Development of sustainable approaches for converting the organic waste to bioenergy

Sustainable organic waste valorisation: A zero-waste approach

The annual increase in global organic waste generation emphasises the need to develop a sustainable management platform to address environmental concerns. This study aims to explore sustainable treatments for the conversion of organic waste into energy in pursuit of zero-waste. The organic waste generated from the animal feed industry (referred to as WF) was used for the model compound in this study. 8.5 wt% of lipids were extracted from the WF, which contained unidentified impurities. Acid-catalysed transesterification yielded less than 80 wt% biodiesel might be due to the reversible reaction. In contrast, non-catalytic transesterification resulted in a significantly higher biodiesel yield (95.6 wt%), suggesting that this method was more effective at converting impure lipids into biodiesel compared to acid-catalysed transesterification. These results indicate the potential advantages of the non-catalytic approach, particularly when dealing with impure lipid sources. To minimise the generation of waste in the process, the WF residue produced after lipid extraction was converted into combustible gas (syngas) through pyrolysis. CO2 was used as a reactive medium in pyrolysis. In one-stage pyrolysis, the gas yield under CO2 was comparable to that under N2, indicating that CO2 did not react effectively with the volatiles derived from the WF residue. Enhanced CO2 reactivity was achieved via catalytic pyrolysis using a nickel-impregnated catalyst. Consequently, the combustible gas yield under CO2 was much higher than that under N2. This approach might contribute to maximising the efficiency of converting organic waste into renewable energy while simultaneously consuming CO2 during pyrolysis, thereby enhancing the sustainability of this approach.

Biowaste to bioenergy nexus: Fostering sustainability and circular economy

Existing fossil-based commercial products present a significant threat to the depletion of global natural resources and the conservation of the natural environment. Also, the ongoing generation of waste is giving rise to challenges in waste management. Conventional practices for the management of waste, for instance, incineration and landfilling, emit gases that contribute to global warming. Additionally, the need for energy is escalating rapidly due to the growing populace and industrialization. To address this escalating desire in a sustainable manner, access to clean and renewable sources of energy is imperative for long-term development of mankind. These interrelated challenges can be effectively tackled through the scientific application of biowaste-to-bioenergy technologies. The current article states an overview of the strategies and current status of these technologies, including anaerobic digestion, transesterification, photobiological hydrogen production, and alcoholic fermentation which are utilized to convert diverse biowastes such as agricultural and forest residues, animal waste, and municipal waste into bioenergy forms like bioelectricity, biodiesel, bio alcohol, and biogas. The successful implementation of these technologies requires the collaborative efforts of government, stakeholders, researchers, and scientists to enhance their practicability and widespread adoption.

A comprehensive review on unleashing the power of hydrogen: revolutionizing energy systems for a sustainable future

Population growth and environmental degradation are major concerns for sustainable development worldwide. Hydrogen is a clean and eco-friendly alternative to fossil fuels, with a heating value almost three times higher than other fossil fuels. It also has a clean production process, which helps to reduce the emission of hazardous pollutants and save the environment. Among the various production methodologies described in this review, biochemical production of hydrogen is considered more suitable as it uses waste organic matter instead of fossil fuels. This technology not only produces clean energy but also helps to manage waste more efficiently. However, the production of hydrogen obtained from this method is currently more expensive due to its early stage of development. Nevertheless, various research projects are underway to develop this method on a commercial scale.

A comprehensive comparative study on microwave- assisted pyrolysis products derived from raw and digested organic waste, with emphasis on sewage sludge, food waste, and livestock manure

This study focused on characterizing sewage sludge, food waste, and livestock manure, representative of continuously generated organic wastes, along with their anaerobic digestion residues. Microwave assisted pyrolysis was employed to investigate the relationship between the properties of the raw organic wastes and the resulting pyrolysis products, utilizing the R-program for analysis. Evaluation of the pyrolysis products of these six organic wastes revealed that char yield was primarily influenced by ash and fixed carbon contents, with higher yields observed in residues from anaerobic digestion compared to the original organic waste. Liquid and gaseous product quantities were found to increase with volatile content, while high-fat content within the volatile fraction notably enhanced liquid product yields, impacting syngas production. Analysis of syngas composition indicated a negative correlation between high nitrogen content in the feedstock and H2 generation. Furthermore, examining the correlation between chemical properties of organic waste and pyrolysis products revealed a proportional increase in protein components with nitrogen content, suggesting potential improvements in pyrolysis efficiency through raw material pretreatment enhancements by the R program.

Creation of Environmentally Friendly Super "Dinitrotoluene Scavenger" Plants

Pervasive environmental contamination due to the uncontrolled dispersal of 2,4-dinitrotoluene (2,4-DNT) represents a substantial global health risk, demanding urgent intervention for the removal of this detrimental compound from affected sites and the promotion of ecological restoration. Conventional methodologies, however, are energy-intensive, susceptible to secondary pollution, and may inadvertently increase carbon emissions. In this study, a 2,4-DNT degradation module is designed, assembled, and validated in rice plants. Consequently, the modified rice plants acquire the ability to counteract the phytotoxicity of 2,4-DNT. The most significant finding of this study is that these modified rice plants can completely degrade 2,4-DNT into innocuous substances and subsequently introduce them into the tricarboxylic acid cycle. Further, research reveals that the modified rice plants enable the rapid phytoremediation of 2,4-DNT-contaminated soil. This innovative, eco-friendly phytoremediation approach for dinitrotoluene-contaminated soil and water demonstrates significant potential across diverse regions, substantially contributing to carbon neutrality and sustainable development objectives by repurposing carbon and energy from organic contaminants.

