Characterization of Ralstonia insidiosa C1 isolated from Alpine regions: Capability in polyhydroxyalkanoates degradation and production.

This study ventures into the exploration of potential poly-3-hydroxybutyrate (PHB) degradation in alpine environments. PHB-degrading bacteria were identified in both campus soil, representing a residential area, and Mt. Kurodake soil, an alpine region in Hokkaido, Japan. Next-generation sequencing analysis indicated that the campus soil exhibited higher microbial diversity, while Ralstonia insidiosa C1, isolated from Mt. Kurodake soil, displayed the highest proficiency in PHB degradation. R. insidiosa C1 efficiently degraded up to 3% (w/v) of PHB and various films composed of other biopolymers at 14 °C. This bacterium synthesized homopolymers using substrates such as 3-hydroxybutyric acid, sugars, and acetic acid, while also produced copolymers using a mixture of fatty acids. The analysis results confirmed that the biopolymer synthesized by strain C1 using glucose was PHB, with physical properties comparable to commercial products. The unique capabilities of R. insidiosa C1, encompassing both the production and degradation of bioplastics, highlight its potential to establish a novel material circulation model.

Advances in Biological Wastewater Treatment Processes: Focus on Low-Carbon Energy and Resource Recovery in Biorefinery Context.

Advancements in biological wastewater treatment with sustainable and circularity approaches have a wide scope of application. Biological wastewater treatment is widely used to remove/recover organic pollutants and nutrients from a diverse wastewater spectrum. However, conventional biological processes face challenges, such as low efficiency, high energy consumption, and the generation of excess sludge. To overcome these limitations, integrated strategies that combine biological treatment with other physical, chemical, or biological methods have been developed and applied in recent years. This review emphasizes the recent advances in integrated strategies for biological wastewater treatment, focusing on their mechanisms, benefits, challenges, and prospects. The review also discusses the potential applications of integrated strategies for diverse wastewater treatment towards green energy and resource recovery, along with low-carbon fuel production. Biological treatment methods, viz., bioremediation, electro-coagulation, electro-flocculation, electro-Fenton, advanced oxidation, electro-oxidation, bioelectrochemical systems, and photo-remediation, are summarized with respect to non-genetically modified metabolic reactions. Different conducting materials (CMs) play a significant role in mass/charge transfer metabolic processes and aid in enhancing fermentation rates. Carbon, metal, and nano-based CMs hybridization in different processes provide favorable conditions to the fermentative biocatalyst and trigger their activity towards overcoming the limitations of the conventional process. The emerging field of nanotechnology provides novel additional opportunities to surmount the constraints of conventional process for enhanced waste remediation and resource valorization. Holistically, integrated strategies are promising alternatives for improving the efficiency and effectiveness of biological wastewater treatment while also contributing to the circular economy and environmental protection.

Dark fermentative hydrogen production: Potential of food waste as future energy needs.

Globally, food waste (FW) is found to be one of the major constituents creating several hurdles in waste management. On the other hand, the energy crisis is increasing and the limited fossil fuel resources available are not sufficient for energy needed for emerging population. In this context, biohydrogen production approach through valorization of FW is emerging as one of the sustainable and eco-friendly options. The present review explores FW sources, characteristics, and dark fermentative production of hydrogen along with its efficiency. FW are highly biodegradable and rich in carbohydrates which can be efficiently utilized by anaerobic bacteria. Based on the composition of FW, several pretreatment methods can be adapted to improve the bioavailability of the organics. By-products of dark fermentation are organic acids that can be integrated with several secondary bioprocesses. The versatility of secondary products is ranging from energy generation to biochemicals production. Integrated approaches facilitate in enhanced energy harvesting along with extended wastewater treatment. The review also discusses various parameters like pH, temperature, hydraulic retention time and nutrient supplementation to enhance the process efficiency of biohydrogen production. The application of solid-state fermentation (SSF) in dark fermentation improves the process efficiency. Dark fermentation as the key process for valorization and additional energy generating process can make FW the most suitable substrate for circular economy and waste based biorefinery.

Quantification of the Monomer Compositions of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(3-hydroxyvalerate) by Alkaline Hydrolysis and Using High-Performance Liquid Chromatography.

