Carbon accounting of negative emissions technologies integrated in the life cycle of spirulina supplements.

Carbon dioxide removal (CDR) technologies are considered essential to accomplish the Paris Agreement targets. Given the important contribution of the food sector to climate change, this study aims to investigate the role of two carbon capture and utilization (CCU) technologies in decarbonizing the production of spirulina, an algae product commonly consumed for its nutritional characteristics. The proposed scenarios considered the replacement of synthetic food-grade CO2 in Arthrospira platensis cultivation (BAU scenario) with CO2 from beer fermentation (BRW) and CO2 from DACC (direct air carbon capture) (SDACC), representing two alternatives with great potential in the short and medium-long term, respectively. The methodology follows the Life Cycle Assessment guidelines, considering a cradle-to-gate scope and a functional unit equivalent to the annual production of spirulina in a Spanish artisanal plant. Results showed a better environmental performance of both CCU scenarios as compared to BAU, reaching a reduction of greenhouse gas (GHG) emissions of 52 % in BRW and of 46 % in SDACC. Although the brewery CCU offers a deeper carbon mitigation of spirulina production, the process cannot reach net zero GHG emissions due to residual burdens across the supply chain. In comparison, the DACC unit could potentially supply both the CO2 needed in spirulina production and work as a CDR to compensate residual emissions, which opens the door for further research on its technical and economic feasibility in the food sector.

Closed-loop organic waste management systems for family farmers in Brazil.

Family farmers in Brazil could diversify their sources of income and improve agriculture practices by adopting circular economy principles on their farms. Closed-loop technological systems can be used to manage organic waste and produce fertiliser and biogas thereby generating revenue. Anaerobic Digestion (AD) is a proven technology that can produce digestate (i.e. fertiliser) and biogas from organic waste, although digestate application in soil and crops without treatment can have adverse effects. However, in practice, there is a lack of knowledge about the benefits of recycling organic waste in farming communities in Brazil. Therefore, the main aim of this paper is to provide conceptual design configurations of closed-loop systems that manage organic waste and generate revenue for small farms in Brazil. A literature review of selected technologies and interviews with Brazilian family farmers were used to inform the components of the proposed conceptual designs. The proposed designs are based on circular economy principles, incorporating AD, pyrolysis for biochar, hydroponics and vermifiltration in various configurations. A complete closed-loop system consisting of a 7.5 m3 digester, pyrolysis unit, a combined hydroponic and vermifilter unit and a shredder is estimated to cost around USD$1600 (R$ 6600). The flexibility of the proposed systems has the potential to increase resilience and income for small-scale farmers, whilst encouraging good practices for waste management. The conceptual designs can be used as a basis for further research and development of small-scale organic waste management solutions in Brazil.

Global Environmental Engineering for and with Historically Marginalized Communities.

Marginalized communities lack full participation in social, economic, and political life, and they disproportionately bear the burden of environmental and health risks. This special issue of Environmental Engineering Science, the official journal of the Association of Environmental Engineering and Science Professors (AEESP), reports research on the unique environmental challenges faced by historically marginalized communities around the world. The results of community-based participatory research with an Afro-descendant community in Columbia, Native American communities in Alaska, United States, villagers in the Philippines, disadvantaged communities in California, United States, rural communities in Mexico and Costa Rica, homeless encampments in the San Diego River (United States) watershed entrepreneurs in Durban, South Africa, and remote communities in the island nation of Fiji are presented. The research reported in this special issue is transdisciplinary, bringing engineers together with anthropologists, sociologists, economists, and public health experts. In the 13 articles in this special issue, some of the topics covered include inexpensive technologies for water treatment, novel agricultural strategies for reversing biodiversity losses, and strategies for climate change adaptation. In addition, one article covered educational strategies for teaching ethics to prepare students for humanitarian engineering, including topics of poverty, sustainability, social justice, and engineering decisions under uncertainty. Finally, an article presented ways that environmental engineering professors can engage and promote the success of underrepresented minority students and enable faculty engaged in community-based participatory research.

