The Grandest Challenge of All: The Role of Environmental Engineering to Achieve Sustainability in the World's Developing Regions

Urban means more than just megacities

There appears to be an overemphasis in applying discipline knowledge to problems of large megacities without appropriate consideration of how the context of the problem differs as one moves along the spectrum of rural to largely urban environments. Currently, megacities (population >5–10 million) are viewed by many as the new frontier (especially in regard to more sustainable energy management). In fact, more than half of urban populations in developing regions live in cities with <500,000 people (UN, 2011), and cities with <200,000 inhabitants make up 12–48% of some countries’ total populations (Oakley and Jimenez, 2012). Even though megacities will continue to experience increased population growth, most future urban population growth is expected to occur in cities of <500,000 people (Cohen, 2006). There are many important areas to study in these contexts. For example, within an urban environment, social, gender, and spatial inequalities serve as barriers for residents to access the numerous social, environmental, and economic benefits provided by green space (Wright Wendel et al., 2011, 2012) and much of this green space is also associated with engineering infrastructure. Therefore, engineers have opportunities to collaborate with other disciplines to address these inequalities and ensure equitable opportunities that result in sharing of benefits.

Moreover, small cities are also underserved in areas of government support for environmental services and suffer from financial, institutional, and technology constraints (UN-Habitat, 2006). In terms of nutrient flows, populations in small cities in developing regions are clearly linked by geography, watersheds, and many social–economic factors to surrounding agricultural zones that provide opportunities for reclaiming water and embedded nutrients found in domestic wastewater (Verbyla et al., 2013b). Additionally, the environmental needs in informal urban settlements (i.e., urban slums ^c ), often located within larger cities, are equally challenging and may differ from the needs of small cities. Access to environmental services is remarkably lower in these informal settlements, which currently house 860–880 million of the world's urban population (UN, 2015; UN-Habitat, 2015). These informal urban settings also often have serious problems with violence, safety, and personal security, making them extremely challenging work environments.

Rural area considerations

Rural areas are important: almost half of the world's population still resides in rural communities and the provision of services in these areas is often neglected. For example, access to improved water and sanitation has consistently lagged in rural areas and 9 of 10 open defecators reside there (WHO and UNICEF, 2014). Furthermore, rural residents are known to depend more on the environment for their economic livelihood than their urban colleagues (WRI, 2005). Rural areas also present a different set of challenges when compared with urban or periurban areas. For example, while management of environmental services in urban locations may be overseen by parastatal corporations or private enterprises, the rural community is often left to manage its own systems in developing regions (Schweitzer and Mihelcic, 2012). Table 1 summarizes these and other important issues to consider when working in vastly different contexts that span the rural to urban environment. The information in this table demonstrates that despite the numerous challenges that each of these areas present, there are numerous opportunities to innovate.

GHGs and climate change

There is an important and expanding role for the skills of environmental engineers that can be applied to developing region issues related to carbon and climate. However, this first requires an understanding of the differences in regional contributions and ambient concentrations of pollutants and their impact. For example, the GHG emission intensity (i.e., level of GHG emissions per unit of economic output) is higher in developing countries than it is in more industrialized countries. The emission profiles for major GHGs are also documented to differ with a country's development status (Table 2). However, historical contributions to global GHG emissions from 36 countries with developed or emerging economies (e.g., United States, China, European Union, Russia, India, Japan, Brazil, Canada, and S. Korea) account for ∼70% of GHG emissions, while there are 173 other countries that account for only 20% of the total global emissions (Baumert et al., 2005). Looking to the future, extrapolating trends from individual country pledges to reduce GHG emissions out to 2030 will still lead to an emissions gap between developed and developing regions of 14–17 Gt CO₂e (UNEP, 2014b).

These differences point to regional- and country-specific opportunities to develop solutions to mitigate GHG emissions and adapt to the changing climate in developing regions. Least developed countries and small island developing states have negligible GHG emissions and reduction of these is probably not critical for global mitigation efforts; however, the impact of climate change on their health and social and economic well-being is potentially large and catastrophic. Global climate change currently represents a relatively lower risk to human health compared with other environmental burdens; however, the mortality impacts of climate change-sensitive health outcomes point to increases in mortality caused by heat, coastal flooding, diarrheal disease, malaria, dengue, and undernutrition (WHO, 2014). Furthermore, impacts of climate change are projected to be greatest for those living in small island developing states and other coastal regions, megacities, and mountainous and polar regions. The impact is also expected to be significant on child health by the 2030s (WHO, 2014).

Climate change is also expected to disproportionately impact communities that rely on snowmelt for their water supply. It also may increase water quality problems associated with algal blooms or surface water runoff from temperature increases and extreme weather events, and the resiliency of water, energy, and food infrastructure will be challenged from more intense cyclone activities (IPCC, 2014). In addition, the access to WASH services, food, and energy infrastructure and the resulting impact on human health and the environment will differ for populations living in small island developing states (UNEP, 2014c) compared with those residing in dry high-altitude Andean regions of South America (Vergara et al., 2011). There is also currently less effort placed in investigating anthropogenic changes to the hydrologic cycle in most developing regions. As one example, the estimated impacts from climate change were found to be greater than agricultural expansion and associated land use in a wetter and lower altitude region of the Andes, which were found to potentially result in insufficient recharge for springs that provide WASH services to rural developing communities (Fry et al., 2012). There is thus a large role for environmental engineering in understanding how adaptation applies to a country's or development region's unique geographical and socioeconomic setting.

