A potential slow-release fertilizer based on biogas residue biochar: Nutrient release patterns and synergistic mechanism for improving soil fertility.

The large yield of anaerobic digestates and the suboptimal efficacy of nutrient slow-release severely limit its practical application. To address these issues, a new biochar based fertilizer (MAP@BRC) was developed using biogas residue biochar (BRC) to recover nitrogen and phosphorus from biogas slurry. The nutrient release patterns of MAP@BRC and mechanisms for enhancing soil fertility were studied, and it demonstrated excellent performance, with 59% total nitrogen and 50% total phosphorus nutrient release rates within 28 days. This was attributed to the coupling of the mechanism involving the dissolution of struvite skeletons and the release of biochar pores. Pot experiments showed that crop yield and water productivity were doubled in the MAP@BRC group compared with unfertilized planting. The application of MAP@BRC also improved soil nutrient levels, reduced soil acidification, increased microbial populations, and decreased soil heavy metal pollution risk. The key factors that contributed to the improvement in soil fertility by MAP@BRC were an increase in available nitrogen and the optimization of pH levels in the soil. Overall, MAP@BRC is a safe, slow-release fertilizer that exhibits biochar-fertilizer interactions and synergistic effects. This slow-release fertilizer was prepared by treating a phosphorus-rich biogas slurry with a nitrogen-rich biogas slurry, and it simultaneously addresses problems associated with livestock waste treatment and provides a promising strategy to promote zero-waste agriculture.

Municipal solid waste management for low-carbon transition: A systematic review of artificial neural network applications for trend prediction.

Improper municipal solid waste (MSW) management contributes to greenhouse gas emissions, necessitating emissions reduction strategies such as waste reduction, recycling, and composting to move towards a more sustainable, low-carbon future. Machine learning models are applied for MSW-related trend prediction to provide insights on future waste generation or carbon emissions trends and assist the formulation of effective low-carbon policies. Yet, the existing machine learning models are diverse and scattered. This inconsistency poses challenges for researchers in the MSW domain who seek to identify and optimize the machine learning techniques and configurations for their applications. This systematic review focuses on MSW-related trend prediction using the most frequently applied machine learning model, artificial neural network (ANN), while addressing potential methodological improvements for reducing prediction uncertainty. Thirty-two papers published from 2013 to 2023 are included in this review, all applying ANN for MSW-related trend prediction. Observing a decrease in the size of data samples used in studies from daily to annual timescales, the summarized statistics suggest that well-performing ANN models can still be developed with approximately 33 annual data samples. This indicates promising opportunities for modeling macroscale greenhouse gas emissions in future works. Existing literature commonly used the grid search (manual) technique for hyperparameter (e.g., learning rate, number of neurons) optimization and should explore more time-efficient automated optimization techniques. Since there are no one-size-fits-all performance indicators, it is crucial to report the model's predictive performance based on more than one performance indicator and examine its uncertainty. The predictive performance of newly-developed integrated models should also be benchmarked to show performance improvement clearly and promote similar applications in future works. The review analyzed the shortcomings, best practices, and prospects of ANNs for MSW-related trend predictions, supporting the realization of practical applications of ANNs to enhance waste management practices and reduce carbon emissions.

Forecasting meteorological impacts on the environmental sustainability of a large-scale solar plant via artificial intelligence-based life cycle assessment.

