• Energy Research

Waste-to-energy supply chains are important potential contributors to minimising the environmental impacts of municipal solid waste by reducing the amounts of waste sent to landfill, as well as the fossil fuel consumption and environmental footprints. Accounting for the spatial and transport properties of the waste-to-energy supply chains is crucial for understanding the problem and improving the supply chain designs. The most significant challenge is the distributed nature of the waste generation and the household energy demands. The current work proposes concepts and a procedure for targeting the size of the municipal solid waste collection zone as the first step in the waste-to-energy supply chains synthesis. The formulated concepts and the provided case study reveal trends of reducing the net greenhouse gas savings and energy recovery by increasing the collection zone size. Population density has a positive correlation with the greenhouse gas saving and energy recovery performance. For smaller zone size the energy recovery from waste approaches and in some cases may surpass the energy spent on waste transportation. The energy recovery and greenhouse gas savings remain significant even for collection zones as large as 200 km2. The obtained trends are discussed and key directions for future work are proposed.

COVID-19 has caused great challenges to the energy industry. Potential new practices and social forms being facilitated by the pandemics are having impacts on energy demand and consumption. Spatial and temporal heterogeneities of impacts appear gradually due to the dynamics of pandemics and mitigation measures. This paper overviews the impacts and challenges of COVID-19 pandemics on energy demand and consumption and highlights energy-related lessons and emerging opportunities. The discussion on energy-related issues is divided into four main sections: emergency situation and its impacts, environmental impacts and stabilising energy demand, recovering energy demand, and lessons and emerging opportunities. The changes in energy requirements are compared and analysed from multiple perspectives according to available data and information. In general, although the overall energy demand declines, the spatial and temporal variations are complicated. The energy intensity has presented apparent changes, the extra energy for COVID-19 fighting is non-negligible for stabilising energy demand, and the energy recovery in different regions presents significant differences. A crucial issue has been to allocate and find energy-related emerging opportunities for the post pandemics. This study could offer a direction in opening new avenues for increasing energy efficiency and promoting energy saving.

Abstract The aim of this study is to develop a novel framework for the optimisation of downstream oil supply chains with emission-cost nexus and performance analysis. A P-graph based model has been developed to support the decisions of the distribution plan in the supply chain. This created the possibility to consider constraints, including the material balance, the sending capacity of refineries and storage depots, and the transport capacity of railways, barges and pipelines. Three scenarios, covering standard conditions, pipeline disruption, and demand increase, are analysed. The proposed novel method supports the decision-making of downstream oil supply chains and provides insight into the reduction of environmental influences. The results reveal that priority should be given to measures for reducing NOx emission (both Greenhouse and dangerous pollution gas) and the emission factors of barge transport, as this can bring great environmental benefit. When NOx emission for railways and barges is reduced by 5%, 1,435 kCNY/month could be saved. If the emission of the barges is reduced by 5%, this can save 1,289 kCNY/month of environmental cost. The proposed method is handy for analysis under non-standard conditions, such as transport facility disruption and demand increase. It would help in the design a distribution plan from a more comprehensive view, and to provide further direction for reducing the environmental footprint.

Abstract Achieving and attaining sustainability of a society's existence and functioning constitutes a problem of enormous breadth, involving complex interactions among actors of varying backgrounds, personal and institutional goals. The contribution of process optimisation by engineering communities to the development of concepts and tools for improved sustainability has been substantial. This article presents an overview of process optimisation and Process Integration paradigms and the most relevant recent works, relevant to sustainability improvement. Based on this background, recent contributions to the field published in the current Special Issue of Process Integration Contribution to Cleaner Production have been analysed. The analysis shows the progress that has been made in energy and water efficiency, as well as waste management, including waste-to-energy, pollution prevention and remediation.

Lignocellulosic waste is one of the most abundant and potential feedstocks for anaerobic digestion (AD), but the energy efficiency is limited by the lignocellulosic composition which is recalcitrant to biodegradation. Pre- treatment of feedstock and the post-treatment of biogas and digestate play a significant role in enhancing the AD efficiency as well as the product utilisation. This study aims to determine the cost-optimal pre-and post- treatment pathway for an AD of lignocellulosic waste by applying P-graph. The economic balance between the main operating cost, yield and quality of products were considered. The treatment options were overviewed followed by a case study considered a different combination of physical, chemical and biological pre- treatments, biogas post-treatment (combine heat and power, fuel cell, biomethane, biofuel) and digestate treatments. A total of 9 pre-treatments for lignocellulosic waste, 2 digestate post-treatments and 9 post- treatments for biogas were evaluated in this study. Chemical pre-treatment by CaO, post-treatment by H2S removal with membrane separation for biomethane production and without the composting of digestate is suggested as the optimal treatment pathway for lignocellulosic waste.

Anaerobic digestion (AD) serves as a promising alternative for waste treatment and a potential solution to improve the energy supply security. The feasibility of AD has been proven in some of the technologically and agriculturally advanced countries. However, development is still needed for worldwide implementation, especially for AD process dealing with municipal solid waste (MSW). This paper reviews various approaches and stages in the AD of MSW, which used to optimise the biogas production and quality. The assessed stages include pre-treatment, digestion process, post-treatment as well as the waste collection and transportation. The latest approaches and integrated system to improve the AD process are also presented. The stages were assessed in a relatively quantitative manner. The range of energy requirement, carbon emission footprint and the percentage of enhancement are summarised. Thermal hydrolysis pre-treatment is identified to be less suitable for MSW (-5% to +15.4% enhancement), unless conducted in the two-phase AD system. Microwave pre-treatment shows consistent performance in elevating the biogas production of MSW, but the energy consumption (114.24-8,040 kWeh t-1) and carbon emission footprint (59.93-4,217.78 kg CO2 t-1 waste) are relatively high. Chemical (∼0.43 kWeh m-3) and membrane-based (∼0.45 kWeh m-3) post-treatments are suggested to be a lower energy consumption approach for upgrading the biogas. The feasibility in terms of cost (scale up) and other environmental impacts (non-CO2 footprint) needs to be further assessed. This study provides an overview to facilitate further development and extended implementation of AD.

Abstract The greenhouse gas emissions footprint and global warming potential are widely-used for environmental sustainability studies. However, environmental sustainability is far wider than carbon emissions and climate change. This review aims to highlight the importance of considering air pollutants in optimisation studies and evaluate the limitation of the current assessments for air emissions, particularly in relation to transportation. The source of air pollutants is firstly overviewed with special attention on non-stationary sources, freight and sea transportation. The type of measurement to obtain the emission data and the available optimisation models on transport mode choice selection were then summarised. The strengths and Weaknesses' have been indicated. The identified gap includes greenhouse gas and air pollutants not being evaluated simultaneously and the interaction between the different pollutants are not being adequately considered. A better assessment framework and impact categories classification are consequently required. The summarised assessment model of transportation mode choice shows that the current viewpoint on low emissions, green or environmental sustainability options refers to carbon dioxide as a part of greenhouse gas. Attention towards a better emission assessment and management has been supported in this study through critical discussion. The next step of this work is to develop a methodology to measure greenhouse gas and air pollutants simultaneously by considering the synergistic effect and the discussed limitation. It is important for minimising the potential of footprint shifting and poor decision-making.