Enhanced Microstructure and Wear Resistance of Ti-6Al-4V Alloy with Vanadium Carbide Coating via Directed Energy Deposition.

Ti-6Al-4V alloys are known for their suboptimal tribological properties and are often challenged by durability issues under severe wear conditions. This study was conducted to enhance the alloy's wear resistance by forming a hardened surface layer. Utilizing directed energy deposition (DED) additive manufacturing with a diode laser, vanadium carbide particles were successfully integrated onto a Ti-6Al-4V substrate. This approach deviates from traditional surface enhancement techniques like surface hardening and cladding, as it employs DED additive manufacturing under parameters akin to those used in standard Ti-6Al-4V production. The formed vanadium carbide layer achieved a remarkable thickness of over 400 µm and a Vickers hardness surpassing 1500 HV. Pin-on-disk test results further corroborated the enhanced surface wear properties of the Ti-6Al-4V alloy following the additive-manufacturing process. These findings suggest that employing vanadium carbide additive manufacturing, under conditions similar to the conventional DED process with a diode laser, significantly improves the surface wear properties of Ti-6Al-4V in metal 3D-printing applications.

Enhanced continuous biohydrogen production using dynamic membrane with conductive biofilm supporter.

The present study investigated the effect of a conductive biofilm supporter on continuous production of biohydrogen in a dynamic membrane bioreactor (DMBR). Two lab-scale DMBRs were operated: one with a nonconductive polyester mesh (DMBR I) and the other with a conductive stainless-steel mesh (DMBR II). The highest average hydrogen productivity and the yield were 16.8% greater in DMBR II than in DMBR I, with values of 51.64 ± 0.66 L/L-d and 2.01 ± 0.03 mol H2/mol hexoseconsumed, respectively. The improved hydrogen production was concurrent with a higher NADH/NAD+ ratio and a lower ORP (Oxidation-reduction potential). Metabolic flux analysis implied that the conductive supporter promoted H2-producing acetogenesis and repressed competitive NADH-consuming pathways, such as homoacetogenesis and lactate production. Microbial community analysis revealed that electroactive Clostridium sp. were the dominant H2 producers in DMBR II. Conclusively, conductive meshes may be useful as biofilm supporters of dynamic membranes during H2 production for selectively enhancing H2-producing pathways.

Effect of bioaugmentation using Clostridium butyricum on the start-up and the performance of continuous biohydrogen production.

This study aimed to mitigate the instability in the start-up and continuous performance of dark fermentative biohydrogen production using heat-treated sludge by the addition of an exogenous H2-producing strain. Continuous fermentation augmented with Clostridium butyricum showed the highest average biohydrogen production rate (HPR) as 50.35 ± 2.56 and 58.57 ± 5.03 L/L-d with H2-producing butyric and acetic acid pathways, whereas the fermenters without bioaugmentation showed the termination of biohydrogen production in 3 days of continuous operation with non H2-producing lactic acid pathway and H2-consuming propionic acid pathway. The bioaugmentation blocked the growth of the competitors for hexose such as Streptococcus, Lactobacillus and Megasphaera, and provided H2-producer dominated microbiome with not only Clostridium butyricum, but also Clostridium puniceum and Clostridium neuense originated from heat-treated sludge. Bioaugmentation of a H2-producing strain would be a reliable dissemination strategy for dark fermentative biohydrogen production by minimizing the influence of seed sludge population.

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.

Critical challenges and technological breakthroughs in food waste hydrolysis and detoxification for fuels and chemicals production.