Although large-scale solar (LSS) is a promising renewable energy technology, it causes adverse impacts on the ecosystem, human health, and resource depletion throughout its upstream (i.e., raw material extraction to solar panel production) and downstream (i.e., plant demolition and waste management) processes. The LSS operational performance also fluctuates due to meteorological conditions, leading to uncertainty in electricity generation and raising concerns about its overall environmental performance. Hitherto, there has been no evidence-backed study that evaluates the ecological sustainability of LSS with the consideration of meteorological uncertainties. In this study, a novel integrated Life Cycle Assessment (LCA) and Artificial Neural Network (ANN) framework is developed to forecast the meteorological impacts on LSS's electricity generation and its life cycle environmental sustainability. For LCA, 18 impact categories and three damage categories are characterised and assessed by ReCiPe 2016 via SimaPro v. 9.1. For ANN, a feedforward neural network is applied via Neural Designer 5.9.3. Taking an LSS plant in Malaysia as a case study, the photovoltaic panel production stage contributes the highest environmental impact in LSS (30 % of human health, 30 % of ecosystem quality, and 34 % of resource scarcity). Aluminium recycling reduces by 10 % for human health, 10 % for ecosystem quality, and 9 % for resource scarcity. The emissions avoided by the forecasted LSS-generated electricity offset the environmental burden for human health, ecosystem quality, and resource scarcity 12-68 times, 13-73 times, and 18-98 times, respectively. The developed ANN-LCA framework can provide LSS stakeholders with data-backed insights to effectively design an environmentally conscious LSS facility, considering meteorological influences.

Curbing global solid waste emissions toward net-zero warming futures.

No global analysis has considered the warming that could be averted through improved solid waste management and how much that could contribute to meeting the Paris Agreement's 1.5° and 2°C pathway goals or the terms of the Global Methane Pledge. With our estimated global solid waste generation of 2.56 to 3.33 billion tonnes by 2050, implementing abrupt technical and behavioral changes could result in a net-zero warming solid waste system relative to 2020, leading to 11 to 27 billion tonnes of carbon dioxide warming-equivalent emissions under the temperature limits. These changes, however, require accelerated adoption within 9 to 17 years (by 2033 to 2041) to align with the Global Methane Pledge. Rapidly reducing methane, carbon dioxide, and nitrous oxide emissions is necessary to maximize the short-term climate benefits and stop the ongoing temperature rise.

Exploring the factors influencing consumer behaviours and practices towards sustainable WEEE management in Putrajaya, Malaysia.

The disposal practises and preferences of household waste from electrical and electronic equipment disposal (WEEE) are essential components in material flow analysis (MFA). Nevertheless, the synergistic of consumers' behaviours and preferences with the disposal of different WEEE has yet to be investigated in depth. This study examined several consumer features of WEEE management using a quantitative questionnaire survey, including consumers' disposal behaviours and preferences. As a Malaysian federal government administrative centre, and model of a contemporary and sustainable Malaysian city, Putrajaya was chosen as the study area. Using stratified random sampling, the questionnaire was distributed through face-to-face and online surveys among households across 20 precincts within Putrajaya. From June 2021 to January 2022, 500 surveys were distributed over seven months, and IBM SPSS Statistic version 26 was used to analyse the data. The result shows that 80% of respondents have a good knowledge of WEEE management and are fully aware of the dangerous materials they have in their WEEE. 75% said they would recycle their WEEE, but only 44% said they would separate it from other household wastes. It was also shown that 88% of the household were willing to pay a collection fee of at least RM 10 for each collection. This analysis found that Extended Producer Responsibility (EPR) mechanisms can assist in overcoming weaknesses in WEEE management by including beneficial schemes to incentivise consumers to improve current waste policies. In the meantime, governments, media, and local non-governmental organisations may help by increasing awareness of effective and sustainable WEEE management.

Post-COVID-19 pandemic and the Paris agreement: a socioeconomic analysis and carbon emissions forecasting in developed and developing countries.

The COVID-19 pandemic caused profound impacts on the global economy, resulting in a sharp drop in carbon emissions as energy demand fell. The emissions reduction due to past extreme events often follows with a rebound after the economy recovers, but the pandemic's impacts on the long-term carbon emissions trend remain unknown. This study forecasts the carbon emissions of Group of Seven (G7) as developed countries and Emerging Seven (E7) as developing countries using socioeconomic indicators and artificial intelligence-powered predictive analytics to assess the pandemic's impacts on the long-term carbon trajectory curve and their progress toward achieving the Paris Agreement goals. Most E7's carbon emissions have strong positive correlations (> 0.8) with the socioeconomic indicators, whereas most G7's correlate negatively (> 0.6) due to their decoupled economic growth from carbon emissions. The forecasts show higher growth rates in the E7's carbon emissions after the rebound in the pandemic scenario compared to the pandemic-free scenario, while the impact on the G7's carbon emissions is negligible. The overall impact of the pandemic outbreak on long-term carbon emissions is small. Still, its short-term positive impact on the environment should not be misunderstood, and stringent emissions reduction policies must be implemented urgently to ensure the achievement of Paris Agreement goals. Graphical Abstract: Research methodology for assessing the pandemic's impacts on the G7 and E7 countries' long-term carbon trajectory curve. Supplementary Information: The online version contains supplementary material available at 10.1007/s10098-023-02508-0.

