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Biofilm based systems and the hybrid between activated sludge and biofilms have been popularly applied for wastewater treatment. Unlike the suspended biomass, the biofilm concentration and kinetics on the media cannot be easily measured. In this study, a novel and easy-to-use approach has been developed based on pulse-flow respirometer to characterize the biofilm stoichiometry and kinetics in situ. With the new designed breathing reactor, the mutual interference between the magnetic stirring and biofilm media that happened in the conventional breathing reactor was solved. Moreover, Microsoft Excel based programs had been developed to fit the oxygen uptake rate curves with dynamic nonlinear regression. With this new approach, the yield coefficient, maximum oxidation capacity, and half-saturation constant of substrate for the heterotrophic biofilms in a fix bed reactor were determined to be 0.46 g-VSS/g-COD, 67.0 mg-COD/(h·L-media), and 4.4 mg-COD/L, respectively. Those parameters for biofilm ammonia oxidizers from a moving bed biofilm reactor were determined to be 0.17 g-VSS/g-N, 18.6 mg-N/(h·L-media), and 1.2 mg-N/L, respectively, and they were 0.11 g-VSS/g-N, 20.9 mg-N/(h·L-media), and 0.98 mg-N/L for nitrite oxidizers in the same biofilms. This study also found that the maximum specific substrate utilization rate for detached biofilms increased by 3.2 times, indicating that maintaining biofilm integrity was very important in the kinetic tests. Using this approach, the biofilm kinetics on the media can be regularly measured for treatment optimization.

To improve the ductility of Al3Ti alloy, the continuous shape memory alloy NiTi fiber (CSMAR) was introduced into intermetallic Al3Ti matrix for fabricating the novel CSMAR-Al3Ti composite in this work. Microstructure characterizations demonstrated that the CSMAR-Al3Ti composite mainly consists of Al3Ti layer, NiTi fiber, eutectic area and interfacial reaction layer. EBSD results indicated that the eutectic area is made up of Al3Ti and Al3Ni phases, the Al3Ti phase shows a strong [001] crystallographic oriented structure, while the Al3Ni phase has a non-textured structure. TEM results showed that the interfacial reaction layer between NiTi fiber and eutectic area is a multiple phase mixture, including various Ti-Al and Ni-Al intermetallics. Furthermore, TEM and HRTEM analyses revealed a newly formed Ti2Ni layer between NiTi fiber and interfacial reaction layer. Tensile test results confirmed that the CSMAR-Al3Ti composite could effectively improve the ductility of the Al3Ti alloy. Based on the systematic investigations of interfacial microstructure characterization, mechanical behavior and fracture morphology observation, it is found that the toughening mechanism of CSMAR-Al3Ti composite is related to the interfacial fine grain strengthening effect with the gradual distribution characteristic. In addition, the excellent metallurgical bonding between fiber reinforcement and matrix is also beneficial to the mechanical properties. Keywords: Al3Ti alloy, NiTi fiber, Interfacial characterization, Mechanical behavior

In this work, to improve the ductility of Al3Ti alloy, a multi-phase intermetallic mixture structure was achieved by the post annealing treatments (AT) on the as-fabricated continuous shape memory alloy NiTi fiber reinforced Al3Ti composite (CSMAR-Al3Ti). Experimental results revealed that the multi-phase intermetallic mixture structure displays a multi-layer characteristic, including the newly formed intermetallic layer and the eutectic area. Microstructure characterization and formation mechanism confirmed that the newly formed intermetallic layer consists of NiAl, Al3Ni2 and Al3Ti phases, and the eutectic area still consists of Al3Ni and Al3Ti phases. The results of compression and tensile tests indicated that the multi-phase intermetallic mixture structure can simultaneously improve the maximum strength and the failure strain of the monolith Al3Ti alloy. Based on the systematic investigations, it is found that the toughening mechanism is related to the multi-layer characteristic of the multi-phase intermetallic mixture structure, which is beneficial to the crack blunting, crack deflecting and load transformation during the deformation process. Furthermore, the multi-phase intermetallic mixture structure achieved by the 48 h post annealing treatment is the most effective method to improve the ductility of Al3Ti alloy.

In order to investigate the influence of service temperature on the mechanical properties of Ti–5Al-2.5Sn ELI titanium alloy, the tensile tests were performed on the polycrystalline Ti–5Al-2.5Sn ELI titanium alloy samples under a wide temperature range from 20 K to 300 K. The scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) tests were conducted to analyze the fracture behavior evolution, crystallographic orientation, grain boundary characterization and dislocation configuration of the samples. Besides, the deformation mechanism of Ti–5Al-2.5Sn ELI titanium alloy was also thoroughly investigated. Experimental results indicate that the Ti–5Al-2.5Sn ELI titanium alloy displays the single dislocation slipping deformation behavior at room temperature, whereas the coupling of dislocation slipping and twinning deformation behaviors dominate at the cryogenic temperature. The twinning deformation improves the plastic deformation capacity of Ti–5Al-2.5Sn ELI titanium alloy by coordinating the crystallographic orientation, promoting the boundary rotating and the dislocation slipping abilities, which induces the acceptable low-temperature elongation and occurs frequently with the decreasing test temperature. On the other hand, the dislocation strengthening effect resulting from a large number of dislocation structures also contributes to promoting the ultimate tensile strength of the Ti–5Al-2.5Sn ELI titanium alloy under cryogenic temperature.

