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Abstract This research proposes a novel, three-tier AI-based scheme for the allocation of carbon–neutral mobility hubs. Initially, it identified optimal sites using a genetic algorithm, which optimized travel times and achieved a high fitness value of 77,000,000. Second, it involved an Ensemble-based suitability analysis of the pinpointed locations, using factors such as land use mix, densities of population and employment, and proximities of parking, biking, and transit. Each factor is weighted by its carbon emissions contribution, then incorporated into a suitability analysis model, generating scores that guide the final selection of the most suitable mobility hub sites. The final step employs a traffic assignment model to evaluate these sites’ environmental and economic impacts. This includes measuring reductions in vehicle kilometers traveled and calculating other cost savings. Focusing on addressing sustainable development goals 11 and 9, this study leverages advanced techniques to enhance transportation planning policies. The Ensemble model demonstrated strong predictive accuracy, achieving an R-squared of 95% in training and 53% in testing. The identified hubs’ sites reduced daily vehicle travel by 771,074 km, leading to annual savings of 225.5 million USD. This comprehensive approach integrates carbon-focused analyses and post-assessment evaluations, thereby offering a comprehensive framework for sustainable mobility hub planning.

Anaerobic digestion (AD) is a process that converts biodegradable wastes into methane (CH4) gas, reducing the waste's size efficiently. The methane gas can be used as biofuel for power generation due to its explosive properties. The biogas could be upgraded to bio-compressed natural gas (Bio-CNG), which could be utilised as a fuel in the community. Biogas or methane yield from the AD process of sewage sludge (SS) usually is undesirable due to the lack of vital components, such as carbohydrates, proteins and fats, with higher inert substances or moisture content. Therefore, the optimisation of the AD process for SS feedstock is needed to increase its biogas yield. In this study, the anaerobic co-digestion (ACoD) with other wastes, such as corn silk (CS), food wastes (FW), cattle manure (CM), and palm oil mill effluent (POME), is investigated through a simulation model in SuperPro Designer. The biogas upgrading technologies, namely chemical and water scrubbing, are studied in this model to investigate the biogas purification efficiency for producing methane-rich biogas gas that meets international standards (>90 % CH4 and

The risk of surgical site infections (SSIs) is highly associated with the level of microbial contamination settled on a patient's wound. Low or zero microbial contamination could reduce the risk of patients contracting SSIs. To date, the state of microbial contamination in an operating room (OR) for pre- and post-surgery is rarely examined. This exploration is crucial as a patient undergoing surgery tends to contract the SSI if the microbial contamination is high. This study aims to identify the number of microbes present in the OR for pre- and post-surgical procedures. Microbial sampling was performed on 15 ORs in 6 private hospitals located on the western coast of Peninsular Malaysia. Before the microbial sampling, cleanroom performance testing (CPT) was performed to ensure the compliance of operating parameters with the International Organization for Standardization (ISO) Class 7. The CPT was conducted based on ISO 14644-1, Institute of Environmental Science Recommended Practice (IES-RP-CC006.2), and National Environmental Balancing Bureau (NEBB) Procedural Standards for Certified Testing of Cleanrooms. The CPT procedures involved verifying the cleanroom operating parameters: air change rate, differential room pressure, relative humidity (RH), and air temperature. The CPT shows that the air change rate, differential room pressure, RH, and air temperature fell within the recommended operating conditions, ranging from 28/h - 45/h, 6.8 Pa - 22.3 Pa, 51.8 % – 58.9 %, 18.2 °C – 21.6 °C, respectively. The microbes were measured in two phases: pre- and post-surgical procedures. The present study confirms that the microbial contamination for post-surgical procedures increased significantly compared to pre-surgical procedures. The increase in microbial contamination of pre- and post-surgical procedures ranged from 49 to 81 colony-forming units (CFU).

Biochar is a carbonaceous porous material produced by pyrolysis under oxygen-anoxic conditions. It has been widely adopted as an adsorbent to remove various pollutants from contaminated water due to its distinctive characteristics such as high porosity and surface-to-volume ratio, abundant functional groups, etc. One of the major problems in utilising biochar as an adsorbent is the recovery and sustainable management of the spent biochar. To determine the potential and reusability of biochar for wastewater treatment, the desorption and regeneration processes to reactivate the biochar should be studied and explored. This study aims to identify the desorption characteristics of sodium ions (Na+) on hydrothermal nitric acid pre-treated empty fruit bunch biochar (HNO3 EFB-BC). Different desorption eluents, i.e., tap water, deionised water, hydrochloric acid (HCl), sulphuric acid (H2SO4), sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). Among these eluents, HCl was chosen as the best desorbing agent for Na+, due to the highest desorption efficiency (66.23 %), at a concentration of 0.1 M. By using HCl, the exhausted HNO3 EFB-BC was regenerated up to six cycles. The Na+ desorption efficiency of HNO3 EFB-BC can be maintained as high as 69.03 % and 57.77 %, respectively, in the first two cycles. The efficiency of Na+ desorption remained as high as 18.85 %, after six successive adsorption and desorption experiments. The results have proven the potential of HNO3 EFB-BC as a cost-effective adsorbent for the sustainable remediation of saline solution. It also provided new insights to researchers on the desorption characteristics of HNO3 EFB-BC and display its potential to be regenerated from other cationic pollutants. Future desorption and regeneration studies should be performed using the actual saline soil or water with a mixture of pollutants to illustrate the effects of adsorbates on the performance of the regeneration process.