An integrated life-cycle greenhouse gas protocol accounting on oil palm trunk and empty fruit bunch biofuel production.

Improper discard of oil palm trunk and empty fruit bunch renders massive greenhouse gases. Turning these palm wastes into solid biofuels could aid in carbon reduction. The embodied environmental impacts of the solid biofuel densification process are neglected in carbon emission quantification studies applying Greenhouse Gas Protocol while the significance of classifying the system's direct and indirect carbon emissions were overlooked in those utilising life cycle assessment. Despite the prospect of both methodologies to complement their limitations for carbon emissions quantification, no study integrates both methodologies to investigate direct and indirect emissions systematically from a life cycle perspective. An integrated framework of life cycle assessment and Greenhouse Gas Protocol is developed to quantify the direct and indirect carbon emissions of oil palm trunk and empty fruit bunch densification from cradle-to-gate for three pellet plants in Indonesia and Malaysia. The emissions are categorised into three emission scopes: Scope 1, Scope 2, and Scope 3 according to the Greenhouse Gas Protocol, integrated with avoided emissions which are quantified via life cycle assessment. The pellet plants generate 534.7-732.3 kg CO2-eq/tonnepellet per hour, in which Scope 1 (i.e., direct emissions) is the major emission scope due to high emissions from wastewater production and drying fuel combustion. Washing equipment (169.2-439.0 kg CO2-eq/tonnepellet per hour) and burners (87.1-214.5 kg CO2-eq/tonnepellet per hour) are the hotspots found in the pellet plants. Producing empty fruit bunch pellets could reduce 62.0-74.1 % of emissions than landfilling the empty fruit bunch. Empty fruit bunch pellet and oil palm trunk pellet are recommended to co-fire with coal to phase down coal usage in achieving COP26 pledge. This study provides data-driven insights for quantifying carbon emissions through the integrated framework and could be a reference in future life cycle carbon footprint studies of the biomass densification process.

Policy-driven municipal solid waste management assessment using relative quadrant eco-efficiency: A case study in Malaysia.

Despite studies encouraging sustainable waste management, most municipal wastes remain in landfills, particularly in developing countries. Lack of holistic planning and national policy alignment might impair the waste management facility implementation. Policy-driven waste treatment scenarios should be designed to strongly link to the local conditions when assessing the eco-efficiency impacts of the waste management system. Taking Malaysia as a case study, a relative quadrant life cycle eco-efficiency indicator is developed to investigate the eco-efficiency of waste treatment scenarios. The relative quadrant life cycle eco-efficiency indicator depicts the eco-efficiency of various waste management scenarios. Compared with Scenario S1 - business-as-usual (i.e., 71.5% open landfill, 10% sanitary landfill, 1% composting, 17.5% recycling), five waste treatment scenarios (S2-S6) are designed based on Malaysia's existing and future policy targets. Scenario S5 (15.5% sanitary landfill, 22.25% composting, 22.25% anaerobic digestion, 40% recycling) and Scenario S6 (5% sanitary landfill, 22.25% composting, 22.25% anaerobic digestion, 40% recycling, 10.5% incineration) demonstrate that the 40% recycling rate is 32.9-33.6 times more environmentally favorable and 10-20% more economically viable than business-as-usual. Another four scenarios (NS1-NS4) are designed to investigate zero waste in landfills and the need to implement incineration or material recovery. Scenario NS3 suggests increasing incineration capacity to 33% could be an option should incineration is implemented. Adopting home or centralized windrow composting and increasing 2.5-5.5 times of current Feed-in Tariff rates are recommended to improve the eco-efficiency of the waste treatment scenarios. This study could facilitate policymakers to set waste minimization targets and incentives through various scenarios via sensitivity and comparative analyses.

