Search

Wastewater sludge is used as an alternative fuel due to its high organic content and calorific value. However, influent characteristics and operational practices of wastewater treatment plants (WWTPs) can increase the sulfur content of sludge, devaluing it as a fuel. Thus, we investigated the biochemical mechanisms that elevate the sulfur content of sludge in a full-scale industrial WWTP receiving wastewater of the textile dyeing industry and a domestic WWTP by monitoring the sulfate, sulfur, and iron contents and the biochemical transformation of sulfate to sulfur in the wastewater and sludge treatment streams. A batch sulfate reduction rate test and microbial 16S rRNA and dsrB gene sequencing analyses were applied to assess the potential and activity of sulfate-reducing bacteria and their effect on sulfur deposition. This study indicated that the primary clarifier and anaerobic digester prominently reduced sulfate concentration through biochemical sulfate reduction and iron–sulfur complexation under anaerobic conditions, from 1247 mg/L in the influent to 6.2~59.8 mg/L in the industrial WWTP and from 46.7 mg/L to 0~0.8 mg/L in the domestic WWTPs. The anaerobic sludge, adapted in the high sulfate concentration of the industrial WWTP, exhibited a two times higher specific sulfate reduction rate (0.13 mg SO42−/gVSS/h) and sulfur content (3.14% DS) than the domestic WWTP sludge. Gene sequencing analysis of the population structure of common microbes and sulfate-reducing bacteria indicated the diversity of microorganisms involved in biochemical sulfate reduction in the sulfur cycle, supporting the data revealed by chemical analysis and batch tests. [ABSTRACT FROM AUTHOR]

The seasonal variation in concentration of transparent exopolymer particles (TEPs), particulate organic carbon (POC) and particulate organic nitrogen (PON) were investigated together with floc size and the concentration of suspended particulate matter (SPM) along the cross‐shore gradient, from the high turbid nearshore toward the low‐turbid offshore waters in the Southern Bight of the North Sea. Our data demonstrate that biophysical flocculation cannot be explained by these heterogeneous parameters, but requires a distinction between a more reactive labile ("fresh") and a less reactive refractory ("mineral‐associated") fraction. Based on all data, we separated the labile and mineral‐associated POC, PON, and TEP using a semi‐empirical model approach. The model's estimates of fresh and mineral‐associated organic matter (OM) show that great parts of the POC, PON, and TEP are associated with suspended minerals, which are present in the water column throughout the year, whereas the occurrence of fresh TEP, POC, and PON is restricted to spring and summer months. In spite of a constantly high abundance of total TEP throughout the entire year, it is its fresh fraction that promotes the formation of larger and faster sinking biomineral flocs, thereby contributing to reducing the SPM concentration in the water column over spring and summer. Our results show that the different components of the SPM, such as minerals, extracellular OM and living organisms, form an integrated dynamic system with direct interactions and feedback controls. Plain Language Summary: Particles suspended in coastal waters occur as loose aggregates of tiny mineral and organic particles, also known as flocs. Their mass concentration is higher in winter than in summer, but their sizes are smaller in winter. The seasonal cycle of phytoplankton activity drives this phenomenon. In spring, phytoplankton blooms and starts to produce fresh and sticky organic matter. This glue binds particles together after collisions and promotes increasingly larger and yet stable flocs. Analytical lab methods cannot distinguish between the freshly produced sticky and the older inactive organic material that is stored in the sediments and entrained into the water by erosion and resuspension. Therefore, previous studies were not able to detect the relation between the occurrence of the sticky material and the floc‐sizes in coastal waters. However, our innovative model approach allows a separation into both fractions. We observe a clear increase in floc sizes during spring and summer when fresh sticky organic material is available. As larger particles sink faster, they are removed from the water column, which allows a higher light penetration. In this way, phytoplankton is exposed to changing conditions, an illustration of how direct interactions and feedback loops occur in an integrated dynamic system. [ABSTRACT FROM AUTHOR]

