncertainty and have implications for social stability at various scales that need to be taken very seriously. Globally, about 500 million people already live in areas where water consumption exceeds the locally renewable water resources by a factor of two (Mekonnen and Hoekstra 2016): this includes parts of India, China, the Mediterranean region and the Middle East, Central Asia, arid parts of sub-Saharan Africa, Australia, Central and Western South America, and Central and Western North America and areas where nonrenewable resources (i.e., fossil groundwater) continue to decrease have become highly vulnerable and dependent on water transfers from areas with abundant water.

To address this complex challenge and to give cities practicable solutions, innovative integrated urban planning approaches are urgently needed. Particularly approaches that can leverage on potential synergies of climate change mitigation and adaptation approaches and measures may enable cities to take more comprehensive action to become more resilient to climate change impacts. The water-energy-food (WEF) nexus approach (Hoff 2011), which has gained momentum rapidly in recent years, is one possible way to affect such integrated urban planning. The WEF nexus approach highlights interlinkages between the water, energy, and food sectors, such that it takes much energy to supply freshwater and remove and treat wastewater or that much water is needed to produce energy and food (ADB 2013). The approach aims to optimize the water and energy systems in a synergetic manner while also considering and optimizing food production. The concept underlines responsible governance (GWSP 2014) and that a new perception of water is needed, with the water-food link being of the highest social and political significance (ADB 2013). Further, innovative integrated urban planning approaches also need to focus on key challenges as entry points in cities that can support implementation of the United Nations Sustainable Development Goals (SDGs). In the context of water, energy, and food security in cities, these are in particular zero hunger (SDG 2), clean water and sanitation (SDG 6), affordable and clean energy (SDG 7), sustainable cities and communities (SDG 11), and climate action (SDG 13).

Wastewater recycling and reuse, or water reclamation with resource recovery, is one such key entry point, as wastewater management is a serious challenge in many rapidly transforming cities worldwide with serious public and environmental health implications. Particularly in regions where water is scarce, wastewater is a water resource: less than 1% of it is the stuff that smells and the rest is just water and can be used again countless times. Wastewater also provides a direct link to the sectors energy and food: it can be used to produce energy, thereby improving energy security, or upgrade land quality and as organic fertilizer improving food security. Nutrients such as phosphorus and nitrogen, for example, are needed as fertilizer for agricultural production. Phosphorus (P) belongs to the naturally occurring of Earth’s substances that have been exploited to the extent that extractable phosphorus resources are predicted to become scarce or exhausted in the next 50 to 100 years (Steen 1998) and an estimated 22% of global P demand could be satisfied by recycling human urine and feces worldwide (Mihelcic et al. 2011). Thus, wastewater has intrinsic values that are gaining in importance; it is a renewable resource as long as humans are around, its reuse can offer means to support water, energy, and food security and hence implementation of the SDGs, and hence its reuse has high-impact potential.

However, even in the face of these challenges, the pattern of using a lot of water, and using it only once, is surprisingly stubborn: a long time ago, when European cities with open drains were rife with epidemics, the discovery that cholera is a waterborne disease triggered public awareness for the need to protect water resources. This led to a process of institutionalization by which the responsibility for the protection of public health through the provision of safe drinking water came to rest with the city-level public authorities. As a result, where before there were individual private wells and cesspits, the supply of water and discharge of wastewater became centrally organized, which necessarily was large in size in order to cover an entire city’s area. This large size determined certain design parameters for these systems to function: to deliver water to households, water pipes need a certain level of pressure, implying a certain volume of water. Then, to flush wastewater out of city areas to sewage treatment plants usually located at the urban periphery, again a certain volume of water is needed to prevent pipes from clogging. Provision of water in many cities in various world regions is mainly a question of energy needed to lift groundwater or pump water over large horizontal distances. In most Western cities where also energy is usually abundantly available and inexpensive, the norm is that drinking water flows freely from the tap 24/7. With unlimited supply, the resulting per person’s daily water use in Western cities ranges from about 100 to 200 liters or more. This amount is not necessarily related to the quantity of water a person may need to maintain hygiene and health. In a city like Munich in Southern Germany in a temperate climate, average daily water consumption per capita is 128 liters, of which only 3% is used for drinking and cooking, while 35 liters are dedicated to flushing the toilet and the rest for household cleaning purposes, etc. (SWM 2015). In the Western world, the consumption of water is not commonly strictly regulated under water scarcity even in drought situations as in California in recent years, unless there is a crisis, as in Cape Town today. Instead, local governments tend to invest into procuring more freshwater.