With the growing interest in bioplastics, there is an urgent need to develop rapid analysis methods linked to production technology development. This study focused on the production of a commercially non-available homopolymer, poly(3-hydroxyvalerate) (P(3HV)), and a commercially available copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)), through fermentation using two different bacterial strains. The bacteria Chromobacterium violaceum and Bacillus sp. CYR1 were used to produce P(3HV) and P(3HB-co-3HV), respectively. The bacterium Bacillus sp. CYR1 produced 415 mg/L of P(3HB-co-3HV) when incubated with acetic acid and valeric acid as the carbon sources, whereas the bacterium C. violaceum produced 0.198 g of P(3HV)/g dry biomass when incubated with sodium valerate as the carbon source. Additionally, we developed a fast, simple, and inexpensive method to quantify P(3HV) and P(3HB-co-3HV) using high-performance liquid chromatography (HPLC). As the alkaline decomposition of P(3HB-co-3HV) releases 2-butenoic acid (2BE) and 2-pentenoic acid (2PE), we were able to determine the concentration using HPLC. Moreover, calibration curves were prepared using standard 2BE and 2PE, along with sample 2BE and 2PE produced by the alkaline decomposition of poly(3-hydroxybutyrate) and P(3HV), respectively. Finally, the HPLC results obtained by our new method were compared using gas chromatography (GC) analysis.

Ultrasound-controlled acidogenic valorization of wastewater for biohydrogen and volatile fatty acids production: Microbial community profiling.

The present study explored the influence of ultrasound on acidogenic fermentation of wastewater for the production of biohydrogen and volatile fatty acids/carboxylic acids. Eight sono-bioreactors underwent ultrasound (20 kHz: 2W and 4W), with an ultrasound duration ranging from 15 min to 30 days, and the formation of acidogenic metabolites. Long-term continuous ultrasonication enhanced biohydrogen and volatile fatty acid production. Specifically, ultrasonication at 4W for 30 days increased biohydrogen production by 3.05-fold compared to the control, corresponding to hydrogen conversion efficiency of 58.4%; enhanced volatile fatty acid production by 2.49-fold; and increased acidification to 76.43%. The observed effect of ultrasound was linked to enrichment with hydrogen-producing acidogens such as Firmicutes, whose proportion increased from 61.9% (control) to 86.22% (4W, 30 days) and 97.53% (2W, 30 days), as well as inhibition of methanogens. This result demonstrates the positive effect of ultrasound on the acidogenic conversion of wastewater to biohydrogen and volatile fatty acid production.

Effect of metals on the regulation of acidogenic metabolism enhancing biohydrogen and carboxylic acids production from brewery spent grains: Microbial dynamics and biochemical analysis.

The present study reports the mixed culture acidogenic production of biohydrogen and carboxylic acids (CA) from brewery spent grains (BSG) in the presence of high concentrations of cobalt, iron, nickel, and zinc. The metals enhanced biohydrogen output by 2.39 times along with CA biosynthesis by 1.73 times. Cobalt and iron promoted the acetate and butyrate pathways, leading to the accumulation of 5.14 gCOD/L of acetic and 11.36 gCOD/L of butyric acid. The production of solvents (ethanol + butanol) was higher with zinc (4.68 gCOD/L) and cobalt (4.45 gCOD/L). A combination of all four metals further enhanced CA accumulation to 42.98 gCOD/L, thus surpassing the benefits accrued from supplementation with individual metals. Additionally, 0.36 and 0.31 mol green ammonium were obtained from protein-rich brewery spent grain upon supplementation with iron and cobalt, respectively. Metagenomic analysis revealed the high relative abundance of Firmicutes (>90%), of which 85.02% were Clostridium, in mixed metal-containing reactors. Finally, a significant correlation of dehydrogenase activity with CA and biohydrogen evolution was observed upon metal addition.

Design and evaluation of gas fermentation systems for CO2 reduction to C2 and C4 fatty acids: Non-genetic metabolic regulation with pressure, pH and reaction time.

Addressing the carbon emissions through microbial mediated fermentation is an emerging interest. Custom designed and fabricated gas fermentation (GF) systems were evaluated to optimize the headspace pressure, pH (6.5, 7.5, and 8.5), fermentation time, and substrate concentration by employing enriched homoacetogenic chemolithoautotrophs in non-genetic approach. Headspace pressure showed marked influence on the metabolic conversion of inorganic carbon to acetic and butyric acids with 26% higher productivity than the control (atmospheric pressure). Maximum volatile fatty acid (VFA) yield of 3.7 g/L was observed at alkaline pH (8.5) under 2 bar pressure at carbon load of 10 g/L, 96 h). Acetic (3.0 g/L) and butyric (0.7 g/L) acids were the major products upon conversion of 85% of the inorganic substrate. A better in-situ buffering (ß = 0.048) at pH 8.5 along with higher reductive current (RCC: -4.4 mA) depicted better performance of GF towards CO2 reduction.