Description of Sporanaerobium hydrogeniformans gen. nov., sp. nov., an obligately anaerobic, hydrogen-producing bacterium isolated from Aravali hot spring in India

An obligately anaerobic bacterium XHS1971T, capable of degrading cellulose and xylan, was isolated from a sediment sample of Aravali hot spring, Ratnagiri, India. Cells of strain XHS1971T were Gram-stain-negative, spore-forming, motile, long-rods. Growth was observed at temperatures 30-50 °C (optimum 40-45 °C), pH 5.0-10.0 (optimum pH 8.0) and NaCl concentrations 0-0.5% (optimum 0%). Generation time of strain XHS1971T was 5 h under optimised growth conditions. Strain XHS1971T showed the ability to metabolise different complex and simple sugars constituting lignocellulosic biomass. Glucose was fermented majorly into hydrogen, formic acid, acetic acid, and ethanol, whereas carbon dioxide, butyric acid, lactic acid and succinic acid were produced in traces. 16S rRNA gene analysis of strain XHS1971T revealed < 94.5% homology with Cellulosilyticum lentocellum DSM5427T followed by Cellulosilyticum ruminicola JCM14822T, identifying strain as a distinct member of family Lachnospiraceae. The major cellular fatty acids (> 5%) were C14:0, C16:0, C18:0, and C16:1 ω7c. The genome size of the strain was 3.74 Mb with 35.3 mol% G + C content, and genes were annotated to carbohydrate metabolism, including genes involved in the degradation of cellulose and xylan and the production of hydrogen, ethanol and acetate. The uniqueness of strain was further validated by digital DNA-DNA hybridisation (dDDH), Average Nucleotide Identity (ANI), and Average Amino Acid Identity (AAI) values of 22%, 80%, and 63%, respectively, with nearest phylogenetic affiliates. Based on the detailed analyses, we propose a new genus and species, Sporanaerobium hydrogeniformans gen. nov., sp. nov., for strain XHS1971T (= MCC3498T = KCTC15729T = JCM32657T) within family Lachnospiraceae.

Impact of leachate and landfill gas on the ecosystem and health: Research trends and the way forward towards sustainability

Globally, a whopping increase in solid waste (SW) generation and the risks posed by climate change are major concerns. A wide spread practice for disposal of municipal solid waste (MSW) is landfill, which swells with population and urbanization. Waste, if treated properly, can be used to produce renewable energy. The recent global event COP 27 mainly stressed on production of renewable energy to achieve the Net Zero target. The MSW landfill is the most significant anthropogenic source of methane (CH₄) emission. On one side, CH₄ is a greenhouse gas (GHG), and on the other it is a main component of biogas. Wastewater that collects due to rainwater percolation in landfills creates landfill leachate. There is a need to understand global landfill management practices thoroughly for implementation of better practices and policies related to this threat. This study critically reviews recent publications on leachate and landfill gas. The review discusses leachate treatment and landfill gas emissions, focusing on the possible reduction technology of CH₄ emission and its impact on the environment. Mixed leachate will benefit from the combinational therapy method because of its intricate combination. Implementation of circular material management, entrepreneurship ideas, blockchain, machine learning, LCA usage in waste management, and economic benefits from CH₄ production have been emphasized. Bibliometric analysis of 908 articles from the last 37 years revealed that industrialized nations dominate this research domain, with the United States having the highest number of citations.

Breakdown of biomass for energy applications using microwave pyrolysis: A technological review

The agricultural industry faces a permanent increase in waste generation, which is associated with the fast-growing population. Due to the environmental hazards, there is a paramount demand for generating electricity and value-added products from renewable sources. The selection of the conversion method is crucial to develop an eco-friendly, efficient and economically viable energy application. This manuscript investigates the influencing factors that affect the quality and yield of the biochar, bio-oil and biogas during the microwave pyrolysis process, evaluating the biomass nature and diverse combinations of operating conditions. The by-product yield depends on the intrinsic physicochemical properties of biomass. Feedstock with high lignin content is favourable for biochar production, and the breakdown of cellulose and hemicellulose leads to higher syngas formation. Biomass with high volatile matter concentration promotes the generation of bio-oil and biogas. The pyrolysis system's conditions of input power, microwave heating suspector, vacuum, reaction temperature, and the processing chamber geometry were influence factors for optimising the energy recovery. Increased input power and microwave susceptor addition lead to high heating rates, which were beneficial for biogas production, but the excess pyrolysis temperature induce a reduction of bio-oil yield.

Photocatalytic degradation of reactive dyes using natural photo-smart pigment-A novel approach for waste water re-usability

The present study is aimed at an efficient photocatalytic degradation of industrially important reactive dyes using phycocyanin extract as a photocatalyst. The percentage of dye degradation was evidenced by a UV-visible spectrophotometer and FT-IR analysis. The degraded water was checked for its complete degradation by varying pH from 3 to 12. Furthermore, the degraded water was also analyzed for water quality parameters and was found to meet industrial wastewater standards. The calculated irrigation parameters like magnesium hazard ratio, soluble sodium percentage, and Kelly's ratio of degraded water were within the permissible limits, which enables its reusability in irrigation, aquaculture, as industrial coolants, and domestic applications. The calculated correlation matrix shows that the metal influences various macro-, micro-, and non-essential elements. These results suggest that the non-essential element lead can be effectively reduced by increasing all the other micronutrients and macronutrients under study except sodium metal.

Environmental remediation at vegetable marketplaces through production of biowaste catalysts for biofuel generation

Large quantities of vegetable biowaste are generated at marketplaces, usually in highly populated locations. On the other hand, nearby markets, hotels, and street shops generate much cooking oil waste and dispose of them in the sewage. Environmental remediation is mandatory at these places. Hence, this experimental work concentrated on preparing biodiesel using green plant wastes and cooking oil. Biowaste catalysts were produced from vegetable wastes and biofuel generated from waste cooking oil using biowaste catalysts to support diesel demand and Environmental remediation. Other organic plant wastes such as bagasse, papaya stem, banana peduncle and moringa oleifera are used as heterogeneous catalysts of this research work. Initially, the plant wastes are independently considered for the catalyst for biodiesel production; secondary, all plant wastes are mixed to form a single catalyst and used to prepare the biodiesel. In the maximum biodiesel yield analysis, the calcination temperature, reaction temperature, methanol/oil ratio, catalyst loading and mixing speed were considered to control the biodiesel production. The results reveal that the catalyst loading of 4.5 wt% with mixed plant waste catalyst offered a maximum biodiesel yield of 95%.