Environmental engineers are well positioned to work in the top five global sectors that contribute to GHG emissions: (1) electricity and heat, (2) transportation, (3) industry, (4) land use changes, and (5) agriculture (WRI, 2005). A discussion on particular levels of GHG emission reduction potential in these five sectors, including co-benefits, barriers, and coverage by national actions and international cooperative initiatives, is provided elsewhere (UNEP, 2014b). Importantly, less carbon-intensive infrastructure and the adaption of existing infrastructure to a lower GHG emission trajectory are possible for all five of these sectors. Research is needed to assess and innovate ways to establish low-cost and functional transportation systems that balance the benefits and environmental and social costs of travel (Bruun and Givoni, 2015). In addition, developing regions are urbanizing rapidly and the rate of new building construction is higher than in developed regions. Cities also account for 70% of energy use and up to half of GHG emissions (Seto et al., 2014).

There will be a need to develop and implement renewable energy technologies and energy efficiency strategies; however, these must be appropriate, that is, they should use materials and technology that are culturally, economically, and socially suitable to the area in which they are implemented (Mihelcic et al., 2009). For example, one challenge to advancing renewable energy in small island developing states is determining the most appropriate implementation scale of waste-to-energy conversion technologies (UNEP, 2014c). It will also be important to understand how rapid increases in population and affluence in developing regions will impact the contribution and composition of global GHG emissions.

Moreover, a lot of urban energy use is associated with space heating and cooling and hot water provision, which can account for half of building energy consumption (UNEP, 2015). Researching ways to overcome technological and socioeconomic barriers in the implementation of urban district energy systems will be important for expanding and newly created cities to follow a development trajectory with lower carbon intensity. For example, district energy systems are appropriate because they are more climate resilient, more resource efficient, and have lower carbon intensity. They combine energy efficiency improvements with renewable energy integration; integrate the production and supply of heat and cooling with the provision of hot water and electricity; and emphasize the use of local resources and optimize energy efficiency (UNEP, 2015). Furthermore, energy efficiency measures are known to contribute to economic growth, social development, and improved public health. However, improved understanding is needed to determine the magnitude of these positive outcomes, their cultural acceptability, and how they are interrelated while also demonstrating how action on climate change will assist efforts to achieve goals of economic growth and sustainable development (UNEP, 2011; AfDB, 2012; World Bank, 2012).

Other carbon-containing air pollutants

In addition to carbon dioxide, combustion of fossil fuels results in the emission of other carbon-containing air pollutants, including particulate matter, carbon monoxide, and hazardous air pollutants. Concentrations of particulate matter are higher in countries with lower levels of development, and health burdens associated with ambient and indoor exposure to air pollutants are well documented (Smith, 1993; Bruce et al., 2000). In fact, the world's average PM₁₀ concentrations range from 26 to 208 μg/m³ by development region, with the higher values of this range reported in the Americas, sub-Saharan Africa, and Asia (WHO, 2015).

There is still, however, a lack of data on reported PM₁₀ (or PM_2.5) concentrations in many remote locations, especially sub-Saharan Africa (as well as other conventional air pollutants). Traditional fuel use and cultural preferences related to cooking, heating, and gender allocation of work are known to disproportionately expose women to indoor air with high levels of particulate matter, carbon monoxide, and hazardous air pollutants (Bruce et al., 2000). Furthermore, air emissions and the efficiency of traditional and new generations of household cookstove technology have been assessed (Jetter and Kariher, 2009); however, there is a need to better understand stove performance during the use phase and their overall contribution to climate change (Anenberg et al., 2013).

The energy ladder theory (Smith, 1993) predicts that household fuel type will improve as a household's social and economic statuses increase, resulting in less exposure to particulate matter. However, some families will use their newly acquired economic resources for other household needs instead of purchasing better fuel. Furthermore, as was discussed previously in the Integrate Rural to Urban Differences section, transitioning to different fuels may just redistribute the environmental risk from local populations to regional and global populations.

Measuring disease burden: risk assessment and disability-adjusted life years

Environmental health risks are the product of hazard and culturally influenced exposure. Historically, development and infrastructure improvements have altered ecosystems and created new industrial processes, resulting in the emergence of chemical and microbial hazards. Environmental professionals responded to this in the 1970s and 1980s by developing a risk assessment framework (NRC, 1983) and used it to establish regulations for reducing exposure to pollutants in the environment. For example, risk assessment was used in the United States to determine maximum contaminant levels (MCLs) for pollutants in drinking water. Many of these MCLs were determined based on a tolerable maximum probability of 1:10,000 to 1:1,000,000 that chronically exposed individuals would develop cancer in their lifetime; probabilities that were orders of magnitude lower than the background incidence of cancer in the United States at the time (Munro and Travis, 1986; Mara et al., 2010). However, many MCLs were developed in a postindustrialized setting with relatively low rates of communicable diseases and also during a time when society was developing concern about cancers caused by exposure to chemical pollutants.

Many developing countries have adopted an environmental risk management approach that is based on approaches that were developed for the United States or Europe (e.g., the use of MCLs for managing risk in drinking water). However, the overall health situation varies drastically for different geographical and cultural settings. In the 1990s, the WHO proposed a new measure for disease burden: the disability-adjusted life year (DALY), which incorporates the number of years of life lost due to early death and illness (Murray and Lopez, 1996). This measure helps visualize the extent to which a disease contributes to a region's overall health burden.