Organosolv pretreated birch sawdust for the production of green hydrogen and renewable chemicals in an integrated biorefinery approach.

Sustainable production of fuels and chemicals is the most important way to reduce the carbon footprint in the environment. Forest based abundant lignocellulosic biomass as a renewable feedstock can be an attractive source of biofuels and biochemicals. This study evaluated the production of hydrogen (H2) along with platform chemicals from an organosol pretreated birch sawdust (SD). Acidogenic fermentation (AF) of pretreated SD resulted in production of green H2 (121.4 mL/gVS) along with short (17.8 g/L) and medium (2.64 g/L) chain carboxylic acids. Further integration of AF with anaerobic digestion (AD) in a biorefinery framework offered production of biomethane (bioCH4: 246 mL/gVS) from the leftover SD from AF. Integration of bioH2 with bioCH4 at different time interval of digestion showed 8-14 L biohythane formation ran with a H2 fraction of 1.6-0.3 H2/(H2 + CH4) documenting energy content of 8-9.08 kJ/gVS.

Upgrading the value of anaerobic fermentation via renewable chemicals production: A sustainable integration for circular bioeconomy.

The single bioprocess approach has certain limitations in terms of process efficiency, product synthesis, and effective resource utilization. Integrated or combined bioprocessing maximizes resource recovery and creates a novel platform to establish sustainable biorefineries. Anaerobic fermentation (AF) is a well-established process for the transformation of organic waste into biogas; conversely, biogas CO2 separation is a challenging and expensive process. Biological fixation of CO2 for succinic acid (SA) mitigates CO2 separation issues and produces commercially important renewable chemicals. Additionally, utilizing digestate rich in volatile fatty acid (VFA) to produce medium-chain fatty acids (MCFAs) creates a novel integrated platform by utilizing residual organic metabolites. The present review encapsulates the advantages and limitations of AF along with biogas CO2 fixation for SA and digestate rich in VFA utilization for MCFA in a closed-loop approach. Biomethane and biohydrogen processes CO2 utilization for SA production is cohesively deliberated along with the role of biohydrogen as an alternative reducing agent to augment SA yields. Similarly, MCFA production using VFA as a substrate and functional role of electron donors namely ethanol, lactate, and hydrogen are comprehensively discussed. A road map to establish the fermentative biorefinery approach in the framework of AF integrated sustainable bioprocess development is deliberated along with limitations and factors influencing for techno-economic analysis. The discussed integrated approach significantly contributes to promote the circular bioeconomy by establishing carbon-neutral processes in accord with sustainable development goals.

Green Hydrogen-Compressed natural gas (bio-H-CNG) production from food waste: Organic load influence on hydrogen and methane fusion.

Biogenic hydrogen (bioH2) enriched compressed natural gas (bio-H-CNG or biohythane) is emerging interest due to its feasibility to use in the existing transportation infrastructure with induced environmental benefits. This study evaluated the production of bioH2and biomethane (bioCH4) towards bio-H-CNG formation at a varying organic load (OL: 30,40,50 g COD/L) of food waste (FW). Acidogenic reactor operated with FW at 40 g COD/L showed the highest cumulative bioH2production while elevated OL (50 g COD/L)showedhigher cumulative bioCH4production (CMP: 11.92 L) from the methanogenic reactor. BioH2 and bioCH4 produced at different time intervals were combined to assess bio-H-CNG. The nature of biocatalyst and OLsignificantly regulated the composition of bio-H-CNG varying between 0.1 and 0.3 of H2/(H2+CH4) ratio accounting for5-12.6 kJ/g COD. Chain elongation, converting short (C2-C4) to medium-chain fatty acids(Caproic acid,1.16 g/L) was specifically observed during the acidogenic process.

Influence of initial uncontrolled pH on acidogenic fermentation of brewery spent grains to biohydrogen and volatile fatty acids production: Optimization and scale-up.