Microbial assemblage for solid waste bioremediation and valorization with an essence of bioengineering

Environmental solid waste bioremediation is a method of treating contaminated solid waste that involves changing ecological conditions to foster the growth of a broad spectrum of microorganisms and the destruction of the target contaminants. A wide range of microorganisms creates metabolites that may break down and change solid waste-based pollution to various value-added molecules. Diverse bioremediation technologies, their limitations, and the procedure involve recycling solid waste materials from the environment. The existing environmental solid waste disposal services are insufficient and must be upgraded with more lucrative recovery, recycling, and reuse technologies to decrease the enormous expenditures in treatment procedures. Bioremediation of solid waste eliminates the toxic components. It restores the site with the advent of potential microbial communities towards solid waste valorization utilizing agriculture solid waste, organic food waste, plastic solid waste, and multiple industrial solid wastes.Bioengineering on diverse ranges of microbial regimes has accelerated to provide extra momentum toward solid waste recycling and valorization. This approach increases the activity of bioremediating microbes in the commercial development of waste treatment techniques and increases the cost-effective valuable product generation. This framework facilitates collaboration between solid waste and utilities. It can aid in establishing a long-term management strategy for recycling development with the advent of a broad spectrum of potential microbial assemblages, increasing solid waste contamination tolerance efficiency and solid waste degradability. The current literature survey extensively summarises solid waste remediation valorization using a broad spectrum of microbial assemblages with special emphasis on bioengineering-based acceleration. This approach is to attain sustainable environmental management and value-added biomolecule generation.

Tomato as a Natural Source of Dyes in the Food Industry: A Patent Data Analysis

BACKGROUND

Foods that promote health benefits are being increasingly used. Innovative techniques, such as nanotechnology, have been used to improve functional properties, sensory characteristics, or the conservation of foods.

OBJECTIVE

The objective of this study was to identify the technological domain of patents for tomato products with or without nanotechnology and elucidate the technological advances associated with the recent use of tomatoes as a natural food dye in the food industry by exploring patent documents.

METHODS AND RESULTS

The search was conducted using the Espacenet and INPI databases. There was an increase in patent document applications employing nanotechnology in 2013, with a peak between 2017 and 2018. China is the lead country in the number of patent applications. In Brazil, the patent applications are variable, and the food industry is most involved in studies on tomatoes as a natural food dye. Most patent deposits using nanotechnology were from companies, and the main sources of the patent application were the food and pharmaceutical industries.

CONCLUSION

There is an increasing trend for the use of tomatoes as natural food dyes, produced with or without nanotechnology, and number of patents filed yearly. New technologies are being developed in several application areas.

A critical review on pretreatment and detoxification techniques required for biofuel production from the organic fraction of municipal solid waste

The organic fraction of municipal solid waste (OFMSW) is a widely-available promising feedstock for biofuel production. However, the presence of different inhibitors originating from fruit and food/beverage wastes as well as recalcitrant lignocellulosic fractions hampers its bioconversion. This necessitates a pretreatment to augment the biodigestibility and fermentability of OFMSW. Hence, this review aims to provide the in-vogue inhibitory compound removal and pretreatment techniques that have been employed for efficient OFMSW conversion into biofuels, i.e., hydrogen, biogas, ethanol, and butanol. The techniques are compared concerning their mode of action, chemical and energy consumption, inhibitor formation and removal, economic feasibility, and environmental sustainability. This critique also reviews the existing knowledge gap and future perspectives for efficient OFMSW valorization. The insights provided pave the way toward developing energy-resilient cities while addressing environmental crises related to generating OFMSW.

Lignocellulose dissociation with biological pretreatment towards the biochemical platform: A review

Lignocellulose utilization has been gaining great attention worldwide due to its abundance, accessibility, renewability and recyclability. Destruction and dissociation of the cross-linked, hierarchical structure within cellulose hemicellulose and lignin is the key procedure during chemical utilization of lignocellulose. Of the pretreatments, biological treatment, which can effectively target the complex structures, is attractive due to its mild reaction conditions and environmentally friendly characteristics. Herein, we report a comprehensive review of the current biological pretreatments for lignocellulose dissociation and their corresponding degradation mechanisms. Firstly, we analyze the layered, hierarchical structure of cell wall, and the cross-linked network between cellulose, hemicellulose and lignin, then highlight that the cracking of β-aryl ether is considered the key to lignin degradation because of its dominant position. Secondly, we explore the effect of biological pretreatments, such as fungi, bacteria, microbial consortium, and enzymes, on substrate structure and degradation efficiency. Additionally, combining biological pretreatment with other methods (chemical methods and catalytic materials) may reduce the time necessary for the whole process, which also help to strengthen the lignocellulose dissociation efficiency. Thirdly, we summarize the related applications of lignocellulose, such as fuel production, chemicals platform, and bio-pulping, which could effectively alleviate the energy pressure through bioconversion into high value-added products. Based on reviewing of current progress of lignocellulose pretreatment, the challenges and future prospects are emphasized. Genetic engineering and other technologies to modify strains or enzymes for improved biotransformation efficiency will be the focus of future research.

Fight for carbon neutrality with state-of-the-art negative carbon emission technologies

After the Industrial Revolution, the ever-increasing atmospheric CO2 concentration has resulted in significant problems for human beings. Nearly all countries in the world are actively taking measures to fight for carbon neutrality. In recent years, negative carbon emission technologies have attracted much attention due to their ability to reduce or recycle excess CO2 in the atmosphere. This review summarizes the state-of-the-art negative carbon emission technologies, from the artificial enhancement of natural carbon sink technology to the physical, chemical, or biological methods for carbon capture, as well as CO2 utilization and conversion. Finally, we expound on the challenges and outlook for improving negative carbon emission technology to accelerate the pace of achieving carbon neutrality.

