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Turbulent water jets remain a critical study area, particularly the relation of the water flow with air entrainment and its role in energy dissipation at different hydraulic structures. Plunge pools, formed by the impact of jets on water cushions, play a pivotal role in energy dissipation. Understanding the complex flow dynamics within these pools is essential for designing efficient hydraulic structures. In this research, we present a comprehensive investigation of different numerical simulations, defining two-phase (air-water) in different ways, and them compare with experimental measurements. The primary objective is to analyze the pressure distribution at the bottom of a plunge pool induced by a vertical jet and understand the importance of accurately defining air-water flow in the dynamics of the jet into the pool. Our study bridges the gap between empirical data and computational modeling, shedding light on the intricate behavior of such flows with different method-based solvers: VOF, sub-grid, and multi-phase Euler. Various computational domains, mesh configurations, and analyses spanning different time periods, frequencies, and scales were considered. [ABSTRACT FROM AUTHOR]

Tsunamis are a significant coastal hazard that pressurise sediment pore water, which can potentially induce liquefaction, enhance erosion and scour, and undermine the stability of beach sediments supporting natural and built infrastructure in the coastal nearshore environment. Tsunami-induced pressurisation of pore water is attributed to (a) mechanical pressurisation associated with the soil skeleton's tendency to contract or expand around the soil's pore fluid under the changing overlying water weight and (b) seepage of tsunami water into and out of the sand bed. The pore fluid compressibility, which is influenced by air entrainment due to water table fluctuations caused by the tides, can significantly influence development of stabilising and destabilising hydraulic gradients during tsunami runup and drawdown, respectively. Previous work has effectively assumed a constant air content in sand beds and neglected (a) the compression and dissolution of entrained air that influences the pore fluid compressibility and (b) the interaction between saturated sediment underlying sediment with entrained air. By considering the gas kinetics influencing the pore fluid compressibility in a seepage–deformation model, the effect of different pore fluid compressibility assumptions, thickness of sediment with entrained air, initial degree of saturation and tsunami wave properties (height and duration) were studied. The thickness of sediment containing entrained air, the assumed pore fluid compressibility assumption and subtle differences in the initial degree of saturation can significantly influence the predicted maximum depth and duration of tsunami-induced liquefaction. [ABSTRACT FROM AUTHOR]

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For example, rainfall was shown to enhance seagrass biomass in an Australian seagrass meadow on Mabuiag Island (where the seagrass community includes species from the genera I Cymodocea, Halodule, Thalassia, Halophila, Enhalus, i and I Syringodium i ) throughout a 30-day trial ([92]). Organic carbon in seagrass sediments is influenced by seagrass canopy complexity, turbidity, wave height, and water depth. Keywords: chlorophyll a fluorescence; factorial experiment; growth rate; North Aegean Sea; seagrass EN chlorophyll a fluorescence factorial experiment growth rate North Aegean Sea seagrass 301 313 13 08/09/22 20220801 NES 220801 1 Introduction Seagrasses are flowering, rooted plants that form extensive meadows in shallow sandy to muddy coastal waters worldwide ([39]), receiving about 10-20% of the incident irradiance at the water surface ([31]; [32]). I Cymodocea nodosa i (Ucria) Ascherson is a common seagrass species in the Mediterranean Sea and in the Canary Isles ([32]) that grows relatively fast compared to other seagrass genera ([94]). High-salinity brine discharges from seawater desalination plants can also negatively impact seagrass meadows [103]. [Extracted from the article]