Plastic production and its end-of-life management pose a significant environmental footprint. The mitigation strategies of the plastic industry are comparatively attainable than the other hard-to-abate sector. However, the involvement of different stakeholders is needed. The life cycle analysis proposed in this study allocated the environmental footprint to stakeholders based on the game theory concept. It addresses the limitation of previous approaches that do not guarantee the stakeholders from different stages will participate in the initiatives with the lowest net environmental footprint due to the dissatisfaction or imbalance in the allocated unburdening footprint (benefit) and burdening footprint. The applicability of the proposed approach is demonstrated through a plastic recycling case study. An allocation of 82 % of environmental benefit to the producer, 14 % to the manufacturer, and 4 % to the user are suggested to achieve efficiency (lowest external interference) and stable cooperation (participation in recycling). This work serves as an initial assessment in demonstrating the integration of the game theory concept in environmental footprint allocation or Life Cycle Assessment.

Carbon emissions neutrality has been a strategic target of many countries. Most of them have set the deadline at around the middle of this century in spite of very few already achieved. Different kinds of policies and strategies have been made during the past years, including the Carbon Border Adjustment Mechanism (CBAM) from the EU. The CBAM is a carbon tariff on carbon emissions intensive products, such as cement and some electricity. It was imported by the EU currently being legislated as part of the European Green Deal and will to take effect in 2026 with reporting starting in 2023. As the largest economic partner of the EU, China export a large number of products to the EU every year. China has also promised achieving the carbon neutrality target by 2060. It could be predictable that the CBAM would have significant impact on the industrial activities, exportation and the progress of the carbon neutrality of China. However, it is not clear that what impacts and how significance it would be. It is crucial and urgent to explore the impacts of CBAM on the carbon emissions of China and relevant policies. This work makes a review on the state of the art on this topic, the development of CBAM and potential impacts on the carbon neutrality target of China, providing support for relevant research in the future.

Plastic pollution is a serious sustainability issue facing the global community. Fragments of macroplastics and microplastics pollute terrestrial and aquatic ecosystems, while nanoplastics can also degrade air quality. The recent COVID-19 pandemic also exacerbated the problem. Large-scale commercial use of plastics recycling technologies is hindered by various socio-economic barriers. In particular, cross-contamination of mixed plastic streams is prevalent due to imperfect waste segregation. The concept of Plastics Recycling Networks is introduced to facilitate planning of reverse supply chains using optimization models. In this work, basic Linear Programming and Mixed-Integer Linear Programming models are developed for matching sources of waste plastic with plastic recycling plants within Plastics Recycling Networks. These models allocate streams while considering the ability of recycling plants to tolerate contaminants. Two illustrative case studies are analyzed to demonstrate the effectiveness of the models, and policy implications for mitigation of plastic pollution are discussed. These models enable planning of networks with some tolerance for contaminants in plastic waste, and can be the basis for developing new variants to handle additional real world aspects.

Greenhouse Gas Footprint minimisation and security of energy supply are important components of sustainability. Achieving these can be offered by the combination of technologies demonstrated by the Horizon 2020 project RESHeat presented in this work. The technology captures, stores and uses solar energy efficiently, employing Photovoltaic-Thermal and Thermal Solar collectors combined with underground heat storage and heat pumps. As a result, the proposed system has been shown to be capable of catering for more than 90 % of the energy demands of residential buildings and bears the potential to reduce more than 80 % of the Greenhouse Gas Footprint compared with the mode of using grid power only. Future project activities will focus on completing the technology demonstrations and a thorough sustainability evaluation – including further footprints and economic viability.

Composting is a biological process that converts organic waste into compost, an organic fertiliser. As a waste management technology, the use of composting in managing food waste is gaining more attention these days. In recent years, many studies have been done to analyse the research trend in solid waste management using bibliometric analysis, which showed the potential to analyse food waste composting trends using this tool. Bibliometric analysis is used in this study to map and visualise the food waste composting research trend indexed in the SCOPUS database between 1987 and 2021. One thousand seven research papers were exported from the SCOPUS database during the study period, VOSviewer and Microsoft Excel were used to analyse the exported data. The results show that there were 1,007 publications with 31,335 citations. An increasing trend in publication numbers was observed, especially in the recent 15 y. China, US and India are the top 3 contributed countries in this research subject over the 34 y research period, with the US being the top contributed country before 2000. In recent years, China has become the major contributor to food waste composting research. Keywords analysis was done using VOSviewer, and “soil” was found to be strongly linked to the food waste composting research, followed by “emission” and “organic matter”. The appearance of strongly linked keywords such as “emission” and “landfill” reveals the potential environmental issues that are the major criteria to be of concern when working on food waste composting. The presence of keywords such as “soil”, “plant”, “application”, and “organic matter” indicates the potential of compost usage as soil amendments. An upward trend in the publication numbers is likely to continue in the next decade. Further study on environmental issues and compost quality might contribute to the safety and efficient use of compost in a soil application.

