Eutrophication impact potential of solid waste management options in Harare

Six municipal solid waste management options (A1– A6) in Harare were developed and analyzed for their eutrophication impact potentials under the Life Cycle Assessment (LCA) methodology. All the options started with waste collection and transportation to a centralized waste treatment centre where a combination of various municipal solid waste management and treatment methods were considered under the different options. Results show that landfilling and material recovery for reuse and recyle are the only MSW management processes that contributes to negative eutrophication potential giving options that had landfilling (A1, A4 and A6) an overall edge. The doubling of recycling rate under A5 and increasing it to atleast 25% under A6 result in below zero eutrophication impact potentials. Results reveal that anaerobic digestion and incineration contribute to increased eutrophication potential under all the options they were considered hence need for further assessments considering other impact categories to determine the most sustainable option. water to Harare and Chitungwiza. The eutrophication of Lake Chivero is not a welcome development considering its threats to the availability of potable water for Harare and Chitungwiza. It has led to increased costs for potable water production partly contributing to the erratic potable water supplies in most parts of Harare currently being experienced. Bauman and Tillman (2004) described eutrophication as a phenomenon with the potential of affecting terrestrial and aquatic ecosystems due to nutrient enrichment namely Nitrogen (N) and phosphorus (P) in water systems. The MSW generated in Harare has an excess of biowaste constituting over 60% (UNEP, 2011) hence if improperly managed can lead to nutrient enrichment in water bodies leading to eutrophication. Magadza (2003) reported that the breakdown in hygiene has led to nutrient rich surface run-off from uncollected MSW and illegal MSW dumps significantly contributing to Lake Chivero eutrophication. The design and development of sustainable MSW management option for Harare becomes a necessity to address the human health challenges and availability of freshwater that guarantee the long term consistent supply of potable water for Harare residents. Life Cycle Assessment (LCA) has proven to be an effective tool for designing and developing sustainable and integrated MSW management as it aids the assessment of environmental loads of different MSW options (Miliute and Kazimieras Staniškis, 2010; Rives et al., 2010; Koci and Trecakova, 2011; Stucki et al., 2011; Gunamantha and Sarto, 2012; Fernández-Nava et al., 2014). Therefore, this work is an LCA based comparative study to assess the eutrophication impact potential of different MSW management options for Harare. The objective being to determine the option with the least eutrophication impact potential in light of the reported eutrophic status of the potable water sources in Harare. 2 MATERIALS AND METHODS 2.1 Description of study area The study area is Harare the capital city of Zimbabwe with an estimated population of 1,485,231 (Zimstat, 2013) and covering an area of 960.6 km 2 at an altitude of 1483 m. An estimate of 325,266 tons of MSW is generated per year (Mshandete and Parawira, 2009, Muchandiona et al., 2013, Pawandiwa, 2013, Mbiba, 2014, Hoornweg and Bhada-Tata, 2012, Emenike et al., 2013) in Harare with 60% indiscriminately collected and dumped at Pomona dumpsite the only official dumpsite whose capacity is exhausted by 2020 (Chijarira, 2013). The waste that is generated in Harare is estimated to have average composition of 42% biodegradable waste, 33% plastics, 8% metals, 14% paper and 3% glass (Nyanzou and Steven, 2014, Mudzengerere and Chigwenya, 2012). Harare sits upstream and on the catchment of its potable water source (Lake Chivero) making all the MSW management activities in Harare contributing towards the reported super eutrophic levels of the Lake. Underground water in Harare has also been reported to have been contaminated with nutrients, metals, acids and coliform bacteria (Muchandiona et al., 2013, Love et al., 2006, Eukay and Kharlamova, 2014, Kharlamova et al., 2016). 