Abstract

Water crises are already stressing societies, economies, and the environment worldwide and especially developing countries. The expected growth in population, urbanization and economic activity, as well as the impact of climate change, will exacerbate the situation in the coming decade. In developed countries, conventional water supply and wastewater disposal systems ensure safe access to drinking water, sanitation and wastewater services. The worldwide application of conventional systems is, however, only possible to a limited extent. The reason for this is that these systems are designed for certain climatic conditions and also do not consider the varying requirements regarding water supply and wastewater disposal typical for developing countries. Although there are alternative water supply and wastewater disposal systems that have proved to be successful throughout the developing world, there are still several barriers to their worldwide adoption. To increase the establishment of these approaches this paper focuses on aspects of particular relevance for developing countries, namely: water reuse (untreated wastewater), alternative sewerage (settled and simplified sewerage), alternative wastewater treatment (waste stabilization ponds, constructed wetlands and up-flow anaerobic sludge blanket reactors) and management of water losses (real and apparent losses).

INTRODUCTION

There are several water-related crises worldwide and especially in regions in developing countries that are also affected by high water stress. Given that the worldwide growth in population and economic development will focus on Asia and Africa, the collapse of the water sector seems, at first sight, a burden of developing countries. However, the strong accumulation of risks associated with insufficient water supply (such as food crises) and wastewater disposal (such as health risks) highlights that the ensuing effects ultimately affect societies and economies worldwide. Also, the World Economic Forum underlines in its Global Risk Reports the vital role of water for societies, economies and the environment. The Global Risk Report is published annually and summarizes the top global threats facing the world. In this regard, water crises were identified as one of the top three risks each year over the period from 2012 to 2017 (see Table 1).

Table 1

Top three global risks in terms of impact 2012–2017

 2012 2013 2014 2015 2016 2017 
1st Major systemic financial failure Major systemic financial failure Fiscal crises Water crises Failure of climate change mitigation and adaptation Weapons of mass destruction 
2nd Water supply crises Water supply crises Climate change Rapid and massive spread of infectious diseases Weapons of mass destruction Extreme weather events 
3rd Food shortage crises Chronic fiscal imbalances Water crises Weapons of mass destruction Water crises Water crises 
 2012 2013 2014 2015 2016 2017 
1st Major systemic financial failure Major systemic financial failure Fiscal crises Water crises Failure of climate change mitigation and adaptation Weapons of mass destruction 
2nd Water supply crises Water supply crises Climate change Rapid and massive spread of infectious diseases Weapons of mass destruction Extreme weather events 
3rd Food shortage crises Chronic fiscal imbalances Water crises Weapons of mass destruction Water crises Water crises 

Note: Table created with information from World Economic Forum (2017).

The worldwide use of conventional water supply and wastewater disposal systems is only possible to a limited extent. Conventional approaches are usually associated with the application of high-tech solutions requiring vast organizational and operational knowledge as well as large financial resources which developing countries are not able to cope with. Also, the design of conventional systems such as wastewater and sludge treatment is based on certain climatic criteria and thus may not be used worldwide. However, there are alternative approaches, which have proved to be successful throughout the developing world. But several barriers limit their worldwide implementation. To increase the understanding of these approaches, this paper gives an overview of aspects for water supply and wastewater disposal of particular relevance for developing countries, namely: water reuse, alternative sewerage, alternative domestic wastewater treatment, and water losses. For this purpose, the field of application, particular benefits and risks are discussed. In this regard, it must be highlighted that the aspects given shall not be deemed as exhaustive.

WATER REUSE

As the world's demand for water is rising, water reuse has gained increasing importance and is considered as an integral part of sustainable water resource management. While in developed countries environmental standards ensure safe water reuse, this method is practiced only to some extent in developing countries, which poses high environmental and health risks.

There is a variety of triggering mechanisms which promote the reuse of water. Jiménez & Asano (2008) identified the lack of water as the most critical driver in both developed and developing regions. Especially in the Middle East and North Africa, water reuse is driven exclusively by extreme water scarcity. In developed regions in North America, Europe and Oceania more stringent regulations, as well as environmental constraints, are a decisive factor in the reuse of water. In contrast, in Sub-Saharan Africa, Asia as well as in Central and South America water reuse is mainly driven by the lack of sanitation in addition to water scarcity which leads to the reuse of untreated wastewater. According to the Pan-American Health Organisation, only 14% of the wastewater in Latin America is treated before it is discharged into surface waters, with only 6% of that treated within adequate limits. Hence, it can be assumed that the reuse of insufficiently treated wastewater also occurs in areas with access to sanitation and wastewater treatment (Jiménez & Asano 2008).