User-friendly approaches or methods that could facilitate communication effectively with policymakers and the public have been a target in developing models for a low carbon emissions economy. Graphical tools offer physical insight and a better understanding of the advantages of the proposed solution or system design, as well as the constraint of the proposed strategies. This article reviews the classical and existing graphical approaches, showing the timeline and trend of some tool series and implementation methods for climate change mitigation. The discussion surrounded the approaches for low carbon buildings and renewable energy development. The future and emerging direction for a low carbon emissions economy are also discussed to tackle the flexibility and reliability issues of the graphical tool for better applicability.

A sustainable circular economy could be generally achieved via process analysis and optimisation. The circular system or design has to be optimised based on sustainability (economically, environmentally and socially) rather than focus on the degree of circularity in the view that circular is not equivalent to sustainable. The articles that compose this Virtual Special Issue (VSI) provide an overview of process analysis and optimisation works that could contribute to a sustainable circular economy. The selected articles ranged from energy, water, and solid waste recovery to negative emission technologies-related topics.

Plastics are among the most-used materials globally, with thousands of different grades and a wide range of applications. However, its end-of-life management is a common issue, despite most plastics produced today containing highly recyclable thermoplastics. The quality of recycled plastic material should be enhanced as it depends on several factors, such as cross-contamination, presence of additives, impurities and degradation rate. In this study, a comparative analysis of thermochemical characteristics of virgin and recycled commonly-used thermoplastic polymer, high-density polyethylene (HDPE), was performed to study the impact of recycling on the material properties. The proximate and ultimate analysis, identification of functional groups and thermal behaviour were performed to study the chemical changes in the recycled and virgin material. The results showed that recycled HDPE started to degrade at a lower temperature than virgin HDPE, with a lower degradation rate (92.7 wt.%) compared to virgin HDPE (99.6 wt.%) due to the presence of impurities and other factors. Calorific values of both samples were comparable, while the degree of crystallinity was 79.8 % for virgin HDPE and around 19 % lower for recycled HDPE samples. Significant differences between recycled and virgin material were also obtained in terms of melting and crystallisation enthalpies.

Among the most pressing environmental issues is the rapidly increasing accumulation and fragmentation of plastic waste materials, particularly in freshwater and marine environments. In this study, polyethylene terephthalate (PET) plastic waste, as one of the major environmental concerns, was exposed to various aquatic environments in the form of plastic bottles and non-woven fibres to investigate the end-of-life behaviour and the formation of micro-, and nanoplastics during the degradation process. The research focuses on tracking plastic waste in model waters (with pH values of 4, 7 and 10) and real waters (seawater and tap water). Both the solid and liquid phases were analysed for fragmentation and leaching of plastics after one month of observation. In the solid phase, gravimetric analysis, presence of functional groups by Fourier Transform Infrared Spectroscopy (ATR-FTIR), morphology and size by optical microscope were measured. In the liquid phase, ecological parameters (pH, conductivity, turbidity, chemical oxygen demand (COD) and total organic carbon (TOC)) and micro/nanoplastic formation (particle size and FTIR analysis under the microscope) were characterised. The results show that PET debris litter to the aquatic environment, in the form of non-woven fibres, has greater negative environmental impacts on turbidity, COD and micro/nano fragment formation. The outcomes of this study indicate a potentially hazardous risk of improperly treated plastic material in various aquatic environments, especially with the type of material structure, such as fibre structure, due to the increased release of micro/nanoplastic into the aquatic environment, which may have serious eco-toxicological effects on wildlife. This study underlies that due to the rapid fragmentation of fibrous PET plastic material, the latter should be properly collected and processed.

Circular Economy and Cradle to Cradle Design have been gaining significant attention in minimising the life cycle environmental footprint of a product or service. However, it remains challenging to model multiple cycles where the products could be finitely or infinitely recovered through upcycling or downcycling, depending on the quality changes, and used as a material in the different product life cycles. This study aims to summarise the Life Cycle Assessment (LCA) methods that consider the cascade utilisation and upcycling of a product which will also apply to the case of plastic recycling. The methodological challenges, particularly for secondary and tertiary plastic recycling, are highlighted. The mini-review is intended to identify the limitation of current assessment methods for the subsequent development of an improved LCA in future work.

