Multi-objective operation optimization of spent coffee ground torrefaction for carbon-neutral biochar production.

Many energy-intensive processes are employed to enhance biomass fuel properties to overcome the difficulties in utilizing biomass as fuel. Therefore, energy conservation during these processes is crucial for realizing a circular bioeconomy. This study develops a newly devised method to evaluate SCG biochars' higher heating value (HHV) and predict moisture content from power consumption. It is found that the increasing rates of HHV immediately follow decreases in power consumption, which could be used to determine the pretreatment time for energy conservation. The non-dominated sorting genetic algorithm II (NSGA-II) maximizes SCG biochar's HHV while minimizing energy consumption. The results show that producing SCG biochar with 23.98 MJ∙kg-1 HHV requires 20.042 MJ∙kg-1, using a torrefaction temperature of 244 °C and torrefaction time of 27 min and 43 sec. Every kilogram of biochar with an energy yield of 85.93 % is estimated to cost NT$ 12.21.

Application of regression and artificial neural network analysis of Red-Green-Blue image components in prediction of chlorophyll content in microalgae.

This study presented a novel methodology to predict microalgae chlorophyll content from colour models using linear regression and artificial neural network. The analysis was performed using SPSS software. Type of extractant solvents and image indexes were used as the input data for the artificial neural network calculation. The findings revealed that the regression model was highly significant, with high R2 of 0.58 and RSME of 3.16, making it a useful tool for predicting the chlorophyll concentration. Simultaneously, artificial neural network model with R2 of 0.66 and low RMSE of 2.36 proved to be more accurate than regression model. The model which fitted to the experimental data indicated that acetone was a suitable extraction solvent. In comparison to the cyan-magenta-yellow-black model in image analysis, the red-greenblue model offered a better correlation. In short, the estimation of chlorophyll concentration using prediction models are rapid, more efficient, and less expensive.

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.

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.

Catalytic microwave torrefaction of microalga Chlorella vulgaris FSP-E with magnesium oxide optimized via taguchi approach: A thermo-energetic analysis.

Biochar is a promising material and fuel for environmental sustainability. Microalgal biochar is produced using catalytic microwave torrefaction of Chlorella vulgaris FSP-E residue with magnesium oxide as a microwave absorber to enhance heating. Using Taguchi experimental design (TED) and Analysis of Variance (ANOVA), the effects of microwave power, catalyst concentration, and duration on energy yield are investigated. Both TED and ANOVA confirm the significant effects of microwave power and catalyst concentration, while only a slight effect from duration. The calorific values of produced biochar (21.12-26.22 MJ⋅kg-1) are close to coal. The maximum deoxygenation and carbonization extents are 56.69% and 35.23%, respectively. The optimal parameter combination of low microwave power (450 W), low duration (25 min), and high catalyst concentration (10 wt% MgO) poses the highest upgrading energy index (UEI) value. This confirms that better energy efficiency leans towards light torrefaction conditions with maximized catalyst concentration to produce the maximum energy yield while consuming the least electricity input.

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.

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.

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.

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.

Optimizing and Characterizing Geopolymers from Ternary Blend of Philippine Coal Fly Ash, Coal Bottom Ash and Rice Hull Ash.

Geopolymers are inorganic polymers formed from the alkaline activation of amorphous alumino-silicate materials resulting in a three-dimensional polymeric network. As a class of materials, it is seen to have the potential of replacing ordinary Portland cement (OPC), which for more than a hundred years has been the binder of choice for structural and building applications. Geopolymers have emerged as a sustainable option vis-à-vis OPC for three reasons: (1) their technical properties are comparable if not better; (2) they can be produced from industrial wastes; and (3) within reasonable constraints, their production requires less energy and emits significantly less CO2. In the Philippines, the use of coal ash, as the alumina- and silica- rich geopolymer precursor, is being considered as one of the options for sustainable management of coal ash generation from coal-fired power plants. However, most geopolymer mixes (and the prevalent blended OPC) use only coal fly ash. The coal bottom ash, having very few applications, remains relegated to dumpsites. Rice hull ash, from biomass-fired plants, is another silica-rich geopolymer precursor material from another significantly produced waste in the country with only minimal utilization. In this study, geopolymer samples were formed from the mixture of coal ash, using both coal fly ash (CFA) and coal bottom ash (CBA), and rice hull ash (RHA). The raw materials used for the geopolymerization process were characterized using X-ray fluorescence spectroscopy (XRF) for elemental and X-ray diffraction (XRD) for mineralogical composition. The raw materials' thermal stability and loss on ignition (LOI) were determined using thermogravimetric analysis (TGA) and reactivity via dissolution tests and inductively-coupled plasma mass spectrometry (ICP) analysis. The mechanical, thermal and microstructural properties of the geopolymers formed were analyzed using compression tests, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Using a Scheffé-based mixture design, targeting applications with low thermal conductivity, light weight and moderate strength and allowing for a maximum of five percent by mass of rice hull ash in consideration of the waste utilization of all three components, it has been determined that an 85-10-5 by weight ratio of CFA-CBA-RHA activated with 80-20 by mass ratio of 12 M NaOH and sodium silicate (55% H2O, modulus = 3) produced geopolymers with a compressive strength of 18.5 MPa, a volumetric weight of 1660 kg/m³ and a thermal conductivity of 0.457 W/m-°C at 28-day curing when pre-cured at 80 °C for 24 h. For this study, the estimates of embodied energy and CO2 were all below 1.7 MJ/kg and 0.12 kg CO2/kg, respectively.