Lignocellulose biohydrogen towards net zero emission: A review on recent developments.

This review mainly determines novel and advance physical, chemical, physico-chemical, microbiological and nanotechnology-based pretreatment techniques in lignocellulosic biomass pretreatment for bio-H2 production. Further, aim of this review is to gain the knowledge on the lignocellulosic biomass pretreatment and its priority on the efficacy of bio-H2 and positive findings. The influence of various pretreatment techniques on the structure of lignocellulosic biomass have presented with the pros and cons, especially about the cellulose digestibility and the interference by generation of inhibitory compounds in the bio-enzymatic technique as such compounds is toxic. The result implies that the stepwise pretreatment technique only can ensure eventually the lignocellulosic biomass materials fermentation to yield bio-H2. Though, the mentioned pretreatment steps are still a challenge to procure cost-effective large-scale conversion of lignocellulosic biomass into fermentable sugars along with low inhibitory concentration.

Microalgae cultivation strategies using cost-effective nutrient sources: Recent updates and progress towards biofuel production.

Scientists are grabbing huge attention as well as consciousness on non-renewable energy sources for the global energy crises because of gradual increase in oil price, fast depletion or low availability of resources, and the release of more toxic-gases (CO2, SOx, NxO) during exhaustion, etc. Due to such hitches, the key need is to find alternative biofuels or feedstocks to replace fossil fuel energy demands worldwide. Currently, microalgae have become intrigued feedstock candidates (3rd generation source of biofuel) to replace nearly 50-60 % of fossil fuels due to high production of biomass and oil, mitigating CO2 and wastewater remediation. The present work demonstrated the current developments and future perspectives on large-scale algal cultivation strategies for the biorefinery economy. In addition, various advanced cultivation techniques adopted for enhanced biomass production and cost-effective methods for bioenergy production were detailly discussed.

Enhancing biohydrogen gas production in anaerobic system via comparative chemical pre-treatment on palm oil mill effluent (POME).

Biological hydrogen production using palm oil mill effluent (POME) as a carbon source through dark fermentation process has been suggested to be a promising bioenergy potential and enacts as alternative renewable energy source. Results have indicated that among various 1.5% (w/v) chemical pre-treatments (sodium hydroxide, NaOH; hydrochloric acid, HCl; sulphuric acid, H2SO4; phosphoric acid, H3PO4 and nitric acid, HNO3) on POME, using H3PO4 would generate maximum biohydrogen production of 0.193 mmol/L/h, which corresponded to a yield of 1.51 mol H2/mol TCconsumed with an initial total soluble carbohydrate concentration of 23.52 g/L. Among H3PO4 concentrations (1%-10%), the soluble carbohydrate content and the biohydrogen produced was highest and increased by 1.70-fold and 2.35-fold respectively at 2.5% (w/v), as compared to untreated POME. The batch fermentation maximum hydrogen production rate and yield of 0.208 mmol/L/h and 1.69 mol H2/mol TCconsumed were achieved at optimum pre-treatment conditions of pH 5.5 and thermophilic temperature (60 °C). This study suggests that chemical pre-treatment approaches manage to produce and improve the carbohydrate utilisation process further. Continuous fermentation in CSTR at the optimum conditions produce heightened 1.5-fold biohydrogen yield for 2.5% H3PO4 at 6 h HRT as compared to batch scale. Bacterial community via next-generation sequencing analysis at optimum HRT (6 h) revealed that Thermoanaerobacterium thermosaccharolyticum registered the highest relative frequency of 20.24%. At the class level, Clostridia, Bacilli, Bacteroidia, Thermoanaerobacteria, and Gammaproteobacteria were identified as the biohydrogen-producing bacteria in the continuous system. Insightful findings from this study suggest the substantial practical utility of dilute chemical pre-treatment in improving biohydrogen production.

Bioelectrochemical systems in aid of sustainable biorefineries for the production of value-added products and resource recovery from wastewater: A critical review and future perspectives.