Figure 2 shows that in less developed regions, the composition of the disease burden is much different than it is in developed regions. Neglected tropical diseases, diarrheal diseases, malaria, tuberculosis, respiratory infections, and other communicable diseases cause a greater disease burden in developing regions than noncommunicable diseases (e.g., cancer, cardiovascular diseases, diabetes, endocrine diseases); the opposite is true for higher-income countries (Murray et al., 2012). In fact, lower respiratory infections and diarrheal diseases continue to cause the highest and second highest burdens of all diseases in the world, with >80% of this disease burden concentrated in low-income countries (WHO, 2008).

OPEN IN VIEWER

FIG. 2.

Contribution of communicable and infectious diseases to the overall disease burden in different global regions in 1990 and 2010 (includes neglected tropical diseases, diarrhea, lower respiratory infections, malaria, tuberculosis, HIV/AIDS, nutritional deficiencies, as well as neonatal and maternal disorders; does not include any other noncommunicable diseases; data from Murray et al., 2012). Note that the increases observed in Eastern Europe and Southern sub-Saharan Africa are primarily due to tuberculosis and/or HIV/AIDs.

The composition of the disease burden in developing and transitioning regions is also changing rapidly. As shown in Fig. 2, between 1990 and 2010, transitioning regions in Asia, North Africa, the Middle East, and Latin America have seen dramatic shifts in the composition of the overall disease burden. For example, in 1990, nearly half of the disease burden in these regions resulted from communicable diseases. By 2010, musculoskeletal disorders, injuries, mental and behavioral disorders, cancer, and cardiovascular diseases comprised a greater percentage of the overall health burden (Murray et al., 2012). This shift was not observed in less developed regions such as South Asia, Oceania, and sub-Saharan Africa, where the majority of the disease burden continues to originate from communicable diseases, neonatal disorders, and nutritional deficiencies (Murray et al., 2012).

Connecting development interventions with health outcomes

Environmental engineering is uniquely positioned to bridge the gap between sustainable development and health. However, while much previous effort has focused on controlling the adverse effects of environmental factors, protecting the environment from human activities, removing contaminants from air and water, managing waste, and preventing pollution (Mihelcic et al., 2003; AAEE, 2009), the outcomes of this work have not always been directly correlated with culturally appropriate and specific health outcomes. As the discipline transitions forward, environmental engineering will need to bridge this gap and evaluate health outcomes as was discussed for Grand Challenge 1. This has already been done on a broad scale; for example, WASH improvements have been associated with global health impacts (Prüss-Ustün et al., 2014). However, links between technology or culturally appropriate behavior-driven development interventions and health are not as well studied.

In one example, researchers estimated that implementing rainwater harvesting could reduce DALYs by 9% for urban dwellers in 37 West African cities, and if combined with point-of-use water treatment, the reduction could increase to 16% (Fry et al., 2010). In another example, despite the demonstrated effectiveness of solar water disinfection in the laboratory, researchers were unable to find strong evidence that the use of solar water disinfection in rural Bolivia significantly reduced rates of gastrointestinal illness (Mäusezahl et al., 2009). A third example from Malawi demonstrated that the increased prevalence of schistosomiasis resulted from changes in fishing techniques to increase yield, which drove snail-feeding fish into deeper waters, causing increased abundance of disease vector snails (Stauffer et al., 2006).

Finally, environmental enteropathy, an inflammation in the intestines that prevents the absorption of nutrients, can lead to child mortality, chronic malnutrition, and reduced cognitive development. It can occur in an infant or young child because of inadequate sanitation or hygiene that leads to pathogen exposure from the domestic environment, caretaker's body, drinking water, eating utensils, or even toys (Humphrey, 2009). Environmental enteropathy can be prevented by appropriate interventions in WASH, but further research on the causes and treatments of environmental enteropathy is still required (Humphrey, 2009). This type of research, which links technological and behavioral interventions with specific health outcomes, requires the integration of expertise across multiple disciplines, in this case, public health and social and environmental sciences.

Preventing the emergence of microbial hazards through ecosystem/infrastructure management

The strategies for controlling microbial hazards in developing regions can be quite complex. Many infectious diseases have emerged or spread as a result of structural anthropogenic changes made to ecosystems that have been facilitated or assessed by engineers (Table 3). For example, habitats have been altered to develop hydroelectricity and irrigated agriculture; however, this practice resulted in increased habitats for snail vectors of schistosomiasis in sub-Saharan Africa (Steinmann et al., 2006). Intensive food production and animal-feeding operations (intended to increase food security) have enabled pathogens to transfer hosts (from animals to humans) and created strains with increased antibiotic resistance (Graham et al., 2008).

In fact, many of the disease emergence mechanisms summarized in Table 3 are, in part, a result of development practices originally intended to increase food security and/or to eliminate poverty. This information points to a challenge of health consequences of environmental contamination, changing land use, infrastructure construction, habitat fragmentation, urbanization, and addressing demand for water, energy, and food, particularly when the cultural practices of those people most effected are not considered. Also important to consider is the role environmental engineering has in managing disease associated with pandemic viruses that may be found in the urban and agricultural water cycles (Wigginton et al., 2015).

Preventing the emergence of chemical hazards

Many chemical hazards have recently been introduced into developing regions due to globalization of the world economy (Faber, 2008). While the shifting disease burden in these transitional regions is partly explained by WASH improvements, increased affluence, and the fact that people are living longer, the emergence of new chemical contaminants may also be partially responsible for the shift in disease burden from one centered on microbial hazards and communicable diseases to one that is more centered on emerging chemical hazards. This may be partially responsible for the increased incidence of some cancers and endocrine diseases (Soto and Sonnenschein, 2010). The transition to a green economy (Grand Challenge 7) will require application of the principles of green chemistry (Anastas and Warner, 1998) to eliminate or reduce chemical hazards in developing regions.