Wastewater as a water resource, on the other hand, is often underutilized worldwide. Globally, it is likely that over 80% of wastewater is released to the environment without adequate treatment (WWAP 2012, 2015). On average, high-income countries treat about 70% of the wastewater they generate, while that ratio drops to 38% in upper middle-income countries and to 28% in lower middle-income countries, and in low-income countries, only 8% of industrial and municipal wastewater undergoes treatment of any kind (Sato et al. 2013). Of the wastewater that is treated, reuse rates are generally low: Table 1 lists a few countries globally for which data exists (FAO 2016) as examples:

Table 1 FAO AQUASTAT data on global treated wastewater reuse rates
Full size table

Table 1 shows that treated wastewater directly reused globally is estimated at 11,6%. There are vast differences in water reuse even between countries in the same region. Many European countries, for example, have a wastewater collection and treatment rate of over 93%, but the reuse rate in Cyprus is 92% and in France and Spain 10% and 16%, respectively, and in contrast in the UK is 4%, in Italy 1%, and in Germany less than 1% (FAO 2016). Being an industrialized or high-income country hence does not seem directly indicative of water reuse rates. However, water scarcity may be an indicator considering the high rankings in water reuse of Middle Eastern countries shown in the table, but also not always, as we can see in the reuse rate difference, for instance, between Italy and Spain. It seems that the factors determining water reuse are complex and may involve climatic, institutional, cultural, and other differences.

Centralized sewage systems, though very commonly implemented in cities worldwide, are not free of challenges: they have very high capital, operation, and maintenance costs, where the largest amount of the capital cost is commonly due to the amount of piping needed. Many of these systems were built over a hundred years ago and are in need of large-scale repairs. In the USA, the cost of maintaining water-related infrastructure is estimated at 1 trillion USD over 25 years (AWWA 2012). Further, as mentioned above, centralized sewage systems are very water and energy intensive. Hence, these systems may not be the best option for every location. Further, they cannot function properly with reduced amounts of water and energy. Under climate change-related water scarcity and uncertainty, these systems are not resilient and pose considerable risk to public health in case of malfunction. Nonetheless, centralized sewage systems continue to be maintained in many cities and continue to be implemented in cities lacking or with inadequate wastewater management worldwide.

For cities with inadequate wastewater management, alternative technology options are not yet readily available. Many technological solutions exist, but have been mostly implemented at building scale. Further, water reuse has so far mainly been tested for agricultural purposes rather than reuse in urban areas and for urban water needs. We hypothesize that between the city and building scales, the neighborhood scale is well suited to water reclamation with resource recovery for various reasons: many cities worldwide are, as described, struggling to provide sufficient safe drinking water to burgeoning urban populations and deal effectively with resulting wastewater. Different types of water demands have different water quality requirements: for example, the water quality needed differs for drinking, agricultural irrigation, and toilet flushing. Treatment options of wastewater can also vary depending on water reuse demands, and these in turn may differ between different neighborhoods. Hence, reclaiming water and tailoring its quality to different demand-dependent reuses has the potential to replace a significant amount of current freshwater demand, thus reducing pressure on freshwater sources and on local government water supply. Further, some neighborhoods may be difficult to connect to centralized systems, e.g., slum areas, or may be connected to a sewerage system, which is not working properly. In these cases a decentralized approach may be suitable. These areas are “windows of opportunity” in which water reuse demand can be catered to with short piping distances with less energy requirement and less opportunity for water wastage through leakages. The treatment process can be used to generate biogas or electricity for cooking or lighting locally, meeting part of the energy demand. The process can further be used to produce organic fertilizer for crop cultivation as well as soil quality remediation, e.g., in urban or peri-urban agriculture. These products of the water reclamation process are market and business opportunities as part of a revenue stream that can support the running of such a system. Such a “Nexus Model” could enable cities to be more autonomous of water, energy, and food availability or price fluctuation and hence more resilient to climate change impacts.

In this chapter we describe a typical rapidly expanding town, Leh, in the semiarid Ladakh region in the Indian Himalaya and the challenges it faces, outline some alternative technology options currently available for water reclamation with resource recovery that may act as catalyzers, and then discuss how these alternatives and the “Nexus Model” apply to the case of Leh and the implications for the climate change resilience of cities worldwide.

A Case Study Town in a Semiarid Region: Leh, Ladakh, India

This case study is described very briefly in this chapter, as it only serves to illustrate a typical case of a rapidly expanding town in a region where water resources are scarce and which is facing the challenge of identifying an alternative technological solution to wastewater management.

Leh town, the capital of the Ladakh semiautonomous region of India, is located in a remote semiarid region in the Himalayas in the Indus River Valley at an altitude of 3,500 m above sea level. Adjoining a dense historical town center, Leh’s urban area is spread throughout a green valley of agricultural fields and groves of trees watered by a dense network of streams fed by glacial and snow melt water, surrounded by a desert landscape (Fig. 1). This intricate cultural landscape is the product of hundreds of years of very careful management of these limited water resources. With such a water management system enabling food and social security, Leh was a traditional agricultural irrigation society until only a few decades ago (Norberg-Hodge 1991).

