*3.4. Human Health*

Figure 7 shows that all the MSW management options have negative human health impact potentials with option A5 having the highest reduction of −268 DALYs (an overall disease burden measure quantitatively expressed as the total number of years lost due to ill-health, disability or premature or early death) followed by A3 and A2 with human health reduction potentials of −247 and −216 DALYs, respectively. A1 and A6 have human health reduction potentials of −174 and −119 DALYs, respectively. A4 leads to the least reduction in human health of −36 DALYs. Results from Table 5 sensitivity analysis show that no materials recovery effort is necessary under A5 as reduction in human impact potential will be realised even without materials recovery. However, under A6, sensitivity analysis indicates a 9% materials recovery is sufficient to attain zero human health impact potential.

**Figure 7.** Human health impact potentials.

### **4. Discussion**

LCIA results show that scenario A6 is the best option with regards to acidification while scenario A2 is the worst option. MSWM option A1 is the best scenario considering eutrophication potential and A3 is the worst. In terms of global warming and human health impact potential, A5 is the best option and A4 is the worst MSWM option. Overall, MSWM option A5 emerges as the best option for managing MSW in Harare as shown in Table 6. This is confirmed from findings by Sharma and Chandel [111] that MSWM systems that combines incineration, anaerobic digestion, composting and materials recovery have the least environmental impacts.


**Table 6.** Ranking of MSW management options.

The recovery of landfill gas for combined heat and power (CHP) generation under the current study is attributed to the reduction of impact potentials across all the impact categories under consideration, except for A4 under acidification, in the MSWM options that incorporated landfilling because energy recovery from waste bring significant environmental benefits [95,110,112–116]. Khandelwal et al. [64], in their review of 153 LCA based MSWM studies published between 2013 and 2018, had 9 studies concluding the appropriateness of AD compared to biodegradable waste landfilling. The same review noted the conclusions from 11 studies regarding the appropriateness of landfilling with landfill gas recovery for CHP generation. This was also noted by Yadav and Samadder [62] in their review analysis of 91 LCA studies on MSWM undertaken from 2006 to 2017 in Asian countries with 5% of the reviewed studies reporting the relative environmental friendliness and sustainability of landfilling with landfill gas recovery—an observation that was also observed by Menikpura et al. [117].

Yadav and Samadder [62] further observed that incineration was reported as a better option than landfilling by 9% of the reviewed studies largely due to the reduced methane emissions associated with incineration. This observation is in agreement with this study's conclusions with regards to human health and global warming impact categories since MSWM options A2, A3 and A5 that incorporated incineration bring more global warming and human health impact potential reductions than A1, A4 and A6 which incorporated landfilling. Cleary [65], like Yadav and Samadder [62], also noted the better performance of thermal treatment with regards to global warming, which is consistent with this study's findings. Thermal treatment was also reported to perform better than landfilling in a critical review of 222 published LCA studies on SWM systems in general, accessed from 216 peer reviewed articles and 15 public reports undertaken by Laurent et al. [63] and Laurent et al. [66].

Overall review results by Yadav and Samadder [62] show that 71% of the reviewed LCAs found landfilling to be the worst or least preferred MSWM treatment option with 8% of the studies concluding incineration to be the worst or least preferred MSW treatment option among other treatment options due to its associated harmful emissions in the form of dioxins and furans as well as human toxicity. Cleary [65], in their review of 20 LCA-based MSWM assessments undertaken and published in peer-reviewed journals between 2002 and 2008, observed that 19 studies confirmed the low environmental performance of landfilling. A review by Abeliotis [60] of 21 LCA studies further observed that landfilling was reported as the worst option for managing and treating MSW, as was observed by Mendes et al. [118], Hong et al. [109], Wanichpongpan and Gheewala [116], Cherubini et al. [95] and Miliut¯ e and Staniškis [ ˙ 102]. However, despite these reported low environmental performances

of landfilling, it performed better than incineration with regards to acidification and eutrophication impact potentials under this study. This is also contrary to observations made by Cleary [65], who noted the better performance of thermal treatment compared to landfilling with regards to eutrophication and acidification impact categories.

