Optimal aeration area of cathode electrode in the batch type of microbial fuel cells with non-woven interface.

Microbial fuel cells (MFCs) are based on the biochemical reaction of microorganisms to decompose organic wastewater for converting chemical energy into power energy. MFCs are considered an environmentally friendly technology that is gaining popularity due to their simultaneous digestion and energy production abilities. To enhance its real application in wastewater treatment, this study proposes to use a non-woven material for replacing the usage of expensive membranes in MFCs. In addition, the study aims to consider a series of different aeration areas of cathode electrodes for finding an optional design. Results have shown that the adoption of non-woven with 0.45 µm can effectively prohibit the diffusion of oxygen into the anode chamber. Moreover, the non-woven material played an important role as an interface between the anode and cathode, enhancing the MFC performance. The usage of suitable non-woven material can replace the role of the membrane when applied in real wastewater applications. The results have shown that the case study where a combination of a 50% aeration area of the cathode electrodes with 25% exposure of the cathode plate in the air yielded relatively better aeration in terms of a higher current density of 250 mA/m2, higher power density of 220 mW/m2, and higher open voltage circuit of 0.4 V, compared to other case studies considered. These results indicate the optimal aeration configuration for MFCs applied in commercial wastewater treatment in the future.

Life cycle assessment of a biomass based chemical looping combustion.

Chemical looping combustion (CLC) is a promising technology that generates energy while inherently separating carbon dioxide from air using oxygen carriers. This allows for an efficient and cost-effective means of carbon capture and storage. Current CLC systems use coal with metal oxides for combustion in the fuel reactor, thus, resulting in some environmental impacts. Recent life cycle assessment (LCA) of CLC studies have indicated the environmental impacts of conventional coal-based CLC, especially on the global warming potential. To mitigate these environmental impacts, this study proposes the use of a biomass-based CLC and evaluates its impacts using LCA. A case study in the Philippines is adopted where rice husks are used as biomass feedstock. A kilowatt-hour of electricity generated from the CLC plant is utilized as the functional unit. A relative comparison of environmental impacts was considered between the coal-based power plant, the coal-based CLC plant, and the biomass-based CLC plant. The single score results have shown that the biomass-based CLC has the least environmental impacts relative to the coal-based power plant and the coal-based CLC plant. However, it is noted that water consumption is the main drawback of utilizing rice husks as CLC biomass feedstock. The majority of the environmental impacts of the coal-based CLC and the coal-based power plant were derived from upstream processes such as coal mining and processing. With the use of rice husks as CLC biomass feedstock, net negative emissions were achieved.

Design of biorefineries towards carbon neutrality: A critical review.

The increase in worldwide demand for energy is driven by the rapid increase in population and exponential economic development. This resulted in the fast depletion of fossil fuel supplies and unprecedented levels of greenhouse gas in the atmosphere. To valorize biomass into different bioproducts, one of the popular and carbon-neutral alternatives is biorefineries. This system is an appropriate technology in the circular economy model. Various research highlighted the role of biorefineries as a centerpiece in the carbon-neutral ecosystem of technologies of the circular economy model. To fully realize this, various improvements and challenges need to be addressed. This paper presents a critical and timely review of the challenges and future direction of biorefineries as an alternative carbon-neutral energy source.

Biohydrogen in a circular bioeconomy: A critical review.

Hydrogen produced from biomass feedstocks is considered an effective solution in moving toward a decarbonized economy. Biohydrogen is a clean energy source that has gained global attention for adoption as it promises to mitigate climate change and human environmental damage. Through the circular economy framework, sustainable biohydrogen production with other bioproducts while addressing issues such as waste management is possible. This study presents a comprehensive review of the various biomass feedstocks and processing technologies associated with biohydrogen generation, as well as the possible integration of existing industries into a circular bioeconomy framework. The currently standing challenges and future perspectives are also discussed.

Life cycle assessment of microalgal biorefinery: A state-of-the-art review.

Microalgal biorefineries represent an opportunity to economically and environmentally justify the production of bioproducts. The generation of bioproducts within a biorefinery system must quantitatively demonstrate its viability in displacing traditional fossil-based refineries. To this end, several works have conducted life cycle analyses on microalgal biorefineries and have shown technological bottlenecks due to energy-intensive processes. This state-of-the-art review covers different studies that examined microalgal biorefineries through life cycle assessments and has identified strategic technologies for the sustainable production of microalgal biofuels through biorefineries. Different metrics were introduced to supplement life cycle assessment studies for the sustainable production of microalgal biofuel. Challenges in the comparison of various life cycle assessment studies were identified, and the future design choices for microalgal biorefineries were established.

Smart sustainable biorefineries for lignocellulosic biomass.

