Ultrafiltration Membrane Fouling in Side-stream Aerobic Granular Sludge Membrane Bioreactor

The integration of low-pressure membrane filtration and aerobic granular sludge (AGS) reactor leads to a novel environmental biotechnological process with strong potential to overcome membrane fouling and demonstrate excellent wastewater treatment performance. However, membrane fouling mechanisms in the AGS based membrane bioreactor (MBR) are lack of systematic elaboration. In the present work, a bench-scale AGS reactor was operated for over seven months in order to investigate the effects of granule evolution, initial water flux and membrane material on membrane fouling behavior and reversibility. After 143 days of operation, complete granulation was successfully achieved in the AGS reactor which showed 97.6±1.7 % organic degradation, 94.3±2.0% NH3-N removal, 90.6±0.8% total nitrogen removal and 98.9±1.0% PO43--P removal. The remarkable AGS effluent quality led to a reduction in the fouling layer formation compared to the filtration occurred before complete granulation. The combined cake-complete model demonstrated that dominant fouling mechanism is cake layer formation. The polyethersulfone (PES) membrane exhibited a better antifouling performance compared to the polyvinylidene fluoride (PVDF) membrane regardless of the AGS effluent composition. The experimental data suggest the existence of a threshold flux for fouling reversibility when PES membrane is applied to treat the AGS effluent. The combination of physical cleaning and operating under the threshold flux can effectively control the fouling degree in side-stream aerobic granular sludge membrane bioreactor (AGSM). This, in turn, can reduce the operating cost caused from chemical cleaning and membrane replacement. Overall, the findings of this study provide comprehensive insights into the membrane fouling mechanisms and control strategy in a side-stream AGSM that will contribute towards its large-scale application in wastewater treatment

Effects of water level fluctuation on thermal stratification in a typical tributary bay of Three Gorges Reservoir, China

Xiangxi River is a typical tributary of Three Gorges Reservoir (TGR) in China. Based on field observations in 2010, thermal stratification was significant in most months of the year. Through field data analysis and numerical simulations, the seasonal and spatial variation of thermal stratification as related to the impact of the operation of TGR were investigated. Thermal stratification was most pronounced from April to September in the Xiangxi River tributary. Air temperature (AT) and water level (WL) were the two dominant variables impacting thermal stratification. AT affected the surface water temperature promoting the formation of thermal stratification, and high WLs in TGR deepened the thermocline depth and thermocline bottom depth. These results provide a preliminary description of the seasonal variation and spatial distribution of thermal stratification, which is important for better understanding how thermal stratification affects algae blooms in Xiangxi River

A high-frequency non-resonant elliptical vibration-assisted cutting device for diamond turning microstructured surfaces

In recent years, research has begun to focus on the development of non-resonant elliptical vibration-assisted cutting (EVC) devices, because this technique offers good flexibility in manufacturing a wide range of periodic microstructures with different wavelengths and heights. However, existing non-resonant EVC devices for diamond turning can only operate at relatively low frequencies, which limits their machining efficiencies and attainable microstructures. This paper concerns the design and performance analysis of a non-resonant EVC device to overcome the challenge of low operational frequency. The structural design of the non-resonant EVC device was proposed, adopting the leaf spring flexure hinge (LSFH) and notch hinge prismatic joint (NHPJ) to mitigate the cross-axis coupling of the reciprocating displacements of the diamond tool and to combine them into an elliptical trajectory. Finite element analysis (FEA) using the mapped meshing method was performed to assist the determination of the key dimensional parameters of the flexure hinges in achieving high operational frequency while considering the cross-axis coupling and modal characteristics. The impact of the thickness of the LSFH on the sequence of the vibrational mode shape for the non-resonant EVC device was also quantitatively revealed in this study. Moreover, a reduction in the thickness of the LSFH can reduce the natural frequency of the non-resonant EVC device, thereby influencing the upper limit of its operational frequency. It was also found that a decrease in the neck thickness of the NHPJ can reduce the coupling ratio. Experimental tests were conducted to systematically evaluate the heat generation, cross-axis coupling, modal characteristics and diamond tool’s elliptical trajectory of a prototype of the designed device. The test results showed that it could operate at a high frequency of up to 5 kHz. The cross-axis coupling ratio and heat generation of the prototype are both at an acceptable level. The machining flexibility and accuracy of the device in generating microstructures of different wavelengths and heights through tuning operational frequency and input voltage have also been demonstrated via manufacturing the micro-dimple arrays and two-tier microstructured surfaces. High-precision microstructures were obtained with 1.26% and 10.67% machining errors in wavelength and height, respectively

Antifungal mechanisms of the antagonistic bacterium Bacillus mojavensis UTF-33 and its potential as a new biopesticide

Biological control has gradually become the dominant means of controlling fungal disease over recent years. In this study, an endophytic strain of UTF-33 was isolated from acid mold (Rumex acetosa L.) leaves. Based on 16S rDNA gene sequence comparison, and biochemical and physiological characteristics, this strain was formally identified as Bacillus mojavensis. Bacillus mojavensis UTF-33 was sensitive to most of the antibiotics tested except neomycin. Moreover, the filtrate fermentation solution of Bacillus mojavensis UTF-33 had a significant inhibitory effect on the growth of rice blast and was used in field evaluation tests, which reduced the infestation of rice blast effectively. Rice treated with filtrate fermentation broth exhibited multiple defense mechanisms in response, including the enhanced expression of disease process-related genes and transcription factor genes, and significantly upregulated the gene expression of titin, salicylic acid pathway-related genes, and H2O2 accumulation, in plants; this may directly or indirectly act as an antagonist to pathogenic infestation. Further analysis revealed that the n-butanol crude extract of Bacillus mojavensis UTF-33 could retard or even inhibit conidial germination and prevent the formation of adherent cells both in vitro and in vivo. In addition, the amplification of functional genes for biocontrol using specific primers showed that Bacillus mojavensis UTF-33 expresses genes that can direct the synthesis of bioA, bmyB, fenB, ituD, srfAA and other substances; this information can help us to determine the extraction direction and purification method for inhibitory substances at a later stage. In conclusion, this is the first study to identify Bacillus mojavensis as a potential agent for the control of rice diseases; this strain, and its bioactive substances, have the potential to be developed as biopesticides

