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Microbial electrolysis cells (MECs) are a new bio-electrochemical method for converting organic matter to hydrogen gas (H2). Palm oil mill effluent (POME) is hazardous wastewater that is mostly formed during the crude oil extraction process in the palm oil industry. In the present study, POME was used in the MEC system for hydrogen generation as a feasible treatment technology. To enhance biohydrogen generation from POME in the MEC, an empirical model was generated using response surface methodology (RSM). A central composite design (CCD) was utilized to perform twenty experimental runs of MEC given three important variables, namely incubation temperature, initial pH, and influent dilution rate. Experimental results from CCD showed that an average value of 1.16 m3 H2/m3 d for maximum hydrogen production rate (HPR) was produced. A second-order polynomial model was adjusted to the experimental results from CCD. The regression model showed that the quadratic term of all variables tested had a highly significant effect (P

The intrinsic advancement of lithium-ion batteries (LIBs) for application in electric vehicles (EVs), portable electronic devices, and energy-storage devices has led to an increase in the number of spent LIBs. Spent LIBs contain hazardous metals (such as Li, Co, Ni, and Mn), toxic and corrosive electrolytes, metal casting, and polymer binders that pose a serious threat to the environment and human health. Additionally, spent LIBs may serve as an economic source for transition metals, which could be applied to redesigning under a closed-circuit recycling process. Thus, the development of environmentally benign, low cost, and efficient processes for recycling of LIBs for a sustainable future has attracted worldwide attention. Therefore, herein, we introduce the concept of LIBs and review state-of-art technologies for metal recycling processes. Moreover, we emphasize on LIB pretreatment approaches, metal extraction, and pyrometallurgical, hydrometallurgical, and biometallurgical approaches. Direct recycling technologies combined with the profitable and sustainable cathode healing technology have significant potential for the recycling of LIBs without decomposition into substituent elements or precipitation; hence, these technologies can be industrially adopted for EV batteries. Finally, commercial technological developments, existing challenges, and suggestions are presented for the development of effective, environmentally friendly recycling technology for the future.

Microbial electrolysis cells (MECs) are perceived as a potential and promising innovative biotechnological tool that can convert carbon-rich waste biomass or wastewater into hydrogen (H2) or other value-added chemicals. Undesired methane (CH4) producing H2 sinks, including methanogens, is a serious challenge faced by MECs to achieve high-rate H2 production. Methanogens can consume H2 to produce CH4 in MECs, which has led to a drop of H2 production efficiency, H2 production rate (HPR) and also a low percentage of H2 in the produced biogas. Organized inference related to the interactions of microbes and potential processes has assisted in understanding approaches and concepts for inhibiting the growth of methanogens and profitable scale up design. Thus, here in we review the current developments and also the improvements constituted for the reduction of microbial H2 losses to methanogens. Firstly, the greatest challenge in achieving practical applications of MECs; undesirable microorganisms (methanogens) growth and various studied techniques for eliminating and reducing methanogens activities in MECs were discussed. Additionally, this extensive review also considers prospects for stimulating future research that could help to achieve more information and would provide the focus and path towards MECs as well as their possibilities for simultaneously generating H2 and waste remediation.

Cellulosic ethanol production has received global attention to use as transportation fuels with gasoline blending virtue of carbon benefits and decarbonization. However, due to changing feedstock composition, natural resistance, and a lack of cost-effective pretreatment and downstream processing, contemporary cellulosic ethanol biorefineries are facing major sustainability issues. As a result, we've outlined the global status of present cellulosic ethanol facilities, as well as main roadblocks and technical challenges for sustainable and commercial cellulosic ethanol production. Additionally, the article highlights the technical and non-technical barriers, various R&D advancements in biomass pretreatment, enzymatic hydrolysis, fermentation strategies that have been deliberated for low-cost sustainable fuel ethanol. Moreover, selection of a low-cost efficient pretreatment method, process simulation, unit integration, state-of-the-art in one pot saccharification and fermentation, system microbiology/ genetic engineering for robust strain development, and comprehensive techno-economic analysis are all major bottlenecks that must be considered for long-term ethanol production in the transportation sector.