Effects of electropulsing treatment (EPT) on the microstructure evolution, mechanical properties and crack healing of intermetallic Al3Ti alloys were studied in this work. In order to investigate the athermal effect caused by EPT, conventional heat treatment (CHT) was conducted for comparison. The compressive stress-strain curves demonstrated that the failure strains of Al3Ti alloy increase under both the EPT and CHT conditions, while the increment of failure strain of Al3Ti alloy treated by EPT is higher than that treated by CHT. Fracture surface analysis confirmed that the intrinsic brittle fracture of Al3Ti alloy evolves into the quasi-cleavage fracture with increasing frequency of EPT. Based on the systematic investigation into the microstructure evolution, mechanical properties and fracture surface observation, the influence mechanism of EPT on Al3Ti alloy was found to be related to the improvements of atomic diffusion and dislocation movement, which results from the coupling of thermal effect and athermal effect by EPT. Furthermore, the thermal compressive stress and athermal effect could heal the local micro-crack and decrease the crack width of Al3Ti alloy by EPT. Therefore, EPT can work as a novel method for improving the plastic deformation capacity of Al3Ti alloy.

Intermetallic Al3Ti alloys with different volume fractions of residual aluminum were synthesized via reactive foil sintering in vacuum condition using commercial purity aluminum foils and Ti-6Al-4V alloy foils. Microstructure evolution, elemental analysis, fracture mechanism and phase identification were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) technique, respectively. Mechanical properties were measured by quasi-static compression and Vickers hardness tests. Experimental results indicated that the ductile phase Al distributes in the grain boundaries of the brittle matrix Al3Ti, which increases the compression failure strain of the Al3Ti alloy dramatically compared with the monolithic intermetallic Al3Ti alloy. The compressive stress-strain curve showed a typical elastic-plastic deformation behavior. Moreover, it also demonstrated that the post-heat treatment plays an important role in the mechanical properties due to the formation of α-Al2O3 and Al3Ti grain coarsening. Keywords: Intermetallic, Residual aluminum, Mechanical property, Post heat-treatment

Biofilms developed on support materials with large apertures can be used as live and in-situ formed membranes for solids separation in biofilm-based dynamic membrane bioreactors (bDMBRs). Unlike polymer membranes, biofilms are live, and their composition and structure vary, which further impacts the biofilm resistance. This study repeatedly observed that while starting up a bDMBR to treat biodegradable wastewater, the filtration resistance increased rapidly at the beginning and decreased to a low level corresponding with biofilm succession that was impelled by a variation in the food/microorganism (F/M) ratio. During the rapid rising stage, the F/M ratio was high. Moreover, Meganema, Rhodobacter, Bdellovibrio, Rhizobium, Micobacterium, and Bacillus were the dominant bacterial genera in the biofilms. This promoted biofilm attachment and growth by an excessive secretion of extracellular polymeric substances (EPSs). Consequently, the early biofilms were less permeable and exhibited a resistance of 15.6 × 1011 m−1 on the ninth day. As the start-up time increased and the F/M ratio decreased, the biofilm microbial community was altered significantly, with Legionella, Reyranella, Meganema, Hyphomicrobium, and a few uncultured_bacterium being dominant. Accordingly, the biofilm became more permeable and exhibited a resistance of 0.09 × 1011 m−1 on the 46th day. Then, a flux of 42 L/m2·h was achieved at a pressure of 0.1 kPa. This study indicated that the accumulated resistance in a bDMBR could decrease spontaneously without cleaning by the regulation of the biofilm succession on the support material.

This study revealed that, Thiothrix eikelboomii, a well-known filamentous bacterium that causes sludge bulking, could also interfere oxygen transfer during wastewater treatment. The volumetric oxygen transfer coefficient (KLa) in filamentous-bulking sludge (FBS) was found to be 43% lower than that in floc-forming sludge (FFS) at similar biomass concentrations, partially because the filamentous bacteria had increased the sludge apparent viscosity. The KLa value for FBS, however, was still significantly lower than that for FFS even if both sludges had similar apparent viscosity. Numerous tiny and free-swimming filaments were observed to attach on the air bubble surface, presumably reducing the liquid film renewal and increasing the liquid film thickness. Moreover, the filaments were co-coated with extracellular polymeric substances of protein and polysaccharide, which could make them performing like “amphiphilic molecules” of surfactants to hinder oxygen transfer. Therefore, the particular surface property of filaments and their interaction with air bubbles could also impact oxygen transfer. Thiothrix eikelboomii was identified to be the responsible filamentous bacterium that lowered the KLa value, while other filamentous bacteria with short filaments did not interfere oxygen transfer. This study implies that controlling sludge bulking benefits not only sludge settling but also oxygen transfer.