Improving approaches to manage disease

Risk management approaches for developing regions should assess disease burdens and cultural constraints, not simply the probability of diseases. Collaborations with social scientists are needed to understand the distribution and stratification of disease burdens (e.g., how diseases affect genders or cultural/socioeconomic groups in different ways) and the ways in which history and traditions shape disease patterns. Risk management must also address gaps that may exist between risk perception and reality, understanding that community perceptions about disease may be strongly tied to cultural traditions and that there may be social and environmental consequences of the disconnects between perception and reality (Cairns, 2015; Whiteford and Vindrola, 2015b; Whiteford et al., 2016).

New molecular tools and techniques can help better understand the relationship between exposure and disease. For example, multiplex, lab-on-chip molecular assays allow for simultaneous detection of multiple pathogens (Tan et al., 2014) and multiplex immunoassays can detect antibodies in saliva (Griffin et al., 2011). These tools will enable researchers to understand which hazards people may have been recently exposed to, providing unique insights into the etiologic agents and vectors associated with disease transmission. Developments in this field could have important impacts, especially in developing regions and with respect to global outbreaks of infectious diseases (e.g., cholera, Ebola virus, Chagas, malaria). These new tools and techniques may allow for future validation of existing risk assessment models (a task that has been difficult in the past due to limitations of traditional epidemiology).

Quantification of water–energy nexus

Many studies have quantified the energy profile for large water and wastewater utilities in developed world settings (EPRI, 2002; U.S. DOE, 2006; Carlson and Walburger, 2007) or water demand for energy production (U.S. DOE, 2006; Pate et al., 2007; Tidwell et al., 2009). Fewer studies have explored these relationships in developing regions. As one example, the material and human energy required to produce, install, and operate four household-level and four community water source-level interventions was determined in Mali (Held et al., 2013). The systematic analysis of water–energy nexus is also lacking, especially in developing regions that will face more challenges in securing energy for water or water for energy. For example, the expansion of coal power plants in China and India has been determined unfeasible because greater than 50% are located in areas facing water scarcity (Rodriguez et al., 2013).

In the United States, ∼4% of electricity consumption is used for providing water and wastewater services (U.S. DOE, 2006; Stillwell et al., 2011) and about 41% of the total freshwater withdrawals are used for thermoelectric generation (Kenny et al., 2009). In Latin America, 30–40% of operational costs associated with water supply are from energy use (Rosas, 2011). This is thought to be from inefficient system design and operation, poor condition of the assets, low level of metering, reliance on groundwater, and complex topography that may serve low population density areas of service (WWAP, 2014). However, about one half of all countries in the world regard managing water resources for energy production as a low to medium priority.

In contrast, only about one third of low HDI countries value the use of water for energy production as a low to medium priority. The use of water resources for domestic water supply and agriculture is still ranked as the highest priority by majority of countries in the world and managing water resources for ecosystems and the environment is rated as a priority primarily by countries with very high HDI (UNEP, 2012).

Quantifying the water–energy nexus, however, is highly dependent on technologies, scale of implementation, and geographical context. For example, energy consumption for water treatment in developed regions ranges from 0.2 to 1.5 kWh/m³ water depending on technologies, and wastewater reuse is known to require less energy than more advanced technologies (Cornejo et al., 2014). Furthermore, it is challenging to define energy use by water sector; for example, the energy used for water distribution is estimated to account for 17% and 29% of the total electricity in small-scale and large-scale systems, respectively (Kumar and Karney, 2007) (similar difficulties exist to define water use by the energy sector).

Natural waste stabilization pond systems used for wastewater treatment throughout the world require negligible energy inputs (Cornejo et al., 2013) compared with 0.3–1.4 kWh/m³ water required for a typical activated sludge with nitrification process now employed in some developed regions (Lazarova et al., 2012). In contrast, household and small-scale water systems using principles of self-supply (Sutton, 2004; MacCarthy et al., 2013) and natural wastewater management technologies that take advantage of photosynthesis, gravity, solar disinfection, and natural assimilation/filtration capacities of land minimize energy use associated with mechanical energy and material inputs (Muga and Mihelcic, 2008).

Regarding the transportation fuels sector, much of the developed world has moved to more water-intensive fuels associated with hydraulic fracturing, biofuels, and hydroelectricity (WWAP, 2014), but it is unknown how this will progress in developing regions.

Integrated water and energy management

Water and energy management still operates primarily within individual sectors in most countries. The effectiveness of water management options to improve resource use efficiency and reduce environmental impacts is typically only examined on the water side. For example, water and wastewater utilities in developed regions typically consider energy management within the water sector (Table 4). However, energy professionals are not actively involved in water resource management in most global locations (Bowles and Henderson, 2012; Weinzierl and Schilling, 2013; Olmstead, 2014). As such, water and energy tend to be regulated separately in most contexts (Hussey and Pittock, 2012).

Due to the segmental management of water and energy, several issues have surfaced. Strategies in energy planning have resulted in some unintended consequences in water and food systems that need not be repeated as developing regions expand energy production. For example, biofuels can relieve the stress of fossil fuel demand, but they require a large amount of water in feedstock cultivation (e.g., 9,000–100,000 L/GJ for corn) and conversion process (e.g., 47–50 L/GJ for ethanol) while competing with domestic water use (World Economic Forum, 2011).