Lignocellulosic biomass (LCB) is considered as a sustainable feedstock for a biorefinery to generate biofuels and other bio-chemicals. However, commercialization is one of the challenges that limits cost-effective operation of conventional LCB biorefinery. This article highlights some studies on the sustainability of LCB in terms of cost-competitiveness and environmental impact reduction. In addition, the development of computational intelligence methods such as Artificial Intelligence (AI) as a tool to aid the improvement of LCB biorefinery in terms of optimization, prediction, classification, and decision support systems. Lastly, this review examines the possible research gaps on the production and valorization in a smart sustainable biorefinery towards circular economy.

COVID-19 and industrial waste mitigation via thermochemical technologies towards a circular economy: A state-of-the-art review.

The increasing awareness of waste circular economy has motivated valorization strategies for minimizing resource consumption and waste production in the private sector. With the rise of various industrial wastes and with the emergence of COVID-19 wastes, a sustainable approach is needed to mitigate the growing concern about wastes. Thermochemical treatment technologies in the form of direct combustion, torrefaction, pyrolysis, and gasification have been identified to have vital roles in the value-creation of various waste streams. Moreover, the alignment of thermochemical processes for waste mitigation concerning the circular economy framework needs to be established. Accordingly, a comprehensive review of the different thermochemical treatment options for industrial and the novel COVID-19 medical wastes streams is conducted in this study. This review focuses on highlighting the instrumental role of thermochemical conversion platforms in achieving a circular economy in the industrial sector. Various strategies in waste mitigation through various thermochemical processes such as management, recovery, reduction, and treatment are discussed. The results show that thermochemical technologies are beneficial in addressing the sustainability concerns on mitigating wastes from the industrial sector and wastes brought by the COVID-19 pandemic. This also includes the current issues faced as well as future perspectives of the thermochemical conversion technologies.

Microplastic degradation as a sustainable concurrent approach for producing biofuel and obliterating hazardous environmental effects: A state-of-the-art review.

As plastics have been omnipresent in society ever since their introduction in 1907, global plastic production has ballooned in the 20th century or the Plasticene Era (Plastic Age). After their useful life span, they deliberately or accidentally, are disposed of in the environment. Influenced by different factors, plastics undergo fragmentation into microplastics (MPs) and present hazardous risks in all life forms including humans. Obliterating MPs from the environment has been a global challenge for the attainment of sustainable development goals (SDGs). This review aims to present MP degradation routes with a great focus on the thermodegradation and biodegradation routes as sustainable routes of MP degradation. These routes can achieve the reduction and obliteration of MPs in the environment, thus reducing their hazardous effects. Moreover, the thermodegradation of MPs can produce fuels that help solve the dilemma of energy security. Overall, continued research and development are still needed, however, these novel approaches and the increased awareness of the microplastics' hazards give us hope that we can achieve sustainable development in the near future.

Energy balance of torrefied microalgal biomass with production upscale approached by life cycle assessment.

Torrefaction is a thermochemical process used to convert the biomass into solid fuel. In this study, torrefaction increased the raw microalgal biomass' energy content from 20.22 MJ⋅kg-1 to 27.93 MJ⋅kg-1. To determine if more energy is produced than energy consumption from torrefaction, this study identified the energy balance of torrefied microalgal biomass production based on a life cycle approach. The energy analysis showed that, among all processes, torrefaction had the least amount of energy demand. The experimental setup, defined as scenario A, revealed that the principal source of energy demand, about 85%, was consumed on the microalgal growth using a photobioreactor system. A sensitivity analysis was also performed to determine the varying energy demand for torrefied microalgal biomass production. The different types of cultivation methods and various production scales were considered in scenarios B to D. Scenario D, which represented the commercial production-scale, the energy demand drastically decreased by 59.46% as compared to the experimental setup (scenario A). The open-pond cultivation system resulted in the least energy requirement, regardless of the production scale (scenarios B and C) among all the given scenarios. Unlike scenarios A and D, scenarios B and C identified the drying process to consume a high amount of energy. All the scenarios have shown an energy demand deficit. Therefore, efforts to decrease the energy demand on the upstream processes are needed to make the torrefied microalgal biomass a viable alternative energy source.

Green additive to upgrade biochar from spent coffee grounds by torrefaction for pollution mitigation.