Lignocellulosic fractionation is highly desirable for the efficient transformation of polymeric sugars into renewable fuels, chemicals, and materials. Thus, γ-valerolactone (GVL) has attracted attention as an advanced platform chemical, which can be synthesized directly from bioderived products, such as levulinic acid, furfural, and hydroxymethylfurfural, as well as via one-pot catalytic transformation of renewable sugars (cellulose, hemicellulose, and fructose). GVL, when combined with acid and water in a certain ratio, has unique solvent characteristics to deconstruct biomass and solubilize lignin and xylose with reduced toxin generation. GVL is suitable for downstream processing, and thus, it promotes a self-sustainable, closed-loop biorefinery approach. Therefore, in this review, we comprehensively summarized the recent updates and catalytic approaches for GVL production, as well as their applications in biomass deconstruction. Additionally, we introduced the research topic, biomass structure, and natural recalcitrance, and described the merits and demerits of conventional pretreatment methods adopted in the literature so far. Finally, we discussed advancements in GVL-based biorefinery, challenges, and future perspectives.

Date biomass is a carbon-rich renewable resource that can be considered a potential carbon-rich substrate for energy generation over anaerobic digestion (AD). However, due to its complex nature, appropriate pretreatment is necessary to achieve a higher methane yield. Hence, the current study was envisioned to evaluate the influence of three different pretreatment strategies, namely acid, alkali, and hydrothermal pretreatment on biochemical methane potential (BMP) of seven diverse sorts of Algerian date biomass, namely Pedicels, Fibrilium, Petiole, Fruit bunch, Spath, Palm, and its mixture. Among all the pretreatment conditions, alkaline pretreatment highly influenced the lignin composition of date biomass and showed higher BMP. Among all sorts of biomass, higher BMP was detected through Palm as 295.9 mL CH4/g-TS, whereas the lowest BMP values were recorded with Petiole as 226.74 mL CH4/g-TS. Among all the experimental variations, ammonium pretreated Palm biomass documented the highest substrate conversion efficiency (63.80%), which correlates well with the observed higher BMP values. Nevertheless, there was a very marginal improvement in BMP detected in the case of other pretreatment strategies compared to alkaline pretreatment. This might be due to the efficacy of the applied pretreatment method on delignification of date biomass.

This review focuses on the current developments and new insights in the field of dark fermentation technologies using wastewater as carbon and nutrient source. It has begun with the type of wastewaters (sugar rich, toxic and industrial) employed in the H 2 production and their production performances with pure (or) mixed microbiota as seeding source in the batch reactors. Secondly, well-documented continuous system performances and their failure reasons were examined along with the enhancement possibilities in ways of strategies. A SWOT analysis has been performed to validate the strength and weakness of the continuous systems towards its industrialization and possible scheme of the integration methods have been illustrated. Additionally, an outlook has been provided with enlightening the remedies for its success. Moreover, the practical perspectives of the continuous systems are highlighted and challenges towards scale up are mentioned. Finally, the possible integrative approaches along with continuous systems towards the bioH 2 technologies implementation are enlightened.

Microbial electrolysis cell (MEC) is a potentially attractive green technology to tackle the global warming and energy crisis, which employs electrochemically active bacteria to convert organic matter into hydrogen or a wide range of chemicals, such as methane, acetate, hydrogen peroxide, ethanol, and formic acid, without causing environmental pollution. Until now, probably the cleanest and the most efficient method of producing hydrogen has been MEC. However, this technology is still in its infancy period and poses various challenges towards up-scaling and widespread applications, such as such as lower hydrogen production rate (HPR), high internal resistance, complicated architecture, and expensive materials. New advances are needed in biofilm engineering, materials for electrodes and reactor configuration for successful real-world application of this technology. Thus, the present review deals with development of practical MEC technology and includes the following sections: firstly a general introduction to MECs; their operating principles, thermodynamics of MEC, and energy or voltage losses in the MEC system were provided. Followed by a section on the critical factors affecting MEC performance; microorganisms, anode, cathode, membrane or separator, fuel sources, the state-of-art MECs designs, other key operational factors, and its potential application in microbial production of value added products are discussed in detail. Afterwards, current challenges involved in developing practical MEC systems are highlighted, and outlooks for future development are also suggested. The review aims to assist researcher and engineers to gain fundamental understandings of MEC, and it also provides several future research directions and a road map on how to overcome the barriers, so the MEC technology can be further advanced and applied in larger scale.

Hydrogen gas has tremendous potential as an environmentally acceptable energy carrier for vehicles. A cutting edge technology called a microbial electrolysis cell (MEC) can achieve sustainable and clean hydrogen production from a wide range of renewable biomass and wastewaters. Enhancing the hydrogen production rate and lowering the energy input are the main challenges of MEC technology. MEC reactor design is one of the crucial factors which directly influence on hydrogen and current production rate in MECs. The rector design is also a key factor to up-scaling. Traditional MEC designs incorporated membranes, but it was recently shown that membrane-free designs can lead to both high hydrogen recoveries and production rates. Since then multiple studies have developed reactors that operate without membranes. This review provides a brief overview of recent advances in research on scalable MEC reactor design and configurations.