Vegetation flow is commonly studied for subcritical flow motions, while in supercritical flow, the presence of vegetation often leads to enhancement of flow self‐aeration, which would in turn alter the flow hydraulics and water‐plant interaction. This paper presents an experimental investigation of aerated water flow cascading down a vegetated stepped chute. The 21.8° sloping chute is equipped with a 12‐m‐long uniformly stepped invert section. The 0.12‐m‐high steps have grate‐shaped rough top surface covered by 0.07‐m‐high flexible artificial plants, and three vegetation densities are tested in skimming flows, in addition to the reference cases of smooth steps and rough steps covered by bare grate only. The air‐water flow properties and free‐surface fluctuations are systematically measured from the upstream clear‐water region to the downstream fully developed aerated region. The experiment results demonstrate that, compared to a man‐made concrete stepped chute, the presence of vegetation cover on the steps reduces the overall self‐aeration and unsteady fluctuating motions of the flow, while it enhances the dissipation of the flow kinetic energy. The present finding also suggests that the modification to flow aeration and energy loss in the vegetated flow over macrostep‐shaped roughness is dependent on the flow regime which is primarily determined by the flow rate for a given slope and step‐induced macroroughness height. Key Points: Flow aeration and flow resistance are studied in supercritical stepped chute flow with and without vegetation on the step surfacesVegetation on steps reduces flow self‐aeration and unsteady fluctuating motions compared to engineered concrete stepsVegetation on steps enhances energy dissipation and air‐water mixing by producing more small‐size bubbles in water [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of turbulent air-water mixture flows under spilling breaking waves by using a mixture-flow model. The model is extended from the earlier 2D numerical framework NEWFLUME, which solves the Reynolds-averaged Navier-Stokes (RANS) equations for mean flow motions. The turbulence closure is accomplished by a modified k − ε two-equations model, in which the effect of entrained bubbles on turbulence production and dissipation is considered by incorporating additional buoyancy terms. A transient equation based on two-fluid formulation is solved for air bubble transport. The present model is validated by comparing the simulated free surface displacement, void fraction, mean velocity and turbulence kinetic energy against existing experimental data and the previous numerical results. The effects of the additional convective term in transient equation of void fraction and the bubble-induced turbulence term in turbulence transport equation are further explored. The results reveal that the additional convective term in the transient equation of void fraction plays an essential role of suppressing unphysical turbulence growth and bringing correct amount of air entrainment into water during wave breaking processes. The additional bubble-induced turbulence production and dissipation terms become effective after wave breaks when the void fraction has been appropriately modeled, and they can further reduce the simulated turbulence intensities in spilling breaking wave, rendering a better agreement with the experimental measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • The VOF simulations of air entrainment phenomena in a water column are conducted. • Jet velocity and column dimensions affect the air entrainment. • Three main patterns are identified: dispersed bubbles, medium air pockets and large air pockets. • Low jet Reynolds and Froude numbers ensure the fluid does not overflow. This study focuses on computational fluid dynamics (CFD) modelling of the air entrainment phenomena in water columns which are commonly used in processing plants. The CFD model is first validated against experimental data. Then, a comprehensive set of CFD simulations are conducted to understand the effect of inlet jet velocity, nozzle diameter, tank diameter, and tank height on the bubble formation. Three main patterns are identified: dispersed bubbles, medium air pockets (MAP) and large air pockets (LAP). For the dispersed bubble case, the initially formed air pockets break into smaller bubbles and hence the water level rises linearly. For the MAP case, the size of the air pockets remains larger than for the dispersed bubble case, though, with time they burst at the surface. Finally, for the LAP case, the inkling jet interacts violently with the wall and hence large air pockets are trapped within the column, causing the overflow of the fluid. The flows are further analysed using non-dimensionless Reynolds and Froude numbers, providing an acceptable range of operating parameters that ensure the fluid does not overflow. [ABSTRACT FROM AUTHOR]

The Froude scaling laws have been used to model a wide range of water flows at reduced size for almost a century. In such Froude scale models, significant scale effects for air-water flows (e.g. hydraulic jumps or wave breaking) are typically observed. This study introduces novel scaling laws, excluding scale effects in the modelling of air-water flows. This is achieved by deriving the conditions under which the governing equations are self-similar. The oneparameter Lie group of point-scaling transformations is applied to the Reynolds-averaged Navier-Stokes equations, including surface tension effects. The scaling relationships between variables are derived for the flow variables, fluid properties and initial and boundary conditions. Numerical simulations are conducted to validate the novel scaling laws for (i) a dam break flow interacting with an obstacle and (ii) a vertical plunging water jet. Results for flow variables, void fraction and turbulent kinetic energy are shown to be self-similar at different scales, i.e. they collapse in dimensionless form. Moreover, these results are compared with those obtained using the traditional Froude scaling laws, showing significant scale effects. The novel scaling laws are a more universal and flexible alternative with a genuine potential to improve laboratory modelling of air-water flows. [ABSTRACT FROM AUTHOR]

