*Article* **Determination of the Least Impactful Municipal Solid Waste Management Option in Harare, Zimbabwe**

**Trust Nhubu 1,\* and Edison Muzenda 1,2**


Received: 12 September 2019; Accepted: 12 October 2019; Published: 1 November 2019

**Abstract:** Six municipal solid waste management (MSWM) options (A1–A6) in Harare were developed and analyzed for their global warming, acidification, eutrophication and human health impact potentials using life cycle assessment methodology to determine the least impactful option in Harare. Study findings will aid the development of future MSWM systems in Harare. A1 and A2 considered the landfilling and incineration, respectively, of indiscriminately collected MSW with energy recovery and byproduct treatment. Source-separated biodegradables were anaerobically treated with the remaining non-biodegradable fraction being incinerated in A3 and landfilled in A4. A5 and A6 had the same processes as in A3 and A4, respectively, except the inclusion of the recovery of 20% of the recoverable materials. The life cycle stages considered were collection and transportation, materials recovery, anaerobic digestion, landfilling and incineration. A5 emerged as the best option. Materials recovery contributed to impact potential reductions across the four impact categories. Sensitivity analysis revealed that doubling materials recovery and increasing it to 28% under A5 resulted in zero eutrophication and acidification, respectively. Increasing material recovery to 24% and 26% under A6 leads to zero acidification and eutrophication, respectively. Zero global warming and human health impacts under A6 are realised at 6% and 9% materials recovery levels, respectively.

**Keywords:** municipal solid waste management; life cycle assessment; life cycle impacts; life cycle stages; eutrophication; global warming; human health; acidification; Harare; Zimbabwe

### **1. Introduction**

The annual global municipal solid waste (MSW) generation rate is projected to reach 2.2 billion metric tons per annum by 2025 from 1.3 billion metric tons per annum in 2012 [1]. Member countries of the Organization for Economic Co-operation and Development (OECD) however, are reporting a reduction in MSW generation [2]. Dramatic population increase in urban areas within Africa and Asia was singled out by the United Nations [3] as a typical phenomenon that leads to the astronomical increase in MSW generation. Standards of living, rapid urbanization, ever increasing population and obtaining economic environments in a given locality were cited as some of the factors that influence MSW generation [4–7]. Dongquing et al. [8] also cited the type and abundance of a region's natural resources apart from the above mentioned factors as a factor that influences MSW generation.

The best way to identify and manage solid waste streams is the fundamental environmental issue globally, both in industrialised and developing nations [9]. Global initiatives are supporting the prioritization of solid waste management (SWM) because it is viewed an important facet for the sustainable development of any country [10]. Sustainable development is the reduction of ecological footprints while improving quality of life for current and future generations within the earth's capacity limit [11]. UNDESA [12] Agenda 21 of the Rio Declaration on Environment and Development affirmed

the need for environmentally friendly waste management since it is an environmental issue of major concern in maintaining the quality of the earth's environment.

### *1.1. Solid Waste Management Dynamics in Developed Nations*

Solid waste (SW) mass production characterised human life since the formation of non-nomadic communities around 10,000 BC [13]. Seadon [14] argued that small communities could bury the SW they generated in environments surrounding their settlements or dispose it in rivers, which could not prevent the wide spread of diseases or foul odours from accumulated SW and filth emanating from increased population densities that characterised the formation of non-nomadic communities. Exceptional cases on waste management existed Worrell and Vesilind [13] reported that by 200 BC, organised (SWM) systems had been under implementation in Mohenjo–Daro, an ancient Indus Valley metropolis, and the Chinese had established disposal police to enforce waste disposal laws. Melosi [15] also reported that by 500 BC, the Greeks had issued a decree that banned the disposal of waste in streets and organised first accepted MSW dumps in the Western world.

Middle Ages' city streets were characterised by odorous mud with stagnant water, soil, household waste and excreta from both humans and animals creating favorable conditions for disease vectors [16]. Therefore, the disposal of biodegradable or organic waste in streets is argued to have partly contributed to the Black Death of the 1300s that occurred in Europe [13,16,17]. Developments in SWM in developed nations were and are initiated to address environmental, land use, natural resources depletion, human health, climate change, waste value, aesthetic, economic, public information and participation issues associated with improper waste disposal [13,16,18–20]. SWM has evolved in developed nations driven by historical forces and mechanisms which can possibly inform the development of SWM strategies in developing nations [20]. Marshall and Farahbakhsh [21] noted five drivers for integrated SWM paradigm in developed nations, namely the environment, climate change, resource scarcity, public health and public awareness and participation.