Dark fermentation is a technically feasible technology for achieving carbon dioxide-free hydrogen production. This review presents the current findings on continuous hydrogen production using dark fermentation. Several operational strategies and reactor configurations have been suggested. The formation of attached mixed-culture microorganisms is a typical prerequisite for achieving high production rate, hydrogen yield, and resilience. To date, fixed-bed reactors and dynamic membrane bioreactors yielded higher biohydrogen performance than other configurations. The symbiosis between H2-producing bacteria and biofilm-forming bacteria was essential to avoid washout and maintain the high loading rates and hydrogenic metabolic flux. Recent research has initiated a more in-depth comparison of microbial community changes during dark fermentation, primarily with computational science techniques based on 16S rRNA gene sequencing investigations. Future techno-economic analysis of dark fermentative biohydrogen production and perspectives on unraveling mitigation mechanisms induced by attached microorganisms in dark fermentation processes are further discussed.

Date biomass is a renewable natural resource since it can be substituted in a comparatively shorter period. Hence it is considered as a possible feedstock for bioenergy motivations through anaerobic digestion (AD). Despite the fact AD is a fully demonstrated technology, the use of new feedstock necessitates detailed investigation. Worldwide several researchers are evaluating methane yield short of paying much consideration to the source type and structural and elemental composition of biomass. Hence, the current study was intended to relate methane yield to those two structural and chemical composition of biomass. In this sense, biochemical methane potential (BMP) for different date biomass, namely Pedicels, Fibrilium, Petiole, Fruit bunch, Spath, Palm, and a mixture of all biomass samples was tested for 30 days. Among all the experimental variations, higher productivity was observed with Palm as 72.60 mL CH4/g VS/days, followed by Spath (66.61 mL CH4/g VS/days), Mixed biomass (64.57 mL CH4/g VS/days), Fruit bunch (64.34 mL CH4/g VS/days), Pedicels (59.06 mL CH4/g VS/days), Fibrilium (57.42 mL CH4/g VS/days), and Petiole (41.17 mL CH4/g VS/days). From the experimental results, it can be concluded that among all the biomass samples, Palm is the best substrate for higher methane production. However, the remaining experimental conditions produced methane yield was comparatively low. This might be due to the composite nature of the substrate with lignin as an insoluble fraction. Hence, Pedicels, Fibrilium, and Petiole biomasses cannot be recommended as a substrate for biogas production without appropriate pretreatment.

In recent years, bioelectrochemical hybrid technology has emerged as an alternative energy conversion device for bioelectricity generation with concurrent waste remediation. The major attractions of this bioelectrochemical technology are eco-friendly nature, energy-saving, and energy transformation with reduced sludge generation. A wide variety of substrates, including complex wastewater, can be employed as a potential substrate to operate the bioelectrochemical cells (BEC). Hence, microbial electro-remediation technologies are aimed towards the enhancement of the metabolic activity of electrochemically active biocatalyst by supplying organic/inorganic nutrients, electron acceptors, or donors, thus stimulating oxidation or reduction of contaminants. In this regard, BEC has gained much attention, in which the control environment is feasible by means of electrical current/voltage that serves as a donor or acceptor for hazardous waste remediation. In the present review, we mainly emphasize the developments and advancements of microbial electro-remediation technologies in the direction of complex hazardous waste remediation. We reviewed and discussed various BEC mediated complex pollutants remediation (ex: aromatics, dye, nitrogen compounds, heavy metals etc.) and its limitations. In conclusion, the future perspectives in the BEC for bioenergy generation with concurrent waste remediation are proposed through numerous aspects and approaches to afford clean energy and the environment.

Since the last century, the search for clean and renewable energy is going on. This process will continue until there is a stable solution available as an alternative to fossil fuels. Several energy-producing products arise from photosynthetic-organisms like biofuel, bioelectricity, and there are various methods also available for the extraction of these products. Microbial fuel cells (MFCs) are energy transducers which convert organic matter directly into electricity, through the process of anaerobic respiration of microorganisms. Now a day’s researchers have taken as a challenge to use algae along with the bacterial communities to provide an organic carbon fuel source for the MFCs. This paper describes the potential application of algal biomass in the field of bioelectricity. Till now, many scientific experiments conducted all around the world to demonstrate how well efficient is this green photosynthetic organism capable of producing electricity along with its other applications like biofuel, demand in the food industry, and much more. The present manuscript aimed to provide an overview of the potential use of algae as a biocatalyst in MFCs. Further, this article also provides the current status of numerous countries which are excelled in the field of bioelectricity generation.

