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•Polyhydroxyalkanoates a potential biopolymer substitute for conventional plastics.•Critically reviewed various waste streams for sustainable and inexpensive PHA production.•Recent ...advances on fermentation strategies & synthetic biology for higher PHA production.•Discussed PHA- nanocomposites and their application in various sectors.•Future perspectives & technical challenges for efficient waste-bioplastic production addressed.
Polyhydroxyalkanoates (PHA) are appealing as an important alternative to replace synthetic plastics owing to its comparable physicochemical properties to that of synthetic plastics, and biodegradable and biocompatible nature. This review gives an inclusive overview of the current research activities dealing with PHA production by utilizing different waste fluxes generated from food, milk and sugar processing industries. Valorization of these waste fluxes makes the process cost effective and practically applicable. Recent advances in the approaches adopted for waste treatment, fermentation strategies, and genetic engineering can give insights to the researchers for future direction of waste to bioplastics production. Lastly, synthesis and application of PHA-nanocomposites, research and development challenges, future perspectives for sustainable and cost-effective PHB production are also discussed. In addition, the review addresses the useful information about the opportunities and confines associated with the sustainable PHA production using different waste streams and their evaluation for commercial implementation within a biorefinery.
•Critical reviews on dark fermentation of food waste (FW).•Current status of dark fermentation with strategies applied for enhancement.•Technical and economical limitation of dark fermentation ...performance of FW.•Strategies to increase H2 yield and gain more energy.•Integrated system converting fermentation effluent to various fuels and chemicals.
Among the various biological routes for H2 production, dark fermentation is considered the most practically applicable owing to its capability to degrade organic wastes and high H2 production rate. Food waste (FW) has high carbohydrate content and easily hydrolysable in nature, exhibiting higher H2 production potential than that of other organic wastes. In this review article, first, the current status of H2 production from FW by dark fermentation and the strategies applied for enhanced performance are briefly summarized. Then, the technical and economic limitations of dark fermentation of FW are thoroughly discussed. Economic assessment revealed that the economic feasibility of H2 production from FW by dark fermentation is questionable. Current efforts to further increase H2 yield and waste removal efficiency are also introduced. Finally, future perspectives along with possible routes converting dark fermentation effluent to valuable fuels and chemicals are discussed.
Biochar is a stable carbonaceous material derived from various biomass and can be utilized as adsorbents, catalysts and precursors in various environmental applications. This review discusses various ...feedstock materials and methods of biochar production via traditional as well as modern approaches. Additionally, the biochar characteristics, HTC process, and its modification by employing steam and gas purging, acidic, basic / alkaline and organo-solvent, electro- and magnetic fields have been discussed. The recent biochar applications for real water, wastewater and industrial wastewater for the abstraction of environmental contaminants also reviewed. Moreover, applications in machine learning and microbial sensors were discussed. In the meantime, analyses on commercial and environmental profit, current ecological concerns and the future directions of biochar application have been well presented.
Ex-situ biomethanation is an emerging technology that facilitates the use of surplus renewable electricity and valorizes carbon dioxide (CO2) for biomethane production by hydrogenotrophic ...methanogens. This review offers an up-to-date overview of the current state of ex-situ biomethanation and thoroughly analyzes key operational parameters affecting hydrogen (H2) gas-liquid mass transfer and biomethanation performance, along with an in-depth discussion of the technical challenges. To the best of our knowledge, this is the first review article to discuss microbial community structure in liquid and biofilm phases and their responses after exposure to H2 starvation during ex-situ biomethanation. In addition, future research in areas such as reactor configuration and optimization of operational parameters for improving the H2 mass transfer rate, inhibiting opportunistic homoacetogens, integration of membrane technology, and use of conductive packing material is recommended to overcome challenges and improve the efficiency of ex-situ biomethanation. Furthermore, this review presents a techno-economic analysis for the future development and facilitation of industrial implementation. The insights presented in this review will offer useful information to identify state-of-the-art research trends and realize the full potential of this emerging technology for CO2 utilization and biomethane production.
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•Recent advances in ex-situ biomethanation are comprehensively reviewed.•H2 gas-liquid mass transfer is a bottleneck for ex-situ biomethanation.•Trickle bed reactor is the most efficient reactor for obtaining higher CH4 content.•H2 starvation led to a shift in microbial community structure.•Profitability of ex-situ biomethanation depends on the cost of H2 production.
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•Water washed coal fly ash (WFA) was used as a support for development of Cu catalyst.•Synergistic effect of Cu loading on Fe sites of WFA was observed for p-NP reduction.•Cu/WFA ...showed ~3 × 105 times higher estimated rate constant than other Cu catalysts.•Cu(0)/Fe(II) on WFA was main driving force for enhancement of catalytic reaction.•Cu/WFA catalyst showed successful recycling and phytotoxicity tests.