Low-Temperature Pretreatment of Biomass for Enhancing Biogas Production: A Review

Low-temperature pretreatment (LTPT, Temp. < 100 °C or 140 °C) has the advantages of low input, simplicity, and energy saving, which makes engineering easy to use for improving biogas production. However, compared with high-temperature pretreatment (>150 °C) that can destroy recalcitrant polymerized matter in biomass, the action mechanism of heat treatment of biomass is unclear. Improving LTPT on biogas yield is often influenced by feedstock type, treatment temperature, exposure time, and fermentation conditions. Such as, even when belonging to the same algal biomass, the response to LTPT varies between species. Therefore, forming a unified method for LTPT to be applied in practice is difficult. This review focuses on the LTPT used in different biomass materials to improve anaerobic digestion performance, including food waste, sludge, animal manure, algae, straw, etc. It also discusses the challenge and cost issues faced during LTPT application according to the energy balance and proposes some proposals for economically promoting the implementation of LTPT.

Phycocyanin from Spirulina platensis bio-mimics quantum dots photocatalytic activity: A novel approach for dye degradation

In our present study, the photocatalytic degradation of malachite green (MG) an organic dye was carried out using a phycocyanin extract of Spirulina platensis under the irradiation of sunlight. The aim of the present study is to incorporate a simple, novel, an eco-friendly, and cost-effective degradation of dyes without using any harmful metals and chemicals. It was observed that 25 ppm of MG dye got degraded nearly to 100 % at 3 h. The UV absorbance studies indicate the absence of a peak at 620 nm which is a conclusive evidence for MG dye degradation. An optimization study of MG dye degradation was evaluated by Response Surface Methodology using Minitab module 20.4.0.0 statistical software and its percentage of degradation was statistically analyzed using analystat. The FT-IR studies of raw spectra show minimal variation; however, the deconvoluted spectra in the region of 1600-1700 cm^-1 indicate the variation in the secondary structure of amide I bands that leads to the dye degradation. The dye degradation study mainly follows the first-order kinetics between the time intervals of 60-180 min. The characteristics of degraded water were assessed by a TOC analyzer. The value of total inorganic carbon (TIC) in MG before treatment was 90 mg/L and seems to be slightly high when compared to MG after treatment which was found to be 87.65 mg/L and the adsorbent-treated water with a low value of 54.25 mg/L. These results well matched with the characteristics of normal water. The presence of phycocyanin in the degraded water was effectively removed by treating with activated carbon and it was confirmed with fluorescence analysis. These results support that the MG dye degradation was exhibited by phycocyanin extract and bio-mimics the quantum dot photocatalytic activity.

Medium-chain fatty acid production from Chinese liquor brewing yellow water by electro-fermentation: Division of fermentation process and segmented electrical stimulation

Electro-fermentation (EF) has been proposed as a method to improve the yield of medium-chain fatty acid (MCFA). In this study, MCFA production from Chinese liquor wastewater (yellow water) was investigated and corresponding composite electron donors (lactate and ethanol in yellow water) were investigated by different electrical stimulation modes. The caproate yield under whole period electrical stimulation increased by 250.9% compared with open circuit. The oxidation-dominated and reduction-dominated periods of the fermentation process were divided, and the segmented electrical stimulation experiment showed the caproate yield under reduction-dominated EF system further increased by 288.5% compared with open circuit. The microbial diversity analysis demonstrated that Clostridium 12 might be enriched better by keeping open circuit during EDs consumption, meanwhile the bacteria with potential negative effects on CE were inhibited. The electrical stimulation mode of EF process was optimized and provided a new way to recycle organic wastewater.

Circular Economy of Construction and Demolition Waste: A Case Study of Colombia

This paper presents the results of research into construction and demolition (C&D) waste in Colombia. The data and analyses are shown in a local and Latin American context. As the situation in Colombia is quite similar to that in many developing countries worldwide, this research and its findings are potentially applicable to similar economies. Several factors were calculated and compared in order to evaluate which best fit the data from Colombia. We also included an experimental characterization and analysis of several key types of C&D waste from important infrastructure projects in Colombia, specifically by using the X-ray diffraction and scanning electron microscopy techniques. For the quantification of CDW, a calculation was performed based on the area and four factors of volume and density, followed by an econometric analysis of the detailed information using the Hodrick–Prescott filter, which revealed the CDW trends. Our results revealed that there are limitations regarding the availability of information and effective treatments for this waste, as well as shortcomings in education and other issues, not only for Colombia but also for other countries in Latin America.

Biotechnological advances in biomass pretreatment for bio-renewable production through nanotechnological intervention

Globally, the fossil fuel reserves are depleting rapidly and the escalating fuel prices as well as plethora of the pollutants released from the emission of burning fossil fuels cause global warming that massively disturb the ecological balance. Moreover, the unnecessary utilization of non-renewable energy sources is a genuine hazard to nature and economic stability, which demands an alternative renewable source of energy. The lignocellulosic biomass is the pillar of renewable sources of energy. Different conventional pretreatment methods of lignocellulosic feedstocks have employed for biofuel production. However, these pretreatments are associated with disadvantages such as high cost of chemical substances, high load of organic catalysts or mechanical equipment, time consuming, and production of toxic inhibitors causing the environmental pollution. Nanotechnology has shown the promised biorefinery results by overcoming the disadvantages associated with the conventional pretreatments. Recyclability of nanomaterials offers cost effective and economically viable biorefineries processes. Lignolytic and saccharolytic enzymes have immobilized onto/into the nanomaterials for the higher biocatalyst loading due to their inherent properties of high surface area to volume ratios. Nanobiocatalyst enhance the hydrolyzing process of pretreated biomass by their high penetration into the cell wall to disintegrate the complex carbohydrates for the release of high amounts of sugars towards biofuel and various by-products production. Different nanotechnological routes provide cost-effective bioenergy production from the rich repertoires of the forest and agricultural-based lignocellulosic biomass. In this article, a critical survey of diverse biomass pretreatment methods and the nanotechnological interventions for opening up the biomass structure has been carried out.