Fig. 1
figure 1

Geographical location and cultural landscape of Leh

Full size image

Today, traditional practices are increasingly making way to changing lifestyles and alternative sources of income. Leh has a population of around 60,000 (Census of India 2011). The town has developed very rapidly in recent decades, particularly due to tourism industry growth: according to the Leh Tourist Board, in 2017, 260,000 tourists visited Leh. The vast majority of these visit Leh in summer between April and October because of the very harsh winter conditions. In order to cater to these tourists, hundreds of hotels and guesthouses have opened in Leh. Whereas the traditional Ladakhi dry toilets do not consume any water and also households used water extremely sparingly for centuries – probably as little as 20 liters per capita per day even in recent decades – tourist accommodations are increasingly building en suite bathrooms with flush toilets and showers to enhance their attractiveness and thus income from tourism. This has very rapidly pushed up water demand and ensuing wastewater generated, which the local government is struggling to address.

This rapid urbanization patterns is posing several development challenges for Leh. Leh does not have a sewage system, and hotels and guesthouses dispose of wastewater mainly through septic tanks and soak pits that are not properly managed. Therefore, sewage seeps into the ground posing a public health risk as groundwater is the main source of drinking water. At the same time, the current water supply system is very energy intensive: groundwater is extracted via tube wells from the Indus River aquifer, which are located at the banks of the Indus River. From there, the water is lifted 200–300 m vertically and several kilometers horizontally to Leh. In addition, the local government supplies water from the aquifer underneath Leh using bore wells. This water supply system is very energy intensive but manages to supply water only for a few hours per day. As a result, almost all hotels and guesthouses, wanting to ensure functionality of flush toilets and showers, have built private bore wells, at a further energy cost. This has led to unchecked large-scale groundwater abstractions and adversely also added to the pollution, because private bore wells are often located too close to water pollution sources. The main source of energy in Leh for electricity is hydropower, but this energy supply is not stable, and Leh faces regular power cuts. Therefore also many hotels and guesthouses have their own diesel power generators, to bridge power supply gaps. As mentioned above, Leh was almost entirely self-sustained until very recently in terms also of food. Until only a few decades ago, there was a very limited variety of food available. However, it was locally produced using organic fertilizer from the Ladakhi dry toilets. Today in contrast, an estimated 30% of agricultural fields have fallen barren, and almost all food is imported, which comes at a further energy cost. Further, this pushes up the price particularly of fresh vegetables, which in winter are not sufficiently available for the local population. Hence, serious questions of water, energy, and food security present themselves in Leh that need to be addressed urgently. These could further be exacerbated with climate change impacts, such as glacier retreat.

“Business as Usual” Technology Option in Leh

To address the wastewater issue, the local government is currently building a centralized sewerage system in Leh comprising around 80 km of piping. A central wastewater treatment plant is planned at the foot of Leh, where wastewater is to be treated and discharged to the Indus River. As per national government guidelines (CPHEEO 1999), currently, the local government aims to provide 75 liters of potable water per capita per day (Lpcd). However, actually the local government provides water only for a few hours per day due to the local power constraint.

The centralized sewerage system in Leh was designed in 2009 by an international consultant. Its design is based on assumptions that may provide challenges in the future: the system is designed for the year 2040 and a projected population of 80,000. It assumes that all households will be connected to the system and consume 135 Lpcd, which is required by national government guidelines once an urban area has a centralized sewage system (CPHEEO 1999) and which is also required to flush the system. The local population is expected to pay the service charge to cover operation and maintenance costs. However, perhaps less than half of households currently own a flush toilet, only about half have private water connections, and about only half of these pay their water bills. The cost of connecting to the centralized sewerage system and the necessary sanitary infrastructure to consume 135 Lpcd of water is to be borne by the households. Thus, there is a fair degree of uncertainty in how many households will ultimately connect. It is not planned that hotels and guesthouses should connect, although these produce far more wastewater, because these are expected to develop their own on-site treatment systems. Energy is seen as the only current bottleneck to the centralized sewage systems operation. But large-scale solar energy development is also planned in Ladakh, which will be expected to supply Leh more reliably with energy. Water resources available through the Indus River and its aquifer are also considered ample.

Thus, with the implementation of the centralized sewerage system, the local population is being urged to consume about six times as much water as before. This, to many Ladakhis who have been using water extremely sparingly for centuries and are very much aware that they live in a desert, seems preposterous and even immoral. During the implementation of the centralized sewage system since 2014, it has become apparent that not all of Leh town can be connected to this system. For the remaining parts, hence, another solution needs to be found.

Alternative Technology Solutions and Urban Water Reclamation with Resource Recovery: State of the Art

In this section, we discuss a limited number of water reclamation with resource recovery best practice case study examples, collected from literature. These were chosen to represent different climatic, geographical, and cultural contexts worldwide, as well as a range of alternative technology options specific to different water reuse demands and in particular highlighting potential for the “Nexus Model” at neighborhood scale. Ten case studies are chosen (Table 2).

Table 2 Best practice examples of water reclamation with resource recovery
Full size table

In the following, each case study is described briefly in terms of its context, the type of technology and reuse it is catering to, and its advantages and challenges.

