Editorial: Biofuels and Bioproducts From Anaerobic Processes: Anaerobic Membrane Bioreactors (AnMBRs)

New biodegradable waste treatment configurations and technologies have arisen to support the transition of treatment plants toward resource recovery facilities. The interest in Anaerobic Membrane Biological Reactor (AnMBR) technology is increasing due to the advantages related to combine anaerobic digestion with membrane filtration. Thanks to the complete retention of anaerobic microorganisms, AnMBRs have the capacity to efficiently recover most of the energy potential in biodegradable waste streams in the form of biogas and produce high-quality effluents with low biomass production

FeAl and NbAl3 intermetallic- HVOF coatings: structure and properties

Transition metal aluminides in their coating form are currently being explored in terms of resistance to oxidation and mechanical behavior. This interest in transition metal aluminides is mainly due to the fact that their high Al content makes them attractive for high-temperature applications. This is also a reason to study their resistance to wear; they may be suitable for use in applications that produce a lot of wear in aggressive environments, thus replacing established coating materials. In this study, the microstructure, microhardness, and wear and oxidation performance of FeAl and NbAl3 coatings produced by highvelocity oxy-fuel spraying are evaluated with two main aims: (i) to compare these two coating systems¿a commonly studied aluminide (FeAl) and, NbAl3, an aluminide whose deposition by thermal spraying has not been attempted to date¿and (ii) to analyze the relationship between their microstructure, composition and properties, and so clarify their wear and oxidation mechanisms. In the present study, the higher hardness of niobium aluminide coatings did not correlate with a higher wear resistance and, finally, although pesting phenomena (disintegration in oxidizing environments) were already known of in bulk niobium aluminides, here their behavior in the coating form is examined. It was shown that such accelerated oxidation was inevitable with respect to the better resistance of FeAl, but further improvements are foreseen by addition of alloying elements in that alloy

Feasibility of using low pressure cold gas spray for the spraying of thick ceramic hydroxyapatite coatings

This article deals with the production of thick ceramic hydroxyapatite coatings obtained by Low Pressure Cold Gas Spray (LPCGS) system. Several factors such as powder microstructure, surface roughness and cold gas spray system are here discussed in the build‐up process. The use of nanocrystalline powder composed by fine agglomerates and needle‐like shape microstructure allows the realignment and compaction of individual crystallites to form thick deposits. In addition, the activation of the substrate surface results convenient for the first impinging particles anchored properly. Then, layer by layer, particles can remain attached leading to coating build‐up. Additionally, the use of low shock pressure as well as constant feeding system provided by LPCGS system lead to homogeneous coatings in comparison with High Pressure Cold Gas Spray (HPCGS) system. The successful coating build‐up has been achieved not only by the use of an agglomerated feedstock powder, but also by previous surface treatment and the use of the low pressure system. The obtaining of HA components by LPCGS is promising within biomedical field. An improvement of component strength is also suggested by means of thermomechanical analysis of the powder. The performance of a post heat‐treatment leads to an increase in HA strength, as well as crystal size

Start-up and HRT Influence in Thermophilic and Mesophilic Anaerobic Digesters Seeded with Waste Activated Sludge

Since thermophilic anaerobic digestion represents an efficient alternative to mesophilic anaerobic digestion, multiple studies have been developed to compare their performance and viability. One of the problems related to thermophilic anaerobic digestion is the availability of an adequate seed to start-up the process. The goal of this study is to evaluate the possibility of using waste activated sludge (WAS) as a seed for both mesophilic (35 °C) and thermophilic (55 °C) anaerobic digesters fed with a real sludge waste (primary and secondary sludge mixture) based on the gradual substitution of synthetic substrate by real feed. The obtained results show that mesophilic and thermophilic anaerobic digesters were rapidly stabilized within 60 and 85 days at a hydraulic retention time (HRT) of t = 35 and 30 d with 450 and 520 mL biogas per g CODt added and 65 % and 72 % as methane content, respectively. Moreover, HRT was progressively reduced in order to assess the maximum organic load thatcan be treated in the thermophilic reactor. The minimum HRT reached was t = 8 d with a VS removal efficiency of 50.32 % and a biogas yield index of 440 mL biogas per g VS added (54 % as methane content)

The effect of hot treatment on composition and microstructure of HVOF iron aluminide coatings in Na2SO4 molten salts

The paper deals with the hot corrosion performance of FeAl base intermetallic HVOF coatings in molten Na2SO4 at 850 C in an isothermal process over the span of 45 h under static conditions. The test was validated with electron microscopy and compositional analyses in the cross-section area, as well as x-ray diffraction techniques. All the coatings were characterized by Al-depleted regions, intersplat oxidation and different stoichiometric ratios of iron aluminides. The results were discussed in relation to the formation of oxide scales on the surface after exposition to corrosive media, as well as heterogeneity and defects of the sprayed coatings. The Fe40Al (at.%) powder showed quite uniform phase distribution after spraying and preserved its integrity after corrosion test; the FeCr25% ? FeAl-TiAl-Al2O3 (wt.%) and Fe46Al-6.55Si (at.%) powders exhibited interface oxidation, with localized corrosion attacks proceeding through particle boundaries and microcrack networks with no evidence of Na and S penetration. FexAly alloys are susceptible to accelerated damage and decohesion of the coating, whereas the formation of sulfides is observed at certain points

Influence of Cold Gas Spray process conditions on the microstructure of Fe-based amorphous coatings

Fe-based amorphous metallic coatings were prepared by Cold Gas Spray process. Through this study, the effects of the process conditions such as spraying distance, gas pressure and temperature on the microstructure of as-sprayed coatings are evaluated. Microstructural studies show that the coatings can present a densely layered structure with porosity below 0.5% and thickness around 800 μm depending on the process conditions. Precipitation of nanocrystals in as-sprayed coatings is observed and present results show its dependence on the thermal and kinetic energy implicated in the process. In general, when gas temperature and pressure decreased, in the studied range, coatings displayed a dense and amorphous structure

Enhancing the bioactivity of polymeric implants by means of cold gas spray coatings

Nanostructured anatase coatings were built-up on biocompatible polyetheretherketone (PEEK) by means of cold gas spray (CGS). Titanium layer was previously desposited, which acted as bond coat between PEEK and metal oxide. Semicrystalline polymer was not degraded during the spraying process and starting composition of titanium dioxide was not affected. TiO2 was homogeneously obtained onto CGS Ti layer and completely covered the piece. Primary human osteoblasts were seeded onto biomaterials and in vitro cell experiments provided evidence to confirm that nanostructured anatase coatings deposited by cold gas spray improve the performance of PEEK implants

Sliding wear behavior of Fe-Al coatings at high temperatures

The medium and high temperature tribological behavior of different iron aluminide thermal spray coatings was investigated. Several powders synthesized through different routes (ball milling, self-decomposition, and self-propagating high-temperature sintering (SHS)) were evaluated. High heterogeneity of conventional High Velocity Oxygen Fuel (HVOF) coatings plays a vital role in their sliding performance, but as long as their integrity is preserved under high temperature oxidizing conditions, the wear rates are found to be acceptable, as it occurs in the case of ball milled Fe-40Al (at.%) powder. The friction phenomenon and wear mechanisms were analyzed in detail through the wear track morphology, contact surface, and friction coefficients. The occurrence of brittle phases in the sprayed coatings, which are also present when tested at high temperatures, appeared to be crucial in accelerating the coating failure