Expanding the anaerobic digestion map: A review of intermediates in the digestion of food waste

Anaerobic digestion is a promising technology as a renewable source of energy products, but these products have low economic value and process control is challenging. Identifying intermediates formed throughout the process could enhance understanding and offer opportunities for improved monitoring, control, and valorisation. In this review, intermediates present in the anaerobic digestion process are identified and discussed, including the following: volatile fatty acids, carboxylic acid, amino acids, furans, terpenes and phytochemicals. The key limitations associated with exploiting these intermediates are also addressed including challenging mixed cultures of microbiology, complex feedstocks, and difficult extraction and separation techniques

Life cycle assessment of electricity generation from sugarcane bagasse hydrochar produced by microwave assisted hydrothermal carbonization

Microwave assisted hydrothermal carbonization (MAHTC) is a promising strategy for fuel production from sugarcane bagasse. Even though microwave heating has been reported to facilitate product (hydrochar) yield, energy properties and heating efficiency during hydrothermal carbonization (HTC) process, the environmental consequences of MAHTC treatment were still not clear. This study evaluated the environmental impact associated with 1 MJ electricity generation from sugarcane bagasse hydrochar through life cycle assessment (LCA) method, focusing on the critical role of process-based parameters to provide insights for optimization of MAHTC treatment. Specifically, two different allocation factors (energy content and economic value) and five environmental impact categories (climate change, freshwater eutrophication, freshwater ecotoxicity, human toxicity and fossil depletion) were assessed in this study. The LCA results revealed significant contribution of MAHTC process on climate change and fossil depletion because of large energy consumption used to maintain the system at designed temperature. Discharge of liquid phase from MAHTC process resulted in severe eutrophication impact especially when economic value was used as allocation factor. Gas emission from hydrochar combustion caused most toxicity related impacts indicating essential requirement of further investigation to quantify different gaseous composition. Based on LCA results, sensitivity analysis indicated hydrochar yield and carbon content as the top two influential factors on total environmental consequences. Comparison study with other fuel sources were further conducted to identify the influence of substituted energy sources. The overall results suggested MAHTC as promising method for bagasse utilization and energy retention efficiency as important indicator for optimization of MAHTC treatment or the sake of high-quality products and good environmental performance

Impact of metallic nanoparticles on anaerobic digestion: A systematic review

Anaerobic digestion (AD) is one of the most energy-efficient waste treatment technologies for biodegradable wastes. Owing to the increasing trend of metallic nanoparticle applications in industry, they are ubiquitous to the waste streams, which may lead to remarkable impacts on the performance of the AD process. This review addresses the knowledge gaps and summarises the findings from the academic articles published from 2010 to 2019 focusing on the influences on both AD processes of biochemical hydrogen-generation and methane-production from selected metallic nano-materials. Both qualitative and quantitative analyses were conducted with selected indicators to evaluate the metallic nanoparticles' influences on the AD process. The selected metallic nanoparticles were grouped in the view of their chemical formulations aiming to point out the possible mechanisms behind their effects on AD processes. In summary, most metallic nanoparticles with trace-element-base (e.g. iron, cobalt, nickel) have positive effects on both AD hydrogen-generation and methane-production processes in terms of gas production, effluent quality, as well as process optimisation. Within an optimum concentration, they serve as key nutrients providers, aid key enzymes and co-enzymes synthesis, and thus stimulate anaerobic microorganism activities. As for the nano-additives without trace-element base, their positive influences are relied on providing active sites for the microorganism, as well as absorbing inhibitory factors. Moreover, comparisons of these nano-additives' impacts on the two gas-production phases were conducted, while methane-production phases are found to be more sensitive to additions of these nanoparticles then hydrogen-production phase. Research perspectives and research gaps in this area are discussed

Comparison of environmental impacts of individual meals - Does it really make a difference to choose plant-based meals instead of meat-based ones?

More than one third of global greenhouse gas emissions (GHG) can be attributed to our food system. Limiting global warming to 1.5° or 2 °C will not be possible without reducing GHG emissions from the food system. Dietary change at the meal level is of great importance as day-to-day consumption patterns drive the global food production system. The aim of this paper was to assess the life cycle environmental impact of a sample of meals from different cuisines (chilli, lasagne, curry and teriyaki meals) and their meat-based, vegetarian, vegan, and whole-food vegan recipe variations. The environmental impacts (global warming, freshwater eutrophication, terrestrial acidification and water depletion potential) of 13 meals, made with 33 different ingredients, were estimated from cradle to plate using Life Cycle Assessment (LCA). Results showed that irrespective of the type of cuisine, the plant-based version of meals (vegan and whole-food vegan) had substantially lower environmental impacts across all impact categories than their vegetarian and meat-based versions. On average, meat-based meals had 14 times higher environmental impact, while vegetarian meals had 3 times higher environmental impact than vegan meals. Substantial reductions in the environmental impacts of meals can be achieved when animal-based ingredients (e.g., beef, cheese, pork, chicken) are replaced with whole or minimally processed plant-based ingredients (i.e., vegetables, legumes) in recipes. Swapping animal-based meals for plant-based versions, and preferably transitioning to plant-based diets, present important opportunities for mitigating climate change and safeguarding environmental sustainability

Measuring the Impact of the COVID-19 Lockdown on Crime in a Medium-Sized City in China

