Critical review of biochemical pathways to transformation of waste and biomass into bioenergy

Enhancing biomass conversion to bioenergy with machine learning: Gains and problems

The growing concerns about environmental sustainability and energy security, such as exhaustion of traditional fossil fuels and global carbon footprint growth have led to an increasing interest in alternative energy sources, especially bioenergy. Recently, numerous scenarios have been proposed regarding the use of bioenergy from different sources in the future energy systems. In this regard, one of the biggest challenges for scientists is managing, modeling, decision-making, and future forecasting of bioenergy systems. The development of machine learning (ML) techniques can provide new opportunities for modeling, optimizing and managing the production, consumption and environmental effects of bioenergy. However, researchers in bioenergy fields have not widely utilized the ML concepts and practices. Therefore, a comparative review of the current ML techniques used for bioenergy productions is presented in this paper. This review summarizes the common issues and difficulties existing in integrating ML with bioenergy studies, and discusses and proposes the possible solutions. Additionally, a detailed discussion of the appropriate ML application scenarios is also conducted in every sector of the entire bioenergy chain. This indicates the modernized conversion processes supported by ML techniques are imperative to accurately capture process-level subtleties, and thus improving techno-economic resilience and socio-ecological integrity of bioenergy production. All the efforts are believed to help in sustainable bioenergy production with ML technologies for the future.

A concise review on waste biomass valorization through thermochemical conversion

Due to an increase in industrialization and urbanization, massive amounts of solid waste biomass are speedily accumulating in our environment, which poses several adverse effects on habitat and human health thus becoming a matter of discussion in the environmental community. With reference to the circular economy, continuous efforts have been put forward for setting up an organised management approach in combination with an efficient treatment technique for increasing the profitable utilization of solid waste. This review aims to provide a systematic discussion on the recent thermochemical technologies employed for converting waste biomass generated from different sources into valuable products like biochar, bio-oil, heat, energy and syngas. The article further focuses on a few important aspects of thermochemical conversion of waste biomass to useful products like technical factors affecting thermochemical processes, applications of by-products of thermochemical conversion, and biological pretreatment of waste biomass. The review assists interesting recent and scientific trends for boosting up the systematic management and valorization of solid waste through low-cost, efficient, environment-friendly and sustainable technologies.

Fast analysis of straw proximates based on partial least squares using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a rapid measurement technique based on the spectroscopic absorption bands of specific functional groups within biomass. Its main advantages include simple preparation, precise analysis, and the ability to analyze multiple components simultaneously. Fast analysis of straw proximates (moisture, ash, and fixed carbon) has been investigated by means of NIRS. A total of 144 samples were collected, the spectral data were analyzed by partial least squares (PLS) regression and support vector regression (SVR) with four wavelength selection methods. PLS combined with competitive adaptive reweighted sampling (CARS) provided excellent predictive performance for moisture, ash, and fixed carbon. For moisture prediction, the values of RP2, RMSEP and RPD were 0.7202, 0.8196, and 2.11, respectively. For ash prediction, the values of RP2, RMSEP and RPD were 0.9307, 0.5901, and 3.69, respectively. For fixed carbon prediction, the values of RP2, RMSEP and RPD were 0.8504, 0.2735, and 2.76, respectively. Fast analysis of proximates of corn stover was possible using this NIRS system.

Dual valorization of coastal biowastes for tetracycline remediation and biomethane production: A composite assisted anaerobic digestion