A novel Cu catalyst was developed using water-washed coal fly ash (WFA) as a support material for catalytic reduction of p-nitrophenol (p-NP) in the presence of NaBH4. Cu/WFA showed ~ × 105 times higher estimated rate constant kobs-p-NP/CCu (L min−1 gCu−1) compared with Cu/SiO2, Cu/Al2O3, and other Cu catalysts previously reported. Surprisingly, we obtained a significant lower price value (Price’/K) (0.027–0.068 USD/L min−1) for Cu/WFA in comparison with other Cu catalysts and precious metallic catalysts (Pd, Au, Ag, and Pt). Various surface analyses and additional experiments using Fe/SiO2, Cu/Fe2O3/SiO2, and Cu/HCl-treated WFA demonstrated that Cu(0) nanoparticles were well loaded on the surface of WFA, where Fe elements were abundant, resulting in a dramatic enhancement of the Cu/WFA catalytic activity. Particularly, X-ray photoelectron spectroscopy revealed the abundance of Cu(0)/Fe(III) and Cu(0)/Fe(II) in the WFA surface. This indicates that Cu(0) was the main driving force for the activation of Had molecule, and that the reduction of Fe(III) to Fe(II) by NaBH4 can accelerate the reduction of Cu(II) to Cu(0). Recycling and phytotoxicity tests showed that Cu/WFA can be applied as a reusable catalyst with low environmental impact, revealing the remarkable potential of non-precious metal/WFA catalyst in the field of environmental remediation.
Microbial electrolysis cell (MEC) is a bioelectrochemical technology that can produce hydrogen gas from various organic waste/wastewater. Extra voltage supply (>0.2 V) is required to overcome cathode ...overpotential for hydrogen evolution. In order to make MEC system more sustainable and practicable, it is necessary to minimize the external energy input or to develop other alternative energy sources. In this study, we aimed to improve the energy efficiency by intermittent energy supply to MECs (setting anode potential = −0.2 V). The overall gas production was increased up to ∼40% with intermittent energy input (on/off = 60/15sec) compared to control reactor. Cathodic hydrogen recovery was also increased from 62% for control MEC to 69–80% for intermittent voltage application. Energy efficiency was increased by 14–20% with intermittent energy input. These results show that intermittent voltage application is very effective not only for energy efficiency/recovery but also for hydrogen production as compared with continuous voltage application.
•Intermittent energy supply to MECs used instead of continuous energy supply.•Overall gas production was increased up to ∼41% with intermittent MECs.•Shorter duty length (more frequent energy on/off) was better.•Energy efficiency, recovery, and hydrogen recovery was improved 8–29%.
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•First attempt to utilize kenaf biomass (KB) for cost effective, sustainable PHB production.•Studied various pretreatment methods to utilize KB as feedstock for PHB ...production.•Pretreatment process enhanced saccharification of KB without fermentation inhibitors.•PHB produced exhibited similar structural and thermal properties alike standard PHB.•PHA accumulation, PHB yield using KB hydrolsates was similar to the synthetic sugars mixture.
Kenaf biomass (KB) was employed as feedstock for the synthesis of polyhydroxybutyrate (PHB) using Ralstonia eutropha to replace conventional petroleum-derived polymers. Various pretreatments followed by enzymatic saccharification were applied to release monomeric sugars from KB for PHB production. The effects of increasing concentration of Na2CO3 + Na2SO3 (NaC + NaS) pretreated KB hydrolysates (20–40 g/L) on PHB production were investigated. NaC + NaS pretreated KB hydrolysates (30 g/L) exhibited maximum 70.0% PHA accumulation, with PHB titers of 10.10 g/L and PHB yields of about 0.488 g/g of reducing sugar produced within 36 h of fermentation. PHA accumulation, PHB yield and R. eutropha growth performance using KB hydrolysates were found to be comparable with those of synthetic sugar mixture. Characterization of the produced PHB in terms of crystalline structure, and thermal properties was done using various analytical techniques and results coincide with standard PHB. Thus, green liquor pretreated KB hydrolysates deliver a promising and economically feasible carbon substrate for PHB production.
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•Low-temperature anaerobic ceramic membrane bioreactor was evaluated.•AnCMBR for treating a dilute FRW and domestic wastewater mixture.•AnCMBR was successfully applied at ambient ...temperature for co-managing DWW and FRW.•Microbial community structure was shifted by the temperature changes.•Methanogenic activity was inhibited at 15 °C in AnCMBR treatment.