Utilization of Aerobic Compression Composting Technology on Raw Mushroom Waste for Bioenergy Pellets Production

Raw mushroom waste has been an enormous solid waste, not only causing a huge cut on profit margin of mushroom industries but also leading to environmental pollution. Unfortunately, the current utilization methods, such as pharmaceutical extractions, are unable to keep up with the waste generation rate due to the large-scale mushroom production. Yet, the utilization of raw mushroom waste to produce biomass pellets for energetic purposes and the role of an electric composter on shortening the processing time remain unexplored. This is important because conventional composting, which takes a relatively long period (e.g., weeks to months), is less practical when it comes to commercial use of the biomass pellets. To explore this issue, an industrial composter with initial compost was utilized to process the raw mushroom waste, followed by pelletization. Extraction of the material inside the composter at different timing was carried out to determine the optimal processing time for optimal texture to form pellets. It was found that prolonged composting hour affected the pelletization process since moisture, which acts as a natural binder, reduced when the composting hour increased. The gross calorific value increased from 14.07 MJ/kg to 18.76 MJ/kg for raw mushroom waste and compost pellets at the fifth hour, respectively. This study revealed that the raw mushroom waste compost could serve as a valuable renewable energy source and that the production of energy-rich biomass compost fuel pellets without using any binder within a short composting duration is achievable with the aid of an in-vessel composter.

Post COVID-19 ENERGY sustainability and carbon emissions neutrality

This review covers the recent advancements in selected emerging energy sectors, emphasising carbon emission neutrality and energy sustainability in the post-COVID-19 era. It benefited from the latest development reported in the Virtual Special Issue of ENERGY dedicated to the 6th International Conference on Low Carbon Asia and Beyond (ICLCA'20) and the 4th Sustainable Process Integration Laboratory Scientific Conference (SPIL'20). As nations bind together to tackle global climate change, one of the urgent needs is the energy sector's transition from fossil-fuel reliant to a more sustainable carbon-free solution. Recent progress shows that advancement in energy efficiency modelling of components and energy systems has greatly facilitated the development of more complex and efficient energy systems. The scope of energy system modelling can be based on temporal, spatial and technical resolutions. The emergence of novel materials such as MXene, metal-organic framework and flexible phase change materials have shown promising energy conversion efficiency. The integration of the internet of things (IoT) with an energy storage system and renewable energy supplies has led to the development of a smart energy system that effectively connects the power producer and end-users, thereby allowing more efficient management of energy flow and consumption. The future smart energy system has been redefined to include all energy sectors via a cross-sectoral integration approach, paving the way for the greater utilization of renewable energy. This review highlights that energy system efficiency and sustainability can be improved via innovations in smart energy systems, novel energy materials and low carbon technologies. Their impacts on the environment, resource availability and social well-being need to be holistically considered and supported by diverse solutions, in alignment with the sustainable development goal of Affordable and Clean Energy (SDG 7) and other related SDGs (1, 8, 9, 11,13,15 and 17), as put forth by the United Nations.

Organic solid waste upgrading under natural gas for valuable liquid products formation: Pilot demonstration of a highly integrated catalytic process

An integrated catalytic process for natural-gas-assisted OSW upgrading is fully demonstrated at a pilot scale, which combines the methanolysis, methano-refining and catalytic liquefaction processes through careful process design and catalyst tailoring. Three types of agricultural and forestry wastes including pelleted wood chip, crushed rice straw and crushed corn stover are used as representatives of OSW for at least a 1-month continuous operation. The products are comprehensively analyzed and the indices for quality control in terms of basic, compositional, and fuel properties, as well as elemental and distillation analyses, are monitored and proved to be satisfactory for practical use. Economic assessment and life cycle analysis are also performed. It is validated that the OSW upgrading process under a natural gas atmosphere exhibits favorable feasibility, stability, operational margins and environmental friendliness. This exploration manifests an alternative route for simultaneous energy supply and waste management with great economic and environmental advantages.

Formation mechanism of NOx precursors during the pyrolysis of 2,5-diketopiperazine based on experimental and theoretical study

Incineration of food waste leads to the release of NO_x pollutants, whereas the formation mechanism of the NO_x precursors (HCN, NH₃, and HNCO) during the initial pyrolysis process is far from well-studied, limiting the source control on NO_x release. In this work, 2,5-diketopiperazine (DKP) was selected as the N-containing model compound to study the formation mechanism of NO_x precursors in food waste pyrolysis, by combining experiments and density functional theory (DFT) calculations. The C1-N2 bond broken via the N2-to-N5 H-transfer possesses the lowest energy barrier, together with the largest reaction rate constants in the range of 400-800 °C. NH₃ can be easily generated with low energy barriers and high rate constants at low temperatures (below 630 °C). Whereas, the rate constants of the pathways for HCN formation will exceed those for NH₃ generation in the range of 630-740 °C. In addition, the DKP pyrolysis can also lead to the formation of HNCO with a very low energy barrier, and it can convert into HCN and NH₃ through further hydrogenation and decomposition. These calculation results are exactly consistent with the experimental results that NH₃ was the main precursor in the range of 400-600 °C, and the yield of HCN exceeded that of NH₃ when the temperature was over 600 °C. Our current work on the formation mechanism of NO_x precursors during the pyrolysis of DKP can provide theoretical guidance for the development of NO_x control technology in the pyrolysis/combustion process of organic waste.

Exploring new marine bacterial species, Alcaligenes faecalis Alca F2018 valued for bioconversion of shrimp chitin to chitosan for concomitant biotechnological applications

The exploitation of chitinous materials seems to be an infinite treasure. To this end, using shellfish waste as the sole carbon/nitrogen source solves environmental challenges while lowering microbial chitinase production costs. Bioconversion of shellfish chitin wastes such as shrimp shells has recently been investigated for the production of enzymes and bioactive materials in order to maximize the utilization of chitin-containing seafood processing wastes. In this study, the bioconversion of chitin to chitosan by Alcaligenes faecalis Alca F2018 revealed the highest chitin deacetylase (CDA) activity of 40.6 U/μg. The resulted low K_m and high V_max values explain the high affinity of the purified CDA to the p-nitroacetanilide substrate. CDA with a molecular weight of 66 KDa was purified from F2018 strain, with a 14.5% yield. FT-IR revealed distinct chitosan peaks and XRD revealed that chitosan samples had lower crystallinity than chitin. TGA analysis revealed that the recovered chitosan samples were more thermally stable. The deacetylation degree percentages of the produced chitosan are in the same range as that of the commercial chitosan, suggesting the promising potential of A. faecalis Alca F2018 to utilize shrimp shells in their raw form in the fermentation media based on its CDA enzyme activity.