Life cycle assessment of bioelectrochemical and integrated microbial fuel cell systems for sustainable wastewater treatment and resource recovery.

Bioelectrochemical system (BES) is an emerging technology that can treat wastewater via microbial activity while producing energy simultaneously. The system can couple with conventional systems to improve system performance. This study aims to compare the environmental performance of BES and the integrated microbial fuel cell (MFC) systems via a life cycle assessment methodology and identify the major environmental hotspots of the system. Fifteen treatment options are assessed with the ReCiPe 2016 characterization method using SimaPro 9.2 software. The results show double chamber air-cathode microbial electrolysis cell (MEC1) and membrane distillation integrated MFC (MD + MFC) treatment options present as the most environmental favourable among the BES and integrated MFC systems, respectively, due to the offset of the environmental loads from the avoided impacts contributed by their value-added by-product, which is hydrogen fuel for MEC1 and tap water for MD + MFC. Electricity consumption dominates the environmental loads of all the BES options for up to 90% of the global warming impact category. The environmental benefits from the electricity generation of BES are minor (i.e., MFC: 0.01-2% while microbial desalination cell: 0.01-7% of the total environmental impact in a system) to offset the environmental loads incurred by the system. Platinum-based cathode incurs 2.5-24 times higher environmental burdens than non-platinum configurations in MFC under the human carcinogenic toxicity impact category. In line with Sustainable Development Goals 6 and 13, this study provides scientific references to wastewater treatment stakeholders in selecting suitable BES and integrated MFC systems to improve water sanitation and address climate change simultaneously.

Environment impact and bioenergy analysis on the microwave pyrolysis of WAS from food industry: Comparison of CO2 and N2 atmosphere.

The alarming output of waste activated sludge (WAS) from industries requires proper management routes to minimize its impact on the environment during disposal. Pyrolysis is a feasible way of processing and valorizing WAS into higher-value products of alternate use. Despite extensive research into the potential of WAS through pyrolysis, the technology's long-term viability and environmental impact have yet to be fully revealed. In addition, the environmental effects of utilizing different pyrolysis atmosphere (N2 or CO2) has not been studied before, although benefits of CO2 reactivity during pyrolysis have been discovered. This study evaluates the process's environmental impact, carbon footprint, and bioenergy yield when different pyrolysis atmospheres are used. The global warming potential (GWP) for a functional unit of 1 t of dried WAS is 203.81 kg CO2 eq. The heat required during pyrolysis contributes the most (63.7%) towards GWP due to high energy usage, followed by the drying process (23.6%). Transportation contributes the most towards toxicity impact (59.3%) through dust, NOx, NH3 and SO2 emissions. The initial moisture content of raw WAS (65%) greatly impacts overall energy consumption and environmental impact. Pyrolysis in an N2 atmosphere will result in a higher overall bioenergy yield (833 kWh/tonne) and a lower carbon footprint (-1.09 kg CO2/tonne). However, when CO2 was used, the specific energy value within the biochar is higher (22.26 MJ/kg) due to enhanced carbonization. The carbon content of gas derived increased due to higher CO yield. From an energy perspective, the current setup will achieve a net positive bioenergy yield of 561 kW (CO2) and 833 kW (N2), where end products like biochar, bio-oil and gas can be used for power production. Despite the energy-intensive process, microwave pyrolysis has excellent potential to achieve a negative carbon footprint. The biochar used for soil amendment served as a good carbon sink. The utilization of CO2 as carrier gases provides a pathway to utilize anthropogenic CO2, which helps reduce global warming. This work demonstrates microwave pyrolysis as a negative emission, bioenergy-producing approach for WAS disposal and valorization.

A systematic review of life cycle assessment of solid waste management: Methodological trends and prospects.