Organic waste has increased as the global population and economy have grown exponentially. Food waste (FW) is posing a severe environmental issue because of mismanaged disposal techniques, which frequently result in the squandering of carbohydrate-rich feedstocks. In an advanced valorization strategy, organic material in FW can be used as a viable carbon source for microbial digestion and hence for the generation of value-added compounds. In comparison to traditional feedstocks, a modest pretreatment of the FW stream utilizing chemical, biochemical, or thermochemical techniques can extract bulk of sugars for microbial digestion. Pretreatment produces a large number of toxins and inhibitors that affect bacterial fuel and chemical conversion processes. Thus, the current review scrutinizes the FW structure, pretreatment methods (e.g., physical, chemical, physicochemical, and biological), and various strategies for detoxification before microbial fermentation into renewable chemical production. Technological and commercial challenges and future perspectives for FW integrated biorefineries have also been outlined.

Biohydrogen and biomethane production from food waste using a two-stage dynamic membrane bioreactor (DMBR) system.

This study examined a two-stage dynamic membrane bioreactor (DMBR) system for biohydrogen and biomethane production from food waste (FW) in mesophilic condition. The two-stage DMBR system enabled high-rate H2 and CH4 production from particulate feedstock by enhanced microorganism retention. Chemical energy in FW was recovered up to 79% as renewable energy. The highest average hydrogen production rate of 7.09 ± 0.42 L/L-d was observed at a hydraulic retention time (HRT) of 8 h in the H2-DMBR, while the highest CH4 average production rate of 0.99 ± 0.02 L/L-d was observed at an HRT of 6 d in the CH4-DMBR. The high specific methanogenic activity of 71.7 mL CH4/g VSS-d was maintained at the short HRT, which also contributed to the high MPR. The genus Clostridium was dominant in the H2-DMBR, while bacterial and archaeal populations in the CH4-DMBR were dominated by the class Clostridia and genera Methanobacterium and Methanosaeta, respectively.

High-rate biohydrogen production from xylose using a dynamic membrane bioreactor.

This study aimed a high-rate dark fermentative H2 production from xylose using a dynamic membrane module bioreactor (DMBR) with a 444-µm pore polyester mesh. 20 g xylose/L was fed continuously to the DMBR at different hydraulic retention times (HRTs) from 12 to 3 h at 37 °C. The maximum average H2 yield (HY) and H2 production rate (HPR) at 3 h HRT were found to be 1.40 ± 0.07 mol H2/mol xyloseconsumed and 30.26 ± 1.19 L H2/L-d, respectively. The short HRT resulted in the maximum suspended biomass concentration (8.92 ± 0.40 g VSS/L) along with significant attached biomass retention (7.88 ± 0.22 g VSS/L). H2 was produced by both butyric and acetic acid pathways. Low HY was concurrent with lactic acid production. The bacterial population shifted from non-H2 producers, such as Lactobacillus and Sporolactobacillus spp., to Clostridium sp., when HY increased. Thus, xylose from lignocellulose is a feasible substrate for dark fermentative H2 production using DMBR.

Effect of genus Clostridium abundance on mixed-culture fermentation converting food waste into biohydrogen.

This study examined the effect of various inocula on mixed-culture dark fermentative H2 production from food waste. Heat-treated and frozen H2-producing granular sludge (HPG) grown with monomeric sugars showed a higher H2 yield, production rate, and acidogenic efficiency along with a shorter lag phase than heat-treated methanogenic sludge. Among three different methods of methanogenic sludge inoculation, inoculation after centrifugation showed better H2 production performance. Propionic acid production and homoacetogenesis were regarded as major H2-consuming pathways when methanogenic sludge was used, whereas only homoacetogenesis was found in HPG-inoculated fermentation. During fermentation, the abundance of Clostridium increased greater than 48-fold for methanogenic sludge and greater than 108-fold for HPG, respectively. The initial abundance of Clostridium showed a linear relationship with the H2 production rate and lag-phase time. The use of inoculum with a high abundance of Clostridium is essential for H2 production from food waste.

Dynamic membrane bioreactor for high rate continuous biohydrogen production from algal biomass.