Energy Generation from Municipal Sludge at Neighborhood Scale: Hamburger Water Cycle, Jenfelder Au, Hamburg, Germany

Jenfelder Au, a new neighborhood in Hamburg, Germany, under construction since 2013 on a former industrial site, is home to 2,000 people. The project focuses on recovering energy from sewage sludge and on reducing water consumption due to toilet flushing using toilets designed to reduce water consumption by 80% (Schönfelder et al. 2013). To optimize energy generation at Jenfelder Au, blackwater (from toilets and urinals) and gray water (from kitchens and bathrooms) collection from households is separated. Separating the blackwater from the gray water has various advantages: despite a higher initial capital cost due to a dual piping system, it reduces the amount of water entering the fermenter used to generate biogas, thus reducing the required size of the fermenter. Further, the blackwater is less diluted, which enhances the fermentation process and resulting amount of biogas. The process also allows for a relatively simple and hence cheaper treatment of the gray water, which also represents the larger amount of the wastewater produced and can hence save costs.

At Jenfelder Au, the daily produced 12 m3 of blackwater is transported using a vacuum piping system to a fermenter, where fats from oil separators and skimmers are added and mixed with organic waste to generate biogas. The biogas produced is then run through a combined heat and power (CHP) unit to generate heat and electricity, which is used to heat the fermenters, as well as being resupplied to households for heating and other energy demands. At Jenfelder Au, the process generates 340,000 m3/year of biogas yielding, after transformation, 370 kWh/person*year of electricity, and 778 kWh/person*year of thermal energy (Schönfelder et al. 2013). The residues from the gray water treatment are also fed into this process. The gray water is treated using a trickling filter, and the clean water channeled to water bodies in the landscape. About 150 tonnes of sludge are produced through the blackwater treatment process yearly, which is used as organic agricultural fertilizer. The cost of the plant was 7,8 million Euros.

Industrial Reuse of Municipal Wastewater in Baotou City, Inner Mongolia, China

Baotou City in Inner Mongolia, Northern China, has a population of 2,6 million inhabitants and is situated in a semiarid climate with long cold dry winters and hot humid summers. In the context of this industrial city, freshwater is scarce and needs to be reserved for potable uses. The main source of freshwater is groundwater, and its levels are declining rapidly. Industrial reuse of treated municipal wastewater is a viable option because this has relatively low water quality requirements compared to other uses. Such uses include use of water in cooling towers and boilers and require a low salt/nutrient content and no suspended solids to avoid blockages and erosion in the cooling system or boilers.

At this water reclamation plant, completed in 2005, wastewater is procured from municipal wastewater treatment plants and treated using a biological aerated filtration (Lahnsteiner et al. n.d.): this has a relatively low space requirement and fulfills the following project requirements; the main objective was to remove the ammonia via nitrification, as nitrogen is a nutrient and would promote bacterial growth inside the cooling tower if left untreated, which would clog the pipes and destroy the system. Another reason is ammonium’s ability to corrode the copper pipes used in heat exchangers. Another benefit is dropping the alkalinity level when removing ammonium, which reduces the acid needed for PH adjustments, and finally nitrification transforms ammonia into nitrate, which will act along with phosphate as a corrosion inhibitor. No denitrification is needed as this water is not being released to the environment, but rather is recycled and reused over and over again in the same plant. This process saves on the costs of water used in the plant, as well as contributes to freshwater resource conservation in the region. The cost of this plant was 7,1 million Euros.

Direct Potable Water Reuse: The New Goreangab Water Reclamation Plant, Windhoek, Namibia

Windhoek, the capital of Namibia with a population of 326,000 inhabitants, is situated in an extremely arid region facing severe water shortages and long draught periods with uncertain rainfall patterns. The main freshwater sources are surface and groundwater, but all the water resources within a 500 km radius have already been utilized by the city. The new Goreangab water reclamation plant (NGWRP), completed in 2002, provides 21,000 m3/day of directly potable water, thus covering part of the demand (Lahnsteiner and Lempert n.d.). The raw water coming to the NGWRP consists of the treated municipal wastewater from the largest treatment plant in the city: from here, the secondary effluent is discharged to maturation ponds as a final conditioning step before being introduced to the NGWRP plant. This water is augmented by 10% using surface water from the Goreangab Dam. This plant was built to replace the old Goreangab water reclamation plant, which has been working since the 1960s but had reached the end of its lifetime in the late 1990s and was no longer considered technologically advanced enough to provide potable water reuse.