Solid waste disposal has led to increasing concerns over resource, health, and environmental problems. These issues have been investigated using the Life Cycle Assessment (LCA) technique which helps identify the roots of varying hazards and allows decision-makers to improve the environmental performance of waste management practices. However, there is a lack of review studies that conducted meta-analysis related to developments in critical methodological steps of LCA on solid waste management. To fill this gap, this review paper examines 15 elements comprising the preference of journals, 13 LCA method-related characteristics, and economic assessment. Insights on the limitations and current practices of LCA applications, along with trends for future research, are provided. 240 studies on the LCA of SWM from 2009 until 2020 were systematically reviewed and classified into two major year-groups (i.e., 2009-2014 and 2015-2020) to investigate the trend changes. Among the studied elements, it is found that energy-related applications are on the increase in LCA studies on solid waste management. Anaerobic digestion facilities nearly double in appearance in the second year-group (2015-2020). There is also a more frequent occurrence of certain characterization methods like ReCiPe and CML. Functional units become more diverse, but are overall mostly defined on a mass basis. A frequently identified issue of many LCAs on solid waste management is the ambiguity of data sources such as out-of-date literature or inconsistent geographical references. By addressing issues of methodological standardization, this review study provides a basis to further increase the reliability of results of future LCA studies on solid waste management.

An integrated life cycle multi-objective optimization model for health-environment-economic nexus in food waste management sector.

Food waste is a universal problem in many countries. In line with Sustainable Development Goals 7 and 12, it is crucial to identify a cost-effective food waste valorization management framework with the least human health and environmental impacts. However, studies on the synergistic effect of life cycle assessment and mathematical optimization interconnected with human health, environment, and economic are relatively few and far between; hence they cannot provide holistic recommendations to policymakers in developing environmental and economic feasibility of food waste management frameworks. Taking Malaysia as a case study, this study proposes a simple and deterministic model that integrates life cycle assessment and multi-objective mathematical optimization to unpack the health-environment-economic wellbeing nexus in food waste management sector. The model evaluates the life cycle human health, environmental, and economic impacts of five food waste disposal and valorization technologies: open landfill, sanitary landfill, aerated windrow composting, high-temperature drying sterilization, and anaerobic digestion, and identifies the optimal food waste valorization configuration solution in Malaysia. Based on the results modeled by SimaPro 9.0 and General Algebraic Modeling System with augmented ε-constraint, valorization of food waste into electricity via anaerobic digestion is the most favorable option, with 146% and 161% reduction of human health and ecosystems, respectively, as compared with open landfill. If cost is combined as an objective function with human health and ecosystems, high-temperature drying sterilization is the most attractive scenario due to the high livestock feed revenue. Among the 10 Pareto-optimal solutions, 9% sanitary landfill, 3% aerated windrow composting, 30% high-temperature drying sterilization, 30% anaerobic digestion to electricity, and 28% anaerobic digestion to cooking gas, is recommended as future food waste management configuration. The sensitivity results demonstrate that prices of electricity, cooking gas, and livestock feed affect the optimal configuration food waste management system.

A Content Review of Life Cycle Assessment of Nanomaterials: Current Practices, Challenges, and Future Prospects.

This paper provides a comprehensive review of 71 previous studies on the life cycle assessment (LCA) of nanomaterials (NMs) from 2001 to 2020 (19 years). Although various studies have been carried out to assess the efficiency and potential of wastes for nanotechnology, little attention has been paid to conducting a comprehensive analysis related to the environmental performance and hotspot of NMs, based on LCA methodology. Therefore, this paper highlights and discusses LCA methodology's basis (goal and scope definition, system boundary, life cycle inventory, life cycle impact assessment, and interpretation) to insights into current practices, limitations, progress, and challenges of LCA application NMs. We found that there is still a lack of comprehensive LCA study on the environmental impacts of NMs until end-of-life stages, thereby potentially supporting misleading conclusions, in most of the previous studies reviewed. For a comprehensive evaluation of LCA of NMs, we recommend that future studies should: (1) report more detailed and transparent LCI data within NMs LCA studies; (2) consider the environmental impacts and potential risks of NMs within their whole life cycle; (3) adopt a transparent and prudent characterization model; and (4) include toxicity, uncertainty, and sensitivity assessments to analyze the exposure pathways of NMs further. Future recommendations towards improvement and harmonization of methodological for future research directions were discussed and provided. This study's findings redound to future research in the field of LCA NMs specifically, considering that the release of NMs into the environment is yet to be explored due to limited understanding of the mechanisms and pathways involved.