A brief review on recent development of multidisciplinary engineering in fermentation of Saccharomyces cerevisiae

Fermentation technology has unprecedented potential to upgrade state-of-art biotechnology and refine the processes used in existing ones, taking into account of complex technical, economic and environmental factors. Given the economic importance and ongoing challenges of biotech sector, multidisciplinary engineering technologies is poised to become an increasingly important tool along with the emergence of modern technology and innovation. This article reviews recent technology advancement in the field of fermentation using Saccharomyces cerevisiae. Interesting research progress has been made by leveraging multiple engineering fields such as electrical engineering, information engineering, electrochemical engineering and new material development, leading to recent development of novel real-time probes (electronic nose technology, analysis of yeast morphology and metabolites, timely control of glucose feed), improved understanding of electro-fermentation (enhanced electronic transfer provision), as well as application of cost-effective and sustainable materials (bioreactor vessel manufactured from textile, and yeast immobilisation support matrix made from abundant natural biomass). To the best of our knowledge, the subject is reviewed for the first time in recent years. Furthermore, this review also constitutes a futuristic S. cerevisiae fermentation process based on the recent advancement discussed.

Relative abundance of lipid types among Chlorella sp. and Scenedesmus sp. and ameliorating homogeneous acid catalytic conditions using central composite design (CCD) for maximizing fatty acid methyl ester yield

The present study has tested the biodiesel potential of two hyper lipid producing strains Chlorella sp. and Scenedesmus sp. in terms of biomass yield, quantity and quality of lipid and fatty acid composition. Biomass yield of Chlorella sp. and Scenedesmus sp. was 1.26 and 1.33 g/L, respectively on day 18 and 20. The lipid content and lipid productivity of Chlorella sp. and Scenedesmus sp. was estimated to be 21.3, 26.5% and 12.33, 14.74 mg/L/d, respectively. Notably, relative abundance of lipid types in both the strains revealed >60% neutral lipids followed by glycolipids and phospholipids in minimal level. Central composite design based optimization revealed 69 and 65.4% FAME yield from Chlorella sp. and Scenedesmus sp. at 3% sulphuric acid and 65 °C reaction temperature. Eventually, higher levels of saturated fatty acids (~45%) and monounsaturated fatty acids (~34%) and make Scenedesmus sp. a promising parent material for workable biodiesel production.

Enzyme mimics in-focus: Redefining the catalytic attributes of artificial enzymes for renewable energy production

Herein, the advantages of enzyme mimetics by redefining the catalytic attributes and implementing artificial enzymes (AEs) for energy-related applications have presented. The intrinsic enzyme-like catalytic characteristics of nanozymes have become a growing area of prime interest in bio-catalysis. The development of AEs has redefined the concept of catalytic activity, opening a wide range of possibilities in biotechnological and energy sectors. Nowadays, power-energy is one of the most valuable resources that enable the development and progress of humanity. Over the last 50 years, fossil fuels' burning has released greenhouse gases and negatively impacted the environment and health. In 2019, around 84% of global primary energy came from coal, oil, and gas. Therefore, a global energy transition to renewable and sustainable energy is urgently needed to generate clean energy as biofuels and biohydrogen. However, to achieve this, the implementation of natural enzymes brings more significant challenges because their practical application is limited by the low operational stability, harsh environmental conditions, and expensive preparation processes. Hence, to accelerate the transition, promising substitutes are AEs, well-defined structures made of organic or inorganic materials that can mimic the catalytic power of natural enzymes. Despite being still in the midst, enzyme mimics overcome the main obstacles for a conventional enzyme. It opens future opportunities to optimize the production of renewable energies with excellent performance, high efficiency, and increasingly competitive prices. Thus, this work is a comprehensive study covering the promising potential of AEs, as biocatalysts, specifically for renewable energy production.

Transitioning Wastewater Treatment Plants toward Circular Economy and Energy Sustainability

Aging infrastructure, increasing environmental regulations, and receiving water environment issues stem the need for advanced wastewater treatment processes across the world. Advanced wastewater treatment systems treat wastewater beyond organic carbon removal and aim to remove nutrients and recover valuable products. While the removal of major nutrients (carbon, nitrogen, and phosphorus) is essential for environmental protection, this can only be achieved through energy-, chemical-, and cost-intensive processes in the industry today, which is an unsustainable trend, considering the global population growth and rapid urbanization. Two major routes for developing more sustainable and circular-economy-based wastewater treatment systems would be to (a) innovate and integrate energy- and resource-efficient anaerobic wastewater treatment systems and (b) enhance carbon capture to be diverted to energy recovery schemes. This Mini-Review provides a critical evaluation and perspective of two potential process routes that enable this transition. These process routes include a bioelectrochemical energy recovery scheme and codigestion of organic sludge for biogas generation in anaerobic digesters. From the analysis, it is imperative that integrating both concepts may even result in more energy- and resource-efficient wastewater treatment systems.

A Review of Composting Process Models of Organic Solid Waste with a Focus on the Fates of C, N, P, and K

To foster a circular economy in line with compost quality assessment, a deep understanding of the fates of nutrients and carbon in the composting process is essential to achieve the co-benefits of value-added and environmentally friendly objectives. This paper is a review aiming to fill in the knowledge gap about the composting process. Firstly, a systematic screening search and a descriptive analysis were conducted on composting models involving the fates of Carbon (C), Nitrogen (N), Phosphorus (P) and Potassium (K) over the past decade, followed by the development of a checklist to define the gap between the existing models and target models. A review of 22 models in total led to the results that the mainstream models involved the fates of C and N, while only a few models involved P and K as target variables. Most of the models described the laboratory-scale composting process. Mechanism-derived models were relatively complex; however, the application of the fractionation of substrates could contribute to reducing the complexity. Alternatively, data-driven models can help us obtain more accurate predictions and involve the fates of more nutrients, depending on the data volume. Finally, the perspective of developing composting models for the fates of C, N, P, and K was proposed.