Plastic pollution has recently emerged as a major global environmental problem, especially during the global pandemic. The problem spans land, ocean, and air pollution via macro-, micro-, and nanoplastics. Despite the availability of different technologies for recycling plastics under a Circular Economy, their deployment has been hampered by challenges stemming from socio-economic factors. For example, poor segregation of waste by consumers leads to cross-contamination of plastic streams that have recovery potential. Although the enhancement of Plastics Recycling Networks (PRNs) is clearly needed, little progress has been achieved worldwide. In this work, a new class of Process Integration (PI) approaches are developed for optimal planning of PRNs. These approaches draw on the proven capabilities of PI for effective decision support. The basic PRN synthesis problem is defined by a set of sources (waste plastic streams) and sinks (recycling plants) using a systems approach. All streams are assumed to consist of a mix of recyclable polymer and non-recyclable contaminants. Each recycling plant has a predefined processing capacity and upper limit on the contaminant level in its feed stream. Graphical Pinch Analysis (PA) is proposed for this PRN synthesis problem. A scenario-based case study where 95.5% of the available waste is recycled demonstrates its practical application. Prospects for future extensions of the PRN synthesis problem are also discussed.

The paper provides an updated overview of the main achievements and ideas presented at the most recent PRES conferences and in the fields which have been covered by them. The conference history now reached a quarter of the century – from 1998 to 2022. The PRES conferences have become one of the main vehicles for spreading Process Integration (PI) into various research directions and fields of possible implementation. The PRES went successfully during the last period challenged by COVID-19 pandemics. Not all conferences managed to adapt well. However, PRES successfully implemented the hybrid mode and learned how to use it efficiently for enlarging the number of speakers as well as the audience while still keeping very intensive and beneficial cross-fertilisation and networking. Some experiences have been shared in this paper. The hybrid mode helped successfully intensify the research efforts on the research challenge, which remained as a consequence of the COVID-19 pandemics – an increased amount of waste and during the life and economy recovery also increasing environmental footprints. This short overview includesProcess Integration with Pinch AnalysisProcess Integration with another approachDevelopment of heat exchanger systems for Process IntegrationOther extensions of Process Integration for wider Process Systems Engineering and recentlyCircular economyEnvironmental footprints and nexuses and justCOVID-19 pandemics energy and environmental consequences and recovery. This paper presents an attempt to demonstrate and make suggestions for the future growth of the Process Integration branching out during the next years.

This work presents the analysis of Siberian Federal District regions major social-ecological-economic statistics based on research of the indicators of the Goal 7 “Ensuring Environmental Sustainability” of UN Millennium Development Goals (MDG). The results are analysed and discussed. Goal 7 contains three objectives and eight indicators. Energy intensity can be considered a key indicator of sustainability. The analysis of the social-economic development programs of the Siberian Federal District regions shows that most of the regions have not yet achieved the indicator levels of Goal 7, and the progress towards the goals is uneven. The regional authorities need to correct the programs of social-economic development in order to achieve the UN MDG goals. The comparison between Goal 7 indicators and goal progress results makes clear that the regions should pay more attention to the social-economic development directions as a basis for the development of the natural, economic and societal capital.

Waste-to-energy conversion such as anaerobic digestion has been widely promoted under the subsidies to decouple from fossil fuel dependence system and its inherent two-fold benefits. It could diversify the renewable energy matrix and divert the waste from the landfill. Co-digestion of two and more feedstocks could enhance bioenergy production and maximise waste recovery. However, the anticipated benefits are not absolute for all circumstances, varying across the type of co-substrate, pretreatment and other settings. The present study aims to overview the life cycle assessment (LCA) and the techno-economic assessment (TEA) of the anaerobic co-digestion processes. The results could provide an insight into the several critical parameters for sustainable co-digestion. Co-digestion of two or more feedstock is favourable since higher anaerobic digestion performances and higher profitability in TEA is shown. Cultivation of energy crops, transportation, pretreatment of feedstock and storage stage each contributes some shares to eutrophication potential (EP), acidification potential (AP), global warming potential (GWP), ozone depletion and fossil depletion. Generally, high anaerobic digestion performances and biogas upgrading can offset the negative environmental impact. Positive net present value is also observed from the co-digestion of feedstock.

Sustainable agriculture is an ongoing research strives for meeting society’s current food demand without compromising the future need and development. Maintaining soil fertility for quality farming is one of the essential parts. However, the wide application of synthetic agrochemicals (e.g., chemical fertiliser) has been a significant contributor to environmental pollution. This review aims to assess the potential of Rhodopseudomonas palustris (R. palustris), a purple non-sulphur bacterium, as a commercialised bio-fertiliser to sustainably promote plant growth. R. palustris is evaluated based on two defined pillars of sustainability, including the effects on plant growth, environmental impact, and feasible production. The effectiveness is based on the improvement of plant growth through the secretion of extracellular metabolites, resistance to abiotic stresses, bioremediation of heavy metals, and mitigation of greenhouse gas emissions. This review suggests the imperative roles of R. palustris as an effective bio-fertiliser in agriculture. However, the scalability of production and application deserved more attention. The potential substrates ranging from different waste streams and formulation methods for R. palustris production are summarised to discuss environmental and economic sustainability.