Bioelectrochemical systems (BES) have the potential to be used in a variety of applications such as waste biorefinery, pollutants removal, CO2 capture, and the electrosynthesis of clean and renewable biofuels or byproducts, among others. In contrast, many technical challenges need to be addressed before BES can be scaled up and put into real-world applications. Utilizing BES, this review article presents a state-of-the-art overall view of crucial concepts and the most recent innovative results and achievements acquired from the BES system. Special attention is placed on a hybrid approach for product recovery and wastewater treatment. There is also a comprehensive overview of waste biorefinery designs that are included. In conclusion, the significant obstacles and technical concerns found throughout the BES studies are discussed, and suggestions and future requirements for the virtual usage of the BES concept in actual waste treatment are outlined.

Fabrication of ordered mesoporous POMs/SiO2-NH2 nanofibers for production of DFF from 5-HMF for cellulose wastewater resource recovery.

5-hydroxymethylfurfural (5-HMF) is a biomass cellulose platform product that can be transformed into the valuable resource 2,5-diformylfuran (DFF). Polyoxometalates (POMs) have important applications in resource recovery technologies and cellulose wastewater treatment. Ordered mesoporous H5PMo10V2O40/SiO2-NH2 (wt%) nanofibers (HPMoV/meso-SiO2-NH2 (wt%)) were synthesized by the combining in-situ fabrication and electrospinning techniques, using H5PMo10V2O40 (HPMoV) and organic-silica as precursors. Aiming the recovery and transformation of 5-HMF, aerobic oxidation of 5-HMF was explored using these nanofibers as catalysts, while the best yield of DFF (90.0%) was obtained upon HPMoV/meso-SiO2-NH2 (23%) nanofibers after 8 h at 120 °C using oxygen (1.0 MPa). The selectivity to DFF was improved by changing the hydrophilicity of the HPMoV@SiO2 nanofibers to hydrophobicity by modifying SiO2 nanofibers with -NH2R compared to mesoporous SiO2 nanofibers, which allowed the formed DFF to be isolated. In the recycling test, HPMoV@SiO2-NH2 showed good performance, and no leaching of active sites from SiO2-NH2 due to the interactions between them occurred after 10 cycles. The production of DFF from the real cellulosic wastewater was obtained with 118% yield based on 5-HMF conversion by HPMoV/meso-SiO2-NH2 (23) and oxygen, which was contributed to the one-pot conversion of sugar, furan and 5-HMF in the wastewater.

Biogas production from beverage factory wastewater in a mobile bioenergy station.

Recently, the production of renewable biogas such as biohydrogen and biomethane from wastewaters through anaerobic fermentation has gained worldwide attention. In the present study, a mobile bioenergy generation station had been constructed based on a high-efficiency hydrogenesis & methanogenesis technology (HyMeTek) developed by Feng Chia University, Taiwan. The substrate was a beverage wastewater having chemical oxygen demand (COD) concentration of 1200 mg/L. This bioenergy station had a feedstock tank (3.8 m3), a nutrient tank (0.8 m3), an acidogenesis tank (AT, 2 m3), two methanogenesis tanks (MT, 4 m3 for each), a membrane bioreactor and a control room. Biogas production rate, methane concentration, COD removal efficiencies, energy efficiency and economical interest of the plant were assessed. The peak total methane production rates for AT (at hydraulic retention time, HRT, 4 h) and MT (at HRT 8 h) were 430 and 7 mL/L·d, respectively. A strategy of shortening HRT was a promising method to enhance biogas quality and energy efficiency. This mobile bioenergy system has commercial potential because it could bring good economic benefit of initial rate of return (58.84%) and payback time (2.68 y).

Hydrothermally extraction of saponin from Acanthophyllum glandulosum root - Physico-chemical characteristics and antibacterial activity evaluation.

