Life cycle sustainability assessment of next generation energy infrastructure in Africa: Is there a case for biohydrogen after biomethane?

Doctoral Thesis


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University of Cape Town

The recovery of energy in the form of biomethane gas from inexpensive biodegradable organic wastes is starting to become a cornerstone of green economy investments. It is possible that such installations could serve as a precursor for the infrastructural development of a hydrogen economy, since biogas processes can be modified to produce hydrogen instead of methane. It is unclear whether such a change would improve or worsen the environmental, social, and economic performance of such waste-to-energy installations. Earlier studies show that the dark fermentation process for biohydrogen production faces several challenges such as low yield and slower production rate. Furthermore, it is unclear whether the biohydrogen production technology offers potential benefits in terms of ecological and socioeconomic sustainability. This study explores the usage of Life Cycle Sustainability Assessment (LCSA) to investigate next generation energy options to support green economies in Africa. LCSA has been advocated by the United Nations Environment Programme (UNEP) to consider the evaluation of all environmental, social and economic negative impacts and benefits in decision-making processes towards more sustainable products throughout their life cycle. This thesis uses LCSA for comparing biomethane versus biohydrogen produced from organic wastes in three settings: agro-industrial processing, represented by brewery wastewater; urban, represented by the organic fraction of municipal solid waste (OFMSW); and rural, represented by cattle manure. In each setting, two end-uses of both fuels are considered, viz. electricity generation (combined heat and power (CHP) systems vs. fuel cell (FC) systems), and as vehicle fuel (compressed natural gas (CNG) vehicles vs. fuel cell (FC) vehicles). According to published information on biogas yields of the substrates (i.e. brewery wastewater, OFMSW, and cattle manure), biomethane achieve a significantly higher energetic yield than biohydrogen estimated at 9.0, 10.5, and 9.7 MJ/kg of volatile solids (VS) for the case of biomethane, and at 4.8, 1.4, and 0.9 MJ/kg of VS in the case of biohydrogen, for the three substrates respectively. This difference in energetic yields significantly impacts on all further sustainability performance of the fuels. Nevertheless, an LCSA comparison was constructed, combining environmental and social life cycle assessment with a life cycle cost calculation to present the overall sustainability performance index of the results. The results show that for the urban setting (exemplified by OFMSW), the application of biomethane in CHP systems provides the highest sustainability performance index (SPI) value estimated at 1.90, while that of vehicle operations in CNG vehicles stands at 1.83. For biohydrogen, the recovery of energy from brewery wastewater in the agro-industrial setting (exemplified by brewery wastewater), the application of biohydrogen in the FC systems commands the SPI value of 1.75, but the vehicle operation in the FC vehicles records a much lower performance value of 0.90. The results clearly indicate that the biomethane technology for the electricity generation offers the most sustainable performance outcome when compared with the biohydrogen technology for the electricity generation which stands at 1.90 and 1.75, respectively. In the case of vehicles operations the application of biomethane in the CNG vehicles records much higher sustainability performance index value when compared to FC vehicles which stands at 1.83 and 0.90, respectively. In the agro-industrial settings the application of the biomethane in the electricity generation systems is equal that of the application of the biomethane in the vehicle operations in the CNG vehicles, which stand at 1.73. In the case of the urban settings the application of biomethane in the electricity generations provides higher sustainability performance index value when compared to the vehicle operations in the CNG vehicles which records the value of 1.90 and 1.83, respectively. In rural settings (exemplified by cattle manure) the application of biomethane produced from cattle manure in CHP systems records high SPI value of 1.75, but application in the CNG vehicles records the SPI value estimated at 1.68. The outcomes of the study thus show that the generation and use of biomethane in all selected settings promises a better sustainability performance, when compared to biohydrogen. Agro-industrial settings, in particular, seem to be very well suited for biohydrogen production, and there is no strong case for the application of biohydrogen technology in both the urban and rural settings. It is observed that the life cycle cost performance is significantly influenced by the application of the fuel (i.e. either in electricity generation, or as fuel for vehicles), and not only by the type of technology implemented (i.e. anaerobic digestion vs. dark fermentation process). Clearly, decision making for implementation of a particular technology requires a sound decision on the demand of a particular fuel type, end application of the fuel and also the type of the technology implemented. It has been reported that the energetic efficiencies in fuel cells for electrical energy generation has reached the efficiency of approximately 80%. The results of this study demonstrate that biohydrogen application for electricity generation seems to be promising for application in agro-industrial settings. This setting has access to skilled technicians required for the operating of the biohydrogen production technology, and also the economic power for the implementation of the biohydrogen technology. Often the implementation of the biomethane technology in the agro-industrial settings is to advance economic savings that result from the installations of the biogas digester. Thus, the private sector can either directly or indirectly play a crucial role in the research and development for the next energy generation infrastructural development. The social aspects need to be considered when analysing the potential role of different energy technologies for sustainable development. Actually, people are accustomed to infrastructural development of biogas installation in rural areas when compared to the biohydrogen technology. The social performance in such settings is faced with serious challenges regarding the level of education among the people and availability of human capacity in terms of skill development for the implementation of the proper infrastructural development. In rural areas, there is a need to effectively pay attention to various stakeholders. It has been reported that in certain instances the energy generation technology can come to a halt if proper stakeholders and community leaders are not well informed about the plan to implement new energy generation technology. This thesis thus demonstrates how UNEP’s call to consider environmental, social and economic dimensions of new developments can be interpreted, with a special focus on technological advancement in energy production systems. The energy sector in Africa faces enormous twin challenges of making a leading development contribution whilst respecting environmental sustainability imperatives. This thesis provides realistic solutions and advice for policy development of implementation of renewable technological options in three types of African settings. In respect to the development of the methodological approach for assessment of energy production systems, this study specifically contributed through developing a stakeholder analysis. The stakeholder analysis presents the framework for mapping of relevant impact indicators across the three dimension of sustainability analysis, for the production of gaseous energy carriers from organic wastes. The approach shows how different participating parties, such as government, companies primarily in the energy sector, end users (domestic users), and non-governmental organizations (NGOs) can collaborate and clearly understood impacts in the three dimension of sustainability. Furthermore, this developed stakeholder analysis within the context of LCSA has a role to play in the policy development by creating awareness between government, energy users and energy companies during energy technological innovations. The stakeholder analysis developed in this study was shown to help determine the social indicators within the context of LCSA. In summary, while hydrogen may soon be applied as an energy carrier in practice, this thesis shows that as long as biohydrogen yields remain much lower than biomethane yields, there is no strong case for admitting biohydrogen technology in both urban and rural settings. At the moment it remains possible that biomethane infrastructural development could serve as a precursor for the infrastructural development for the biohydrogen technology in the agro-industrial settings.