Cities are expected to play a major role in managing climate change in the coming decades. The actual environmental performance of urban centres is difficult to predict due to the complex interplay of technologies and infrastructure with social, economic, and political factors. Machine learning (ML) techniques can be used to detect patterns in high-level city data to determine factors that influence favourable climate performance. In this work, rough set-based ML (RSML) is used to identify such patterns in the Sustainable Cities Index (SCI), which ranks 100 of the world’s major urban centres based on three broad criteria that cover social, environmental, and economic dimensions. These main criteria are further broken down into 18 detailed criteria that are used to calculate the aggregate SCI scores of the listed cities. Two of the environmental criteria measure energy intensity and greenhouse gas (GHG) emissions. RSML is used to generate interpretable rule-based (if/then) models that predict energy utilisation and GHG emissions performance of cities based on the other criteria in the database. Attribute reduction techniques are used to identify a set of 7 non-redundant criteria for energy use and 9 non-redundant criteria for GHG emissions; 6 criteria are common to these two sets. Then, RSML is used to generate rule-based models. A 10-rule model is determined for energy intensity, while an 11-rule model is found for GHG emissions. Both models were reduced further by eliminating rules with weak generalisation capability. A key insight from the rule-based models is that social, environmental, and economic attributes are associated with energy intensity and GHG emissions due to indirect effects.

This paper reviews the Process Integration (PI) development related to the recent Conferences on Process Integration for Energy Saving and Pollution Reduction (PRES conferences) and makes suggestions for the future growth of PI branching out in the future. The conference history is now close to a quarter of the century–from 1998 to 2021, and has been flourishing despite the difficult COVID-19 period. The paper overviews the progresses in Process Integration with Pinch Analysis, heat exchangers and Process Integration, extensions of Process Integration for wider process system engineering, integration of renewable energy sources, Circular Economy, extended environmental footprints, extended water-energy nexus contribution to environmental assessment, COVID-19 pandemics environmental consequences, and ecosystem remediation and waste stream clean-up. Considerable progress in Process Integration has also been achieved thanks to PRES conferences. This overview is an attempt to demonstrate the contribution delivered and make suggestions for the future growth of the PI branching out during the next years. It has become apparent that further improvements of the PI technologies are necessary and possible for achieving sufficient reductions of resource demands and pollution so that available renewables and end-of-pipe cleaning can serve them, minimising the environmental impacts. The key methodology developments enabling this are multi-constraint Pinch Analysis and the joint use of several PI methods for delivering comprehensive macro-analyses.

The most important raw material needed for food production is phosphorus (P), which cannot be replaced by other elements. P is listed as a Critical Raw Material (CRM) for the European Union (EU). It is an element essential for human nutrition and is used for fertiliser production. The key importance of P for human life is evidenced by the fact that if there were not enough P in fertilisers, we would only be able to feed 1/3 of the world’s population. Unfortunately, in Visegrad Group (V4) countries, Poland, Slovakia, Czech Republic, and Hungary, there is a lack of mineral deposits of phosphate rock. Therefore, there is a strong need to cover the demand for the P by importing from countries of varying stability, both economic and political, such as Russia, China, or Morocco. It is risky; if the borders for deliveries of goods are closed, it may be impossible to meet the needs of P. On the other hand, V4 countries have large secondary P resources in P-rich waste, which are lost due to P is not recovered on an industrial scale. The paper presents the importance of P raw materials in V4, the revision of primary and secondary P sources that can be used in agricultural systems, as well as the structure of import and export of P raw materials in these countries. In addition, examples of good phosphorus recovery practices in the V4 countries are presented. They include a list of initiatives dedicated to the sustainable management of P resources, and examples of P recovery projects. Implementation of P recovery for internal P-rich waste in V4 could ensure the safety of food production in this region. Such and similar initiatives may contribute to faster independence of the V4 countries from the import of P raw materials.

Composting of biowaste to organic fertiliser promotes resource recycling with various environmental co-benefits, including mitigation of nutrient loss, greenhouse gas emissions, and soil enrichment. As produced from the pyrolysis of organic waste, biochar could be added to compost for enhanced performances. The use of either compost or biochar or both has shown a positive effect on the overall soil quality, such as increasing soil pH and electrical conductivity, increasing soil organic matter, promoting soil carbon storage, and reducing the bioavailability of heavy metals. However, studies have reported contradictory observations and varying degree on the positive effect of such amendments on the aspects mentioned above. This review aims to evaluate the effect of biochar on composting towards a greener and cleaner process. The interacting mechanisms among biochar, compost and biochar-compost amendment upon soil application are discussed. The addition of biochar to compost effectively reduces nutrient loss and gaseous emission and promotes humification. The presence of biochar enrich specific groups of microbes that encourage nitrogen immobilisation. Biochar is more effective in improving the soil carbon pool, whereas compost has a more direct and persistent impact on the soil pH and cation exchange capacity. Upon applying mixed compost with biochar in soil, the organic amendments reduced heavy metals' bioavailability through the respective mechanisms. Different effects of compost and biochar on the soil properties and microbial community were observed, depending on the amendment type, soil condition and length of the application period.