Saponin was extracted from Acanthophyllum glandulosum root under subcritical water conditions, and effects of root powder and pH of the solution were evaluated on the concentration of the saponin as manifested in its foamability and antioxidant activity using RSM. FT-IR analysis indicated that A. glandulosum root extract had 2 main functional groups (hydroxyl and amide I groups). Saponin with the highest foam height (4.66 cm), concentration (0.080 ppm) and antioxidant activity (90.6 %) was extracted using 10 g of the root powder and pH value of 4. Non-significant differences were observed between the predicted and experimental values of the extraction response variables. The study demonstrated good appropriateness of resulted models by Response Surface Methodology. Furthermore, higher values of R2 was attained for the foamability (>0.81) and antioxidant activity (>0.97), as well as large p-values (p > 0.05) indication of their lack-of-fit response verified the acceptable fitness of the provided models. The extracted saponin also showed bactericidal effect, which shows potential as a natural antibacterial compound.

Recent developments on alternative fuels, energy and environment for sustainability.

Enhancing energy and environmental systems through sustainable development, in particular integrating concepts of circular economy and cleaner production are important for the emerging needs of humankind. In recent years, the developments in alternative sources of renewable energy counterparts has been prompted to substitute the nonrenewable fossil fuel consumptions towards clearner environment. However, environmental problems arising currently must be carefully addressed and to be solved to conserve the energy, water and other environmental resources for the future. This article highlights the recent developments on alternative energy sources that mainly focus on energy and environmental sustainability, that has been discussed on "The 4th International Conference on Alternative Fuels & Energy (ICAFE-2019)", which was held at Taichung City, Taiwan on October 18-21, 2019. Additionally, it provides useful insights from some of the papers published on a virtual special issue (VSI) of the Bioresourse Technology Journal. The highlighted research works in this review can be used as route-map towards sustainable development and energy efficiency.

Review on sustainable production of biochar through hydrothermal liquefaction: Physico-chemical properties and applications.

This review examines in detail the production and characteristics of biochar resulting from hydrothermal liquefaction. Specifically, the impact of feedstocks and different process parameters on the properties and yield of biochar by hydrothermal liquefaction has been thoroughly studied. Hydrothermal liquefaction derived biochars, relative to biochars from high-temperature thermochemical processes retain critical functional groups during carbonization and are therefore promising for a wide range of applications. Most of the review's efforts are to study possible hydrothermal liquefaction biochar applications in various fields, including fuel, metal and dye adsorption, pollutant reduction, animal feed, and biogas catalyst. The feasibility of biochar through the hydrothermal liquefaction process has been analysed via life-cycle assessment and energy evaluation. The article concludes with a brief discussion on possible issues and strategies for the sustainable development of hydrothermal liquefaction-based biochar.

Enhanced photocatalytic performance of metal silver and carbon dots co-doped BiOI photocatalysts and mechanism investigation.

The photocatalytic technology provides a promising and effective strategy for the transformation and degradation of contaminants. Herein, we accurately fabricated a novel ternary photocatalyst, namely, metal silver (Ag) and carbon dots (CDots) co-doped BiOI nanocomposite (Ag/CDots/BiOI) via the reduction method with ionic liquids 1-butyl-3-methylimidazolium iodine ([Bmim]I) at room temperature. The morphologies and microstructures showed the Ag and CDots were uniformly loaded on the surface of BiOI, forming a ternary system. The characterization results implied that an intense interaction was formed between Ag and CDots on the BiOI, which could achieve the broad spectrum utilization of visible light and boosted the photocatalytic performances. The 0.9-Ag/2-CDots/BiOI (0.9 wt% of Ag, 2 wt% of CDots) presented the highest photocatalytic activity with ~ 100% in 4-Chlorophenol, 68.8% in mineralization, and 87.4% in dechlorination in 6 h under visible light illumination. The enhanced photocatalytic activity could be ascribed to the surface plasmon resonance effect of Ag, the up-converted photoluminescence (PL) properties of CDots, and the electron transfer properties of both Ag and CDots. Moreover, a possible photocatalytic reaction mechanism was discussed in detail by band structure analysis and radical scavenger quenching experiments. This study provides a promising approach for promoting the utilization efficiency for solar energy and sustainable environmental remediation.