This two-phase, two-stage study analyzed production of biohydrogen and volatile fatty acids by acidogenic fermentation of brewery spent grains. Phase-1 served to optimize the effect of pH (4-10) on acidogenic fermentation; whereas phase-2 validated the optimized conditions by scaling up the process to 2 L, 5 L, and 10 L. Alkaline conditions (pH 9) yielded excellent cumulative H2 production (834 mL) and volatile fatty acid recovery (8936 mg/L) in phase-1. Extended fermentation time (from 5 to 10 days) upgraded the accumulated short-chain fatty acids (C2-C4) to medium-chain fatty acids (C5-C6). Enrichment for acidogens in modified mixed culture improved fatty acid production; while their consumption by methanogens in unmodified culture led to methane formation. Increased CH4 but decreased H2 content enabled biohythane generation. Scaling up confirmed the role of pH and culture type in production of renewable fuels and platform molecules from brewery spent grains.

Renewable hydrogen production by dark-fermentation: Current status, challenges and perspectives.

Global urbanization has resulted in amplified energy and material consumption with simultaneous waste generation. Current energy demand is mostly fulfilled by finite fossil reserves, which has critical impact on the environment and thus, there is a need for carbon-neutral energy. In this view, biohydrogen (bio-H2) is considered suitable due to its potential as a green and dependable carbon-neutral energy source in the emerging 'Hydrogen Economy'. Bio-H2 production by dark fermentation of biowaste/biomass/wastewater is gaining significant attention. However, bio-H2production still holds critical challenges towards scale-up with reference to process limitations and economic viabilities. This review illustrates the status of dark-fermentation process in the context of process sustainability and achieving commercial success. The review also provides an insight on various process integrations for maximum resource recovery including closed loop biorefinery approach towards the accomplishment of carbon neutral H2 production.

Valorization of volatile fatty acids derived from low-cost organic waste for lipogenesis in oleaginous microorganisms-A review.

To meet environmental sustainability goals, microbial oils have been suggested as an alternative to petroleum-based products. At present, microbial fermentation for oil production relies on pure sugar-based feedstocks. However, these feedstocks are expensive and are in limited supply. Volatile fatty acids, which are generated as intermediates during anaerobic digestion of organic waste have emerged as a renewable feedstock that has the potential to replace conventional sugar sources for microbial oil production. They comprise short-chain (C2 to C6) organic acids and are employed as building blocks in the chemical industry. The present review discusses the use of oleaginous microorganisms for the production of biofuels and added-value products starting from volatile fatty acids as feedstocks. The review describes the metabolic pathways enabling lipogenesis from volatile fatty acids, and focuses on strategies to enhance lipid accumulation in oleaginous microorganisms by tuning the ratios of volatile fatty acids generated via anaerobic fermentation.

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.

Synergy of anoxic microenvironment and facultative anaerobes on acidogenic metabolism in a self-induced electrofermentation system.

Metabolic potential of two different cultures, facultative (FB) and strict anaerobes (AB) under two microenvironments [anoxic (ANOX) and anaerobic (ANA)] was evaluated to understand acidogenic fermentation in a self-induced electrofermentation (EF) system for the production of short-chain fatty acids (SCFA: C2-C4) and biogas. ANA condition positively influenced FB and AB metabolism towards higher acetic (C2:2390 mg/L) and propionic acid (C3: 717 mg/L) production, while butyric acid (C4:1481 mg/L) favored ANOX microenvironment (AB). ANOX microenvironment showed a better self-induced potential compared to ANA metabolism (0.46 V (FBANOX); 0.45 V (ABANOX)). An improved H2 (>30%) fraction was noticed with FB while CH4 production was found favourable with AB. The study illustrated the role of system microenvironment in association with metabolic function towards regulating electrofermentation towards specific products synthesis.

Modified conductive polyaniline-carbon nanotube composite electrodes for bioelectricity generation and waste remediation.

Anode with good electrocatalytic capabilities is more specifically required to reduce the ohimic losses during microbial fuel cell (MFC) operation. Highly conductive polymers viz., Polyaniline (PANi) and Polyaniline/Carbon nanotube (PANi/CNT) composite were prepared by in situ oxidative chemical polymerization method. Anodes were fabricated independently by coating PANi and CNT/PANi composites on the surface of SSM. The fabricated electrodes were evaluated as anode against stainless steel mess (SSM) as cathode during MFC operation. Maximum bioelectricity generation was observed in SSM-PANi/CNT-anode with power density of 48 mW/m2 and COD removal efficiency of 80% compared with SSM-PANi-anode (38 mW/m2; 65%) and SSM-anode (28 mW/m2; 58%). Bioelectrochemical characterization of the electrode materials using cyclic voltammetry and electrochemical impedance spectroscopy showed high electrocatalytic activity of PANi/CNT composite electrode. The study concluded the efficiency of PANi/CNT composite electrodes as bioanode in operation of MFCs towards achieving increased bioelectricity production along with wastewater treatment.