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.

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.

Regionalized Strategies for Food Loss and Waste Management in Spain under a Life Cycle Thinking Approach.

Food loss and waste (FLW) has become a central concern in the social and political debate. Simultaneously, using FLW as a bioenergy source could significantly contribute to closing the carbon cycle by reintroducing energy into the food supply chain. This study aims to identify best strategies for FLW management in each of the 17 regions in Spain, through the application of a Life Cycle Assessment. To this end, an evaluation of the environmental performance over time between 2015 and 2040 of five different FLW management scenarios implemented in a framework of (i) compliance and (ii) non-compliance with the targets of the Paris Agreement was performed. Results revealed savings in the consumption of abiotic resources in those regions in which thermal treatment has a strong presence, although their greenhouse gas (GHG) emissions in a scenario of compliance with climate change targets are higher. In contrast, scenarios that include anaerobic digestion and, to a lesser extent those applying aerobic composting, present lower impacts, including climate change, suggesting improvements of 20-60% in non-compliance and 20-80% in compliance with Paris Agreement targets, compared to the current scenarios.

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.

Process characteristics for microwave assisted hydrothermal carbonization of cellulose.

The process characteristics of microwave assisted hydrothermal carbonization of cellulose was investigated and a first order kinetics model based on carbon concentration was developed. Chemical properties analysis showed that comparing to conventional hydrothermal carbonization, hydrochar with comparable energy properties can be obtained with 5-10 times decrease in reaction time with assistance of microwave heating. Results from kinetics study was in great agreement with experimental analysis, that they both illustrated the predominant mechanism of the reaction depend on variations in the reaction rates of two co-existent pathways. Particularly, the pyrolysis-like intramolecular dehydration reaction was proved to be the predominant mechanism for hydrochar generation under high temperatures. Finally, the enhancement effects of microwave heating were reflected under both soluble and solid pathways in this research, suggesting microwave-assisted hydrothermal carbonization as a more attracting method for carbon-enriched hydrochar recovery.

ADM1 modelling of large-scale covered in-ground anaerobic reactor treating sugarcane vinasse.

In this paper, we demonstrate in a clear procedure the application of the Anaerobic Digestion Model No. 1 (ADM1) to model a large-scale covered in-ground anaerobic reactor (Cigar), processing sugarcane vinasse from a biorefinery in Brazil. The biochemical make-up (carbohydrates, proteins, and lipids) of the substrate was analysed based on the food industry standards. Two distinct subsets of data, based on the sugarcane harvest season for bioethanol and sugar production in 2012 and 2014, were used to direct and cross validate the model, respectively. We fitted measured data by estimating two key parameters against biogas flow rate: the degradation extent (fd) and the first order hydrolysis rate coefficient (khyd). By cross validation we show that the fitted model can be generalised to represent the behaviour of the reactor under study. Therefore, motivated by practical and industrial application of ADM1, for both different reactors types and substrates, we show aspects on the implementation of ADM1 to a specific large-scale reactor for anaerobic digestion of sugarcane vinasse.

Influence of feed/inoculum ratios and waste cooking oil content on the mesophilic anaerobic digestion of food waste.

Information on the anaerobic digestion (AD) of food waste (FW) with different waste cooking oil contents is limited in terms of the effect of the initial substrate concentrations. In this work, batch tests were performed to evaluate the combined effects of waste cooking oil content (33-53%) and feed/inoculum (F/I) ratios (0.5-1.2) on biogas/methane yield, process stability parameters and organics reduction during the FW AD. Both waste cooking oil and the inoculation ratios were found to affect digestion parameters during the AD process start-up and the F/I ratio was the predominant factor affecting AD after the start-up phase. The possible inhibition due to acidification caused by volatile fatty acids accumulation, low pH values and long-chain fatty acids was reversible. The characteristics of the final digestate indicated a stable anaerobic system, whereas samples with F/I ratios ranging from 0.8 to 1.2 display higher propionic and valeric acid contents and high amounts of total ammonia nitrogen and free ammonia nitrogen. Overall, F/I ratios higher than 0.70 caused inhibition and resulted in low biogas/methane yields from the FW.