Effects of hydraulic retention time on biohythane production via single-stage anaerobic fermentation in a two-compartment bioreactor.

Hythane has been well known as a mixture of hydrogen and methane gases but their production is mostly in a different way. The present study dealt with the potential biohythane production in a two-compartment (lower, hydrogenesis; upper, methanogenesis) reactor via a single-stage anaerobic fermentation at mesophilic temperature. The effect of hydraulic retention time (HRT) was tested at 10-2 d using food waste substrate. HRT 2 d resulted in (1) maximum removal efficiencies for COD, carbohydrate, lipid and protein contents with values of 58.5, 58.4, 62.6 and 79.1%, respectively; (2) peak hydrogen and methane production rates of 714 and 254 mL/L-d, respectively; and (3) biogas contents of hydrogen 8.6% and methane 48.0% in the produced gas. At this HRT, Clostridium sensu stricto 2 and Methanosaeta were dominant species in H2 and CH4 compartments, respectively. The novelty of this work is creating a novel two-compartment reactor for single-stage anaerobic biohythane fermentation.

Bioelectricity generation using microalgal biomass as electron donor in a bio-anode microbial fuel cell.

In this study, microalgal biomass waste (Chlorella regularis) was treated while simultaneously producing bioelectricity in a microbial fuel cell (MFC). Algal biomass was the sole electron donor and was enriched with easily biodegradable proteins (46%) and carbohydrates (22%). The generated power density was 0.86 W/m2 and the columbic efficiency reached ∼61.5%.The power generation could be further increased to 1.07 W/m2 by using a biomass waste concentration enhancement strategy with maximum chemical oxygen demand (COD) removal of ∼65.2%. Via direct comparison, the power generation and COD removal capability of the algal-fed MFC was close to that of the commercial acetate-fed MFC. The algae-fed MFC presented superior electrochemical characteristics that were attributed to the complicated composition of the biomass anolyte. It possessed a multiple anode respiring bacterial group and diverse microbial community. Hence, this study provides a new strategy for the utilization of microalgal biomass as a bioresource.

Constructing a cellulosic yeast host with an efficient cellulase cocktail.

Cellulose is a renewable feedstock for green industry. It is therefore important to develop a technique to construct a host with a high cellulolytic efficiency to digest cellulose. In this study, we developed a convenient host-engineering technique to adjust the expression levels of heterologous genes in the host by promoter rearrangement and gene copy number adjustment. Using genes from different glycoside hydrolase (GH) families including GH2, GH3, GH5, GH6, GH7, and GH12 from Aspergillus niger, Trichoderma reesei, and Neocallimastix patriciarum, we constructed a cellulolytic Kluyveromyces marxianus with eight cellulase gene-cassettes that produced a cellulase cocktail with a high cellulolytic efficiency, leading to a significant reduction in enzyme cost in a rice straw saccharification process. Our technique can be used to design a host that can efficiently convert biomass feedstock to biofuel.

Anaerobic hydrogen production from unhydrolyzed mushroom farm waste by indigenous microbiota.

The cultivation of mushrooms generates large amounts of waste polypropylene bags stuffed with wood flour and bacterial nutrients that makes the mushroom waste (MW) a potential feedstock for anaerobic bioH2 fermentation. MW indigenous bacteria were enriched using thermophilic temperature (55°C) for use as the seed inoculum without any external seeding. The peak hydrogen production rate (6.84 mmol H2/L-d) was obtained with cultivation pH 8 and substrate concentration of 60 g MW/L in batch fermentation. Hydrogen production yield (HY) is pH and substrate concentration dependent with an HY decline occurring at pH and substrate concentration increasing from pH 8 to 10 and 60 to 80 g MW/L, respectively. The fermentation bioH2 production from MW is in an acetate-type metabolic path.