Stacking of microbial fuel cells with continuous mode operation for higher bioelectrogenic activity.

The effect of stacking multiple microbial fuel cells for stable power output was evaluated in continuous mode operation. Three single chambered air cathode CMFCs with Nafion (CMFCN), Terry cotton (CMFCT) as membranes and one without membrane (CMFCML) were operated in continuous mode. Maximum power density (PD) and COD removal efficiency was obtained for CMFCN (0.1 W/m2, 50%) followed by CMFCML (0.062 W/m2, 47%) and CMFCT (0.025 W/m2, 39%) and were stable throughout the operation. To increase the power output further, stacking of CMFCs was carried in series/parallel circuitry, which yielded high power density in parallel (2.0 W/m2; 7.2 W/m3) and high voltage in series (1.1 V). Study also evidenced that stacking resulted in high and stable bioelectricity by minimizing the electron losses in comparison to individual CMFCs operation. Stable and high power output signifies the impact of continuous mode operation that constantlty replenishes the substrate.

Food waste biorefinery: Sustainable strategy for circular bioeconomy.

Enormous quantity of food waste (FW) is becoming a global concern. To address this persistent problem, sustainable interventions with green technologies are essential. FW can be used as potential feedstock in biological processes for the generation of various biobased products along with its remediation. Enabling bioprocesses like acidogenesis, fermentation, methanogenesis, solventogenesis, photosynthesis, oleaginous process, bio-electrogenesis, etc., that yields various products like biofuels, platform chemicals, bioelectricity, biomaterial, biofertilizers, animal feed, etc can be utilized for FW valorisation. Integrating these bioprocesses further enhances the process efficiency and resource recovery sustainably. Adapting biorefinery strategy with integrated approach can lead to the development of circular bioeconomy. The present review highlights the various enabling bioprocesses that can be employed for the generation of energy and various commodity chemicals in an integrated approach addressing sustainability. The waste biorefinery approach for FW needs optimization of the cascade of the individual bioprocesses for the transformation of linear economy to circular bioeconomy.

Pre-aeration of food waste to augment acidogenic process at higher organic load: Valorizing biohydrogen, volatile fatty acids and biohythane.

Application of pre-aeration (AS) to waste prior to feeding was evaluated on acidogenic process in a semi-pilot scale biosystem for the production of biobased products (biohydrogen, volatile fatty acids (VFA) and biohythane) from food waste. Oxygen assisted in pre-hydrolysis of waste along with the suppression of methanogenic activity resulting in enhanced acidogenic product formation. AS operation resulted in 97% improvement in hydrogen conversion efficiency (HCE) and 10% more VFA production than the control. Increasing the organic load (OL) of food waste in association with AS application improved the productivity. The application of AS also influenced concentration and composition of fatty acid. Highest fraction of acetic (5.3g/l), butyric (0.7g/l) and propionic acid (0.84g/l) was achieved at higher OL (100g COD/l) with good degree of acidification (DOA). AS strategy showed positive influence on biofuel (biohydrogen and biohythane) production along with the biosynthesis of short chain fatty acids functioning as a low-cost pretreatment strategy in a single stage bioprocess.

Waste biorefinery models towards sustainable circular bioeconomy: Critical review and future perspectives.

Increased urbanization worldwide has resulted in a substantial increase in energy and material consumption as well as anthropogenic waste generation. The main source for our current needs is petroleum refinery, which have grave impact over energy-environment nexus. Therefore, production of bioenergy and biomaterials have significant potential to contribute and need to meet the ever increasing demand. In this perspective, a biorefinery concept visualizes negative-valued waste as a potential renewable feedstock. This review illustrates different bioprocess based technological models that will pave sustainable avenues for the development of biobased society. The proposed models hypothesize closed loop approach wherein waste is valorised through a cascade of various biotechnological processes addressing circular economy. Biorefinery offers a sustainable green option to utilize waste and to produce a gamut of marketable bioproducts and bioenergy on par to petro-chemical refinery.