Objectives: The study examines the variation in the daily incidence of eight acquisitive crimes: automobile theft, electromobile theft, motorcycle theft, bicycle theft, theft from automobiles, pickpocketing, residential burglary, and cyber-fraud before the lockdown and the duration of the lockdown for a medium-sized city in China. Methods: Regression discontinuity in time (RDiT) models are used to test the effect of the lockdown measures on crime by examining the daily variation of raw counts and rate. Results: It is indicated that in contrast to numerous violent crime categories such as domestic violence where findings have repeatedly found increases during the COVID-19 pandemic, acquisitive crimes in this city were reduced during the lockdown period for all categories, while “cyber-fraud” was found more resilient in the sense that its decrease was not as salient as for most other crime types, possibly due to people’s use of the internet during the lockdown period. Conclusions: The findings provide further support to opportunity theories of crime that are contingent upon the need for a motivated offender to identify a suitable target in physical space

Current status of food waste generation and management in China

The current status of FW generation, including its characteristics, management, and current challenges in China, were analyzed, and further suggestions were made with regards to improvement. About 19.50% of the FW generated could be treated under the current designs for treatment capacity in China. FW characteristics show great variability in different economic regions in China, where both treatment efficiency and FW management are poor. Combined pretreatment and three-phase separation is the most used pretreatment method, and of the current FW pilot projects, anaerobic digestion is the most prevalent, accounting for 76.1% of all projects. Significant regional characteristics have been identified regarding FW generation and the treatment capacity for FW processing. Possible factors influencing FW management in China were also discussed. Finally, detailed suggestions are given for further development of FW treatment capacity, particularly regarding potential technical routes and management measures

Development of LCA calculator to support community infrastructure co-design

Purpose LCA tools are increasingly used to support decision making. However, the current generation of tools is mainly targeted at users with significant background in industrial and environmental processes. This paper presents a novel process of developing the LCA Calculator with inputs from community members embedded in a co-design process. It demonstrates how engineering tools can be developed by considering end-user perspectives and used to communicate systems thinking in infrastructure co-design. Methods The process of the LCA Calculator development was informed by the outcomes of community engagement through the co-design process. The method consists of four parts including horizon scanning of suitable technology options, LCA modelling, development of the LCA Calculator and pilot testing of the Calculator with residents from the selected case study community. The case study community are residents of a social housing estate in central London. The estate has a total of 123 flats arranged in three low-rise blocks with shared gardens and courtyards. Three technology options—wormery composting, rainwater harvesting and urban food growing—were used to illustrate the LCA methods and test the Calculator development. Results and discussion The Calculator developed in this project pushes the boundaries beyond expert users to develop a new generation of LCA tools for a wider range of decision makers. The LCA results were communicated using the LCA Calculator in a workshop as part of the co-design process. The communication process was supported by the visual language of the Calculator, information sheets of the technology options and community members’ involvement in the process of the Calculator development. The Calculator provided a solid base on which sustainable design discussions could happen. It provided to the participants valuable insights into the scale of material flow given different design choices—such as the amount of waste generated over a month or the irrigation requirements of a raised bed—and environmental impacts of these options. Conclusions A prototype version of an LCA Calculator software tool has been developed to enable rapid assessment of conceptual design of engineering systems. The LCA Calculator was successfully tested at a community workshop, enabling clear engagement between engineering design choices and resource and environmental impacts. The Calculator facilitated a two-way exchange between community members and infrastructure designers that embeds end-user perspectives in the design and implementation of the infrastructure they use, taking into account lifecycle impacts of technology and material options

Corrigendum to "Effects of organic composition on mesophilic anaerobic digestion of food waste" [Bioresour. Technol. 244 (2017) 213-224]

Yangyang Li, Yiying Jin, Aiduan Borrion, Hailong Li, Jinhui Li (2017) Effects of organic composition on mesophilic anaerobic digestion of food waste, Bioresource Technology, Volume 244, Part 1, November 2017, Pages 213-224 (https://doi.org/10.1016/j.biortech.2017.07.006

Life cycle assessment of biomass densification systems

Several recent life cycle assessments (LCA) of biomass densification have been carried out. This paper reviews data from 19 sources with 48 case scenarios to assess the current status of LCA of biomass densification. It describes the specific units in a reference “gate-to-gate” LCA in relation to the existing studies, and summarises key differences between them. Finally, it provides a qualitative analysis of the associated sources of uncertainty. Existing LCA studies of biomass densification were found to provide insufficient and inconsistent information for full transparency and comparability, due to different choices in system boundary, functional unit, allocation procedure, densification technology and biomass residues. Most of the reviewed studies attributed most of the energy use and greenhouse gas (GHG) emissions to transportation, drying and densification. The energy and GHG emissions of the gate-to-gate densification system were highly sensitive to the technology, feed material used in densification and scale of production. Apart from one study with zero energy consumption as a result of the use of manual operations, the normalised values of energy consumption for the reviewed studies ranged from 20 to 900 kJ MJ-1. Neglecting three outlier values, GHG emissions as mass of CO2-eq for the reviewed studies ranged from 600 t MJ-1 to 50 g MJ-1. Similar variations in result and outlier cases have been reported for other bioenergy processes, by other authors. Assuming that the biggest impact of densification processes is on transport fuel use, and based on 5 studies that reported densification ratios, the net energy and GHG emissions savings resulting from densification ranged from 200 to 1000 kJ MJ-1 and 9 to 50 CO2-eq (g MJ-1), respectively. On this basis, it can be concluded that biomass densification is a worthwhile addition to the biomass energy conversion system. There is a need for more transparent reporting and analysis of uncertainty in the modelling, to better understand the wide variation in outcomes