Even more importantly, biofuel production places pressure on food security because of its demand for food commodity feed stocks (i.e., corn, sugarcane, soy, canola, sunflower, palm oil). Land and water have also been competing priorities for measuring crop production efficiency; land has been the primary focus in agricultural sectors, although future priorities amid water scarcity may require a shift to water-based measures of efficiency (Davies et al., 2011). Furthermore, there is an alignment of food and energy prices because of their overdependence on fossil fuels (UNEP, 2011). Other linkages with food security occur because even though agriculture accounts for 70% of global water withdrawals, food production and its associated supply chain account for only 30% of global energy consumption (WWAP, 2014).

On the other hand, the options to address water shortages such as water transfer and seawater desalination require a considerable amount of energy that places stressors on the energy system and may not be applicable to all developing settings. Due to uncoordinated management, the solutions to one resource system may cause unintended consequences to another system. For example, some locations in Hunan province in China received electricity only every third day in March 2011 because of a rationing strategy in response to power shortages (Olsson, 2012). This caused the interruption of water services because treatment plants and pumping stations were also denied energy.

One analysis of integrated water management identified that data sharing across sectors is called for, but generally will not work without policy support to resolve administrative obstacles such as who will maintain the database, who will pay for it, and who will have access to the shared data (McDonnel, 2008). For example, water management models are typically applied to specific watersheds, requiring a high level of hydrological detail; however, the energy planning models typically deal with political boundaries and are concerned with siting and cost requirements. Reconciling the differences between water management and energy planning models will allow integrated water–energy policy analysis and address the shared needs of different stakeholders in both resource systems. Such a modeling framework should be flexible to allow tailored analyses with different levels of data requirements, different geographical and climatic conditions, and different political contexts so that it can be applied to developing regions.

Research is also needed on how reductions in water demand can be achieved by improvements in energy efficiency (and vice versa), especially in the geographical context of different regions and rural versus urban scales (Grand Challenge 2). There is also a need to develop nontechnological solutions that are applicable to the unique socioeconomic circumstances of developing communities and cities. Furthermore, it is critical to recognize the importance of the two distinctly different political economies of water and energy, especially because energy makes up a significantly larger global economic sector compared to water, which is more localized and smaller in terms of its economic impact. In addition, the rate at which new markets, technologies, and mechanisms of governance develop will differ between the two sectors. There is also a great need to develop pricing models that are not solely based on the market but also consider social, cultural, and distributional impacts (WWAP, 2014).

Immense opportunities also exist to study conflict and resolution as they relate to the water–energy nexus because in many developing regions, energy is currently viewed as a commodity, while water is viewed as a human right. With regard to gender inequities, in most parts of the world, women and girls are responsible for most of the daily work effort associated with managing water and energy (from obtaining water to collecting firewood for cooking). In fact, Held et al. (2013) found that women performed over 99% of the labor associated with seven of eight water supply and household treatment interventions. This discussion also points to opportunities to understand how gender is integrated into a wide variety of development initiatives (e.g., how women use and value the space around a water source, Van Houweling, 2015).

Anaerobic digester technology

Domestic and agricultural waste can also be an important source of energy. For example, ∼35 million household-scale digesters are estimated to be in service throughout the world (UNEP, 2010; Bruun et al., 2014), and China plans to install up to 80 million digesters by 2020 (NDC, 2007). Biogas is an alternative energy source to burning biomass, which is still used for 90% of household energy consumption in developing regions, causing environmental damage through deforestation and health risks from indoor air pollution (IEA, 2006; Surendra et al., 2014). A variety of common wastes can be used to produce biogas through anaerobic digestion: animal wastes, wastewater biosolids, latrine pit contents, and industrial wastes (Venkateswara Rao et al., 2010; Galvin, 2013; Kinyua et al., 2016). Nutrient and organic material associated with the digestate can be recovered and used as a fertilizer or soil amendment. In addition, anaerobic digestion can reduce the amount of GHG emissions that would otherwise be released from the disposal and burning of biomass for fuels and from chemical fertilizer production (Surendra et al., 2014).

However, many of these digesters are small (ranging from 2 to 10 m³) and single stage, being operated under semicontinuous loadings at mesophilic temperatures (between 20°C and 35°C) and under different feeding frequencies (Manser et al., 2015a), conditions that are not necessarily destructive to all human pathogens (Manser et al., 2015b). This has major implications for the safe reuse of potential resources found in the digestate and, importantly, points to the need to better understand the life cycle and fate of geographically relevant pathogens in resource recovery technologies integrated with on-site sanitation (Mehl et al., 2011), anaerobic digestion (Manser et al., 2015b), and wastewater treatment (Verbyla et al., 2013b; Verbyla and Mihelcic, 2015).

There are other nonhealth-related constraints of anaerobic digestion technologies that must be addressed to improve their efficiency, sustainability, and distribution in developing regions (Table 6). For example, it is estimated that only 60% of digesters in China were operating efficiently (Chen et al., 2010) with even lower values in other countries where biogas digesters are less common, such as sub-Saharan Africa (Bond and Templeton, 2011). Many of these digesters are distributed in a decentralized manner and operated by households and small farms. This provides challenges in understanding local cultures so that energy production can be matched to local demand as well as transfer of a technology that requires sophisticated training.

