Municipal Solid Waste Disposal Operational Performance in Wa Municipality, Ghana

Background. The generation and management of solid waste pose potential adverse impacts on human health and the environment. Objective. The present study examines the operational performance of municipal solid waste (MSW) disposal in the Wa Municipality, Ghana. Methods. The study applied both qualitative and quantitative research methods and modelled the Wa Municipality's MSW disposal system using the municipal solid waste decision support tool (MSW DST). Acid gases (sulphur oxides and nitrogen oxides) and total particulate matter that have a direct impact on human health were set as the objective functions for modelling five MSW disposal scenarios. The modelled scenarios were: 1) landfill disposal only; 2) composting and landfill disposal; 3) composting, incineration, refuse derived fuels (RDF) and landfill disposal; 4) separation, composting, incineration, RDF and landfill disposal; and 5) separation, transfer, material recovery, composting, incineration, RDF and landfill disposal. The pollutants chosen as indicators for substance flow analysis included lead, cadmium, arsenic, mercury, copper, chromium, and zinc. Results. Scenarios 4 and 5 produced the least engineering cost of 1 150 000 US $/year for the entire MSW disposal system, whereas scenario 2 produced the highest cost of 1 340 000 US $/year. Scenario 5 produced the least average health impacts of −5.812E-04 lbs/year, while scenario 2 generated the highest engineering cost and produced the highest average health impact of 9.358E-05 lbs/year. Scenarios 5 and 4, which included waste-to-energy conversion in the systems, produced the lowest average health impacts (−5.812E-04 lbs/year and −5.611E-04 lbs/year, respectively). Conclusions. The adoption of an integrated solid waste management concept, including waste-to-energy technologies, will not only help to lessen MSW disposal hazards, but also to produce alternative sources of energy for Ghana and other developing countries. Competing Interests. The authors declare no competing financial interests


Introduction
A number of serious and highly publicized pollution incidents associated with improper waste management practices have led to public concern about the lack of controls, inadequate legislation, and environmental and human health impacts. 1 A waste management hierarchy plan based on the most environmentally sound criteria favors waste prevention/minimization, waste reuse, recycling, and composting. [2][3][4] Despite important technological advancements, including improved legislation and regulatory systems in the field of waste management and more sophisticated health surveillance, the public acceptance of locating waste disposal and treatment facilities in close proximity to human populations is still very low due to concerns about adverse health and environmental effects. 1 Health issues are associated with every step of the handling, treatment, and disposal of waste, both directly (through recovery and recycling activities or other occupations in the waste management industry, by exposure to hazardous substances in the waste, or to emissions from incinerators and landfill sites, vermin, odors and noise), or indirectly (through ingestion of contaminated water, soil, and food). 1,5, 6 The health impacts of solid waste are varied and may depend on numerous factors including the nature of the waste, duration of exposure, population exposed, and availability of prevention and mitigation interventions. 7 Impacts may range from mild psychological effects to severe morbidity, disability, or death. Nevertheless, the literature on the health impacts of solid waste remains limited and inconclusive and there is no clear evidence of adverse health outcomes for the general population Research from waste management, despite widespread concern over the health impacts of landfills. 1,8,9,10 Studies on health impacts from landfills show that living near a waste site is associated with adverse health effects, ranging from allergies to cancer and birth defects. 11 Similarly, Giusti 1 indicates that there is convincing evidence of a high risk of gastrointestinal problems associated with pathogens originating at waste treatment plants. 1 In general, environmental pressures from the generation and management of solid waste include emissions into the air, water and soil, and pose potential impacts on human health and the environment. 11, 12 Thus, environmental policies and strategic measures are required to reduce waste emission and improve waste management practices. 13 Consequently, the foundation of modern waste management is a combination of regulation, design, construction, operation, maintenance, and monitoring features to create an inter-dependent, overlapping system to protect human health and the environment. 14-17

Baseline Scenario in Wa Municipality, Ghana
The most commonly practiced municipal solid waste (MSW) disposal option in the Wa Municipality and the whole of Ghana (as in many other developing countries) involves the collection of mixed waste materials and subsequent dumping at designated sites.
In the Wa Municipality, all of the collected solid waste from residential and commercial areas, institutions, and streets are carried to a dumping ground (Figure 1) at Siriyiri. Siriyiri is located in a separate district -the Wa West District. The Siriyiri disposal site was created in 2001 and has been poorly managed, without any formal material recovery, however, some informal material recovery is undertaken by scavengers (informal waste collectors).  Figure 2 illustrates the MSW flow in the Wa Municipality.
The Siriyiri disposal site is characterized by a low-lying area with a borehole located 300 m away from the disposal site without any precautionary measures. Both liquid (human excreta) and solid wastes are disposed of in the same dumping site ( Figure 3). The borehole water was not tested to determine its quality, although there is high potential for contamination by leachate from the disposal site. The manager of the disposal site reported that the Siriyiri community has protested the location of the disposal site on several occasions, to no avail, and that it represents a breach of environmental justice.