Effects of organic composition on mesophilic anaerobic digestion of food waste.

Anaerobic digestion of food waste (FW) has been widely investigated, however, little is known about the influence of organic composition on the FW digestion process. This study aims to identify the optimum composition ratios of carbohydrate (CA), protein (CP) and lipid (EE) for maintaining high methane yield and process stability. The results show that the CA-CP-EE ratio was significantly correlated with performance and degradability parameters. Controlling the CA-CP-EE ratio higher than 1.89 (CA higher than 8.3%, CP lower than 5.0%, and EE lower than 5.6%) could be an effective way to maintain stable digestion and achieve higher methane production (385-627mL/gVS) and shorter digestion retention (196-409h). The CA-CP-EE ratio could be used as an important indicator for digestion performance. To effectively evaluate organic reduction, the concentration and removal efficiency of organic compositions in both solid phases and total FW should be considered.

Effects of organic composition on the anaerobic biodegradability of food waste.

This work investigated the influence of carbohydrates, proteins and lipids on the anaerobic digestion of food waste (FW) and the relationship between the parameters characterising digestion. Increasing the concentrations of proteins and lipids, and decreasing carbohydrate content in FW, led to high buffering capacity, reduction of proteins (52.7-65.0%) and lipids (57.4-88.2%), and methane production (385-627 mLCH4/g volatile solid), while achieving a short retention time. There were no significant correlations between the reduction of organics, hydrolysis rate constant (0.25-0.66d-1) and composition of organics. Principal Component Analysis revealed that lipid, C, and N contents as well as the C/N ratio were the principal components for digestion. In addition, methane yield, the final concentrations of total ammonia nitrogen and free ammonia nitrogen, final pH values, and the reduction of proteins and lipids could be predicted by a second-order polynomial model, in terms of the protein and lipid weight fraction.

Challenge clusters facing LCA in environmental decision-making-what we can learn from biofuels.

PURPOSE: Bioenergy is increasingly used to help meet greenhouse gas (GHG) and renewable energy targets. However, bioenergy's sustainability has been questioned, resulting in increasing use of life cycle assessment (LCA). Bioenergy systems are global and complex, and market forces can result in significant changes, relevant to LCA and policy. The goal of this paper is to illustrate the complexities associated with LCA, with particular focus on bioenergy and associated policy development, so that its use can more effectively inform policymakers. METHODS: The review is based on the results from a series of workshops focused on bioenergy life cycle assessment. Expert submissions were compiled and categorized within the first two workshops. Over 100 issues emerged. Accounting for redundancies and close similarities in the list, this reduced to around 60 challenges, many of which are deeply interrelated. Some of these issues were then explored further at a policy-facing workshop in London, UK. The authors applied a rigorous approach to categorize the challenges identified to be at the intersection of biofuels/bioenergy LCA and policy. RESULTS AND DISCUSSION: The credibility of LCA is core to its use in policy. Even LCAs that comply with ISO standards and policy and regulatory instruments leave a great deal of scope for interpretation and flexibility. Within the bioenergy sector, this has led to frustration and at times a lack of obvious direction. This paper identifies the main challenge clusters: overarching issues, application and practice and value and ethical judgments. Many of these are reflective of the transition from application of LCA to assess individual products or systems to the wider approach that is becoming more common. Uncertainty in impact assessment strongly influences planning and compliance due to challenges in assigning accountability, and communicating the inherent complexity and uncertainty within bioenergy is becoming of greater importance. CONCLUSIONS: The emergence of LCA in bioenergy governance is particularly significant because other sectors are likely to transition to similar governance models. LCA is being stretched to accommodate complex and broad policy-relevant questions, seeking to incorporate externalities that have major implications for long-term sustainability. As policy increasingly relies on LCA, the strains placed on the methodology are becoming both clearer and impedimentary. The implications for energy policy, and in particular bioenergy, are large.