A morning glory spillway usually has an ogee shaped crest and conveys spill water flow to its downstream vertical shaft followed by a horizontal tunnel. The ungated morning glory spillways should convey variable discharges, which nonlinearly depends on the reservoir water elevation. The variation of discharge for unit length of the crest may cause challenges on design of downstream crest curve (which affects coefficient of discharge and downstream crest negative pressure). Furthermore, formation of a horizontal vortex flow affects the spillway discharge. In this paper, in order to resolve these problems by energy dissipation and water flow aeration, variable size steps are mapped to downstream of the curved ogee crest of morning glory spillway. A finite volume base numerical flow solver is used to investigate the effects of the considered configurations on the hydraulic design parameters. In this work, having verified the pressure and aeration of the flow over an ordinary stepped spillway, the characteristics of flow over geometry of an ordinary morning glory spillway, as well as stepped spillway, are modelled and compared to the available measurements on laboratory hydraulic models. Finally, an existing ordinary morning glory spillway is computationally modelled by considering an alternative design of variable sized steps at downstream crest (by mapping their edges to the ordinary profile of the morning glory spillway). The stepped morning glory spillway alternatives are numerically simulated for various flow rates, and the computed discharge coefficients and energy dissipations are compared with simulation results for ordinary morning glory spillway of the case. [ABSTRACT FROM AUTHOR]

We investigated the hydrodynamics of water entry by aluminum spheres varying in wettability, assisted by nano/microscaled surface morphology. A wide range of contact angle (C.A.: 0° ≤ θ0 < 170°) on the test spheres was prepared via inexpensive single-step anodization method. The water entry events: Splash and cavity formation, were visualized by a high-speed camera to understand the fast transient features affected by the surface wettability. In terms of hydrodynamics, cavity formation and air entrainment during the water entry were analyzed via dynamic wetting of liquid film flow along the sphere surface. It was confirmed that wettability was a determinant factor of both splash shape and cavity formation, especially in hydrophobic condition (90° ≤ θ0). Furthermore, the analysis of dynamic contact angle of liquid film front in this study was able to classify the water entry events more detail than previous literature. In addition, we also recorded audio signals to evaluate acoustic pressures produced by the impact between spheres and water pool. The audio signals, which are expected to be proportional to acoustic pressures, differed when hydrophilic and hydrophobic spheres entered water. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate the efficacy of polymerization of composite resin photocured with different wavelengths and irradiation times by means of ablation techniques with Er:YAG laser. Materials and Methods: A microhybrid composite resin was photocured with argon laser (Coherent, Innova 200-20) at 400 mW/cm2 for 15, 40, 60, 300, and 900 s. The wavelengths used were 476.5, 488.0, 502.7, and 514.5 nm. The samples were ablated with Er:YAG laser at three energy levels (100, 200, and 300 mJ), a fixed frequency of 2 Hz, and water flow of 0.12 ml/s for 10 s. The ablated volume was measured to quantify polymerization. Two-way ANOVA and Tukey's test were used to analyze the data. Results: The results showed a more effective polymerization for the wavelength of 476.5 nm with low irradiation times (15, 40 and 60 s). Longer photoactivation (300 and 900 s) and a wavelength of 488.0 nm resulted in less ablation. Conclusion: The ablation techniques with Er:YAG laser can be used for evaluation of efficacy of polymerization of the composite resin and showed that the wavelengths of 476.5 and 488.0 nm provided the best polymerization rate. [ABSTRACT FROM AUTHOR]

We have conducted molecular dynamics simulations of water flow in carbon nanotubes (CNTs) for (6,6) to (20,20) CNTs at a streaming velocity of 100 m/s. The fluidized piston model (FPM) and the ice piston model (IPM) are employed to drive flow through the CNTs. The results show that the single-file water flow inside (6,6) CNT has a convex upward streaming velocity profile, whereas the velocity profiles in (10,10) to (20,20) CNTs are flat except near the tube wall. The flow structure of cylindrical water in the (8,8) CNT is intermediate between that for the (6,6) CNT and the larger CNTs. The flow parameters are found not to exhibit any dependence on streaming velocity at up to 300 m/s in the (12,12) CNT. The hydrogen bond lifetimes of water flowing in CNTs tend to be longer than for the corresponding equilibrium states, and nonzero flow does not reduce the microscopic structure or structural robustness (hydrogen bond lifetime). Although the atomic density profile varies with tube diameter, reflecting the change in static microscopic structure of flow from single file to cylindrical, tube diameter does not induce a clear transition in streaming velocity, temperature, or hydrogen bond lifetime over this diameter range. The results suggest that water flow in CNTs of this size is more pluglike than Poiseuille type, although the flow structure does not strictly accord with either definition. [ABSTRACT FROM AUTHOR]