Recent insights into the cell immobilization technology applied for dark fermentative hydrogen production.

The contribution and insights of the immobilization technology in the recent years with regards to the generation of (bio)hydrogen via dark fermentation have been reviewed. The types of immobilization practices, such as entrapment, encapsulation and adsorption, are discussed. Materials and carriers used for cell immobilization are also comprehensively surveyed. New development of nano-based immobilization and nano-materials has been highlighted pertaining to the specific subject of this review. The microorganisms and the type of carbon sources applied in the dark hydrogen fermentation are also discussed and summarized. In addition, the essential components of process operation and reactor configuration using immobilized microbial cultures in the design of varieties of bioreactors (such as fixed bed reactor, CSTR and UASB) are spotlighted. Finally, suggestions and future directions of this field are provided to assist the development of efficient, economical and sustainable hydrogen production technologies.

Co-fermentation of water hyacinth and beverage wastewater in powder and pellet form for hydrogen production.

Hydrogen (H2) production potential of water hyacinth (WH) and beverage wastewater (BW) mixture in powder and pellet form at various combination ratios were evaluated. Batch co-fermentation results showed peak biogas production of 105.5 mL and H2 production of 55.6 mL at the combination ratio of 1.6 g WH and 2.4 g BW in pellet form. With the same ratio in pellet form, the maximum H2 production rate 542 mL H2/L-d, maximum specific H2 production rate 869 mL H2/g VSS-d and H2 yield 13.65 mL/g feedstock were obtained, and were 88, 88 and 34% higher than its powder form. The predominant soluble metabolite was acetate in the concentration of 1059-2639 mg COD/L (40-79% of total metabolites) in most runs during co-fermentation of mixed feedstock. Carbon-to-nitrogen ratio and the physical form of the combined feedstock are essential criteria for optimum H2 production. Co-fermentation also alleviates the waste disposal problem of the industries.

High-efficiency hydrogen production by an anaerobic, thermophilic enrichment culture from an Icelandic hot spring.

Dark fermentative hydrogen production from glucose by a thermophilic culture (33HL), enriched from an Icelandic hot spring sediment sample, was studied in two continuous-flow, completely stirred tank reactors (CSTR1, CSTR2) and in one semi-continuous, anaerobic sequencing batch reactor (ASBR) at 58 degrees C. The 33HL produced H2 yield (HY) of up to 3.2 mol-H2/mol-glucose along with acetate in batch assay. In the CSTR1 with 33HL inoculum, H2 production was unstable. In the ASBR, maintained with 33HL, the H2 production enhanced after the addition of 6 mg/L of FeSO4 x H2O resulting in HY up to 2.51 mol-H2/mol-glucose (H2 production rate (HPR) of 7.85 mmol/h/L). The H2 production increase was associated with an increase in butyrate production. In the CSTR2, with ASBR inoculum and FeSO4 supplementation, stable, high-rate H2 production was obtained with HPR up to 45.8 mmol/h/L (1.1 L/h/L) and HY of 1.54 mol-H2/mol-glucose. The 33HL batch enrichment was dominated by bacterial strains closely affiliated with Thermobrachium celere (99.8-100%). T. celere affiliated strains, however, did not thrive in the three open system bioreactors. Instead, Thermoanaerobacterium aotearoense (98.5-99.6%) affiliated strains, producing H2 along with butyrate and acetate, dominated the reactor cultures. This culture had higher H2 production efficiency (HY and specific HPR) than reported for mesophilic mixed cultures. Further, the thermophilic culture readily formed granules in CSTR and ASBR systems. In summary, the thermophilic culture as characterized by high H2 production efficiency and ready granulation is considered very promising for H2 fermentation from carbohydrates.