Microbial electrolysis cells (MECs) are generally regarded as a promising future technology for manufacturing green hydrogen from organic material present in wastewaters and other renewable energy sources. However, the development of inexpensive and high-efficient cathode catalyst is the most critical challenge for MECs to become a commercialized H2 production technology. In this study, a non-noble metal electroformed Ni mesh cathode alternatives to typical cathode material (Pt/CC) was intensively examined in a single-chamber membrane-free MEC. To the best of our knowledge, the use of electroformed Ni mesh as the MEC cathode catalyst has not been reported so far. The MEC was operated in fed-batch mode and the performance of the Ni mesh cathode was compared with that of Pt/CC cathode in terms of columbic efficiencies (75 ± 4% vs. 72.7 ± 1%), overall hydrogen recovery (89.3 ± 4% vs. 90.9 ± 3%), overall energy efficiency (62.9 ± 5% vs. 69.1 ± 2%), the maximum volumetric hydrogen production rate (4.18 ± 1 m3 H2/m3 d vs. 4.25 ± 1 m3 H2/m3 d), volumetric current density (312 ± 9 A/m3 vs. 314 ± 5 A/m3). The obtained results in this study highlight the great potential of using the electroformed Ni mesh catalysts as a viable cathode material for hydrogen production in MECs.

A novel bio-electrohydrolysis system (BEH) based on self-inducing electrogenic activity was designed as pretreatment device to enhance biohydrogen (H2) production efficiency from food waste. Two-stage hybrid operation with hydrolysis in the initial stage and acidogenic fermentation of the resulting hydrolysate (after hydrolysis) for H2 production in the second stage was evaluated. Application of variable external resistances viz., 10 Ω, 100 Ω, 1000 Ω and closed circuit (CC) influenced the hydrolysis of substrate in BEH system and hydrogen production in acidogenic reactor compared to control. Pretreated substrate at 100 Ω documented higher H2 production (1.05 l) than 10 Ω (0.93 l), CC (0.91 l), 1000 Ω (0.88 l) and control operation (0.68 l). Comparatively, 10 Ω documented higher substrate degradation (53.4%) followed by CC (52.42%), 100 Ω (49.51%), 1000 Ω (47.57%) and control (43.68%). Voltammetric profiles were in agreement with the observed bio-electrohydrolysis and H2 production efficiency.

A novel bio-electrohydrolysis system (BEH) based on self-inducing electrogenic activity was designed as a pretreatment device to enhance biohydrogen (H2) production efficiency of food waste. Experimental strategy involved two-stage integrated/hybrid operation with hydrolysis in initial stage followed by acidogenic fermentation for H2 production in second stage. After pre-treatment, catabolized food waste from control (anaerobic) and BEH (closed circuit mode of operation) system was used as substrate in a separate bioreactor to evaluate H2 production in dark-fermentation process. Pretreated-waste from BEH showed higher H2 production (29.12 ml/h; 24th h) than control (26.75 ml/h; 16th h). Higher cumulative H2 production and maximum substrate degradation were also noticed with BEH-pretreated substrate (CHP, 0.91 l; COD, 52.42%) than control (CHP, 0.68 l; COD, 43.68%). Under closed circuitry, anode served as an alternative electron acceptor promoting biotransformation of complex organics to simpler molecules through catabolism.

Remediation of real-field petroleum sludge was studied under self-induced electrogenic microenvironment with the function of variable organic loads (OLs) in bio-electrochemical treatment (BET) systems. Operation under various OLs documented marked influence on both electrogenic activity and remediation efficiency. Both total petroleum hydrocarbons (TPH) and its aromatic fraction documented higher removal with OL4 operation followed by OL3, OL2, OL1 and control. Self-induced biopotential and associated multiple bio-electrocatalytic reactions during BET operation facilitated biotransformation of higher ring aromatics (5–6) to lower ring aromatic (2–3) compounds. Asphaltenes and NSO fractions showed negligible removal during BET operation. Higher electrogenic activity was recorded at OL1 (343 mV; 53.11 mW/m 2 , 100 Ω) compared to other three OLs operation. Bioaugmentation to anodic microflora with anaerobic culture documented enhanced electrogenic activity at OL4 operation. Voltammetric profiles, Tafel analysis and VFA generation were in agreement with the observed power generation and degradation efficiency.