If optical or any type of nonintrusive sensing technique can provide adequate information to reproduce two-phase flow boundary conditions, internal air-water flow structures might be predicted by analytical air entrainment models. For full-scale prototype conditions with typically large Reynolds numbers, ensuring good probe sturdiness and signal processing quality, as discussed in the original paper, does not guarantee a successful collection of detailed air-water flow information at large hydraulic structures in operation. As the discussers implied, the effect of sensor size on bubble detection and measurement of air-water flow properties can vary with the flow's Reynolds number at different model scales. [Extracted from the article]

Objectives: This study measured the water flow commonly used in high-speed handpieces to evaluate the water flow's influence on temperature generation. Different flow speeds were evaluated between turbines that had different numbers of cooling apertures. Method and materials: Two water samples were collected from each high-speed hand-piece at private practices and at the School of Dentistry at São José dos Campos. The first sample was collected at the customary flow and the second was collected with the terminal opened for maximum flow. The two samples were collected into weighed glass receptacles after 15 seconds of turbine operation. The glass receptacles were reweighed and the difference between weights was recorded to calculate the water flow in mL/min and for further statistical analysis. Results: The average water flow for 137 samples was 29.48 mL/min. The flow speeds obtained were 42.38 mL/min for turbines with one coolant aperture; 34.31 mL/min for turbines with two coolant apertures; and 30.44 mL/min for turbines with three coolant apertures. There were statistical differences between turbines with one and three coolant apertures (Tukey-Kramer multiple comparisons test with P < .05). Conclusion: Turbine handpieces with one cooling aperture distributed more water for the burs than high-speed handpieces with more than one aperture. [ABSTRACT FROM AUTHOR]

The air entrainment rate due to inclined liquid jet plunging into a pool was investigated experimentally. Three types of fluids with varying physical properties in terms of viscosity and surface tension were utilized. For the impinging jet test section, nozzles with different inner diameters were selected. The inclination angles and liquid jet velocities at the nozzle outlet were varied and the entrained air rate was measured by the soap meniscus method. Taking the falling velocity of the liquid jet as a characteristic velocity, it was found that the air entrainment rate under the present experimental condition largely depended on the Weber number. From the obtained database, a new empirical model dependent on the Weber number and Laplace length scale is proposed which is capable of predicting the air entrainment flow rate at a mean absolute relative deviation of 21.7 %. [ABSTRACT FROM AUTHOR]

Abstract In this study, a novel step-feed three-stage integrated anoxic/oxic biological aerated filter (STIAOBAF) process was developed to enhance nitrogen removal from the synthetic domestic wastewater through optimizing influent flow distribution ratio (IFDR) for three stage reactors (R1, R2, R3). Long-term operation demonstrated that the maximum nitrogen removal efficiency was achieved at the IFDR of 30%:50%:20%. The corresponding effluent total nitrogen (TN) was less than 10 mg/L, superior to the first A grade discharge standard of China (Effluent TN < 15 mg/L). The IFDR was further optimized to 32%:49%:19% by response surface methodology (RSM) model, thus obtaining the highest TN removal efficiency of 81.4%. Nitrogen profiles suggested the 2nd stage reactor was the greatest significant contributor for nitrogen removal of the whole system. Microbial community analysis revealed that Chloroflexi , Bacteroidetes , Firmicutes , and Acidobacteria were abundant in anoxic zones, while Planctomycetes , Bacteroidetes and Verrucomicrobia were rich in oxic zones. Nitrogen removal-associated functional bacterial groups (Nitrospira , Thauera , Azospira and Candidatus Kuenenia) were also identified, supporting high-rate nitrogen removal through the combination of anoxic denitrification with aerobic simultaneous nitrification and denitrification (SND). The STIAOBAF will offer a compact and robust alternative for advanced nitrogen removal from the sewage. Graphical abstract Image Highlights • The STIAOBAF process was successfully developed to enhance TN removal. • The optimal IFDR of the system was 32%:49%:19%. • Nitrogen removal was attributed to anoxic denitrification with aerobic SND. • Variations in microbial community in aerobic and anoxic zones were observed. • Nitrogen removal-associated functional bacterial groups were identified. [ABSTRACT FROM AUTHOR]