In addition, although biogas digesters can reduce GHG emissions when properly functioning, it is estimated that up to 40% of methane (CH₄) from biogas digesters may be lost due to leaks and direct releases (Bruun et al., 2014). Because methane is a powerful GHG, with a global warming potential 25 times greater than carbon dioxide, improperly operated biogas digesters may be contributing 1% of global GHG emissions, with a projected increase to 2% by 2020 (Bruun et al., 2014). Future emphasis on biogas technology should thus include improved maintenance of existing systems rather than construction (Chen et al., 2010), so the technology helps mitigate and not exacerbate GHG emissions (Bruun et al., 2014). A key component of this will be less expensive gas storage and better distribution to more effectively match gas production with demand because the largest contributor to biogas digester GHG emissions is thought to be the intentional release of excess biogas.

The high cost of anaerobic digestion systems is another major limiting factor in adoption. Environmental engineers also need to identify more affordable ways to recover methane from various wastes using low-cost, but durable, anaerobic digestion systems such as polyethylene tubular systems (Venkateswara Rao et al., 2010; Kinyua et al., 2016).

Reclaiming water

In addition to energy and nutrients, a great resource derived from wastewater is water. Reclaimed water, after site-specific treatment to minimize risk, could be better employed to irrigate and fertilize crops and thus contribute to food security in developing regions. This is important because 20–45 million hectares in the world are now irrigated with reclaimed wastewater (Sato et al., 2013) and approximately three-quarters of the world's irrigated area (192 million hectares) is located in developing regions. Complexing this issue is the unavailability of treatment capacity in many of these locations; that is, 1.5 billion people utilize wastewater collection systems that are not served by any treatment (Baum et al., 2013). Integrating wastewater collection and treatment with water and nutrient recovery, even in small community-managed systems (serving <1,000 residents), can significantly reduce eutrophication potential, embodied energy, and carbon footprint (Cornejo et al., 2013). Further issues to consider are that 87% of small farms are located in Asia and 8% in Africa and 90% of agriculture production in Africa occurs on farms of two hectares or less (UNEP, 2011).

There are also major gains to be made in the overall efficiency of water used for agriculture, which accounts for 70% of the world's water consumption (FAO, 2002). Particularly, it will be important to improve water efficiency of crop production (FAO, 2002). In fact, the future 30 years of improvements in crop production are expected to be from the blue revolution that will utilize new technologies and strategies (FAO, 2002), which may be more appropriate for a vast number of farms that currently depend on rain-fed agriculture. Environmental engineers may want to focus on improving yields of rain-fed agriculture, which accounts for 60% of the world's food and 95% of Africa's cropland (FAO, 2002). Another important component of food security will be the role that urban agriculture plays to improve food security as the shift of populations becomes even further urbanized. Finally, water scarcity will also impact our design and selection of sanitation technology. This is because there may not be sufficient water to operate sanitation technologies that convey waste in sewers and flush toilets, particularly for the 46 million people who live in areas of water scarcity (Fry et al., 2008).

Hygiene and nutrition

In addition to preventing the spread of infectious diseases, the provision of WASH services can also help ensure nutrient absorption from food, particularly in developing regions, where 791 million of the 805 million people estimated to be chronically undernourished reside (FAO, 2014). Of the four Food and Agriculture Organization (FAO) food security indicators, utilization (of nutrients), which includes access to improved water and sanitation, is thought to be the greatest challenge (FAO, 2014). However, existing health impact modeling used to estimate the impact of climate change on undernutrition does not account for nutrient utilization, but instead covers only crop productivity and access (WHO, 2014). Although much progress has been made toward achieving the first MDG of halving those suffering from hunger, incidences of stunting, micronutrient deficiencies, and underweight children remain high throughout developing regions, which may be attributed to diarrheal disease and environmental enteropathy (FAO, 2014; Ngure et al., 2014). It is thus not enough to provide adequate and nutritious food, but importantly sufficient WASH is also required so that food can be properly adsorbed by the human body, particularly in children ≤2 years of age.

For example, the promotion of handwashing (Naughton et al., 2015a) and the use of improved sanitation for those practicing open defecation have been recommended to prevent environmental enteropathy and diarrheal disease, although there is growing concern over children's exposure to fecal contaminants from animals and humans in their play areas (Ngure et al., 2014; Whiteford and Vindrola Padros, 2015a). Thus, environmental engineers, in collaboration with social scientists, will be needed to research the effectiveness of hygiene and sanitation interventions on health burdens caused not only by diarrheal disease but also by stunting and deficiencies in early childhood development. In fact, the concept of baby WASH has been proposed to address the concerns of environmental enteropathy and infectious diseases as an addition to early childhood development programs. This would provide barriers to the key animal and human fecal–oral vectors of hands and hand-to-mouth activity (Ngure et al., 2014).

Solid waste management

The global waste market is currently worth U.S. $410 billion/year (includes collection to recycling), excluding the informal sector (UNEP, 2011). The informal sector, if supported to end exploitation, can create economic well-being, conserve materials, and reduce pollution (Medina, 2000). Sorting and recycling solid waste also generate 10 times more jobs than landfilling or incineration on a per weight basis (UNEP, 2011). However, generation rates, discard rates, and waste composition differ greatly between rural and urban locations and between developed and developing regions (e.g., there is a greater percent of organics in developing waste streams) (Troschinetz and Mihelcic, 2009).

Also, waste composition is expected to change as a country develops or urbanizes, just as health burdens are expected to change. Furthermore, developing communities may seek options to manage waste at smaller scales. For example, factors designated as incentives to advance waste reduction already exist at the household level in some developing communities, specifically in regard to waste reduction and segregation practices, whereas some barriers exist at the national or regional levels, namely government policies and finances (Post and Mihelcic, 2010; Owens et al., 2011). Furthermore, development and demonstration of appropriate methods to safely dispose of municipal solid waste are desperately needed for small cities and towns (Oakley and Jimenez, 2012).