In developing countries, water reuse is usually practiced for agricultural purposes such as irrigation (Asano 2002). Although information concerning agricultural reuse needs to be analyzed carefully due to the insufficient level of reporting, estimates have revealed that several million ha in developing countries are irrigated with untreated or inadequately treated wastewater and that 10% of the world's population consumes crops produced with untreated wastewater (Jiménez & Asano 2008). The reviewed WHO guidelines (2006) ultimately attempt to address the health risks associated with the reuse of insufficiently or untreated wastewater for agricultural purposes in developing countries (see Figure 1). Previous guidelines failed since regulations were too stringent. The reviewed guidelines take into account that developing countries do not have the same resources as developed countries and thus require a different approach to ensure safe water reuse. Instead of regulations, the WHO guidelines recommend a multi-barrier approach consisting of varying protection measures such as the choice of crops, the irrigation method, and alternative wastewater treatment methods. The measures can be used optionally, but the combination of measures is recommended to achieve the best results. Whether the guidelines of the WHO will be adopted successfully is at present not known. Similar concepts, however, have already been successfully implemented. In Chile, for example, the application of crop restriction schemes combined with a general hygiene program reduced the transmission of cholera from the consumption of raw vegetables by 90% (WHO 2006).

Figure 1

Multi-barrier approach (WHO 2006).

Figure 1

Multi-barrier approach (WHO 2006).

Considering the increasing water demand as well as the increase in wastewater production due to population and economic growth while water resources become even more limited, water reuse can be considered as an important alternative source to secure water supply and economic development in the future. However, before water reuse can be fully exploited in developing regions, untreated wastewater use needs to be reduced significantly.

ALTERNATIVE SEWERAGE SYSTEMS

A lack of sufficient sanitation, particularly in the megacities of developing countries, poses major risks. With regard to the proposed estimates that most urbanization and population growth will occur in developing countries, the need for adequate sewerage systems becomes even more urgent.

Settled sewerage is a low-cost sewerage system used particularly in middle- and upper-income areas and is also known as ‘solids-free’ sewerage. It is designed to discharge only the liquid fractions of domestic wastewater into the sewerage system. For this purpose, the wastewater is primarily treated in an interceptor tank installed upstream at each sewer junction to remove total suspended solids, grease and scum. Besides the lower pipe diameter, settled sewerage also differs from conventional sewerage due to the shallow depth at which the pipe is laid. If a settled sewerage system is planned without having any septic tank already installed, the cost may be reduced if multiple households share one tank. The sludge in the tank needs to be removed at regular intervals, namely once every 1 to 5 years. Septic tanks are generally not a suitable treatment option in very densely populated areas. Today, settled sewerage is practiced in both developed countries, e.g., Australia or the United States, and developing countries such as Columbia, Nigeria, and Zambia (Mara 1996).

Simplified sewerage is also a low-cost sewerage system and aims to provide sewerage services to high-density (unplanned) low-income as well as high-income urban areas (Mara 2005). It is characterized by sewer pipes running from one house to another, collecting the wastewater of a complete housing block, which reduces the sewer length significantly, before discharging it into the public network. There are three different routing options, namely, routing through the backyard, the front yard or the pavement (see Figure 2). In front and back yards, sewage pipes can be laid at shallow depths. With backyard or front-yard systems, maintenance usually has to be done by households since sewers run on private property.

Figure 2

Conventional and simplified sewerage (University of Leeds 2000).

Figure 2

Conventional and simplified sewerage (University of Leeds 2000).

Since its development, simplified sewerage has been used all over Brazil. Moreover, the technology has also been transferred to other Latin American countries such as Bolivia, Colombia, Honduras, Nicaragua, Paraguay, and Peru. The countries outside Latin America where simplified sewerage systems have been successfully implemented are mainly limited to Pakistan and Sri Lanka. Especially in Asia and Africa, there is a fundamental lack of understanding of the simplified sewerage concept, in both design and construction. In India, for example, although the applicability of simplified sewerage is considered as very high and it is recommended in the national sewerage and sanitation treatment design manual, its nationwide implementation failed due to a lack of knowledge of the concept at government level, particularly within local government (Mara & Broome 2008). A similar situation occurred in Ethekwini (Durban) in South Africa: although simplified sewerage has been considered as an excellent sanitation solution for South African communities, its implementation failed (Eslick & Harrison 2004). In addition, the lack of adequate operation and maintenance led to system failures, especially in case of backyard routing. However, community-based operation and maintenance is an optional feature of a simplified sewerage system. In this case, pipes are routed along sidewalks, and operation and maintenance are similar to conventional utility maintenance approaches. The success of a community-based operation and maintenance system requires clear communication between local governmental authorities, water utilities and the public during all stages of a project at all levels. In this regard, it is also important to include educational actions relating to operation and maintenance services.