The new plant uses the Multiple Barrier Approach to produce safe drinking water by providing multiple protective barriers between the threat and the end user: the first step is the oxidation by what is known as pre-ozonation, which breaks down complex organic molecules into smaller molecules and increases their biodegradability. The next step is dosing of powdered activated carbon, which provides adsorption to remove important pollutants when needed or in case the pre-ozonation system fails. Then come the coagulation and flocculation steps: adding ferric chloride as a coagulant helps make bigger flocs that will be removed in the dual media filter. This is followed by dissolved air flotation to remove suspended solids and oils as well as bacteria and pathogens and then chemical dosing to raise the pH and to accelerate the oxidation precipitation of iron and manganese on the sand filter. The water is then passed through a dual media filter to remove all the particles and reduce the turbidity as well as the pathogens. After this, the main ozonation takes place to provide disinfection as well as oxidization of persistent organic compounds. This is followed by further chemical dosing and biologically activated carbon filters used to remove any remaining organic matter and provide some disinfection. Next, an ultrafiltration membrane is used to further remove any organics that might have slipped through this far as well as provide even more disinfection. The final step is chlorination to ensure that disinfection is as robust as possible. In this rather complex system, several steps ensure the removal of each type of pollutant. With these steps, the plant delivers drinking water without any difficulties since its startup, in accordance with the World Health Organization (WHO) and South African and Namibian guidelines. Of course such a complex system has a certain price, in this case 12,5 million Euros.

Indirect Potable Reuse/Groundwater Recharge: Torreele/St. André Water Reclamation Plant, Koksijde, Belgium

The Torreele reclamation plant was built in 2002 in the coastal region of Veurne in Belgium, it’s main purpose being indirect potable reuse via means of groundwater recharging (dune recharging) (Van Houtte and Verbauwhede 2012; Wood 2014a). In this recreational area, high tourist influx creates large seasonal variation in water demand. Furthermore, groundwater levels have been declining in the region, and this promotes salty water intrusion from the sea. This plant aims to prevent this and to satisfy the peak demand of water during the tourist season. The operation has two parts: first is the Torreele water reclamation plant which treats the municipal secondary effluent procured from the local wastewater treatment plant up to very high standards, and the second is the St. André dune recharge facility located 2,5 km away, which injects this water into a dune to recharge the groundwater aquifer and then extracts it again for drinking water uses. The water reclamation plant also, as in Windhoek, uses a Multiple Barrier Approach. The water first passes through a micro-screen to catch any potential suspended solids. This is followed by prechlorination stage: this helps to reduce biofouling at the next step, the ultrafiltration membrane. Next, submerged ultrafiltration stage (pore size of 0.1 μm) is used to monitor the effluent’s turbidity. This is followed by post-chlorination and then the main treatment stage, which is reverse osmosis. Finally, the water is disinfected using ultraviolet light, if needed.

Of the water reclaimed by the plant, 70% is used as dune recharge. Here, the water resides in the environmental buffer for 35–55 days with an infiltration rate of 0.35 m/day, after which it is extracted and retreated for drinking water purposes. The St. André water injection facility operates continuously and was only cleaned once after 4 years of operation (soil clogging). A disadvantage is the slow infiltration rate due to the high water table. The recharged water produced in this plant is around 2.500.000 m3/year (285 m3/h), which equates to roughly 45% of the local drinking water demand. The drinking water quality of the aquifer is greatly enhanced as a result of recharging it with high-quality water treated with a Multiple Barrier Approach. Additionally, natural groundwater extraction dropped by 30% or one million cubic meter annually, which means a rise in the groundwater levels in the dunes. This resulted in a sustainable management of the aquifer, improvement of the ecology and the value of the dunes, and improvement of the drinking water quality. The project is further perceived very positively in the public: people are very willing to accept reclaimed water as drinking water that has been processed by nature. Using such environmental buffers can also substantially reduce the cost of water reclamation, and in this case the cost of the plant was 6 million Euros.

Agricultural Reuse and Indirect Potable Reuse via Groundwater Recharge of Municipal Wastewater: Braunschweig, Germany

The water reclamation plant in Braunschweig, a town of 385,000 inhabitants, started in 1894 as one of the earliest so-called constructed wetland treatment concepts in Europe (Klein et al. n.d.). Since then, it has often been modified to extend its capacity and performance. The arrangement that exists now divides the effluent of the local treatment plant over two areas: the first are the irrigation fields dating back to 1894 (275 ha), which is a detention lagoon that flows onto smaller irrigation fields. This area serves as an engineered natural posttreatment for groundwater recharge and baseflow recharge of the Oklo River. In the second part, water is sprinkled over the new large irrigation fields (2700 ha). The advantage of this area is that it has a low groundwater table and sandy soils with low nutrient content. Thus, it can be used for a relatively quick infiltration and decent treatment of the contaminant via soil adsorption before it reaches the groundwater. Using this process, of the 22 million m3 of treated municipal wastewater produced annually, 15 million m3/year of water are reclaimed for sprinkler irrigation and 7 million m3/year as artificial groundwater recharge via the detention lagoon and the irrigation fields.

As the regional water balance is showing large losses due to evaporation and less precipitation in the last decades, reusing the wastewater for agriculture is a real advantage for a sustainable economy and the water balance of the region. The system is very simple but requires a very large amount of area, appropriate soil and groundwater conditions, and a rigorous monitoring program, as well as extensive cooperation and coordination. In order to ensure that groundwater is not being adversely affected, water quality testing of 6 discharge points collected from 500 ha area is undertaken for analysis, and 3 of 33 observation wells are tested each year by the water authorities for a range of chemical and biological parameters.