Public health concerns remain a driver of SWM transformation in the developed world characterised with continued review of public health legislation. The need to reduce land, air and water contamination [20,22] was a primary driver of policy changes in SWM development in the 1970s and beyond [20]. Waste control characterised the SWM policy framework between the 1970s and mid-1980s focusing on daily landfill compacting and covering and incinerator retrofitting for dust control. The SWM policies enacted from the 1980s to date focus on increasing technical standards, starting with control of landfill leachate and gas, reduction of incinerator flue gas and dioxin and the current span covering control of odour at composting and anaerobic digestion (AD) facilities [20]. The last decade of the 20th century saw the increased focus and attention towards the adoption of integrative policy due to the inadequacies of advocating for continued increase in environmental protection only from both the technical (engineering and scientific) and environmental perspective without considering the political, economic, social, cultural and institutional dimensions of SWM [20,23,24]. The waste hierarchy upon which the European Union (EU) current policy on waste is based reignited materials recycling and reuse of the 19th century in the 1970s [20,25] in light of the increasing scarcity of resources. The EU's Second Environment Action Programme of 1977 introduced the waste hierarchy model for SWM priorities derived from the "Ladder of Lansik" [26].

Climate change has also driven the development of SWM from the early 1990s to address greenhouse gas (GHG) emissions from biodegradable waste landfilling, a major contributor of methane gas emissions, complimented with a strong focus on the recovery of energy from SW [20,22]. The concerns by the public on poor SWM practices with their increased awareness have also contributed in driving the developments in SWM [20]. The public became concerned with the location of SWM facilities in the vicinity of their households, 'not in my backyard' (NIMBY), though they appreciate the need of SWM facilities. Therefore, effective communication, wide public knowledge of SWM needs, the active engagement of all stakeholders during the entire SWM cycle have been successful in overcoming NIMBY public behavior and opposition to numerous developmental projects [27] thereby acting as drivers for developments in SWM [21].

### *1.2. Solid Waste Management Dynamics in Developing Nations*

Despite the increase in waste generation, global call and acceptance that waste management must take an integrated approach to derive economic benefits while reducing environmental burdens, Africa is still lagging in this regard. This lag is also being witnessed despite the reported increased globalization as poor SWM challenges and their associated public health impacts are affecting urban environments in many developing nations [22,28,29] one and a half centuries after the sanitary revolution in the EU [30]. Unlike developed nations that are concerned with diseases associated with affluence (cancer, cardiovascular disease, alcohol and drug abuse), poor SWM derived public health impacts in developing nations are evidently manifesting in the form of communicable diseases giving the double headache of dealing with both communicable diseases and emerging diseases of affluence [30]. Public health mostly drives SWM development in developing nations, though other factors as in developed nations are considered because the key priority is waste collection and removal from population centres as it was in European and American cities before the 1960s [20,31–33]. Wilson [20] noted that environmental protection remained relatively low on the SWM priorities despite the presence of legislation prohibiting unregulated waste disposal with minor changes towards its prioritization taking place. The value of waste as a resource is also another vital driver within developing nations currently providing livelihoods to the urban poor through informal recycling [20,22]. Climate change is a significant driver globally with a number of nations having incorporated the municipal solid waste (MSW) sector amongst the sectors considered for low-emission development strategies (LEDs) on the national emission reduction commitments or targets within the nationally determined contributions (NDCs) framework of the Paris agreement under the United Nations Framework on Climate Change Convention (UNFCCC).

A number of similarities do exist between the current conditions characterizing many cities in developing nations and those experienced in European and American cities during the 19th century with regards to increased urbanisation levels, degraded sanitary environment emanating from lack of adequate sanitation and environmental services, inequalities and social exclusions in SWM systems, unprecedented mortality and morbidity levels due to inadequate sanitation, potable water supply and waste disposal services [30]. Thus, developing nations are likely to go through almost similar SWM development pathways as those developed nations went through. However, Marshall and Farahbakhsh [21] argued that despite these similarities, complex local-level-specific technical, political, social, economic and environmental challenges in developing nations have been created from rapid urbanization, increasing population, the fight for economic growth, institutional, governance and authority issues, international influences, along with their interaction with diverse economic, cultural, political and social dynamics which are bringing associated SWM complexities in developing nations.

In developing countries therefore, SWM is complicated by levels of urbanization, economic growth and inequality as well as socio-economic dimensions, governance, policy and institutional issues coupled with international interferences [21] which limit the application of SWM approaches that succeeded in SWM development pathways for developed nations. The understanding of the origins and critical drivers in the past developments in SWM in developed nations provides contextual knowledge on the current changes occurring in developing nations. Simelane and Mohee [34] identified African social norms with their associated concerns including economic and environmental issues, national and regional legislative deficiencies, technological and human resources developments and historical influences among other factors necessitating this lag. Iriruaga [35], on another note, cited low private investment in infrastructure, industry linkages and academic research as the drivers of Africa's inability to effectively derive benefits from the waste it generates. Muzenda et al. [36] identified the increased demand for SWM provision, MSW minimization, and recovery of materials for reuse and recycle, constraining factors including physical, land use and environmental constraints, as

well as demographic and socio-economic factors as the core drivers for the need of integrated waste management (IWM) techniques.