An anaerobic ceramic membrane bioreactor (AnCMBR) has been attracted as an alternative technology to co-manage various organic substrates. This AnCMBR study investigated process performance and microbial community structure at decreasing temperatures to evaluate the potential of AnCMBR treatment for co-managing domestic wastewater (DWW) and food waste-recycling wastewater (FRW). As a result, the water flux (≥6.9 LMH) and organic removal efficiency (≥98.0%) were maintained above 25 °C. The trend of methane production in the AnCMBR was similar except for at 15 °C. At 15 °C, the archaeal community structure did not shifted, whereas the bacterial community structure was changed. Various major archaeal species were identified as the mesophilic methanogens which unable to grow at 15 °C. Our results suggest that the AnCMBR can be applied to co-manage DWW and FRW above 20 °C. Future improvements including psychrophilic methanogen inoculation and process optimization would make co-manage DWW and FRW at lower temperature climates.
Benzoic acid (BA), a secondary metabolite released through root exudates, is considered to be the most common inhibitor that leads to plant autotoxicity, even at low concentrations in closed ...hydroponic systems. In this study, to mitigate BA-driven autotoxicity, the effects of O3 and O3/H2O2 oxidation treatment (O3 concentration: 1, 2, 4, 8 mg L−1, H2O2 concentration: 4, 8 mg L−1) on waste nutrient solution (WNS) were investigated in terms of BA degradation, the rate of germination inhibition (GI), and the rate of root growth inhibition (RI). In the case of O3 treatment, the BA degradation rate improved up to 14.1% as the O3 concentration increased, while alleviation of GI was insignificant (94.6–100%), confirming that a single O3 treatment was unsuitable for mitigating autotoxicity. On the other hand, O3/H2O2 treatment increased BA degradation by up to 24.8%, thereby significantly reducing GI (up to 7.69%) and RI (up to 0.88%). Both the highest BA mineralization rate and phytotoxicity mitigation was observed at BA125 (4–4) (BA mineralization: 16.7%, GI: 12.82%, RI: 11.69%) and BA125 (1–8) (BA mineralization: 17.7%, GI: 7.69%, RI: 0.88%) at each H2O2 concentration. In addition, the operating costs were evaluated by a chemical and electricity cost analysis at the different treatments. As a result, the operating costs of BA125 (4–4) and BA125 (1–8) were calculated to be 0.40 and 0.42 $ L−1 mg−1 of mineralized BA, respectively. After consideration of the mineralization rate, autotoxicity mitigation, and operating cost, BA125 (1–8) was suggested for the optimal treatment condition and our findings would contribute to the alleviation of BA-driven autotoxicity.
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•Inhibition of BA on seed germination and root growth was demonstrated.•O3 and O3/H2O2 treatments were effective in mitigating BA-driven autotoxicity.•The harsh treatment conditions led to the formation of toxic intermediates.•O3/H2O2 treatment was significantly cost- and performance-effective than O3 alone.
Lignin, is the most abundant, renewable and degradable biopolymer available in the nature. The present study exploited purified lignin from wheat straw as reducing, capping and stabilizing agent for ...the green synthesis of silver nanoparticles (Li-AgNPs) under optimized conditions. The analytical studies revealed synthesized Li-AgNPs having a face centered cubic crystalline structure, size ranging ~15–20 nm and the biomolecules comprising majorly phenolic, hydroxyl and carboxylic group of lignin coated on the surface of AgNPs. Li-AgNPs showed significant antimicrobial efficacy against human pathogens namely; Staphylococcus aureus and Escherichia coli and also determined their minimum inhibitory and minimum bactericidal concentration (MIC and MBC). Li-AgNPs also displayed substantial antioxidant activity in terms of well-known enzyme marker viz.; ABTS and DPPH free radical scavenging assay relative to commercial AgNPs. In vitro cytotoxicity assay of Li-AgNPs demonstrated dose-dependent toxicity effects in SKOV3 ovarian cancer cell line (LD50; 150 μg/mL) indicative of promising anticancer agent. Further, H2O2 sensing ability of stabilized Li-AgNPs exhibited its vital role in determining reactive oxygen species. Synthesis of Li-AgNPs is a cheap green technology and could exhibit its commercial use in biomedical, cosmetic, and pharmaceutical industry.
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•Lignin extracted from wheat straw was employed for AgNPs synthesis.•Substantial antibacterial effect of Li-AgNPs against human pathogens•Li-AgNPs displayed significant antioxidant performance using DPPH and ABTS assays.•In vitro cytotoxic activity against ovarian cancer cell SKOV3 exhibited by Li-AgNPs•Colorimetric high sensing and selective ability of synthesized Li-AgNPs for H2O2
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