Abstract Textile dyeing wastewater is characterized by low biodegradability and high nitrogen strength, which is difficult to meet the increasingly stringent discharge requirements. Therefore, the tertiary nutrient and refractory organics removal is considered and aerated biofilter is often adopted. However, the aerobic condition and carbon source shortage restrict tertiary biological nitrogen removal. In this study, iron scrap was introduced as the filter medium to enhance the pollutant removal capacity, and three aerobic biofilters were constructed. Biofilter Fe-CE was filled with iron scrap and ceramisite; biofilter Fe-AC was added with iron scrap and granular activated carbon, and biofilter CE only had ceramisite to pad as control system. After the biofilters were acclimatized by synthetic wastewater and actual dyeing wastewater, the optimal operation parameters based on nitrogen removal were determined as pH 7, gas-water ratio 5:1, hydraulic retention time 8 h and C/N ratio 8.5:1. The iron scraps improved total nitrogen (TN) removal significantly, with TN removal efficiency of 68.7% and 57.3% in biofilter Fe-AC and biofilter Fe-CE, comparing with biofilter CE of 29.9%. Additionally, phosphorus and COD had better removal performance as well when iron scrap existed. Further investigation interpreted the reason for iron's facilitating effect on tertiary nutrient and refractory organics removal. The introduction of iron scrap made the habitat conditions such as pH values, DO concentrations and biomass contents inside the biofilters change towards the direction beneficial for pollutant elimination especially for nitrogen removal. In iron containing biofilters, the majority of nitrogen, phosphorus and organic pollutants were removed in the iron scrap layers, and more pollutants types appeared, implying that iron triggered pollutants to go through more diverse degradation or transformation pathways. Moreover, the phylum Proteoabcteria dominated in samples of ceramisite-containing biofilters, with abundances more than 40%. The iron scrap existence increased the abundances of phyla Bacteroidetes and Firmicutes , and triggered higher abundance of denitrification bacteria. Graphical abstract Image 1 Highlights • Iron improved tertiary nutrient and organics removal in aerated biofilter. • The habitat conditions inside biofilters were changed when iron scrap existed. • Majority of nitrogen, phosphorus and organics were removed in iron scrap layer. • Iron triggered organic pollutants to undergo more diverse degradation pathways. [ABSTRACT FROM AUTHOR]

Highlights • Imbibition and supercritical CO 2 dissolution experiments were conducted in four micromodels possessing different pore-scale characteristics. • We present the fundamental process of the non-equilibrium CO 2 dissolution and coupling with water flow. • We investigate the impacts of pore characteristics on the coupled processes. • A diagram is proposed to quantify the equilibrium/non-equilibrium dissolution transition and network-dependent coupled processes. Abstract Dissolution trapping is one of the most important mechanisms for geological carbon storage (GCS). Recent laboratory and field experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and coupled scCO 2 dissolution and water flow, i.e., scCO 2 dissolution at local pores/pore throats creating new water-flow paths, which in turn enhance dissolution by increased advection and interfacial area. However, the impacts of pore-scale characteristics on these coupled processes have not been investigated. In this study, imbibition and dissolution experiments were conducted under 40°C and 9 MPa using a homogeneous/isotropic hexagonal micromodel, two homogeneous elliptical micromodels with low or high anisotropy, and a heterogeneous sandstone-analog micromodel. The four micromodels, initially saturated with deionized (DI)-water, were drained by injecting scCO 2 to establish a stable scCO 2 saturation. DI water was then injected at different rates with logC a (the capillary number) ranging from −6.56 to −4.34. Results show that bypass of scCO 2 by displacing water is the dominant mechanism contributing to the residual CO 2 trapping, triggered by heterogeneity in pore characteristics or pore-scale scCO 2 -water distribution. Bypass can be enhanced by pore heterogeneity or reduced by increasing transverse permeability, resulting in relatively low (<2% of CO 2 solubility) or high (9–13% of CO 2 solubility) dissolved CO 2 concentration in displacing water. The overall dissolution of residual scCO 2 increases with decreasing C a , and approaches to their solubility at low C a value with sufficient residence time. This main trend is similar to a capillary desaturation curve that represents the relationship between the residual saturation and C a. Spatially, dissolution initiates along the boundary of bypassed scCO 2 cluster(s) in a non-equilibrium manner, and the coupling of water flow and dissolution occurs which fragments the bypassed scCO 2 clusters and enhance scCO 2 dissolution. [ABSTRACT FROM AUTHOR]