A green approach using hydrogen peroxide (H2O2) to intensify the fuel properties of spent coffee grounds (SCGs) through torrefaction is developed in this study to minimize environmental pollution. Meanwhile, a neural network (NN) is used to minimize bulk density at different combinations of operating conditions to show the accurate and reliable model of NN (R2 = 0.9994). The biochar produced from SCGs torrefied at temperatures of 200-300 °C, duration of 30-60 min, and H2O2 concentrations of 0-100 wt% is examined. The results reveal that the higher heating value (HHV) of biochar increases with rising temperature, duration, or H2O2 concentration, whereas the bulk density has an opposite trend. The HHV, ignition temperature, and bulk density of biochar from torrefaction at 230 °C for 30 min with a 100 wt% H2O2 solution (230-100%-TSCG) are 27.00 MJ∙kg-1, 292 °C, and 120 kg∙m-3, respectively. This HHV accounts for a 29% improvement compared to that of untorrefied SCG. The contact angle (126°), water activity (0.51 aw), and moisture content (7.69%) of the optimized biochar indicate that it has higher resistance against biodegradation, and thereby can be stored longer. Overall, H2O2 is a green treatment additive for SCGs solid fuel. This study has successfully produced biochar with greater HHV and low bulk density at low temperatures. The green additive development can effectively reduce environmental pollutants and upgrade wastes into resources, and achieve "3E", namely, environmental (non-polluting green additives), energy (biofuel), and circular economy (waste upgrade). In addition, the produced biochar has great potential in the fields of bioadsorbents and soil amendments.

Microalgal biosorption of heavy metals: A comprehensive bibliometric review.

Heavy metals in the effluents released from industrial establishments pose risks to the environment and society. Prevalent organisms such as microalgae in industrial wastes can thrive in this harmful environment. The connection of the metal-binding proteins of the microalgal cell wall to the metal ions of the heavy metals enables microalgae as an ideal medium for biosorption. The current literature lacks the review of various microalgae used as biosorption of heavy metals from industrial effluents. This work aims to comprehensively review the literature on the use of microalgae as a biosorption for heavy metals. The study summarizes the application of different microalgae for heavy metals removal by identifying the various factors affecting the biosorption performance. Approaches to quantifying the heavy metals concentration are outlined. The methods of microalgae to generate biocompounds to enable biosorption of heavy metals are itemized. The study also aims to identify the materials produced by microalgae to facilitate biosorption. The industrial sectors with the potential benefit from the adoption of microalgal biosorption of heavy metals are recognized. Moreover, the current challenges and future perspectives of microalgal biosorption are discussed.

Reduction of particulate matter and volatile organic compounds in biorefineries: A state-of-the-art review.

A biorefinery is an efficient approach to generate multiple bio-products from biomass. With the increasing demand for bioenergy and bio-products, biorefineries are essential industrial platforms that provide needed demand while significantly reducing greenhouse gas emissions. A biorefinery consists of various conversion technologies where particulate matter (PM) and volatile organic compounds (VOCs) are emitted. The released PM and VOCs pose detrimental health and environmental risks for society. Moreover, the projected rise of global bioenergy demand may lead to an increase in PM and VOCs from biorefineries. With the use of cleaner technologies and approaches, PM and VOCs can be avoided in biorefineries. The study presents the landscape of the research field through a bibliometric review of emissions from a biorefinery. A comprehensive review of works on the reduction of PM and VOCs in a biorefinery is outlined. The study includes a perspective of cleaner technologies and approaches utilized in biorefineries to mitigate these hazardous materials. The results reveal that the employment of life cycle assessment, safety assessment, and green chemistry processes can significantly reduce PM and VOC emissions as well as the consumption of hazardous substances in the biorefinery.

A state-of-the-art review of biowaste biorefinery.

Biorefineries provide a platform for different industries to produce multiple bio-products enhancing the economic value of the system. The production of these biorefineries has led to an increase in the generation of biowaste. To minimize the risk of environmental pollution, numerous studies have focused on a variety of strategies to mitigate these concerns reflected in the vast amount of literature written on this topic. This paper aims to systematically analyze and review the enormous body of scientific literature in the biowaste and biorefinery field for establishing an understanding and providing a direction for future works. A bibliometric analysis is first performed using the CorTexT Manager platform on a corpus of 1488 articles written on the topic of biowaste. Popular and emerging topics are determined using a terms extraction algorithm. A contingency matrix is then created to study the correlation of scientific journals and key topics from this field. Then, the connection and evolution of these terms were analyzed using network mapping, to determine relationships among key terms and analyze notable trends in this research field. Finally, a critical review of articles was presented across three main categories of biowaste management such as mitigation, sustainable utilization, and cleaner disposal from the perspective of the biorefinery concept. Operational and technological challenges are identified for the integration of anaerobic digestion in biorefineries, especially in developing nations. Moreover, logistical challenges in the biorefinery supply-chain are established based on the economics and collection aspect of handling biowaste.

Dataset for off-grid micro-hydroelectric community system under drought conditions.

This submission contains the complete balanced process matrix of an off-grid community system primarily powered by a micro-hydroelectric powerplant. The system is meant to provide the needs of the community for electricity, potable water and ice. The system also considers the provision of a diesel engine generator set as a back-up to provide electricity. The data serves as inputs to simulate the performance of the system under different drought scenarios. The data provided here is in support of the co-submitted article of Aviso et al. [1].