The Jezreel Valley Project for Wastewater Reclamation and Reuse, Israel

Jezreel Valley Project encompasses over 200,000 ha of fertile lands, which are very rich in agricultural produce, surrounded by urban areas with a total of around 250,000 inhabitants (Friedler 1999). The lack of freshwater due to population growth has led this region to rely almost solely on reused water for agriculture: the valley went from receiving 20–30 million m3/year of freshwater from the national water supplier in 1983 to receiving only 7 million m3/year in 1990. Pilot trials for the scheme began in 1996, and by 1999, 80% of agricultural irrigation demand was to be supplied through reused water. The pressing nature of the issue meant that the project needed to be executed quickly. However, the wastewater accruing in the valley was highly polluted with various industrial effluents.

The key concept of the reclamation strategy is to use semi-intensive treatment to quickly remove chemical and bacterial content in a cost-effective manner. This is done through a so-called sequence batch reactor: screen bars are used as pretreatment, followed by anaerobic ponds coupled with anaerobic lagoons. After this, the treated wastewater is transported to stabilization reservoirs via conduits (extensive treatment) in order to passively degrade the toxic and refractory organic matter coming from industrial and domestic sources. The complete operation enables 13 million m3/year of water to be reclaimed. This project shows the trends in semiarid regions with severe water shortages and also that industrially polluted water from urban areas can be used for agricultural irrigation.

Neighborhood Scale Integrated Water Recovery and Energy Generation Solution in the Deep Green District “Lanxmeer” in Culemborg, The Netherlands

Lanxmeer is a small neighborhood in the city of Culemborg with around 250 houses. The concept of this new neighborhood completed in 1999 is the creation of a green space as natural as possible, with storm-, gray-, and blackwater separation, infiltration ponds for groundwater recharge, and a city farm for both education and food-producing purposes in a closed-loop environment (Van Timmeren n.d.; Van Timmeren and Tawil 2006). Buildings utilize both geothermal heat and solar power to stay independent from the municipality’s power grid. There are constructed wetlands (reed beds) to treat gray water and drinking water that comes from the same groundwater used for heating the homes. The core part of the project is a center and hotel, which integrates waste and wastewater treatment as well as energy recovery: the blackwater is fed to a fermenter and used to generate energy with a combined heat and power plant. The resulting biogas is stored in a water tower in inflatable bags. A wind turbine at the top of the tower generates extra electricity.

Culemborg represents a sensitive ecological area where groundwater abstraction and retention (for drinking water) takes place; this is the first time such a permission in the drinking water protection zones has been granted, on the strict condition that it will be built using modern green principles. Thus, the district itself has naturalized and publicly owned green zones including shared gardens between building clusters for relaxation and playing with edible gardens, retention ponds and intensive planting of reed beds, agricultural lands or city farms, and ecological developing areas with infiltration ponds, hayfields, and woodlands, all combined as a very resilient ecosystem with a focus on biodiversity. There are no private gardens in between houses, and this creates a very open and child-friendly space. The fermenters also rely on the green waste generated in those areas, and the farmers rely on the compost for their land. Further, the riverbed was restored to make more space for flood protection and compensate for sealing of new areas due to buildings.

Ecological Settlement in Allermöhe, Hamburg, Germany

Allermöhe eco-settlement, started in 1986, was among the first ecological settlements in Germany, with the last residential houses added in 2002 and a community center finally added in 2007, which added a sense of ownership as a focal point (Rauschning et al. 2009). The project was designed to be highly efficient with respect to energy and resources, with compact single-family homes built with efficient and ecologically friendly materials such as wood, grass, and recycled materials for high-quality insulation and roofs. The main objectives of this project are to involve users and instill a sense of ownership in order to make them accept a new and possibly controversial technology (waterless toilets), have compact family homes with a high level of energy efficiency and usage of renewable technology like solar panels, and to be totally independent from the municipal sewage system and reusing resources internally.

The Allermöhe project uses a composting waterless toilet system, which saves around 40 liters/capita/day. Each toilet is connected via a straight wide chute to the composting chamber in the basement designed to avoid soiling the pipes with feces and causing odor. Eighty percent of the water or urine added to the toilet is evaporated and taken out via the ventilation pipe. Food and organic waste can be disposed of in the toilet directly, and toilet paper is also composted in the toilet. Maintenance once a month needs to be done (mixing the compost, adding organic and garden waste, as well as minerals and activators, etc.), and the house owners or volunteers within the community do this. The compost is removed once every 2 years and is then used in the family’s garden as fertilizer.

Gray water is separated and directed to an underground Imhoff tank for settlement and grease separation. Then it is released in intervals to a vertical subsurface flow constructed wetland, the total area of which is 240 m2. Vertical flow constructed wetlands operate aerobically due to the intermittent feeding of water and are excellent for nutrient removal, which is essential for release into a water body. The water is then directed to a polishing pond and then released to natural water bodies. The effluent quality of the wetlands is checked twice a year by the authorities, and the results surpass the necessary discharge standards.