This study aimed to achieve continuous biohydrogen production from red algal biomass using a dynamic membrane bioreactor (DMBR). The DMBR was continuously fed with pretreated Echeuma spinosum containing 20 g/L hexose. The highest average hydrogen production rate (HPR) of 21.58 ± 1.59 L/L-d was observed at HRT 3 h, which was higher than previous reports for continuous H2 production from biomass feedstock. Metabolic flux analysis revealed that butyric acid and propionic acid were the major by-products of the H2-producing and H2-consuming pathways, respectively, of the algal biomass fermentation. Hydrogen consumption by propionic acid pathway could not be prevented completely by heat treatment. PICRUSt2 analysis predicted that Clostridium sp., Anaerostipes sp., and Caproiciproducens sp. might significantly contribute to the expression of both ferredoxin hydrogenase and propionate CoA-transferase. This study would provide the design and operational information on high-rate bioreactor for continuous hydrogen production using biomass.

Enhanced anaerobic digestion of waste-activated sludge via bioaugmentation strategy-Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) analysis through hydrolytic enzymes and possible linkage to system performance.

In this study, anaerobic digestion of waste-activated sludge was bioaugmented with hydrolytic bacteria, Bacteroidetes uniformis (Bacteroidetes, B) and Clostridium sp. (Firmicutes, F) at various dosages. Bioaugmentation resulted in enhanced methane conversion of waste-activated sludge. The highest methane yield of 298.1 mL CH4/g-COD, 85.2% COD conversion efficiency was obtained when Bacteroidetes uniformis and Clostridium sp. were augmented at 100 and 900 CFU/mL, respectively. The microbial community analysis demonstrated that bioaugmentation increased the proportion of Bacteroidetes, Firmicutes, and Proteobacteria. Furthermore, at the highest methane yield, the principal methanogenic pathway was altered from acetoclastic to a mixture of hydrogenotrophic and acetoclastic; the major species shifted from Methanosaeta concilii to Methanobacterium subterraneum. Predicted gene analysis revealed that increased expression of hydrolases resulted in enhanced methane conversion through bioaugmentation.

High-rate mesophilic hydrogen production from food waste using hybrid immobilized microbiome.

This study examined the feasibility of dark fermentative biohydrogen production from food waste using hybrid immobilization in mesophilic condition. Among four different organic loading rates (OLRs), the highest average hydrogen production rate (HPR) of 9.82 ± 0.30 L/L-d was found at an OLR of 74.7 g hexose/L-d, which was higher than reported values from particulate feedstock in mesophilic condition. The average hydrogen yield (HY) at the condition was 1.25 ± 0.04 mol H2/mol hexoseconsumed. Whereas the average HPR and HY at an OLR 80 g hexose/L-d were 5.82 ± 0.12 L/L-d and 0.64 ± 0.02 mol H2/mol hexoseconsumed, respectively. Metabolic flux analysis showed the low HY was concurrent with the highest propionic acid and homoacetogenis. Bacterial population was shift from Clostridium sp. to non-hydrogen producers including Bifidobacterium, Bacteriodes, Olsenella, Dysgonomonas, and Dialister sp.

Effect of shear velocity on dark fermentation for biohydrogen production using dynamic membrane.

This study examined the effect of shear velocity on biohydrogen producing dynamic membrane bioreactor (DMBR) containing 50 µm polyester mesh as supporting material. Increase of shear velocity up to 6.75 m/h enhanced hydrogen production performance as well as biomass retention in both suspended and attached forms, while wash-out was found at a shear velocity of 11.69 m/h. The highest average HPR, HY, suspended biomass, and attached biomass were 26.56 ± 1.49 L/L-d, 1.78 ± 0.10 mol H2/mol glucoseadded, 9.99 ± 0.11 g VSS/L, and 8.82 g VSS/L, respectively, at a shear velocity of 6.75 m/h. Flux balance analysis showed homoacetogenic pathway decreased at the shear velocity of 4.70 m/h with the increase of hydrogen yield based on consumed substrate. The highest copy numbers of Clostridium butyricum was found at the optimum shear velocity. Shear velocity would be a critical operational criteria for continuous biohydrogen production using DMBR.