Kinetics and thermodynamics dataset of iron oxide reduction using torrefied microalgae for chemical looping combustion.

The reduction of iron oxides transpires through the application of heat wherein a carbon source known as reductant is required. In order to design a chemical looping combustion using iron as an oxygen carrier and torrefied microalgae biomass as a reductant, the kinetics and thermodynamics dataset must be determined. Using the Arrhenius law of reaction, the kinetics dataset was obtained employing the three chemical reaction model such as the first order (C1), the reaction order 1.5 (C1.5), and the second-order (C2). The iron oxide reduction from hematite to metallic iron was sub-divided into three phases wherein phase 1 (Fe2O3 → Fe3O4) is from 365 °C to 555 °C, phase 2 (Fe3O4 → FeO) is from 595 °C to 799 °C, and phase 3 (FeO → Fe) is from 800 °C to 1200 °C. Two torrefied microalgae (Chlamydomonas sp. JSC4 and Chlorella vulgaris ESP-31) were considered as a reducing agent. The kinetics dataset comprise of the activation energy (E), pre-exponential factor (A), and the reaction rate (k) while the thermodynamic dataset consists of the change in enthalpy (ΔH), change in Gibbs energy (ΔG), and change in entropy (ΔS). These kinetics and thermodynamics parameters are essential in understanding the reaction mechanisms of the reduction process of iron oxides enabling process optimization and improvement. Current literature lacks the kinetics and thermodynamics datasets for the reduction of iron oxides using the two torrefied microalgae as reductants. This work provides these datasets which are useful for the design of reactors in chemical looping combustion.

Data set and model code on the optimal operating state of a negative emission polygeneration system.

This article contains the data set and model code for the negative emission polygeneration system described in Tan et al. (2019). The data was generated utilizing an optimization model implemented in LINGO 18.0 and includes information on the operating state of each process unit in the system. The maximum annual profit of the system was determined at different carbon footprint targets. The data set and model code can be utilized for further analysis on the interdependence between the process units of this polygeneration system, its operational and environmental performance, and the potential impact of integrating new process units into the network.

Biorefineries in circular bioeconomy: A comprehensive review.

Biorefinery is a sustainable means of generating multiple bioenergy products from various biomass feedstocks through the incorporation of relevant conversion technologies. With the increased attention of circular economy in the past half-decade with the emphasis of holistically addressing economic, environmental, and social aspects of the industrial-sector, biorefinery acts as a strategic mechanism for the realization of a circular bioeconomy. This study presents a comprehensive review of different biorefinery models used for various biomass feedstocks such as lignocelluloses, algae, and numerous waste-types. The review focuses on how biorefinery is instrumental in the transition of various biomass-based industries in a circular bioeconomy. The results reveal that the social-economic aspect of the industrial sector has a major influence on the full adoption of biorefineries in circular bioeconomy. Biomass wastes have played a major role in the implementation of biorefinery in circular bioeconomy. The current challenges are also presented along with future perspectives.

A comprehensive review of life cycle assessment (LCA) of microalgal and lignocellulosic bioenergy products from thermochemical processes.

Microalgal biomass is a renewable energy source and is considered as a crucial solution in the increasing energy demand and greenhouse gas emissions. Through various thermochemical conversion processes such as torrefaction, pyrolysis, liquefaction, and gasification, biomass can be converted to different bioenergy products. However, the production of these bioenergy products through the aforesaid thermochemical processes entails raw material consumption, energy consumption, and environmental impact. A multitude of studies has been conducted to evaluate the environmental impact of bioenergy products for specific thermochemical processes on a specific biomass feedstock using life cycle assessment. This study aims to comprehensively review the life cycle assessment of bioenergy products from microalgal biomass together with lignocellulosic biomass and through different thermochemical processes. The study identifies the current challenges and potential future works of bioenergy production from different thermochemical processes in the perspective of a life cycle assessment framework.

Investigation of reverse ionic diffusion in forward-osmosis-aided dewatering of microalgae: A molecular dynamics study.

This study aimed to investigate the transport mechanisms of ions during forward-osmosis-driven (FO-driven) dewatering of microalgae using molecular dynamics (MD) simulations. The dynamical and structural properties of ions in FO systems of varying NaCl or MgCl2 draw solution (DS) concentrations were calculated and correlated. Results indicate that FO systems with higher DS concentration caused ions to have lower hydration numbers and higher coordination numbers leading to lower diffusion coefficients. The higher hydration number of Mg2+ ions resulted in significantly lower ionic permeability as compared to Na+ ions at all concentrations (p = 0.002). The simulations also revealed that higher DS concentrations led to higher accumulation of ions in the membrane. This study provides insights on the proper selection of DS for FO systems.