Harnessing coastal biowaste for dual valorization in water treatment and biofuel production holds paramount importance for sustainability and resource challenges. This study investigated the potential of engineered composite (CABC) derived from coastal biowaste-based materials for tetracycline (TC) removal and biomethane production. High-yield calcium carbonate (CaCO3; 95.65%; bivalve shells) and biochar (GA-BC; 41.50%; green macroalgae) were produced and used as precursors for CABC. The characterization results revealed presence of β-CaCO3 and ν2-CO3 aragonite in CaCO3, and composite homogeneity was achieved. The CABC exhibited a maximum TC sorption capacity of 342.26 mg/g via synergistic sorption mechanisms (i.e., surface/pore filling, electrostatic attraction, calcium ion exchange, and chelation). Supplementation of anaerobic digestion process with GA-BC, CaCO3, and CABC was investigated via three consecutive cycles. Biochemical methane potential of glucose as a sole substrate was increased from 157.50 to 217.00, 187.00, and 259.00 mL-CH4, while dual substrate (glucose+TC) treatment was increased from 94.5 to 146.5, 129.0, and 153.00 mL-CH4 for GA-BC, CaCO3, and CABC, respectively. Moreover, system stability and TC removal were increased with the addition of GA-BC (40.90%), CaCO3 (16.30%), and CABC (53.70%). Therefore, this study exemplifies the circular bioeconomy approach, demonstrating the sustainable use of biowaste-derived composite for water treatment and biofuel production.

Pulp-paper industry sludge waste biorefinery for sustainable energy and value-added products development: A systematic valorization towards waste management

The pulp-paper industry is one of the main industrial sectors that produce massive amounts of residual sludge, constituting an enormous environmental burden for the industries. Traditional sludge management practices, such as landfilling and incineration, are restricted due to mounting environmental pressures, complex regulatory frameworks, land availability, high costs, and public opinion. Valorization of pulp-paper industry sludge (PPS) to produce high-value products is a promising substitute for traditional sludge management practices, promoting their reuse and recycling. Valorization of PPIS for biorefinery beneficiation includes biomethane, biohydrogen, bioethanol, biobutanol, and biodiesel production for renewable energy generation. Additionally, the various thermo-chemical technologies can be utilized to synthesize bio-oil, hydrochar, biochar, adsorbent, and activated carbon, signifying potential for value-added generation. Moreover, PPIS can be recycled as a byproduct by incorporating it into nanocomposites, cardboard, and construction materials development. This paper aims to deliver a comprehensive overview of PPIS management approaches and thermo-chemical technologies utilized for the development of platform chemicals in industry. Substitute uses of PPIS, such as making building materials, developing supercapacitors, and making cardboard, are also discussed. In addition, this article deeply discusses recent developments in biotechnologies for valorizing PPIS to yield an array of valuable products, such as biofuels, lactic acids, cellulose, nanocellulose, and so on. This review serves as a roadmap for future research endeavors in the effective handling of PPIS.

Integrated biogas upgrading and medium-chain fatty acids production for more efficient resource recovery

The conversion of carbon dioxide (CO2) from biogas into medium-chain fatty acids (MCFAs) represents an eco-friendly resource recovery approach to reduce dependence on fossil fuels and combat global climate change. This study presented the novel concept of integrated resource recovery by coupling biogas upgrading and MCFAs production for the first time. Initially, the impact of different initial ethanol concentrations on chain elongation was examined, determining that an ethanol concentration of 160 mmol/L maximized MCFAs yield at 45.7 mmol/L. Subsequently, using this optimal ethanol supply, the integrated strategy was implemented by connecting two bioreactors in series and maintaining continuous operation for 160-day. The results were noteworthy: upgraded bio-methane purity reached 97.6 %, MCFAs production rate and carbon-flow distribution reached 24.5 mmol/L d-1 and 76.1 %, respectively. In summary, these promising outcomes pioneer a resource recovery approach, enabling the high-value utilization of biogas and the conversion of CO2 into valuable bio-chemicals.