Opportunities and challenges in data collection

Inherent to advancing sustainable development are tasks related to monitoring, evaluation, and assessment of intervention effectiveness and improvements in health and environmental protection, as well as social and economic well-being. There are large opportunities to use satellite remote sensing and geographical information systems to assess and predict ecosystem responses to environmental change and support development activities in developing regions (Pettorelli et al., 2014; Naughton et al., 2015b).

Recent trends in monitoring, evaluation, and assessment have been toward the use of smart systems that leverage the near ubiquity of telecommunications. Remote sensing and mobile communication technologies are allowing individuals in developing regions to capture and analyze data in real time. In fact, the application of mobile communication technologies to research in developing regions has opened up many research opportunities; for example, determining how payment of water bills with mobile-enabled payment schemes impacts local corruption (Krolikowski, 2014) and how this technology may influence governance of water resources (Mongi et al., 2015). In addition to this machine-to-machine monitoring, there is also increased ability to capture and utilize information from the public through crowd sourcing. These technologies have increased the amount and detail of available data, which in turn lead to better learning and more informed decision-making.

Those working in this area need to partner with governments and other stakeholders to prioritize their objectives with regard to monitoring and evaluation. More importantly, environmental engineers should continue to develop new technologies so that the availability and easy adaption of off-the-shelf systems will allow countries to roll out national monitoring platforms at a lower overall cost. The savings from the development of these systems will allow governments to reallocate funds toward other activities and responsibilities that are often underfunded or do not receive any funding. These include activities related to regulation, governance, and capacity building of local government entities.

Even with advances in data-gathering techniques, one continuing challenge is the lack of sufficient and reliable data. For example, greater than 50% of countries with a low and medium HDI do not have a management system in place for assessing their water resources (UNEP, 2012). In terms of monitoring systems, countries also report problems with monitoring, often associated with inappropriate technology or the total absence of monitoring networks (UNEP, 2012). Water meters, which have been shown to be an effective economic instrument to change behavior, are still not used in most countries (UNEP, 2012). A survey of 181 countries also revealed that 126 did not have data on wastewater generation, treatment, and use (Sato et al., 2013).

The challenge also remains that monitoring data that are collected and analyzed (along with findings and recommendations) need to be accessible and presented in a format that is easy for all stakeholders to understand. Furthermore, a survey of the indicators currently used at the country level for monitoring and measuring the performance of water resources management suggested that development status does not constrain progress in improving water management. While countries reported having available up to 13 indicators to manage their water resource, they use a smaller number of indicators that would allow for more integrated management (e.g., governance [only 2 indicators], risk assessment [only 3 indicators], human health [only 4 indicators], food, agriculture, and rural livelihoods [only 4 indicators], and ecosystems [only 5 indicators]) (UNEP, 2012). There is also need for indicators that address on-the-ground cultural practices that influence demand and use of water and energy (Whiteford and Vindrola Padros, 2015b). Regarding the study of the water–energy nexus discussed previously (Grand Challenge 5), more aggregated data are available on energy than on water provision (WWAP, 2014).

With the passage of the SDGs, organizations and institutions are recognizing the importance of monitoring systems and the value added through coordinated monitoring efforts. In the field of water, wastewater, and ecosystem resources, the WHO and UNICEF created the Joint Monitoring Programme for Water Supply and Sanitation (JMP) and the Global Analysis and Assessment of Sanitation and Drinking Water (GLAAS). UN-Habitat will be developing a complementary tool that will capture data on ambient water quality, expanding on similar data captured under FAO's AQUASTAT. Overall, this GEMI initiative seeks to integrate existing efforts to ensure more harmonized monitoring of the entire water cycle (UN Water, 2016).

Life cycle assessment

In terms of assessing the environmental sustainability of new technologies or strategies, UNEP and Society of Environmental Toxicology and Chemistry (SETAC) have made the mission of their third phase of the Life Cycle Initiative (2015) to enable the global use of credible life cycle knowledge for more sustainable societies. However, there is still much research and knowledge dissemination required for application of LCA in developing regions.

LCA has been used only to a limited extent in developing regions; for example, in developing a tool to assess the sustainability of WASH projects (McConville and Mihelcic, 2007). It has also been used to determine the embodied material (and sometimes the embodied human energy) of community water supply and household treatment (Held et al., 2013), wastewater treatment integrated with resource recovery (Cornejo et al., 2014), types of household latrines (Galvin, 2013), and traditional and improved methods that support food and economic security (e.g., through the production of shea butter) production (Adams, 2015; Naughton, 2016).Thus, there are many research opportunities and applications to sustainable development particularly in environmental engineering to utilize LCA in developing regions.

Two major reasons LCA is used less in developing settings are because of the lack of both inventory and environmental measurement data as well as lack of institutional knowledge and expertise in LCA (Ahmed, 2012; Bjorn et al., 2013). For example, of 100 LCA networks identified by Bjorn et al. (2013), there were only two in Africa, including the African Life Cycle Assessment Network (ALCANET, 2011). Furthermore, none of the 13 life cycle impact assessments of timber products reviewed by Eshun et al. (2011) were developed for tropical areas such as Africa, but rather for developed regions where populations interact differently with their environment. In addition, an environmental impact quantified by LCA such as eutrophication may have a different meaning in a developing region, depending on the access to policy and technology strategies used or nutrient management.