This paper proposes a flyback-circuit-based design of a trigger circuit for a high-power gas switch. By incorporating a flyback circuit in a high-power gas switch, it is possible to generate a high step-up ratio and high-voltage pulse by using a transformer. Furthermore, simple trigger circuit having the minimum possible number of components (transformer and switch) can be realized. When an inductor is used as an energy storage element, energy is stored as a current source, and thus, the element can operate reliably when low impedance exists between the trigger node of the switch after triggering. According to the fundamental operating principle of a flyback circuit, the proposed trigger circuit is designed considering the maximum trigger voltage and energy required for a high-power gas switch. To verify the proposed design procedure and feasibility of the trigger circuit, a compact trigger circuit (7.5 kV, 1.3 mJ/pulse) is simulated using the PSpice program and implemented. Based on this compact circuit, a trigger circuit (20 kV, 100 mJ/pulse) for a triggered vacuum switch (TVS) is developed, and the tests with an actual TVS (3.3 kJ) are carried out. [ABSTRACT FROM AUTHOR]

The floc size distribution (FSD) is crucial to predict cohesive sediment dynamics in aquatic environments. Recently, increasing attention has been given to biofilm effects on the FSDs of suspended particles since the presence of biofilms on particle surfaces may lead to larger flocs and thus higher settling velocities. In this study, results from a settling column experiment conducted by Tang and Maggi (2018; https://doi.org/10.1002/2017JG004165) under nutrient‐free and biomass‐free, nutrient‐affected and biomass‐free, and nutrient‐affected and biomass‐affected conditions, with different suspended sediment concentrations, shear rates, and nutrient concentrations, have been used to validate modeled FSDs that is based on the population balance equation solved by the quadrature method of moments. In addition to the processes of aggregation and breakage, the effects of biofilm are expressed in the growth term of the population balance equation. The logistic growth pattern is used to account for an increase in biomass, which is primarily controlled by the specific growth rate and the carrying capacity. In this study, the biofilm growth rate is assumed nutrient dependent, and the carrying capacity of floc size is hypothesized to be proportional to the Kolmogorov microscale. With eight size classes to interpret a simulated FSD, the predicted and observed FSDs exhibit a reasonable match for all nutrient‐free and biomass‐free, nutrient‐affected and biomass‐free, and nutrient‐affected and biomass‐affected conditions. This simplified bioflocculation model fills the gap between the simulations of the FSDs of cohesive sediments without and with biofilms and has the potential to be included in large‐scale models in the future. Plain Language Summary: In estuaries or adjacent coastal regions, the transport of suspended sediment is responsible for many environmental and engineering issues, for example, siltation and dredging in navigation channels and harbors, water quality, water clarity, pollutants transport, and ecosystem responses. Suspended sediment particles can flocculate and thus can form aggregates with size, shape, density, and settling velocity largely different from the building particles. A challenge to predict the particle behaviors originates from a lack of flocculation models that are able to address the variations in floc size distributions. The aim of this study is to develop a flocculation model that includes besides the "classical" aggregation and breakage driven by turbulence also a biological process, which is biofilm growth. The biofilm growth and its impact on flocculation and thus floc size are simulated in a similar way as the growth of microbes but with different growth rates. The model is validated with laboratory experiments that have shown that the sizes of flocs made solely with sediment particles largely increase when incubated microbes are present. This model provides a sound basis to simulate the behavior of natural particles (minerals, organic, and biological particles) and particles from human origin (plastics) in future environmental risk assessment studies. Key Points: The quadrature‐based multiclass population balance model was used to model the floc size distributions of cohesive sedimentsThe effects of aggregation, breakage, and biofilm growth were included in the modelThe net increase in floc size due to biofilm effects is assumed to follow the logistic growth pattern [ABSTRACT FROM AUTHOR]