The paper presents a new idea of using boundary slip to facilitate hydrodynamic lubrication for zero-entrainment-velocity (ZEV) bearing contacts. The idea entails the bearing contact composed of an oleophobic (slip) and an oleophilic (nonslip) surface. While the nonslip surface drags oil into the ZEV contact, the opposite moving slip surface cannot bring the oil out. The net entrainment of oil thus facilitates hydrodynamic lubrication for the ZEV contact. The idea was validated by ZEV experiments, such that a new retainerless bearing type that incorporates alternately slip and nonslip rolling elements was conceived. The new bearing design fits for wide speed range applications. The optimal characteristics of oleophobic coating required in the new bearing are discussed. [ABSTRACT FROM AUTHOR]

Abstract Experimental measurements were conducted to investigate the upward oil-water flow patterns in a small diameter vertical pipe (0.01 m I.D.) under high temperatures up to 130 °C and high pressures up to 20 MPa. The viscosity of the oil sample was 584.24 mPa s and the density was 1.899 g/cm3 at 30 °C. The effects of pressure, temperature, input water fraction (IWF) and mixture velocity on the flow patterns were systematically investigated. The observed flow patterns were plotted on a flow pattern map in which input water fraction was used as the y -axis and the mixture velocity was used as the x -axis. Based on the measurement results, the following flow patterns were observed: water-in-oil dispersed flow (D w/o), water-in-oil bubbly flow (B w/o), water-in-oil slug flow (S w/o), water-in-oil creep flow (CE w/o), churn flow (Churn) and core annual flow (AF). Phase inversion was not observed in this work. With an increase in temperature at a given input water fraction, S w/o, CE w/o and Churn flow with large water drops tended to transform into B w/o and D w/o with smaller water drops, the CE w/o disappears gradually, and the boundaries in the flow pattern maps tend to occur at lower input water fraction values. The effect of pressure on the flow patterns was found to be opposite to that of temperature. The possible causes leading to the changes in the flow patterns subjected to pressure/temperature variations were provided in terms of changes in density ratio, interfacial tension, and viscosity ratio of oil and water. Highlights • Heavy oil-water vertical flow pattern maps under high temperature/pressure were constructed. • Effects of temperature and pressure on flow patterns were investigated. • Effect of properties of oil and water has been considered on the flow patterns. [ABSTRACT FROM AUTHOR]

Infrared cameras are widely used for the detection of fugitive gas leaks and for quantifying gas emissions. While the gas detection sensitivity in the presence of noise is now well understood, we show that wind-turbulence-induced thermal fluctuations place a fundamental lower limit on gas detection sensitivity. While for many gases the lower limit is too low to be important, we show that for some gases it places a real limitation on measurements when the background is a near-ground surface. [ABSTRACT FROM AUTHOR]

The bottom-inlet aerator can efficiently protect a spillway chute surface from cavitation damage due to high-flow velocities. This aerator, unlike conventional ones, is especially preferred at low Froude numbers and with wide spillway chutes to overcome submerged aerator conditions. In this study, the aeration performance of bottom-inlet aerators was investigated for different Froude numbers and ramp heights. Some practical formulas based on experimental and numerical data were obtained to estimate the air entrainment coefficient (and thus the average air concentration) of the bottom-inlet aerators. The findings were compared to some empirical results in published literature for conventional aerators, and then discussed. [ABSTRACT FROM AUTHOR]

The deammonification process, which includes nitritation and anammox bacteria, is an energyefficient nitrogen removal process. Starting up an anammox process in a wastewater treatment plant (WWTP) is still widely believed to require external seeding of anammox bacteria. To demonstrate the principle of a non-seeded anammox start-up, anammox bacteria in potential sources must be quantified. In this study, seven digesters, their substrates and reject water were sampled and quantitative polymerase chain reaction (qPCR) was used to quantify both total and viable anammox bacteria. The results show that mesophilic digesters fed with nitrifying sludge (with high sludge ages) can be classified as a reliable source of anammox bacteria. Sludge hygienization and dewatering of digestate reduce the amount of anammox bacteria by one to two orders of magnitude and can be considered as a sink. The sampled reject waters contained on average >4.0 × 104 copies mL-1 and the majority of these cells (>87%) were viable cells. Furthermore, plants with side-stream anammox treatment appear to have higher overall quantities of anammox bacteria than those without such treatment. The present study contributes to the development of sustainable strategies for both startup of anammox reactors and the possibility of improving microbial management in WWTPs. [ABSTRACT FROM AUTHOR]