Electrically Conductive Natural Rubber Composite Films Reinforced with Graphite Platelets

Green natural rubber (NR) composites reinforced with synthetic graphite platelets, using alginate as a thickening and dispersing agent, were successfully developed to improve mechanical properties, chemical resistance, and electrical conductivity. The fabrication was performed using a latex aqueous microdispersion process. The research demonstrated the effective incorporation of graphite platelets into the NR matrix up to 60 parts per hundred rubbers (phr) without causing agglomeration or phase separation. Graphite incorporation significantly improved the mechanical strength of the composite films. NR with 60 phr of graphite exhibited the highest Young's modulus of 12.3 MPa, roughly 100 times that of the neat NR film. The reinforcement also strongly improved the hydrophilicity of the composite films, resulting in a higher initial water absorption rate compared to the neat NR film. Moreover, the incorporation of graphite significantly improved the chemical resistance of the composite films against nonpolar solvents, such as toluene. The composite films exhibited biodegradability at about 21% to 30% after 90 days in soil. The electrical conductivity of the composite films was considerably enhanced up to 2.18 × 10-4 S/cm at a graphite loading of 60 phr. According to the improved properties, the developed composites have potential applications in electronic substrates.

Efficient co-production of reducing sugars and xylooligosaccharides via clean hydrothermal pretreatment of rape straw

Hydrothermal treatment was applied to pretreat rape straw for the efficient co-production of reducing sugars and xylooligosaccharides. It was observed that hydrothermal treatment using water as solvent and catalyst destructed the compact structure of rape straw and increased its enzymatic digestion efficiency from 24.6% to 92.0%. Xylooligosaccharide (3.3 g/L) was acquired after the treatment under 200 °C for 60 min (severity factor Log Ro = 4.7). With increasing pretreatment intensity from 3.1 to 5.4, the hemicellulose removal increased from 14.4% to 100%, and the delignification was raised from 12% to 44%. Various characterization proved that the surface morphology of treated material showed a porous shape, while the cellulose accessibility, lignin surface area and lignin hydrophobicity were greatly improved. Consequently, hydrothermal pretreatment played a vital role in the sustainable transformation of biomass to valuable biobased compounds, and had a wide range of application prospects in lignocellulosic biorefining.

Gasification of biomass for syngas production: Research update and stoichiometry diagram presentation

Gasification is a thermal process that converts organic materials into syngas, bio-oil, and solid residues. This mini-review provides an update on current research on producing high-quality syngas from biomass via gasification. Specifically, the review highlights the effective valorization of feedstocks, the development of novel catalysts for reforming reactions, the configuration of novel integrated gasification processes with an assisted field, and the proposal of advanced modeling tools, including the use of machine learning strategies for process design and optimization. The review also includes examples of using a stoichiometry diagram to describe biomass gasification. The research efforts in this area are constantly evolving, and this review provides an up-to-date overview of the most recent advances and prospects for future research. The proposed advancements in gasification technology have the potential to significantly contribute to sustainable energy production and reduce greenhouse gas emissions.

Emerging trends and advances in valorization of lignocellulosic biomass to biofuels

Sustainable technologies pave the way to address future energy demand by converting lignocellulosic biomass into fuels, carbon-neutral materials, and chemicals which might replace fossil fuels. Thermochemical and biochemical technologies are conventional methods that convert biomass into value-added products. To enhance biofuel production, the existing technologies should be upgraded using advanced processes. In this regard, the present review explores the advanced technologies of thermochemical processes such as plasma technology, hydrothermal treatment, microwave-based processing, microbial-catalyzed electrochemical systems, etc. Advanced biochemical technologies such as synthetic metabolic engineering and genomic engineering have led to the development of an effective strategy to produce biofuels. The microwave-plasma-based technique increases the biofuel conversion efficiency by 97% and the genetic engineering strains increase the sugar production by 40%, inferring that the advanced technologies enhances the efficiency. So understanding these processes leads to low-carbon technologies which can solve the global issues on energy security, the greenhouse gases emission, and global warming.

Effect of nano-metal doped calcium peroxide on biomass pretreatment and green hydrogen production from rice straw

In this study, calcium peroxide was modified and doped with metal-based nanoparticles (NP) to enhance the efficiency of pretreatment and biohydrogen generation from RS. The findings revealed that the addition of MnO2-CaO2 NPs (at a dosage of 0.02 g/g TS of RS) had a synergistic effect on the breakdown of biomass and the production of biohydrogen. This enhancement resulted in a maximum hydrogen yield (HY) of 58 mL/g TS, accompanied by increased concentrations of acetic acid (2117 mg/L) and butyric acid (1325 mg/L). In contrast, RS that underwent pretreatment without the use of chemicals or NP exhibited a lower HY of 28 mL/g TS, along with the lowest concentrations of acetic acid (1062 mg/L) and butyric acid (697 mg/L). The outcome showed that supplementation of NP stimulated the pretreatment of RS and improved the formation of acetic and butyric acid through the regulation of metabolic pathways during acidogenic fermentation.