Abstract Estuarine and coastal regions are often characterized by a high variability of suspended sediment concentrations in their waters, which influences dredging projects, contaminant transport, aquaculture and fisheries. Although various three-dimensional open source software are available to model the hydrodynamics of coastal water with a sediment module, the prediction of the fate and transport of cohesive sediments is still far from satisfied due to the lack of an efficient and robust flocculation model to estimate the floc settling velocity and the deposition rate. Single-class and sometimes two-class flocculation models are oversimplified and fail to examine complicated floc size distributions, while quadrature-based or multi-class based flocculation models may be too complicated to be coupled with large scale estuarine or ocean models. Therefore, a three-class population balance model was developed to track the sizes and number concentrations of microflocs, macroflocs and megaflocs, respectively. With the assumption of a fixed size of microflocs and megaflocs, only four tracers are needed when coupled with the open-source TELEMAC system. It enables better settling flux estimates and better addresses the occurrence and concentration of larger megaflocs. This tri-modal flocculation model was validated with two experimental data sets: (1) 1-D settling column tests with the Ems mud and (2) in-situ measurements at the WZ Buoy station on the Belgian coast. Results show that the flocculation properties of cohesive sediments can be reasonably simulated in both environments. It is also found that the number of macroflocs created, when a larger macrofloc breaks up, is a statistical mean value and may not be an integer when applying the model in the field. Graphical abstract Image Highlights • The sizes of flocs are dynamically altered because of particle aggregation and breakage. • A three-class population balance flocculation model was developed. • This flocculation model has been successfully implemented in the open source TELEMAC. • Four tracer variables, representing the floc size distributions, were included in TELEMAC. • The model was validated with settling column tests and field measurements. [ABSTRACT FROM AUTHOR]

[Purpose] The purpose of this study was to investigate the effects of the menstrual cycle on the static balance of healthy young women. [Subjects and Methods] Eighteen healthy young subjects (mean age 19.1 years; weight 57.5 kg; height 159.9 cm) participated in this study. The Good Balance system was used to measure the postural sway speed and velocity moment of subjects in the static standing posture. Subjects were measured for static balance between 1 and 3 days after menstruation and 13 days after menstruation. [Results] The velocity moment of postural sway was significantly higher at 13 days after menstruation. [Conclusion] Our results indicate that the menstrual cycle affects the static balance of healthy subjects. During the menstrual cycle, intensity for balance exercises in females should be carefully controlled for injury prevention.

[Purpose] The purpose of this study was to determine the effects on the trunk length and pelvic torsion of healthy individuals that arise from crossing the right leg while sitting. [Subjects and Methods] The subjects in this study were 30 healthy individuals consisting of 18 males and 12 females. The subjects were instructed to sit on a chair, the height of which was adjustable, so that their knee and hip joints were bent at 90°. For the study, they sat stripped to the waist, with the back and hips bare. They were then instructed to perform a one-leg-crossed sitting posture by placing the right leg on the top of the left knee. A spinal posture test was performed to measure the subjects' trunk length and pelvic torsion by using a three-dimensional image-based spinal diagnostic system. [Results] The results of the three-dimensional spine examination showed statistically significant decreases in trunk length and pelvic torsion after the one-leg-crossed sitting posture. [Conclusion] In this study, the right leg-crossed sitting posture led to a decrease in the right trunk length with time and, in terms of pelvic torsion, increased the posterior rotation of the right pelvis when compared with the left pelvis.

[Purpose] The study was conducted to determine the effect of horse riding simulation combined with blindfolding on healthy individuals' balance and gait. [Subjects and Methods] Thirty subjects were randomly divided into an experimental group (n=15) and a control group (n=15). The subjects in the experimental group covered their eyes using a blindfold, climbed onto a horse riding simulator, and performed the horse riding simulation exercise. The control group took part in the horse riding exercises without a blindfold. All of the subjects performed the 20 minutes long exercise once a day, five times a week, over a four-week period. [Results] The experimental group showed significant improvement in static balance, dynamic balance, velocity, and cadence compared to pre-intervention measurements. In addition, the control group showed significant improvement in static balance, dynamic balance, single support, and cadence compared to pre-intervention measurements. Significant differences in post-training gains in static balance, dynamic balance, and cadence were observed between the experimental group and the control group. [Conclusion] Subjects that performed horse riding simulation exercise after blindfolding showed significant improvements in balance and cadence compared to the control group.