This study aims to assess the environmental footprint of the increasing share of renewable energy and global energy demand. The considered footprints, including GHG emission, NOx emission, SO2 emission and water consumption, are expressed in eco-cost. The assessment indicated that the eco-cost of global energy consumption increased, comparing 2009 (1.66 x 1012 EUR) and 2019 (2.06 x 1012 EUR). This suggests the increasing energy demand (+ 33 %) dominates the positive effect of the renewable energy transition. A significant reduction (= ~38 % - 52 %) on the dependency of nonrenewable energy is required to offset the effect of increasing global demand in 2050 without a substantial increase in eco-cost than 2009 and 2019. However, when referring to the European Union case, it was decreased where 2.05 x 1011 EUR in 2009 and 1.65 x 1011 EUR in 2019. It is progressing towards environmental footprint mitigation, provided by the marginal increase in energy demand (+ 0.4 %) and an increase in renewable energy share. The analysis could serve as a guideline for appropriate policy implications towards a sustainable energy system.

Biochar has a broad application owning to its physicochemical properties and low cost by origin (by-products or generated from waste). Wide research attention received is the application to the soil as carbon sequestration. In contrast to the efficiency evaluation, the overall cost feasibility and environmental performance of the application still deserves broader analysis and discussion. This study aims to enumerate the advantages, and potential drawbacks of the different applications, in term of cost and the environmental footprints. The other alternatives (e.g. the conventional methods) in achieving the same purpose are compared. Special attention is given to the application of biochar to the soil as carbon sequestration. This study could serve as a guideline in evaluating the pros and cons of biochar application to ensure the unburdening footprints can offset the burdening footprint associated with the generation and other downstream processes towards sustainability.

Enabling a higher share of renewables in power planning at the municipal and regional scale is essential for offering local communities a path to sustainable development. However, the utilisation of renewables also carries certain environmental burdens which have to be accounted for in the process of system design and planning. The current paper takes this issue as a departure point, adding the electrical energy storage as a degree of freedom and its influence on the environmental footprints – represented by Greenhouse Gas and Water Footprints. The proposed model and the illustration case study clearly demonstrate the strong dependence of the footprints on the size of the storage facility. Future work should extend the model to account for all essential problem features – including a longer planning horizon, additional footprints and their inter-relationships, as well as the interaction with the economic performance of the system.

Waste treatment and recovery is a critical management challenge. It plays an essential role in narrowing the circular economy loop by reintegrating the products into the system when they reach the end of life. This study aims to assess the waste composition of the EU-27 and identifies the potential carbon emission footprint (CF) reduction through waste treatment transition of bio-waste in mixed municipal solid waste (MMSW). The relationship between the waste composition and socio-economic factors is evaluated by regression analysis. This is to estimate the missing data (in not well-documented countries) on the share of bio-waste in MMSW. Based on the amount of biowaste disposal to the landfill, the potential of CF can be determined when proportionally decreased by the estimated share through waste recovery. The emission reduction potential is different across the countries and waste types due to the differences in the avoided emission through treatment options (e.g. the current countries’ energy mix – the portion of renewable and non-renewable energy). A saving ranging from 35 - 75 % of CF reduction can be achieved in the EU. The results illuminate the significant contribution of bio-waste recovery as a mean for CF reduction and generation of renewable energy. Sensitivity analysis can be conducted in the future work, and the scope of assessment can be extended to cover a broader range of environmental footprints for a more comprehensive comparison.

Thousands of conferences held all over the world annually are closely related to the theme of environmental sustainability. Various methods and measures have been presented in the effort to reduce environmental impacts. However, the impact of the conference itself receives relatively less attention. This study proposed a mathematical model to identify the optimal conference locations with minimal environmental footprints in travelling to and from the conference by the participants. The historical data of Conference on Process Integration for Energy Saving and Pollution Reduction (PRES) consisting the origin of the participants is applied to demonstrate the location selection. The model is developed to include air transport for short and long distances where the environmental impact is considered in the form of external cost. Participants are geographically distributed into points considering the capital of countries. Socio-economic and geographic data are used to estimate the expected number of participants through a linear regression model. Population, the absolute difference in religion, the distance between countries (with a positive impact on total attendance) and continent conservation (negative impact) were found to be significant. The result suggests the Czech Republic as the optimal location with the external cost of about 242 € / cap. The subsequent locations are Estonia and Romania. Future studies can cover multi-objective decision making, including price and more problematically quantified features as safety, health issues and attractiveness.

Seasonal availability of supply and demand market of biomass is one of the challenges for its energy conversion. A suitable production planning approach is required to consider the dynamic characteristic. This study aims to identify the production rate, inventory and supply flow of biomass by integrating Pinch Analysis and mathematical model. Storage to overcome the deficits of biomass supply at the following time interval is also identified. The demonstrated case study suggested a fix production rate of 22,000 GJ/month and adapted to 6,167 GJ/month after the pinch point to meet the fluctuating demand. The required inventory is also suggested. For example, 3,167 GJ of product (bio-oil) inventory on Month 4 to meet the following demand, and with 3,764.1 GJ (301 t) of biomass as storage to overcome the supply deficit (fluctuated) in the following month. The mathematical approach optimises the biomass network flow (allocation) at each time intervals (Month). Emission and transporting cost, as well as the energy content of the biomass resources, are considered. Pinch Analysis serves as an effective tool in providing a starting solution dealing with fluctuating supply and demand for further planning.