The better environmental performance of recycling and thermal treatment of plastics and paper compared to landfilling, as shown by the best performance of A5 which combined incineration and recovery of materials together with AD, was observed by Laurent et al. [63] and Laurent et al. [66] in their reviews consistent with findings by Michaud et al. [119], Lazarevic et al. [120] and Tyskeng and Finnveden [121]. Materials recovery and recycling are environmentally appropriate and sustainable as they lead to reduced environmental impacts potentials [60,62–66,102]. This is confirmed by the better performances of A5 compared to A3 and of A6 compared A4 under this study; sensitivity analysis results that reveal an inverse relation between materials recovery levels and the magnitudes of environmental impact potentials.

Differences in results from LCA studies were observed by Laurent et al. [66] who noted little agreements with regards to the conclusions and no definite agreement except for landfilling with regards to which amongst thermal treatment, anaerobic digestion and recycling is most preferable for managing or treating plastic, paper, organics and metals. De Feo and Malvano [122] observed that the best IMSWM option is subject to the examined impact categories, hence the differences amongst impact categories considered render other MSWM or treatment methods environmentally sustainable while simultaneously rendering others as unsustainable. Khandelwal et al. [64] singled out the heterogeneous nature of MSW as a factor that makes no single MSW treatment method capable to be applied to all the MSW fractions, inevitably resulting in different LCA results from region to region due to differences in MSW generation and composition, MSWM structures, system boundaries, MSWM practices and the choice of impact categories.

### **5. Conclusions**

LCIA results show that scenario A6 is the best option with regards to acidification while scenario A2 is the worst option. MSW management option A1 is the best scenario considering eutrophication potential and A3 is the worst. In terms of global warming and human health impact potential, A5 is the best option and A4 is the worst MSW management option. Overall, MSW management option A5 emerges the best option for managing MSW in Harare as shown in Table 6. This is confirmed from findings by Sharma and Chandel [111] that MSW management that combines incineration, anaerobic digestion, composting and materials recovery has the least environmental impacts. Therefore, the LCA results from this study will inform the design and development of future integrated MSWM systems with reduced environmental and human health impacts. Furthermore, the study will provide a baseline for design and development of further studies to assess economic affordability, social acceptability, renewable energy and job creation potential of the LCA-identified integrated MSWM system with least environmental impact potential. The compositing option for the organic fraction of the MSW instead of anaerobic digestion should also be incorporated in future LCA studies. The study had its own limitations due to the unavailability of quality and reliable data on waste generation and transportation. Therefore, studies to quantify the waste generation and composition in Harare must be undertaken to give reliable data that could be used for further LCIA of MSWM options for Harare.

**Author Contributions:** The work is part of T.N.'s study towards a PhD under the supervision of E.M. at the University of Johannesburg. T.N. conceptualized the research proposal with E.M. giving guidance regarding the methodological framework. T.N. applied for software from the Life Cycle Initiative in partnership with the UN Environment and Pre-sustainability under the 2017 Life Cycle Awards and his proposal was awarded the Life Cycle award that provided the Simapro 8.5.2 and associated databases. T.N. also applied for research funds from the National Geographic Society under their Early Careers scientist which was awarded to facilitate fieldwork and data collection for the study. E.M. gave guidance in scenario development with T.N. responsible for setting up the input output systems on the Simapro software interface for simulation. T.N. actively analysed the results and undertook sensitivity analysis under the supervision of E.M. T.N. prepared the manuscript with E.M. doing the editing, supervision and reviewing.

**Funding:** This research was funded by Life Cycle Initiative in partnership with the United Nations Environment Programme (UNEP), PRé Sustainability and Federation of Indian Chambers of Commerce and Industry (FICCI) through the Life Cycle Assessment award. The National Geographic Society funded fieldwork, grant number HJ-170ER-17. The University of Johannesburg funded Trust Nhubu's PhD studies.

**Acknowledgments:** The authors acknowledge the Life Cycle Initiative for awarding the project the 2017 Life Cycle award in the form of Simapro software that was used to carry out the LCIA. The authors are also grateful to the National Geographic Society for awarding the project the early career grant. The Zimbabwe Environmental Management Agency, Zimbabwe National Statistical Agency, Harare City Council are greatly appreciated for assistance with data for the study. The University of Johannesburg is greatly appreciated for funding these studies.

**Conflicts of Interest:** No conflict of interest declared.