Effects of Water Level Fluctuation on Thermal Stratification in a Typical Tributary Bay of Three Gorges Reservoir, China

Xiangxi River is a typical tributary of Three Gorges Reservoir (TGR) in China. Based on field observations in 2010, thermal stratification was significant in most months of the year. Through field data analysis and numerical simulations, the seasonal and spatial variation of thermal stratification as related to the impact of the operation of TGR were investigated. Thermal stratification was most pronounced from April to September in the Xiangxi River tributary. Air temperature (AT) and water level (WL) were the two dominant variables impacting thermal stratification. AT affected the surface water temperature promoting the formation of thermal stratification, and high WLs in TGR deepened the thermocline depth and thermocline bottom depth. These results provide a preliminary description of the seasonal variation and spatial distribution of thermal stratification, which is important for better understanding how thermal stratification affects algae blooms in Xiangxi River

A Mobile Localization Method in Smart Indoor Environment Using Polynomial Fitting for Wireless Sensor Network

The main factor affecting the localization accuracy is nonline of sight (NLOS) error which is caused by the complicated indoor environment such as obstacles and walls. To obviously alleviate NLOS effects, a polynomial fitting-based adjusted Kalman filter (PF-AKF) method in a wireless sensor network (WSN) framework is proposed in this paper. The method employs polynomial fitting to accomplish both NLOS identification and distance prediction. Rather than employing standard deviation of all historical data as NLOS detection threshold, the proposed method identifies NLOS via deviation between fitted curve and measurements. Then, it processes the measurements with adjusted Kalman filter (AKF), conducting weighting filter in the case of NLOS condition. Simulations compare the proposed method with Kalman filter (KF), adjusted Kalman filter (AKF), and Kalman-based interacting multiple model (K-IMM) algorithms, and the results demonstrate the superior performance of the proposed method. Moreover, experimental results obtained from a real indoor environment validate the simulation results

Effect of lime addition on the mineral structure and compressive strength of magnesium containing pellets

Addition of MgO in pellets was proved to have an unfavorable effect on the compressive strength of roasted pellets. For increasing the strength of magnesium containing pellets, lime was further added to prepare pellets with different basicity. SEM-EDS, XRD and Rietveld refining were applied to study the phase composition and microstructure of pellets. Results showed that the compressive strength of roasted lime added pellets was higher than magnesium containing pellets, which increases firstly and then decreases with the increase of basicity. The pellets with a basicity of 0.4 had a maximum strength and a minimum porosity, which were 3318 N/pellet and 18.92% respectively. Under a similar strength level, lime added pellets with a basicity of 0.6 had a higher porosity than magnesium containing pellets, which were 22.11% and 28.32% respectively. Compressive strength of roasted pellets is affected by the incompletely mineralized magnesium olivine, pores, liquid phase, as well as (Mg,Fe)O·FeO phase

Interaction among Hydrological, Environmental, and Ecological Processes in Aquatic Ecosystems

In the context of climate change and human disturbance, the hydrological and environmental processes in aquatic ecosystems have undergone significant changes, which could affect the material cycle and energy conversion processes required by aquatic organisms to maintain life [...

Impacts of Water Level Rise on Algal Bloom Prevention in the Tributary of Three Gorges Reservoir, China

Water level fluctuation plays an important role in algal blooms within the side arms. Field observations of the impacts of fluctuations of water level in Xiangxi Bay (XXB), one of the tributaries of the TGR, were analyzed from 2008 to 2010. Water level rise can result in increases as well as decreases in Chl. a, which depends on the water circulation patterns in the XXB. Those effective/ineffective water circulation patterns in preventing algal blooms in the XXB were based on the tributary inflow but also from the intrusion flow from the TGR. Flow velocity, thermal structure, hydrodynamic characteristics including water age, the turbulent eddy viscosity, the buoyancy frequency, the mixing depth, and the ratio of the euphotic depth and the mixed layer depth were evaluated for these scenarios. It is showed that the effective water circulation patterns in the XXB occurred when there was a converging of the inflow from the upstream with an intrusive overflow, lower-interflow, underflow or the combination from the TGR mainstream. Larger daily WL fluctuation and a longer duration of WL rise would enhance algal bloom prevention in the XXB. These results can provide assistance in managing the operation of water levels in TGR. © 2016 Elsevier B.V

Study on sticking mechanism of pellets under low H2/CO conditions

In order to examine the sticking behavior of the pellets in the gas-based reduction shaft furnace under low H /CO conditions and determine its influencing factors, the sticking behavior of pellets under different temperatures and H /CO ratios was studied by SEM, EDS and reduction kinetics. The results indicated that when the temperature is raised from 800 °C to 980 °C, the sticking index of pellets increased from 5% to 78.82%. Different H /CO ratios under low H /CO conditions caused a variance in the sticking index. The sticking index of pellets was 57.61% under H /CO = 1.8. The sticking phase between the adjacent pellets is mainly metallic iron phase. The mechanism of the sticking during the reduction process was the growth of newly formed fibrous metallic iron between the adjacent pellets. Further, fibrous metallic irons were hooked together to gather and thicken until being metal iron phase agglomerates