Non-potable and Indirect Potable Reuse, NEWater, Singapore

The NEWater project (NeWater Study 2002; NuWater n.d.; PUB n.d.; Wood 2014b), under construction and completed in stages from 2000 to 2017, is the pillar of Singapore’s sustainability strategy. It produces high-grade drinking water from wastewater and passes 150,000 tests including the WHO standards. There are currently five NEWater plants in the country, and they provide 40% of the total national water demand, which is expected to rise to 55% by 2060. The majority of the water is used for industrial uses, but in dry seasons this water is mixed with the raw water from the reservoir before being further treated for domestic supply.

The treatment process in the NEWater project is as follows: a pretreatment is conducted using coarse and fine screens, primary sedimentation, biological tanks, and secondary clarifier. Next, microfiltration serves as a basic treatment step to remove any turbidity including pathogens. This protects the following stage, reverse osmosis from clogging and fouling: here a membrane basically removes everything to a scale even of single ions, and so only pure water is allowed through. This is followed by disinfection using ultraviolet light: this is used as a robustness measure, as both the previous stages also provide disinfection. The resulting ultraclean water is delivered to the industries via a dedicated pipe network. In the dry season, around 10% of this ultraclean water is mixed with the raw water in the reservoir, and the city’s waterworks then further treat this mix before being delivered to consumers as tap water. The five plants produce 773 million liters daily of reclaimed water and cost 400–500 million Euros to construct.

The treatment process is monitored online using the sampling and monitoring program of various characteristics that are continuously monitored. In the event of a failure, the plant automatically shuts down. The water produced undergoes a rigorous investigation twice a year by a panel comprised of the National Environment Agency plus experts in engineering, microbiology, toxicology, and water chemistry. It has thus far always exceeded international standards. The project has won 23 national and international awards over the years and is generally very well regarded. Although the water is not used directly as a potable source, an awareness campaign informing of the NEWater treatment process was so successful that a poll conducted in 2002 revealed that 98% of respondents would drink NEWater, and 82% would drink it directly without mixing.

Pomona Water Reclamation Plant with Integrated Aquaculture-Wetland Ecosystem, Los Angeles County, California, USA

California is a severely water-stressed region, and its main source of potable water is imported water from outside, such as the Colorado River. However, this supply can vary according to environmental, political, and energy consumption factors. The imported water is usually used and then disposed of directly to the ocean or via the San Gabriel River which leads to the ocean. Therefore, there have been serious efforts to upgrade all the treatment plants to tertiary treatment facilities as well as encourage water reuse. Operation in the Pomona Water Reclamation Plant started as early as 1927 (Costa-Pierce 1998; LACDS 2010).

In this system, wastewater is given primary treatment with screening and primary sedimentation tanks. Then secondary treatment with an aerated activated sludge process removes organic material, followed by a secondary clarifier. This is then followed by a tertiary step with chlorination and activated carbon plus anthracite gravity filters and another chlorination step with a contact tank for disinfection. To remove the inorganic nitrogen and phosphorus to avoid eutrophication, a further polishing step is employed using an aquaculture-wetland ecosystem. This simultaneously produces aquatic food and removes the nutrients from the final water. This system consists of a 28 m3 buffer tank, three ponds with an area of 200–240 m2 and a depth of 1 m, and a 100 m2 artificial wetland. The reclaimed water quantity is 56.8 million liters/day. It is used for landscaping and nonagricultural irrigation, as well as industrial reuse and groundwater recharge. About 30.3 million liters/day is reused at 190 different sites. The rest is put into the unlined section of the San Gabriel River, which supports groundwater recharge.

Lessons Learned on Water Reclamation with Resource Recovery

To briefly summarize some concluding findings from this review of best practices, the following can be learned: the intended target of the water reuse must be based on the needs and conditions of the region. That is, it makes little sense to have direct potable reuse in an area with sufficient water resources due to the inhibitive energy and cost requirements. Agricultural reuse of water has lower treatment requirements and thus costs than potable or service water reuse, but the effect of nutrients or harmful substances remaining in reclaimed water particularly on food crops but also on soil, groundwater, etc. needs to be carefully assessed. In terms of energy, to maximize energy recovery via biogas generation, fats and oils as well as organic waste from kitchens and restaurants can be added to the anaerobic digesters. This greatly increases production of biogas. Finally, there is an inverse relationship between the simplicity of a system and the area required for that system. Thus, simple and passive systems like constructed wetland treatment often require a lot of space but use less or no energy and are simple to operate and maintain. On the other hand, systems like reverse osmosis are highly complex, expensive, and require a lot of energy, but are very compact in size. It follows that at each potential location for an alternative technological solution to water reclamation with resource recovery, a host of different factors including cultural, geographical, institutional, financial, and many others need to be taken into account, in order to find a solution that works.