Simplified and settled sewerage systems have proved to be successful in many urban areas throughout the developing world, offering the same health benefits as conventional systems with lower costs. Nevertheless, there are still several barriers to their worldwide adoption, mainly due to insufficient transfer of knowledge.

ALTERNATIVE DOMESTIC WASTEWATER TREATMENT

Although there are numerous technologies to treat wastewater, the trend is towards high-technology approaches as used in developed countries. Such treatment systems are associated with, among others, a high technical, operational as well as financial burden and thus are of only limited suitability in developing countries. As a result, the objectives concerning wastewater treatment differ to some extent significantly between developed and developing countries (see Table 2). Also, since most wastewater produced in developing countries originates from domestic water usage, the main objective of wastewater treatment focuses on the removal of organic and microbial loads to an acceptable level only.

Table 2

Key factors for wastewater treatment in developing and developed countries

Factor Developed countries Developing countries 
high treatment efficiency • • • • • (C) • • • •  
high operational reliability • • • • • (C) • • • • • (C) 
low sludge production • • •  • • • • • (C) 
low land requirements • • • • • (C) • •  
low environmental impact • • • •  • •  
low operational costs • • •  • • • • • (C) 
low construction costs • •  • • • • • (C) 
high operational sustainability • • •  • • • • • (C) 
high simplicity •  • • • • • (C) 
• • • • • : extremely important → • : no impact; C critical factor 
Factor Developed countries Developing countries 
high treatment efficiency • • • • • (C) • • • •  
high operational reliability • • • • • (C) • • • • • (C) 
low sludge production • • •  • • • • • (C) 
low land requirements • • • • • (C) • •  
low environmental impact • • • •  • •  
low operational costs • • •  • • • • • (C) 
low construction costs • •  • • • • • (C) 
high operational sustainability • • •  • • • • • (C) 
high simplicity •  • • • • • (C) 
• • • • • : extremely important → • : no impact; C critical factor 

Note: Table created with information from Mara (2003).

Waste stabilization ponds (WSPs) are large shallow basins in which raw wastewater is treated by natural processes such as sunlight, temperature and sedimentation. WSPs are considered to be the most important method of wastewater treatment in developing countries where sufficient land is available and the temperature is most favorable to their operation, namely in subtropical and tropical regions. A WSP plant usually consists of three pond types, typically arranged in a series with an anaerobic pond first, followed by a facultative pond and by one or more maturation ponds. WSPs offer several of the requirements particularly important for developing countries: they are simple, low cost, highly efficient and robust. Despite WSPs being essentially a simple technology, there are several issues which lead to the failure of WSP plants such as odor pollution or poor effluent quality. However, these failures are usually associated with design, construction and operation failures (Mara 2003).

Constructed wetlands (CWs) are the engineer-made equivalent of natural wetlands and are designed to reproduce and intensify the wastewater treatment processes that occur in natural wetlands. Since solids and other larger particles may cause clogging in the inlet of a CW, wastewater needs primary treatment, e.g., in an anaerobic pond. There are two types of CWs: subsurface and surface flow CWs whereby surface flow CWs have the significant risk of flies and mosquitoes breeding. Since many developing countries are located in subtropical and tropical regions with a high distribution of mosquitoes, subsurface CWs are recommended. Subsurface flow CWs are designed with either vertical or horizontal flow. Vertical flow beds (VFBs) have a higher treatment efficiency and require less area than horizontal flow beds (HFBs). However, the operation of VFBs is more complicated than that of HFBs since VFBs require interval loading. In contrast, HFBs receive wastewater continuously. CWs offer similar benefits as WSPs, are, however, technically more complex, require more maintenance and thus are more expensive in operation. Even so, CWs are increasingly used in urban environments since they are easier to integrate into a neighborhood (Hoffmann et al. 2011).