A study on biofuel produced by catalytic cracking of mustard and castor oil using porous Hβ and AlMCM-41 catalysts

Biofuel is the only novel solution to the increase in the greenhouse effect and bursting energy demand. The catalytic cracking of non-edible vegetable oils, namely castor and mustard was studied to yield gasoline range (C5-C9) hydrocarbons. Hβ (Microporous; pore size <2 nm) and AlMCM-41 (Mesoporous; pore size 2 nm-50 nm) materials with different Si/Al ratios were used as catalysts for cracking purposes. Characterization of these catalysts was done by X-ray diffraction, Surface area analyzer, nitrogen sorption studies, TPD and inductively coupled plasma techniques. Used mustard oil was cracked over AlMCM-41 catalysts in a fixed bed catalytic cracking unit at optimized reaction condition (400 °C, 4.6 h^-1) obtained over Hβ. The liquid and gaseous products were analyzed using gas chromatograph (Shimadzu GC-9A). Among the mesoporous catalysts AlMCM-41 (27) was able to convert 75% of mustard oil into 48% of bioliquid and 30.4% selectivity towards BG. Pongamia, neem, castor, fresh coconut and used coconut oil was also cracked using AlMCM-41 (27) catalyst. The major products of cracking reactions were Castor Bioliquid (CBL) comprising of bio gasoline (BG), bio kerosene (BK) and bio diesel (BD) with less yield of gaseous products. AlMCM-41 converted 98% of castor oil into 85% of CBL and it was tested with ASTM 6751 standard procedures for its calorific value, viscosity and flash point. The sulphur emission from CBL run engine reached lower index. The results exhibited the commercial utility of the CBL in the near future.

Does lipid stress affect performance, fate of antibiotic resistance genes and microbial dynamics during anaerobic digestion of food waste?

The dissemination of antibiotic resistance genes (ARGs) in food waste (FW) disposal can pose severe threats to public health. Lipid is a primary composition in FW, while whether lipid stress can affect ARGs dynamics during anaerobic digestion (AD) process of FW is uncertain. This study focused on the impacts of lipid stress on methane production, fate of ARGs and its microbial mechanisms during AD of FW. Results showed that high lipid content increased methane yield but prolonged hydrolysis and lag time of methane production compared to AD of FW without oil. Moreover, variations of ARGs were more susceptible to lipid stress. Lipid stress could facilitate the reduction of total ARGs abundances compared to the group without oil, particularly restraining the proliferation of sul1, aadA1 and mefA in AD systems (P < 0.05). Mantel test suggested that integrons (intl1 and intl2) were significantly correlated with all detected ARGs (r: 0.33, P < 0.05), indicating that horizontal gene transfer mediated by integrons could be the driving force on ARGs dissemination. Network analysis suggested that Firmicutes, Bacteroidetes, Synergistetes and Proteobacteria were the main potential hosts of ARGs. In addition, under the lipid stress, the reduction of host bacteria was responsible for the elimination of several specific ARGs, thereby affecting ARGs profiles. These findings firstly deciphered ARGs dynamics and their driving factors responding to lipid stress during anaerobic biological treatment of FW.

A comprehensive review of the recent development and challenges of a solar-assisted biodigester system

The extensive use of fossil fuels and the environmental effect of their combustion products have attracted researchers to look into renewable energy sources. In addition, global mass production of waste has motivated communities to recycle and reuse the waste in a sustainable way to lower landfill waste and associated problems. The development of waste to energy (WtE) technology including the production of bioenergy, e.g. biogas produced from various waste through Anaerobic Digestion (AD), is considered one of the potential measures to achieve the sustainable development goals of the United Nations (UN). Therefore, this study reviews the most recent studies from relevant academic literature on WtE technology (particularly AD technology) for biogas production and the application of a solar-assisted biodigester (SAB) system aimed at improving performance. In addition, socio-economic factors, challenges, and perspectives have been reported. From the analysis of different technologies, further work on effective low-cost technologies is recommended, especially using SAB system upgrading and leveraging the opportunities of this system. The study found that the performance of the AD system is affected by a variety of factors and that different approaches can be applied to improve performance. It has also been found that solar energy systems efficiently raise the biogas digester temperature and through this, they maximize the biogas yield under optimum conditions. The study revealed that the solar-assisted AD system produces less pollution and improves performance compared to the conventional AD system.

Avocado-Derived Biomass as a Source of Bioenergy and Bioproducts

The avocado (Persea americana Mill.) is a tree native to Mexico and Guatemala. Avocado consumption, fresh or in the form of processed products, is growing everywhere and it has caused a large number of countries to invest heavily in avocado production. The industrialization of avocado gives as a result a huge amount of waste, not only the peel and stone but also that waste generated by the pruning practices and oil extraction. These biomasses could be converted into raw materials to obtain different types of co-products, but this implies changes in the use of these resources, the design of efficient production systems, and integration to take full advantage of them, e.g., by developing biorefinery models. Therefore, this review firstly gives a snapshot of those residues generated in the avocado industry and provides their chemical composition. Secondly, this review presents updated information about the valorization ways of avocado-derived biomass to obtain bioenergy, biofuels, and other marketable products (starch, protein, phenolic compounds, and biosorbents, among others) using a single process or integrated processes within a biorefinery context. Green technologies to obtain these products are also covered, e.g., based on the application of microwaves, ultrasound, supercritical fluids, etc. As a conclusion, there is a variety of ways to valorize avocado waste in single processes, but it would be promising to develop biorefinery schemes. This would enable the avocado sector to move towards the zero-waste principle.