Biodegradation of willow sawdust by novel cellulase-producing bacterial consortium from wood-feeding termites for enhancing methane production

This study was designed to develop a cellulase-producing bacterial consortium (CBC) from wood-feeding termites that could effectively degrade willow sawdust (WSD) and consequently enhance methane production. The bacterial strains Shewanella sp. SSA-1557, Bacillus cereus SSA-1558, and Pseudomonas mosselii SSA-1568 exhibited significant cellulolytic activity. Their CBC consortium showed positive effects on cellulose bioconversion, resulting in accelerated WSD degradation. After nine days of pretreatment, the WSD had lost 63%, 50%, and 28% of its cellulose, hemicellulose, and lignin, respectively. The hydrolysis rate of treated WSD (352 mg/g) was much higher than that of untreated WSD (15.2 mg/g). The highest biogas production (66.1 NL/kg VS) with 66% methane was observed in the anaerobic digester M-2, which contained a combination of pretreated WSD and cattle dung in a 50/50 ratio. The findings will enrich knowledge for the development of cellulolytic bacterial consortia from termite guts for biological wood pretreatment in lignocellulosic anaerobic digestion biorefineries.

Ce/Pumice and Ni/Pumice as heterogeneous catalysts for syngas production from biomass gasification

This work presents a study of synthesis and characterization of catalysts-based cerium and nickel supported on the pumice stone (Ce/Pumice and Ni/Pumice) to be used in the gasification process of an invasive species present in the Canary Islands, such as Pennisetum setaceum to obtain syngas. Specifically, the effect of the metal impregnated on the pumice, and the effect of catalyst on the gasification process was studied. For this purpose, the composition of the gas was determined and the results obtained were compared with those obtained in non-catalytic thermochemical processes. Gasification tests were performed using a simultaneous thermal analyzer coupled with a mass spectrometer, providing a detailed analysis of the gases released during the process. The results showed that during the catalytic gasification process of the Pennisetum setaceum, the gases produced appear at lower temperatures in the catalytic process that in the non-catalytic process. Specifically, H₂ appears at 640.42 °C and 641.84 °C when Ce/pumice and Ni/pumice were used as catalyst, respectively, compared to 697.41 °C for the non-catalytic process. Moreover, the reactivity at 50 % of char conversion for the catalytic process (0.34 and 0.38 min^-1 for Ce/pumice and Ni/pumice, respectively) was higher than for the non-catalytic process (0.28 min^-1), indicating that the incorporation of Ce and Ni on the pumitic material increases the gasification rate of the char compared to the pumitic support. Catalytic biomass gasification is an innovative technology that can provide new opportunities for research and development of renewable energy technologies, as well as for the creation of green jobs.

Selectivity of reaction pathways for green diesel production towards biojet fuel applications

Green diesel is the second generation biofuel with the same structure as fossil fuels (alkanes), allowing this biofuel to provide excellent fuel properties over biodiesel such as higher energy content and lower hazardous gas emission. Generally, green diesel can be produced through the deoxygenation/hydrogenation of natural oil and/or its derivatives at 200-400 °C and 1-10 MPa over supported metal catalysts. This process comprises of three reaction pathways: hydrodeoxygenation, decarboxylation, and decarbonylation. The extent to which these three different pathways are involved is strongly influenced by the catalyst, pressure, and temperature. Subsequently, the determination of catalyst and reaction condition plays a significant role owing to the feasibility of the process and the economic point of view. This article emphasizes the reaction pathway of green diesel production as well as the parameters influencing the predominant reaction route.