Research
The MSW DST was adopted for this study as it can evaluate various MSW management options and optimizes their environmental burdens, is applicable to both small and large waste management systems, and the developers of the tool allowed it to be used free of charge for the present study.

Methods
The evaluation of MSW disposal operational performance in the Wa Municipality, Ghana was based on the formulation, construction, optimization and scenario analysis of five modelled MSW disposal options through the combination of material flow analysis and substance flow analysis. The data was obtained from both primary and secondary sources, using qualitative and quantitative research methods. The primary data was obtained through passive observation of MSW disposal activities in the Wa Municipality, and the secondary data was obtained through reviewing official reports and journal publications.
Five (5) MSW disposal scenarios, reflecting different MSW disposal systems, were modelled and compared using the MSW DST based on their ability to improve the current situation of MSW disposal in the Wa Municipality. Since the scenarios were assumed not to influence MSW generation, the same amounts and composition of MSW were used in all 5 scenarios. Additionally, the acid gases (sulphur oxides (SOx), nitrogen oxides (NOx)) and total particulate matter (TPM) that have a direct impact on human health were chosen as the objective functions for optimization in the five scenarios.
Nitrogen oxides plays a major role in several environmental and health effects. Breathing air with a high concentration of NOx can irritate airways in the human respiratory system, and exposures of even short duration can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms (such as coughing, wheezing or difficulty in breathing). 19 Similarly, exposure to SO X in ambient air has been associated with reduced lung function, increased incidence of respiratory symptoms and diseases, irritation of the eyes, nose, and throat, and premature mortality. 20 Particulate matter also poses a threat to human health. Tiny particles usually less than 10 micrometers in diameter pose a risk, as they can easily enter human lungs, and possibly enter the bloodstream. 21 For the substance flow analysis, lead, cadmium, arsenic, mercury, copper, chromium, and zinc were chosen as indicators (pollutants) for all five scenarios. The health impacts of these pollutants, assessed through the objective functions of the modelling (NOx and SO X and TPM), were categorized as cancer air, cancer water, non-cancer air, and non-cancer water health impacts.

Conceptual model formulation of the scenario analysis
The MSW disposal system modelled was the Wa Municipality's MSW disposal system. The processes that were modelled included waste generation, collection, transfer, separation (material recovery), composting, combustion, refusederived fuels (RDF), and disposal in a landfill. Five MSW disposal scenarios were formulated, built and analyzed based on uncertainty and sensitivity analysis with the objective of minimizing environmental burdens.
The optimization module of the MSW DST is implemented using CPLEX linear programming solver and is constrained by mass flow equations based on the quantity and composition of waste entering each unit process in the waste management system (i.e., collection, recycling, treatment, and disposal options).
The optimization module uses linear programming techniques to determine the optimum solution consistent with the specified objective, constraints, and mass flow.
The MSW DST modelling process consists of four basic components: process models, waste flow model, optimization model, and a graphic user interface. The process models consist of a set of spreadsheets developed in Microsoft Excel. These spreadsheets use a combination of default and user-supplied data to calculate the cost and life cycle inventory, with the coefficients on a per unit mass basis for the MSW components being modelled for each SW management unit process (collection, transfer, treatment, and disposal). There are a total of eight steps, but five steps are required to complete modelling a scenario.
These steps are presented in Table 1.

Research
Additionally, the following (seven) substances were chosen as indicators for the substance flow analysis: lead, cadmium, arsenic, mercury, copper, chromium, and zinc.
Lead, copper, zinc, arsenic, and chromium in landfills and leachates determines the long-term rehabilitation of the environment. 22, 23 These compounds affect air, surface and groundwater qualities, as well as pose a threat to human health, as some can cause mild mental retardation and cardiovascular diseases. 24-27 Cadmium, mercury, and lead are also indicators for the presence of toxic metals in the atmosphere. 23 Five scenarios were conducted to determine the optimal MSW disposal system based on low engineering costs and minimal environmental burdens. The aim of the modelling and optimization using the MSW DST is to increase decision-makers' awareness with the results of this research in order to reduce the undesirable environmental effects of MSW disposal in the future. Therefore, the results were analyzed on an inventory of stressors by the health impact category of the modelled scenarios.

Functional unit
The functional unit was chosen as the average amount of municipal generated waste in the Wa Municipality per day in the residential sectors based on the residential typology/income level (compoundhouse/low-income, semi-detached/ middle-income, and single-unit/highincome residential dwellings) and one commercial generation sector (the Wa market).
The daily waste generation of Wa (average daily generation of 0.25 kg/ capita/day and 32 ton/day based on the 2017 population projection of 128 873) 28 and household MSW composition and chemical properties in Ghana were considered as the input of the residential sector, as illustrated in Table 2 and 3, respectively. The commercial sector input included the Wa market average daily waste generation of 0.23 kg/day and MSW composition, as shown in Table 4. Thus, the modelled systems consisted of inputs from the residential and commercial sectors.