MSW generation and its disposal are causing enormous environmental and human health challenges in urban environments of developing countries [37–39]. It is considered hazardous and to have toxic impacts on the biological environment, thereby affecting lifestyles and economic activities [40]. This, therefore, calls for the need to sustainably manage waste to reduce its impact in the ecosystem and human health [41]. The need to design and develop integrated waste management (IWM) options that seeks to meet the economic, technical, environmental and social constraints of products or production processes has become paramount and urgent. McDougall et al. [42] defined IWM as a combination of technically sound, economically feasible, environmentally sustainable and socially acceptable collection and treatment processes that handle materials constituting MSW.

### *1.3. Municipal Solid Waste Management in Zimbabwe*

Like many developing countries facing enormous MSW generation and disposal associated environmental and human health challenges in urban environments, the Government of Zimbabwe acknowledged that its urban local authorities (city municipalities, town councils, district councils and local boards) are experiencing major challenges in managing MSW due to rapid population growth. Most of Zimbabwe's local authorities fail to cope with the ever increasing volumes of waste being generated by the public [43]. Several studies have also affirmed that municipal solid waste management (MSWM) is one of the greatest challenges facing urban environments in Zimbabwe [41,44–53]. In Zimbabwe, about 60% of the MSW generated in urban environments is disposed at official dumpsites with the remaining waste being dumped illegally in undesignated areas namely storm water drains, open spaces, alleys and road verges [45]. The dumping of waste in open and illegal dumpsites is not only an eyesore but creates an environment where disease causing vectors can thrive, contribute to air, soil and water pollution and emit greenhouse gases that cause global warming [43].

MSW problems in Harare specifically are evidently manifesting in the form of both surface and groundwater pollution due to the dumping of MSW in waterways and untreated leachate from dumpsites. The storage capacity of the sole official MSW dumpsite in Harare is expected to reach its limit in the next five years [54]. This calls for the need to redefine future MSWM options as well as redefining the models of operating the MSWM facilities considering biogas recovery for electricity generation as well as the production of saleable products from MSW. To date no or few studies have been carried out focusing on determining the most probable integrated MSWM option with the least environmental impacts for Harare. Such study results could possibly inform future decisions and policies on MSWM considering the increasing population, changing lifestyles, global pressure for the need for sustainable cities, the impacts the current MSWM practices have on both the environment and human health as well as the imminent closure of the existing dumpsite whose service life is anticipated to come to an end in 2020. This study, therefore, is a life cycle-based comparative assessment of the various probable MSWM scenarios to be implemented in Harare. The study seeks to identify the scenario with the least burden with regards to human health, acidification, eutrophication and global warming impact categories.

### *1.4. Life Cycle Assessment*

Life cycle assessment (LCA) is a tool that could be used in the design and development of IWM options. LCA holistically quantifies the environmental burdens and impacts for entire products' or processes' life cycles [55]. Winkler and Bilitewski [56] described LCA as a science-based impact assessment methodology for the impacts of a product or system on the environment, which is not purely a scientific tool. LCA application in sustainable MSWM started over two decades ago, as argued by Güereca et al. [57] that it has been applied for MSWM since 1995. The use of LCA for decision making and strategy development in MSWM systems has expanded rapidly over the recent past years as a tool with the capacity to capture and address complexities and interdependencies characterizing

modern IWM systems [58]. Mendes et al. [59] noted the appropriateness of LCA application as a tool for decision making and strategy development in MSWM because of the associated wide differences in spatial locations, waste composition and characteristics, sources of energy, waste disposal options available as well as available nature and size of products from various waste treatment methods. Therefore LCA has emerged as an appropriate holistic method increasingly being applied in MSWM decision making and strategy development processes [60].

LCA has been previously applied to assess the associated impacts of MSWM systems thereby assisting in comparing alternative MSWM systems and/or identifying areas of major concerns that need potential improvements [61]. It has been applied to identify and probe likely negative impacts of various MSWM practices [62] because it is capable of calculating and comparing impacts of different MSWM scenarios [63]. It incorporates environmental impact weighing or valuation to estimate the performance of a specific MSWM scenario [62]. The intensification of MSWM policies in Europe and global call for the implementation of LCA methodology ISO 14044: 2006 standards have resulted in a positive trend towards the adoption of life cycle studies on MSWM [64]. To date, numerous studies have been undertaken worldwide applying LCA to the different MSW life cycle stages that cover the entire life cycle of MSW [60,62–66]. Khandelwal et al. [64] reviewed 153 studies that applied LCA on MSWM, undertaken globally and published between 2013 and 2018. The distribution of the selected LCA studies reviewed by continents showed that 72 were in Asia, 53 in Europe, 10 in North America, 9 in South America, 3 in America, 2 in Africa, 2 addressed generic cities assuming MSW generation, characteristics and associated environmental emissions together with other remaining studies that focused on at least one country. Very few life cycle studies on MSWM were found in Africa and poor LCA methodology penetration in Africa was cited as the cause of the limited LCA studies on MSW. The only two LCA studies found for Africa were done in Nigeria.