2.2 MSW management option 1 – A1 The entire 325,266 tons of MSW generated per year in Harare is indiscriminately collected before any treatment (both biodegradable and nonorganic MSW) and landfilled in a sanitary landfill with biogas recovery and landfill leachate treatment. The recovered biogas is fed into Combined Heat and Power (CHP) plant to produce electricity. 2.3 MSW management option 2 – A2 The entire 325,266 tons of MSW generated per year in Harare is indiscriminately collected before any treatment (both biodegradable and nonorganic MSW) and incinerated in an incinerator with energy recovery, flue gas treatment and treatment of leachate produced during the recovery of the incinerator bottom ash. The incinerator bottom and fly ash is used as material for road construction considering the road infrastructural needs of the country. 2.4 MSW management option 3 – A3 Biodegradable MSW generated amounting to 136,612 tons is digested in an anaerobic digester producing biogas. The biogas is fed into Combined Heat and Power (CHP) generation plant to produce heat and electricity. The remaining non-biodegradable fraction 188,654 tons mixed bag MSW (107,338 tons plastics, 26,021 tons metals, 45,537 tons paper and 9,758 tons glass) is incinerated as in A2 with energy recovery, flue gas treatment and treatment of leachate produced during the recovery of the incinerator bottom ash. The incinerator bottom and fly ash is used as material for road construction considering the road infrastructural needs of the country. 2.5 MSW management option 4 – A4 As in A3 difference being that the remaining non-biodegradable fraction 188,654 tons mixed bag MSW (107,338 tons plastics, 26,021 tons metals, 45,537 tons paper and 9,758 tons glass) is landfilled as in A1 with biogas recovery and landfill leachate treatment. The recovered biogas is fed into Combined Heat and Power (CHP) plant to produce electricity. 2.6 MSW management option 5 – A5 20% of the non-biodegradable MSW amounting to 37,731 tons (21,468 tons plastics, 5,204 tons metals, 9,107 tons paper and 1,952 tons glass) are recovered in the material recovery facility or sorting plant for reuse and recycling. The 80% non-biodegradable MSW remaining from the material recovery facility amounting to 150,923 tons (85,870 tons plastics, 20,817 tons metals, 36,430 tons paper and 7,806 tons glass) is incinerated as in A2 with energy recovery, flue gas treatment and treatment of leachate produced during the recovery of the incinerator bottom ash. The incinerator bottom and fly ash is used as material for road construction considering the road infrastructural needs of the country. 2.7 MSW management option 6 – A6 20% of the non-biodegradable MSW amounting to 37,731 tons (21,468 tons plastics, 5,204 tons metals, 9,107 tons paper and 1,952 tons glass) are recovered in the material recovery facility or sorting plant for reuse and recycling. The 80% non-biodegradable MSW remaining from the material recovery facility amounting to 150,923 tons (85,870 tons plastics, 20,817 tons metals, 36,430 tons paper and 7,806 tons glass) is landfilled as in A1 with biogas recovery and landfill leachate treatment. The recovered biogas is fed into Combined Heat and Power (CHP) plant to produce electricity. 2.8 Life Cycle Assessment The eutrophication impact potential for the six MSW management options was estimated using the LCA methodology with the ISO 14040 standards applied as the basis of the LCA. Simapro version 8.5.2 analyst software and update 852 database were used for the LCA under the ReCiPe 2016 v1.02 endpoint method. The yearly MSW generation of 325,266 tons was used as the functional unit (Fernández-Nava et al., 2014, Beigl and Salhofer, 2004, Cherubini et al., 2009). Waste collection and transportation, landfilling, incineration, anaerobic digestion material recovery, CHP generation, landfill leachate treatment and incineration flue gas treatment were the considered life cycle stages. 3 RESULTS AND DISCUSSIONS Figure 1 shows the LCIA results with regards to the eutrophication impact potential of the six MSW management options. MSW management options A1and A4 leads to reduced extinction rate of species thus reduced eutrophication impact potential with A2 to A6 bringing about an increased species extinction rates. Table 1: Process Contributions to eutrophication Process MSW management options