Compost leachate (CL) is a liquid by-product of compost that contains carbon, nitrogen, phosphorus, potassium and trace elements. It can partially replace the commercial liquid fertilisers to promote plant growth. However, CL may contain heavy metals, phytotoxic substances such as ammonia, organic compounds of low molecular weight, high level of salt and oils. Treatment of leachate is required to avoid the damage on the plant. This paper aims to review the nutrient and physical characteristics of the CL from three types of bio-wastes, i.e. municipal solid waste, animal waste and green waste. The effects of plants treated with CL in terms of rate and nutrient absorption were discussed. The nutrient and physical composition of the leachate is highly variable due to the diversity of the sources and age of the leachate. Compost leachate from municipal solid waste contains the highest chemical oxygen demand (COD) (15,188 – 105,300 mg/L) followed by those from animal waste (6,542 – 100,000 mg/L) and green waste (804 – 1,152 mg/L). The difference in COD is due to the difference in organic carbon content in the biowaste. Other physical parameters, such as electrical conductivity and pH, are correlated with the organic carbon content. For nutrient composition, municipal solid waste leachate contains the highest nitrogen content (630 – 2,438 mg/L), green waste has the highest potassium content (500 – 1,000 mg/L), while animal waste has the highest phosphate content (170 – 500 mg/L). The nutrient contents of CL derived from different biowaste reviewed in this study serves as a guideline for users to estimate the dilution rate and further nutrient formulation required for the application of CL on plants.

This study develops a graphical decision-making tool inspired by the break-even concept. It facilitates the selection of biomass utilisation where the highest possible profit and lowest GHG emissions indicate the optimal choice. The GHG intensity (kg CO2eq/MWh) and GHG price (USD/kg CO2eq) comprise the y-axis and x-axis of the Break-even Based Decision Making (BBDM) tool. The applicability of the tool is demonstrated by a case study where the biomass (switchgrass and wheat straw) is treated with slow pyrolysis for energy generation and/or biochar production. Burning for electricity is generally a preferable option, especially for countries with high GHG intensity. Biochar application as a form of carbon sequestration is suggested at low GHG intensity. This application becomes the preferred option when the GHG price is higher than 0.03 USD/kg CO2eq for switchgrass and higher than 0.01 USD/kg CO2eq for wheat straw. Wheat straw, as agricultural waste, has the advantage of lower GHG footprint while switchgrass offers a higher energy output. In general, the choice of the best use of biomass can be different under different circumstances. The developed tool is able to provide a rigorous basis for decision support when the GHG intensity and GHG price are defined.

Waste recovery and disposal are one of the biggest management challenges. An adequate waste management design is critical in contributing to the development of a sustainable circular economy. There is a need for a systematic and preferably graphical approach to assessing the emissions associated with waste treatment processes followed by strategies for mitigation. This study aims to propose a graphical approach in identifying the appropriate waste management system (WMS) with lower emissions. The proposed graph-based approach termed as Extended-Waste Management Pinch Analysis (E-WAMPA) is an extension to the existing WAMPA. It is distinguishable by three major issues a) Emission intensity of WMS (Net GHG per capita) and stagewise algorithm aims for regional waste management planning are introduced, b) the emissions of recycling are not assumed as zero c) The demonstration is based on the defined targets, projection and power grid mix of EU. A generic methodology of E-WAMPA is presented and followed by the European Union- 28 member states (EU-28) case study to elucidate the application. The considered waste type is the municipal solid waste (MSW), and the assessed emission is GHG. E-WAMPA is capable of suggesting the strategies in fulfilling the targeted emission reduction of a region (e.g. 10 % reduction) and meeting the individual treatment targets. One of the possible strategies is demonstrated on adjusting the WMS of Malta, Greece, Cyprus and Romania. The way forward of E-WAMPA have been discussed as well.

Waste to energy (WtE) is one of the suitable alternatives in handling municipal solid waste (MSW). This study assesses the GHG emissions (CO2eq) of incineration and anaerobic digestion (AD) under different electricity production mix. The electricity production mix of China, Malaysia, Japan, Russia, UK, US (East), Czech Republic, Germany, France and Finland were considered. Incineration has a lower net CO2eq emission in China and Malaysia. However, the AD is environmentally preferable than incineration in Russia, Japan, Czech Republic, Germany, US (East), UK, Finland and France. The net CO2eq emission of incineration in China (9.41 kg CO2eq/t MSW) is lower than a country with greener electricity mix e.g. France (401.76 kg CO2eq/t MSW) where the main electricity source is nuclear. This is due to the higher avoided CO2eq emission compare to generate electricity from fossil fuel. Electricity produces from the WtE process is identified as the major factors in affecting the net CO2eq emission than the other two assessed factors (waste collection and transportation (distance), the efficiency of the WtE process). This suggests energy efficiency plays a significant role in enhancing the net CO2eq emissions and to reduce the carbon intensity of WtE.