Limitations of the scenario analysis
The researchers acknowledge key assumptions and limitations of the present analysis. Studies to characterize the quantity and composition of MSW are often cited as a key factor in selecting waste management processes. 33, 34 The present study applied Ghana and Wa Municipality waste characterization data available in the literature in the modelling and analysis, but could not determine the data quality. The modelling relied on some default data in the model because of the nonavailability of some site-specific data from Ghana and Wa Municipality. The MSW DST does not include models for all possible waste disposal technologies. Therefore, anaerobic digestion and new or emerging technologies, such as waste gasification and pyrolysis were not considered. The study did not place a limit on the amount of waste that any process can accept. In practice, facilities are designed to handle a certain minimum or maximum capacity of waste and, therefore, would be limited in the amount of waste they could process.

Results
The present study identified a number of shortcomings in the Wa

Scenario 1 -Landfill disposal only
Sanitary landfilling is the recommended MSW disposal option for most developing countries and is the desired disposal system in Ghana.
For this scenario, all mixed MSW was collected and disposed of in a sanitary landfill and the human impact categories evaluated to determine the environmental impacts.
The optimal solutions found for NO X , SO X , and TPM as the optimizing objectives for scenario 1 were 5970, 1890, and 358 lbs/year, respectively, and the engineering cost for the entire system was 1 210 000 US $/year. There was no change in the mass flow for all three optimizing objectives, as a total mass flow of 5250 metric tons/year was disposed of in the landfill. Figure  4 shows the mass flow of waste for scenario 1.
The values of the chosen pollutants (lead, cadmium, arsenic, mercury, copper, chromium, and zinc) and their impact categories are presented in Table 5

Scenario 2 -Composting and landfill disposal
Composting and sanitary landfilling are the two most commonly recommended waste management options for the organic waste fraction,   is illustrated in Figure 6.   Research 568 metric tons residue, which was disposed of in a landfill.

Table 3 -Chemical Composition of Household Wastes in Ghana
Similarly, with SO X as the optimizing objective, 558 metric tons/year of pre-sorted recyclables were taken to a recycling plant and 4700 metric tons/year of MSW were sent to a RDF facility to produce pellets. The RDF process produced a residue of 1080 ton of ash, which was disposed of in a landfill.
For the TPM as an optimizing objective, 890 metric tons/year of recyclables were sorted from the total 5250 metric tons/year of MSW and 4360 metric tons/year of MSW was taken to a mixed combustion facility for waste-to-energy (WTE) conversion. The combustion process produced 716 metric tons/year of ashes which were disposed of in a landfill. The mass flows of the waste for scenario 4 are shown in Figure 7.
The optimal engineering cost for scenario 4 was 1 150 000 US $/year, which is lower than the engineering cost for scenarios 1, 2, and 3. Optimizing objectives SO X and TPM had negative optimal solutions, -19800 and -4520 lbs/year, respectively, while objective function NO X had a positive lower optimal solution of 71.7 lbs/ year, which is far lower than the NO X optimal solution for scenario 1 (5970 lbs/year).

Discussion
The results showed that MSW disposal into a sanitary landfill alone does not optimize the minimization of health impacts (NO X , SO X and TPM) compared to MSW disposal in an integrated solid waste management (ISWM) system as shown in Figure 9. This is because local environmental pollution is common in landfills due to the decomposition of waste into constituent chemicals. 35   In terms of the engineering cost, scenarios 4 and 5 produced the lowest engineering cost of 1,150,000 US $/ year for the entire MSW disposal system, whereas scenario 2 produced the highest cost of 1,340,000 US $/year, as indicated in Figure 10.
In terms of health effects, scenario 5 produced the least average health impacts of -5.812E-04 lbs/year, while scenario 2 generated the highest engineering costs and produced the highest average health impact of 9.358E-05 lbs/year, as illustrated in Figure 11. Scenarios 4 and 5, which included WTE conversion in an ISWM system format, produced the lowest average health impacts (-5.611E-04 lbs/year and 5.812E-04 lbs/year respectively) and the lowest engineering costs.  Research countries, such as Japan, for decades in an effort to promote sustainable development initiatives. 41, 45 Wasteto-energy technologies such as incineration not only reduce the quantities of MSW, but can provide alternative sources of energy. Therefore, the implementation of WTE technologies (on small or largescales) in developing countries such as Ghana is inevitable in the future, as WTE technologies can contribute to the reduction of the current highpower deficit affecting economic development in many developing countries.
Many researchers observe that composting (a component of scenario 2) is the cornerstone of sustainable development in the waste sector, and suggest that composting should be a widespread practice in developing countries, because it can be implemented in small and large scales. 46-49 However, large and centralized composting plants are often not economical, due to high operational, maintenance, and transportation costs in developing countries. 44 The viability of commercial composting is usually dependent on the availability of a ready market for the final composted product. Subsistence farming is still widely practiced in most developing countries, with farmers depending on their own animals' droppings for manure. The demand for compost may not be able to meet the production costs in most developing countries.

Conclusions
The present study demonstrated that the ISWM concept has the potential for optimizing the minimization of both the engineering costs and health impacts of MSW disposal.