A comprehensive review on the framework to valorise lignocellulosic biomass as biorefinery feedstocks

An effective pretreatment is the first step to enhance the digestibility of lignocellulosic biomass - a source of renewable, eco-friendly and energy-dense materials - for biofuel and biochemical productions. This review aims to provide a comprehensive assessment on the advantages and disadvantages of lignocellulosic pretreatment techniques, which have been studied at the lab-, pilot- and full-scale levels. Biological pretreatment is environmentally friendly but time consuming (i.e. 15-40 days). Chemical pretreatment is effective in breaking down lignocellulose and increasing sugar yield (e.g. 4 to 10-fold improvement) but entails chemical cost and expensive reactors. Whereas the combination of physical and chemical (i.e. physicochemical) pretreatment is energy intensive (e.g. energy production can only compensate 80% of the input energy) despite offering good process efficiency (i.e. > 100% increase in product yield). Demonstrations of pretreatment techniques (e.g. acid, alkaline, and hydrothermal) in pilot-scale have reported 50-80% hemicellulose solubilisation and enhanced sugar yields. The feasibility of these pilot and full-scale plants has been supported by government subsidies to encourage biofuel consumption (e.g. tax credits and mandates). Due to the variability in their mechanisms and characteristics, no superior pretreatment has been identified. The main challenge lies in the capability to achieve a positive energy balance and great economic viability with minimal environmental impacts i.e. the energy or product output significantly surpasses the energy and monetary input. Enhancement of the current pretreatment techno-economic efficiency (e.g. higher product yield, chemical recycling, and by-products conversion to increase environmental sustainability) and the integration of pretreatment methods to effectively treat a range of biomass will be the steppingstone for commercial lignocellulosic biorefineries.

A novel hybrid organosolv-steam explosion pretreatment and fractionation method delivers solids with superior thermophilic digestibility to methane

Rising environmental concerns and the imminent depletion of fossil resources have sparked a strong interest towards the production of renewable energy such as biomethane. Inclusion of alternative feedstock's such as lignocellulosic biomass could further expand the production of biomethane. The present study evaluated the potential of a novel hybrid organosolv-steam explosion fractionation for delivering highly digestible pretreated solids from birch and spruce woodchips. The highest methane production yield was 176.5 mLCH₄ gVS^-1 for spruce and 327.2 mL CH₄ gVS^-1 for birch. High methane production rates of 1.0-6.3 mL min^-1 (spruce) and 6.0-35.5 mL min^-1 (birch) were obtained, leading to a rapid digestion, with 92% of total methane from spruce being generated in 80 h and 95% of that from birch in 120 h. These results demonstrate the elevated potential of the novel method to fractionate spruce and birch biomass and deliver cellulose-rich pretreated solids with superior digestibility.

Crop Residue Removal: Assessment of Future Bioenergy Generation Potential and Agro-Environmental Limitations Based on a Case Study of Ukraine

This study assesses the bioenergy generation potential of crop residues in Ukraine for the year 2030. Projections of agricultural development are made based on the Global Biosphere Management Model (GLOBIOM) and verified against available Agricultural Member State Modeling (AGMEMOD) results in regard to the six main crops cultivated in Ukraine (wheat, barley, corn, sunflower, rape and soya). Two agricultural development scenarios are assessed (traditional and innovative), facilitating the projection of future crop production volumes and yields for the selected crops. To improve precision in defining agro-environmental limitations (the share of crop residues necessary to be kept on the fields to maintain soil fertility for the continuous cultivation of crops), yield-dependent residue-to-product ratios (RPRs) were applied and the levels of available soil nutrients for regions of Ukraine (in regard to nitrogen, phosphorus, potassium and humus) were estimated. The results reveal the economically feasible future bioenergy generation potential of crop residues in Ukraine, equaling 3.6 Mtoe in the traditional agricultural development scenario and 10.7 Mtoe in the innovative development scenario. The projections show that, within the latter scenario, wheat, corn and barley combined are expected to provide up to 81.3% of the bioenergy generation potential of crop residues.

Biomethane production from anaerobic co-digestion and steel-making slag: A new waste-to-resource pathway

A proof of concept of using steel-making slag to upgrade biogas to biomethane is demonstrated in this study. Biogas is generated from the anaerobic co-digestion of sewage sludge and beverage waste. The CO₂ capture capacity of an alkaline liquor derived from the release of calcium from the steel-making slag is comparable to that of the commercial adsorbent monoethanolamine. Although only 5% of Ca in the steel-making slag was released to the alkaline liquor, 1 ton of steel-making slag could be capable of upgrading 10 m³ of biogas to over 90% methane content. The results also show that pH can be used as a surrogate parameter to monitor and control biogas upgrading. Further research to improve the release of calcium is essential for the acceleration of the weathering process of steel-making slag for subsequent construction applications.

Upgrading of Biogas to Methane Based on Adsorption

Upgrading raw biogas to methane (CH4) is a vital prerequisite for the utilization of biogas as a vehicle fuel or the similar field as well. In this work, biogas yield from the anaerobic fermentation of food waste containing methane (CH4, 60.4%), carbon dioxide (CO2, 29.1%), hydrogen sulfide (H2S, 1.5%), nitrogen (N2, 7.35%) and oxygen (O2, 1.6%) was upgraded by dynamic adsorption. The hydrogen sulfide was removed from the biogas in advance by iron oxide (Fe2O3) because of its corrosion of the equipment. Commercial 13X zeolite and carbon molecular sieve (CMS) were used to remove the other impurity gases from wet or dry biogas. It was found that neither 13X zeolite nor CMS could effectively remove each of the impurities in the wet biogas for the effect of water vapor. However, 13X zeolite could effectively remove CO2 after the biogas was dried with silica and showed a CO2 adsorption capacity of 78 mg/g at the condition of 0.2 MPa and 25 °C. Additionally, 13X zeolite almost did not adsorb nitrogen (N2), so the CH4 was merely boosted to ac. 91% after the desulfurated dry biogas passed through 13X zeolite, nitrogen remaining in the biogas. CMS would exhibit superior N2 adsorption capacity and low CO2 adsorption capacity if some N2 was present in biogas, so CMS was able to remove all the nitrogen and fractional carbon dioxide from the desulfurated dry biogas in a period of time. Finally, when the desulfurated dry biogas passed through CMS and 13X zeolite in turn, the N2 and CO2 were sequentially removed, and then followed the high purity CH4 (≥96%).