Water use within power supply chains has been frequently investigated. A unified framework to quantify the water use of power supply chains deserves more development. This article provides an overview of the water footprint and virtual water incorporated into power supply chains. A water-use mapping model of the power supply chain is proposed in order to map the analysed research works according to the considered aspects. The distribution of water footprint per power generation technology per region is illustrated, in which Asia is characterised by the largest variation of the water footprint in hydro-, solar, and wind power. A broader consensus on the system boundary for the water footprint evaluation is needed. The review also concludes that the water footprint of power estimated by a top-down approach is usually higher and more accurate. A consistent virtual water accounting framework for power supply chains is still lacking. Water scarcity risks could increase through domestic and global power trade. This review provides policymakers with insights on integrating water and energy resources in order to achieve sustainable development for power supply chains. For future work, it is essential to identify the responsibilities of both the supply and demand sides to alleviate the water stress.

Energy is a fundamental element supporting societal development, particularly with the increasing dependency on the Internet of Things. It is also the main contributor to environmental impacts and subsequently, a potential sector for mitigation. Sustainable energy system design considers energy savings and energy efficiency, waste and consumption reduction, process efficiency enhancement, waste heat recovery, and integration of renewable energy. Emerging tools range from advanced Process Integration, modelling, simulation, and optimisation, to system analysis and assessment. This review covers selected emerging studies promoting sustainable system design, including the recent developments reported in the Special Issue (SI) of the 22nd Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (PRES’19). The primary emphasis was to enhance the economic and environmental performance. However, social factors were also highlighted as essential for future sustainable development. The discussion and analysis in this review focus on the most recent developments of (a) heat integration and heat transfer; (b) integrated and newly developed heat exchangers, (c) integration of renewables, and (d) roles in economic and environmental sustainability. The key results are highlighted, and future research ideas are suggested according to their links to a broader context.

The agriculture sector and its development have played an important role in nurturing the modern civilisation. Agriculture produces food through the utilisation of resources, including nutrient, water and soil. Traditional agriculture has met with concern over the emission of greenhouse gas (GHG), drainage of water resource, consumption of fertiliser and production of waste. Optimising agricultural productivity is essential to meet the growing food demand associated with the rapid population growth worldwide. Smart agriculture (SA) is the approach focusing on agricultural practices that increase productivity and resource resilient while reducing GHG emission. SA has incorporated optimal farming management on water usage, fertiliser application and crop’s production through internet-of-things (IoT) and various sensors. A significant amount of solid wastes are generated throughout the agricultural practices. The waste within the system can be precious resource provided an effective waste-to-resource loop is present. The scheduled waste collection system is cost ineffective and not optimum. In smart cities, the sensor-based networks have been used to monitor the waste load in a container and the route of the waste collector to improve the collection efficiency. However, the integration of smart waste management in the SA is still limited. IoT and sensors can improve the waste management loop through the optimisation of waste collection, transportation and utilisation for resource recovery. This review aims to provide an overview of the role of the effective waste-to-resource loop within a smart agricultural system. This could present a better insight on the important elements in defining the role of smart waste management in SA.

Transportation is one of the largest air pollutants as well as the Greenhouse Gas (GHGs) contributors. The inclusion of air pollutants in optimisation studies is less established than the use of CO2 and/or GHGs which are often used as an indicator of environmental sustainability. This study aims to assess environmentally sustainable alternatives for freight transportation by considering both GHG and air pollutants. A case study identifying air emissions of different freight transport modes for moving goods from Rotterdam is presented. The assessed freight transports include articulated lorry, container ship, bulk carrier, and rail operated by diesel. The environmentally sustainable freight transport of the studied route based on the common practice (GHGs only) and the inclusion of air pollutants are discussed. Evaluation of the results shows that transport with lower GHG emissions does not result on PM and SOx as well. A possibility of inappropriate decision making has been consequently highlighted. The impact of loaded capacity in moving the goods on the emission is assessed from the perspective of logistics service provider. A further comprehensive study which includes the entire life cycle is needed as this study only considers the tank to wheel emissions.

The extensive utilisation of microorganisms namely fungi and bacteria for treating organic wastes has been attributed to their efficiency in eliminating pathogen and accelerating the degradation process. Their uses have been found considerably efficient for enhancing waste treatment. Among many methods employed, composting mediated by indigenous microbial communities has gained significant popularity in treating organic waste. Use of cellulolytic microorganisms to expedite the degradation rate of wastes, notably the lignocellulosic components, may prove useful. This paper reviews the application of microorganisms in the waste management technologies that include anaerobic digestion and composting of organic waste with a high lignocellulosic portion, composting of heavy metal contaminated organic waste, and composting at low temperature.

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.