The fluorescence quenching studies of carboxamide namely (E)-N-(3-Chlorophenyl)-2-(3,4,5-trimethoxybenzylideneamino)-4,5,6,7 tetrahydrobenzo[b]thiophene-3-carboxamide [ENCTTTC] by aniline and carbon tetrachloride in six different solvents namely toluene, cyclohexane, n-hexane, n-heptane, n-decane and n-pentane have been carried out at room temperature with a view to understand the quenching mechanisms. The Stern–Volmer (S–V) plots have been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximation model, it was possible to check these bimolecular reactions as diffusion-limited and to estimate independently distance parameter R ′ and mutual diffusion coefficient D . Finally an effort has been made to correlate the values of R ′ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward's empirical relation and Stokes Einstein relation.

Bioremediation of selected endocrine disrupting compounds (EDCs)/estrogens viz. estriol (E3) and ethynylestradiol (EE2) was evaluated in bio-electrochemical treatment (BET) system with simultaneous power generation. Estrogens supplementation along with wastewater documented enhanced electrogenic activity indicating their function in electron transfer between biocatalyst and anode as electron shuttler. EE2 addition showed more positive impact on the electrogenic activity compared to E3 supplementation. Higher estrogen concentration showed inhibitory effect on the BET performance. Poising potential during start up phase showed a marginal influence on the power output. The electrons generated during substrate degradation might have been utilized for the EDCs break down. Fuel cell behavior and anodic oxidation potential supported the observed electrogenic activity with the function of estrogens removal. Voltammetric profiles, dehydrogenase and phosphatase enzyme activities were also found to be in agreement with the power generation, electron discharge and estrogens removal.

The effect of soil concentration on the aerobic degradation of real-field petroleum sludge was studied in slurry phase reactor. Total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) showed effective removal but found to depend on the soil concentration. Aromatic fraction (48.12%) documented effective degradation compared to aliphatics (47.31%), NSO (28.69%) and asphaltenes (26.66%). PAHs profile showed efficient degradation of twelve individual aromatic compounds where lower ring compounds showed relatively higher degradation efficiency compared to the higher ring compounds. The redox behaviour and dehydrogenase activity showed a linear increment with the degradation pattern. Microbial community composition and changes during bioremediation were studied using denaturing gradient gel electrophoresis (DGGE). Among the 12 organisms identified, Proteobacteria was found to be dominant representing 50% of the total population (25% of γ-proteobacteria; 16.6% of β-proteobacteria; 8.3% of α-proteobacteria), while 33.3% were of uncultured bacteria and 16.6% were of firmicutes.

Functional role of biomolecules viz., carbohydrates and proteins on acidogenic biohydrogen (H2) production was studied through the treatment of canteen based composite food waste. The performance was evaluated in an anaerobic sequencing batch reactor (AnSBR) at pH 6 with five variable organic loading conditions (OLR1, 0.854; OLR2, 1.69; OLR3, 3.38; OLR4, 6.54 and OLR5, 9.85 kg COD/m3-day). Experimental data depicted the feasibility of H2 production from the stabilization of food waste and was found to depend on the substrate load. Among the five loading conditions studied, OLR4 documented maximum H2 production (69.95 mmol), while higher substrate degradation (3.99 kg COD/m3-day) was observed with OLR5. Specific hydrogen yield (SHY) vary with the removal of different biomolecules and was found to decrease with increase in the OLR. Maximum SHY was observed with hexose removal at OLR1 (139.24 mol/kg HexoseR at 24 h), followed by pentoses (OLR1, 108.26 mol/kg PentoseR at 48 h), proteins (OLR1, 109.71 mol/kg ProteinR at 48 h) and total carbohydrates (OLR1, 58.31 mol/kg CHOR at 24 h). Proteins present in wastewater helped to maintain the buffering capacity but also enhanced the H2 production by supplying readily available organic nitrogen to the consortia. Along with carbohydrates and proteins, total solids also registered good removal.

Bio-electrochemical treatment (BET) documented effective degradation of real field petroleum sludge over the conventional anaerobic treatment (AnT). BET (41.08%) operation showed enhanced total petroleum hydrocarbons (TPH) removal over AnT (20.72%). Aromatic fraction visualized higher removal (75.54%) compared to other TPH fractions viz., aliphatics, asphaltenes and NSO (nitrogen, sulfur and oxygen) during BET operation. Higher ring aromatics (5-6) documented easy degradation in BET, while AnT was limited to lower ring (2-3) compounds. Voltammetric analysis evidenced simultaneous redox behavior during BET operation due to presence of graphite electrode as electron acceptor, while AnT showed extended reduction behavior only. Self-induced primary and secondary oxidation reactions and capacitive-deionization might have enhanced the degradation capability of BET. BET documented higher charge/capacitance (2810 mJ/1120 mF) than AnT (450 mJ/180 mF). Power output corroborated well with observed results supporting BET performance as fuel cell. Electrodes offer a potential alternative electron acceptor for promoting the degradation of organic contaminants.