Complexity of intersecting socioeconomic and environmental factors

Subsequent research has convincingly demonstrated that factors such as political interests, economic inequalities, social disparities, environmental legacies, and other structural dynamics both enable and constrain community agency (Welker, 2012). These factors combine in complex ways to condition the adoption and sustainability of new technologies (Wells et al., 2016). Moreover, the legitimate involvement of all stakeholders in decision-making processes is known to positively impact the successful implementation of sustainable solutions (Whiteford and Vindrola Padros, 2015a). Unfortunately, most countries, especially those with medium and low HDIs, are making slow progress in engaging stakeholders by providing them access to information, access to decision-making processes, or engaging the public in water resources management (Whiteford et al., 2016).

Africa is particularly notable for falling behind other regions in this regard (UNEP, 2012). Furthermore, Manser et al. (2015b) and Mehl et al. (2011) have demonstrated how engineered technologies now promoted for resource recovery objectives in developed regions in the northern hemisphere may not be sufficient to destroy harmful pathogens common to tropical locations. Users may also adopt such green technology for reasons that are not related to their environmental sustainability (Wilbur, 2014; Trimmer et al., 2016) (e.g., nuisance smells or the issue of flooding in a coastal area may be the drivers in adopting a composting or urine-diverting latrine). There is thus a need to build capacity for community agency to select context-sensitive adaptation strategies and culturally/geographically appropriate technologies with attention to the structural relationships surrounding communities.

One approach to understanding the complexity of intersecting socioeconomic and environmental factors that inform and are informed by local knowledge is to use complex systems modeling and simulation (Winz et al., 2009; Mirchi et al., 2012; Sharawat et al., 2014). However, some of these approaches have been criticized because they rely on cost–benefit (or trade-off) analyses that are based on the principle of maximizing efficiency (Cote and Nightingale, 2012; Andrei and Kennedy, 2013). In developed regions, for example, technology is embedded in the marketplace, which favors efficiency to reduce costs (and wastes) and increase benefits (and profits). Such ideals have influenced Western notions of sustainability, especially in the engineering sector (Bell et al., 2011; Grant et al., 2012; Wan Alwi et al., 2014).

However, in many developing regions, technological systems are often not driven by market forces alone, but instead are embedded in social institutions that operate on different values and principles (Jackson, 2006). For example, in some communities, the operation of water and sanitation systems may be organized through kinship relationships (Fleuret, 1985) or religious institutions (Lansing, 1987), neither of which necessarily makes decisions based on rational notions of efficiency (Orlove and Caton, 2010).

Importance of social science

Recognizing these differences, environmental engineers need to be aware that social science is making two important contributions to situating novel technologies in different cultural and geographic settings. First, by studying how and why people draw on social or moral values to guide decision-making, local perceptions of human–environmental phenomena can be understood. One example of this is the negative reactions at the idea of using resources derived from wastes, such as is often encountered with reclaimed or recycled water.

The social sciences can also help discern how to incorporate local perceptions of purity and pollution into understanding how people engage with waste reclamation technologies and products (Po et al., 2005; Whiteford and Whiteford, 2005; Nancarrow et al., 2008; Rodriguez et al., 2009; Russell and Lux, 2009; Mankad, 2012). Doing so can obviate the inherent problems in using behavioral incentives to encourage changes in practice, which often assume that people are lazy (and therefore require motivation), uninformed (and therefore require education), or self-interested (and therefore require a change in values). In many developing settings, individual choice—and the ability to carry out actions—is often constrained by structural conditions, including social obligation, access to resources, and local politics.

One solution to this challenge is for environmental engineers to incorporate tools such as those employed in social marketing. Social marketing is the application of marketing skills and tools for noncommercial purposes, such as changing perceptions and practices to enhance health status. When applied to the discipline of environmental engineering, this translates into social scientists incorporating ethnographic research methods (e.g., interviews and focus groups) and program evaluation to influence the voluntary behavior of the target population for the benefit of the public (Kotler and Zaltman, 1971; Andreasen, 1995, 2006; Brown, 1997; Lee and Kotler, 2011; Guang and Borges, 2012). This approach has proven especially useful in the context of recovering resources from wastewater (Johnson, 2003; Doria et al., 2009; Dolnicar et al., 2010; Dolnicar and Hurlimann, 2011; Kemp et al., 2012).

A second way in which the environmental engineering discipline needs to understand how social sciences can contribute to the sustainability of context-sensitive technologies is through basic research that results in enhanced understanding of social and cultural settings for technology deployment. The primary unit of development intervention is often the community, which is defined based on the residential proximity of households to one another (Conning and Kevane, 2002; Mansuri and Rao, 2004). However, social science research has shown that communities are not simple geographical constructs, but have multiple sociospatial and sociopolitical meanings to their residents (Israel et al., 1998). Moreover, these meanings can shift, sometimes significantly, depending on the stakeholder groups involved (Billgreen and Holmén, 2008). Water and sanitation systems and watershed and ecosystem management can thus cross multiple communities and be subject to larger institutional arrangements at multiple scales as well as imbalances in the distribution of resources (Linton, 2014; Linton and Budds, 2014; Whiteford et al., 2015a).

Such challenges of scale (Cash et al., 2006) sometimes lead to misunderstandings and miscommunications that can impede the sustainability of water systems (Marston, 2000; Norman et al., 2012; Haarstad, 2014). Social science research shows that communities should not be idealized as internally homogeneous and externally bounded entities. Instead, communities are historically changing networks of actors and institutions operating according to diverse motivations and desires (Wells et al., 2014). From this perspective, the contexts and conditions, as well as the social and spatial scales, in which people make decisions about resource use, can be revealed (MacKinnon, 2010).