### **2. Materials and Methods**

### *2.1. Description of the Study Area*

The study area comprises of Harare (the capital city of Zimbabwe), Chitungwiza, Norton, Ruwa and Epworth local boards with an estimated total population of 2,133,802 people, as shown in Table 1. Harare urban, Chitungwiza and Epworth local boards are located within Harare metropolitan province while Ruwa and Norton local boards are located in Mashonaland East and West respectively, as illustrated in Figure 1. An estimated 60% of the MSW generated in the study area is indiscriminately disposed at official dumpsites, except for Norton, whose MSW is disposed in an engineered sanitary landfill. The remaining 40% of the MSW is illegally dumped in undesignated areas, namely storm water drains, open spaces, alleys and road verges [45]. The capacity of the sole official dumpsite for Harare city, Pomona dumpsite, which covers an estimated area of 100 hectares having been operational since 1985 is expected to be exhausted by 2020 [54].


**Table 1.** Population figures for the study area [67].

One unique feature of the study area is that it sits on the water catchment that drains into water reservoirs (Lake Chivero and Manyame) that supply the study area with potable water as shown in Figure 1. MSW problems in the study area are evidently manifesting in the form of both surface and groundwater pollution. Lake Chivero has been reported to have reached super eutrophic levels partly due to the deposition of MSW which constitutes in excess of biodegradable waste laden in runoff. The

underground water in the study area has also been reported to have been compromised from untreated leachate from dumpsites [52].

**Figure 1.** Location of the study area.

### *2.2. Definition of MSW*

Definitions of MSW vary within countries and between countries and regions making it difficult and confusing to estimate MSW generation in various countries [68]. The variations in definitions bring along challenges and difficulties in LCA studies. Therefore for the purpose of this study, MSW is regarded as the waste that is managed by or on behalf of municipalities as a public service [69] comprising waste generated at households, offices, supermarkets and restaurants. Consequently, in Zimbabwe, local authorities are mandated to manage such MSW [70].

### *2.3. Quantity of MSW Generated in Harare and Its Dormitory Towns*

The MSW annual generation for a given locality, communities, cities or countries, is a core indicator of the pressure exerted by MSW on the environment. It is useful for LCA when the annual generation of MSW is considered the functional unit. Obtaining reliable data on estimates and characteristics of MSW generated in developing countries is a challenge due to incomplete data, lack of equipment like weighbridges, rural to urban migration and low efficiency rates of MSW collection [71]. The development of initiatives that derive benefits from the promotion of sustainable use and management of MSW is hindered by the low availability and quality of data regarding MSW generation and management [34]. In Harare, Zimbabwe, quality and reliable MSW data on waste generation, characteristics and composition necessary for LCA that could inform effective planning for sustainable MSWM are unavailable. In addition the unreliable data available are only from official records of MSW collected and delivered at the official dump site. This MSW data does not capture much of the MSW managed outside the dumpsite management process that would have been generated at various sources [72]. Afon [72] further observed enormous variations of MSW generation on temporal scales (weekday, week of month and month of year) across localities highlighting the need

for longitudinal collection of MSW generation data measurements over a year at sampled households according to their life styles and levels of income if resources and time permit to acquire reliable MSW data. In this study literature data was considered for the estimation of the annual MSW generation for Harare using literature reported per capita MSW generation figures.

Therefore the average per capita MSW generation rate of 0.6 kg/capita/day (0.5 kg/capita/ day [52,73,74], 0.65 kg/capita/day [1,75] and 0.7 kg/capita/day [76]) was considered for the study. The average figure of 0.6 kg/capita per day, though slightly on the higher side of observed figures of 0.42 ± 0.15 kg/capita/day MSW generation in Zimbabwe by Muchandiona et al. [52], it is a reasonable estimate when considering other reported figures from literature. Miezah et al. [77] reported Ghana's daily MSW generation of 12,710 tons considering a daily per capita waste generation rate of 0.47 kg and a population of 27,043,093. Harare and its dormitory towns have a population of 2,133,802 translating to daily and annual MSW generation of 1280 and 467,303 tons, respectively, as shown in Table 2. Due to uncertainties on population data serviced with MSW collection, MSW data normalisation was assumed to have been enabled in the calculations of the per capita waste generation rate datasets that were used to calculate the daily average per capita (0.6 kg) MSW generation for this study to factor in the effects of population changes as proposed by the European Environment Agency [78].