Up-flow anaerobic sludge blanket (UASB) reactors are high-rate anaerobic wastewater treatment units used for high-strength biodegradable industrial and domestic wastewaters. Room temperatures above 20 °C are recommended, to maintain appropriate conditions inside the reactor. For this reason, several UASB reactors have been implemented, particularly in tropical and subtropical developing countries such as Brazil, Columbia, and India. Before raw wastewater may enter an UASB reactor, large particles and sand need to be removed by screening or using a grit collector. The waste sludge produced in an UASB reactor needs to be disposed every few years. Post-treatment is required to reduce the number of fecal bacteria to an acceptable level and to meet the final effluent quality. UASB reactors are technically complex to build, operate and maintain and thus are significantly more expensive than WSPs or CWs. Despite this, where large land areas are not available, such as in densely populated urban areas where WSPs and CWs cannot be built, UASB reactors in combination with adequate post-treatment can be regarded as the most appropriate solution for developing countries (Lomte & Bobade 2015).

WSPs, CWs and UASB reactors have proven to be successful alternatives to conventional wastewater treatment. Nevertheless, their use is often associated with failures and less recognized than conventional systems. Given the increasing amount of discharged untreated wastewater and the infeasibility of conventional systems in developing countries, the promotion of alternative wastewater treatment processes is urgently required.

WATER LOSSES

The overall water losses in the majority of developing countries are estimated in the range of 30–40%. However, since worst-performing utilities are rarely reported, it can be assumed that water losses in developing countries are very likely higher (Kingdom et al. 2006).

To reduce and manage water losses in a distribution network, a comprehensive understanding of the volumes lost is essential. The IWA water balance is a worldwide recognized method to determine the non-revenue water (NRW) components in a water distribution network especially with regard to national and international benchmarking (Farley & Liemberger 2005; Baader et al. 2011). In order to adopt appropriate water loss reduction methods, it is important to analyze the components of NRW both by their volume and their financial impact. As a result, water utilities can focus first on the reduction of those NRW components where investments will generate the highest rate of return. NRW consists of real losses, apparent losses and unbilled authorized consumption. While in developed countries real losses (e.g., all types of leaks) are usually the primary concern, in developing countries apparent losses (e.g., meter inaccuracies or illegal connection) are often also of vital importance (see Figure 3).

Figure 3

Estimates of worldwide non-revenue water, physical losses, and commercial losses. Note: Figure created with data from Kingdom et al. (2006).

Figure 3

Estimates of worldwide non-revenue water, physical losses, and commercial losses. Note: Figure created with data from Kingdom et al. (2006).

The primary tools for the reduction of apparent losses include the improvement of meter reading, data transfer, and data handling as well as the reduction of meter inaccuracies and unauthorized consumption. In many cases, the decrease in apparent losses can be achieved at relatively low cost and thus, it is a good starting point for water utilities due to the short payback time. Pressure management is mainly applied in developing countries to reduce real losses. It aims to reduce the pressure variations during the entire day by keeping the pressure always at a constant level within the constraint of ensuring the minimum required supply pressure at the critical point of the network at any time. Pressure management can also be seen as an immediate and cost-effective solution for reducing real water losses; but particularly in water distribution networks with high levels of leakage such as in developing countries, pressure management only mitigates the impact of real losses, and does not remedy the causes. For this reason, pressure management should only be seen as a partial solution in addition to further methods such as active leakage control, frequent repairs as well as infrastructure management (Baader et al. 2011).

Considering the increasing water-related needs in developing countries, the reduction of water losses offers a high potential to improve water supply. According to Kingdom et al. (2006), halving the NRW level in the developing world is considered to be a reasonable objective offering social, financial as well as ecological benefits, namely:

  • 8 billion m³ of treated water becomes available to service customers;

  • 90 million people could be supplied with treated water without increasing stress on water resources; and

  • US$ 2.9 billion becomes available for water utilities.

CONCLUSION

Requirements regarding water supply and wastewater disposal vary considerably around the world and especially between developed and developing countries. To meet the increasing water-related needs of developing countries, the following approaches and issues are of significant importance: water reuse, alternative sewerage (such as settled and simplified sewerage), alternative wastewater treatment (such as WSPs, CWs and UASB reactors) and the reduction of water losses. However, to reach the full potential of these approaches, the transfer of knowledge needs to be properly addressed, ultimately mastering one of the greatest global threats in the coming decade – namely, water crises.

ACKNOWLEDGEMENTS

This paper would not have been published without the support provided by the program committee of the International Young Water Professionals Conferences organized by IWA, WISA, and YWP-ZA, www.iwaywpconference.org

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