Toward Alternative Technological Solutions in Leh, Ladakh, India, for Water Reclamation with Resource Recovery

Integrated urban planning using the WEF nexus concept, with decentralized urban water reclamation and reuse to conserve water and energy, for small clusters of hotels, guesthouses, and households, could be an alternative development option for Leh. Considering multiple reclamation facilities, the associated decentralized sewerage systems require less water to flush. The reclaimed water could be used locally to regenerate land that is barren for vegetable production, aiding food security. It can also be used to replenish the local groundwater aquifer. In order to cover the power demand of smaller decentralized water reclamation facilities, solar energy can be utilized, augmented by the production of biogas while providing a water quality tailored to local needs in close proximity to irrigation water demand. Larger facilities could also produce biogas and reclaimed water, but in Leh this would have to be supplied/pumped back to where the demand is. This would require an additional distribution system and would entail a significant amount of energy needed for pumping. Biosolids still containing residual nutrients and organic substances can be used as fertilizer in agriculture. This alternative development option can also generate green jobs locally to operate the treatment facilities and to grow and market valuable crops. Given its size, these systems are more flexible and hence resilient to climate change impacts such as decrease in water availability.

Different alternative technological solutions of those mentioned above may be suitable in order to operationalize this particular “Nexus Model” in Leh. Given its semiarid climate, water conservation needs to be considered a first utmost priority. Next to water security, as described above, energy and food security are also issues, hence a water reclamation with resource recovery solution should aim to address these. The local government of Leh town has very limited capacity to address more challenges than it is already doing. Therefore a system should be simple to construct, operate, and maintain, so that it could be run by the local population with some capacity building and training. Given the history of Leh, it is important that the introduction of a new system should have benefits that are evident particularly to the local population. The benefits of the centralized sewerage system are easy to understand, yet these seem to come at a huge and perhaps unreasonable cost, particularly if we consider that the traditional sanitation solution, the Ladakhi dry toilet, was doing its job very effectively in the past without posing health or groundwater pollution risk. What then can be a solution that is also suitable to the tourism industry while being a key element of sustainable development in Leh?

In this study, we have identified constructed wetland treatment (CWT) coupled with a slow sand filtration and an anaerobic digester to produce biogas as a suitable treatment process in Leh. The CWT has a relatively low capital cost, is relatively simple and inexpensive to operate, and needs relatively little maintenance. Further, a CWT is able to operate in winter at very low temperatures. Although the CWT requires a large amount of space, there is enough barren agricultural land in Leh to accommodate it. We identified a pocket in Leh’s agricultural land area that will not be connected to the centralized sewerage system. The pocket has 21 hotels and guesthouses and 29 households, and the amount of wastewater accruing is estimated to be around 60 m3/day. This would result in a CWT area of around 1500 m2, which can be placed in an existing barren field. Through this, the field receives some greening, adding to the pleasant appearance of Leh, and provides reclaimed water for agricultural irrigation to fields nearby. Depending on the type of crop, for example, vegetable, around 1–2 ha of land could be irrigated using the reclaimed water. A small amount of pumping would be needed to convey reclaimed water to the fields that need to be irrigated, but this could be done using solar-powered pumps. The biogas generated could also significantly cover a part of the local energy demand and is estimated to suffice for the cooking requirements of 30–50 people daily. Using this system enables the continuation of the traditional practice of using organic fertilizer for agriculture. The most expensive part of this proposed system would still be the piping needed to collect the wastewater, due also to the fact that this piping has to be 1–2 m underground to avoid freezing in winter. The greening of Leh and production of vegetables can be considered as beneficial also for the tourism industry. Further, the CWT can help to make the wastewater topic in Leh more visible, and hence add to awareness. Although the implementation of such an alternative technological option in Leh would face various challenges, this option seems feasible and can contribute to water, energy, and food security. With these findings, this study can support other cities worldwide in the process of searching for technological alternatives to “business as usual” in wastewater management.

Conclusion

The question of water availability will be critical in identifying which type of water reclamation with resource recovery infrastructure is appropriate for future cities and with climate change at a given location. Water availability, however, cannot be predicted very accurately under climate change impacts. Hence, it is imperative that when “windows of opportunity” open to construct new infrastructures or modify existing ones, these infrastructures are planned to conserve water resources to the full extent possible in order to support the resilience of cities to climate stresses. Further, if possible, they should address water, energy, and food security in order to support implementation of the SDGs. If we had known what we know today, we may have constructed mainstream water management systems differently over a century ago to better conserve water and energy resources. From today’s view, existing systems are diluting a very valuable resource, namely, municipal sewage, to such an extent that it is difficult to recover the valuable resources it contains. Changing existing systems includes a long-term planning horizon to adopt innovative urban planning processes and expand cities’ adaptive capacity. Supporting tools such as economic incentives, refinancing regulation, cross-sector balances, and expert appraisal are needed in order to assist change in terms of various aspects. With such support, urban water reclamation with resource recovery has the potential to be a crucial cornerstone of a climate change resilience strategy in future cities worldwide.