Environmental assessment of food waste valorization in producing biogas for various types of energy use based on LCA approach.

This paper aims to evaluate the environmental impacts of valorizing food waste for three types of energy use, namely electricity and heat, city gas, and biogas fuel as a petrol, diesel, and liquefied petroleum gas substitute for vehicle use, with reference to the Hong Kong scenario. The life cycle based environmental assessment is conducted from bin-to-cradle system boundary via SimaPro 7.2.4 with ReCiPe 1.04. All of the inventory data of included processes is based on reports of government and industrial sectors. The results show that biogas fuel as a petrol substitute for vehicle use is advantageous over other types of energy use in regard to human health and ecosystems, and it is also the best considering the government's future emission reduction targets set out for the power and transport sectors in Hong Kong. By turning 1080 tonnes per day of food waste into biogas vehicle fuel as petrol substitute, it reduces 1.9% of greenhouse gas emissions in the transport sectors, which results a larger decrease of GHG emissions than the achieved mitigation in Hong Kong from 2005 to 2010.

A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong.

Hong Kong is experiencing a pressing need for food waste management. Currently, approximately 3600 tonnes of food waste are disposed of at landfills in Hong Kong daily. The landfills in Hong Kong are expected to be exhausted by 2020. In the long run, unavoidable food waste should be sorted out from the other municipal solid waste (MSW) and then valorized into valuable resources. A simple sorting process involving less behavioural change of residents is, therefore, of paramount importance in order to encourage residents to sort the food waste from other MSW. In this paper, a sustainable framework of food waste collection and recycling for renewable biogas fuel production is proposed. For an efficient separation and collection system, an optic bag (i.e. green bag) can be used to pack the food waste, while the residual MSW can be packed in a common plastic bag. All the wastes are then sent to the refuse transfer stations in the conventional way (i.e. refuse collection vehicles). At the refuse transfer stations, the food waste is separated from the residual MSW using optic sensors which recognize the colours of the bags. The food waste in the optic bags is then delivered to the proposed Organic Waste Treatment Facilities, in which biogas is generated following the anaerobic digestion technology. The biogas can be further upgraded via gas upgrading units to a quality suitable for use as a vehicle biogas fuel. The use of biogas fuel from food waste has been widely practiced by some countries such as Sweden, France, and Norway. Hopefully, the proposed framework can provide the epitome of the waste-to-wealth concept for the sustainable collection and recycling of food waste in Hong Kong.

Food waste collection and recycling for value-added products: potential applications and challenges in Hong Kong.

About 3600 tonnes food waste are discarded in the landfills in Hong Kong daily. It is expected that the three strategic landfills in Hong Kong will be exhausted by 2020. In consideration of the food waste management environment and community needs in Hong Kong, as well as with reference to the food waste management systems in cities such as Linköping in Sweden and Oslo in Norway, a framework of food waste separation, collection, and recycling for food waste valorization is proposed in this paper. Food waste can be packed in an optic bag (i.e., a bag in green color), while the residual municipal solid waste (MSW) can be packed in a common plastic bag. All the wastes are then sent to the refuse transfer stations, in which food waste is separated from the residual MSW using an optic sensor. On the one hand, the sorted food waste can be converted into valuable materials (e.g., compost, swine feed, fish feed). On the other hand, the sorted food waste can be sent to the proposed Organic Waste Treatment Facilities and sewage treatment works for producing biogas. The biogas can be recovered to produce electricity and city gas (i.e., heating fuel for cooking purpose). Due to the challenges faced by the value-added products in Hong Kong, the biogas is recommended to be upgraded as a biogas fuel for vehicle use. Hopefully, the proposed framework will provide a simple and effective approach to food waste separation at source and promote sustainable use of waste to resource in Hong Kong.