Determination of the sludge volume index is key to describing the settling characteristics of sludge in the aeration process of wastewater treatment plants (WWTPs). The two core components of this calculation are the settled sludge volume (SSV) and suspended solids. While the measurement procedure for SSV is generally defined by national or international standards, in practice a wide variety of vessel sizes and shapes are used by operators to monitor WWTP performance. Furthermore, differences in how these tests are carried out can lead to poor data, inefficient WWTP operation and a lack of comparable metrics for WWTP operational monitoring. Thus, there is a requirement to improve operational performance of WWTPs to meet the increasingly stringent legislation regarding discharge limits. The aim of this study was to utilise a novel image-processing system (AutoSSV) to (i) determine its efficacy in describing SSV and (ii) measure and compare different methodologies for measurement of SSV. The AutoSSV system was tested using samples from various WWTPs and the results compared to those determined by standard manual measurement. Both standard and modified settlement tests were conducted on 30 mixed liquor samples, with modified settlement tests consistently resulting in lower SSV measurements. Results from the study showed a strong correlation between the SSV measurements provided by the AutoSSV system and results obtained from current manual measurement methods. The proposed technique would help to standardise the measurement in practice and increase the frequency of monitoring, particularly in small-scale rural WWTPs where there may not be permanent operators on site, and thus provide sufficient performance monitoring for efficient and effective operation. [ABSTRACT FROM AUTHOR]

Three strains of bacteria were isolated and purified from activated sludge for white water treatment in the laboratory. These strains were identified as Bacillus subtilis, Bacillus cereus, and Virgibacillus pantothenticus through a morphological analysis, the MIDI Sherlock automatic microbial identification system, and 16S rRNA methods. The results of the construction of efficient microflora for white water showed that a mass percentage ratio of B. subtilis, B. cereus, and V. pantothenticus of 50%:35%:15% achieved an optimal treatment effect. Analysis by gas chromatograph-mass spectrometer (GC-MS) established that the content of characteristic pollutants in white water decreased notably after treatment with the efficient microflora, and detected the intermediate products of short chain fatty acids, alcohols, and other compounds. Moreover, through measuring the removal rate of chemical oxygen demand (COD), electrical conductivity, and cationic demand (CD), the optimal retention time for white water treatment with the efficient microflora was 4 h to 6 h, and when the removal rate of COD reached approximately 90%, the electrical conductivity and the cationic demand were reduced to lower values. [ABSTRACT FROM AUTHOR]

This paper deals with physics of water aeration. Falling water flow produces air bubbles and water droplets mixture in the air-water interface. This mixture develops in the course of time. A new method of determination of amount of air entrained in water was presented. The method was based on digital image processing. Method allows determination of dynamics of air entrainment depending on several parameters of nozzle as well as on height of falling water flow. [ABSTRACT FROM AUTHOR]

We examined macroinvertebrate drift at 4 sites downstream of Abanakee Dam on the Indian River, NY, on separate days at base-flow conditions and following days during recreational releases (rapid releases supporting white-water rafting enterprises). Macroinvertebrate drift rates were highest near the dam due to high numbers of drifting Simuliidae at both base flow and during a release. At the other 3 sites, Simuliidae were less abundant in the drift, and Chironomidae and Sphaeriidae had especially high drift densities during a release, suggesting a greater vulnerability to catastrophic drift. Macroinvertebrate drift was not affected by differences in stream gradients or shear forces that did differ between sites. Our drift densities during the recreational releases were higher than observations from other studies during natural floods, suggesting greater drift vulnerability to rapid increases (∼15 min) in discharge when flood gates are opened. [ABSTRACT FROM AUTHOR]

A new formulation for the prediction of free surface dynamics related to the turbulence occurring nearby is proposed. This formulation, altogether with a breakup criterion, can be used to compute the inception of self-aeration in high velocity flows like those occurring in hydraulic structures. Assuming a simple perturbation geometry, a kinematic and a non-linear momentum-based dynamic equation are formulated and forces acting on a control volume are approximated. Limiting steepness is proposed as an adequate breakup criterion. Role of the velocity fluctuations normal to the free surface is shown to be the main turbulence quantity related to self-aeration and the role of the scales contained in the turbulence spectrum are depicted. Surface tension force is integrated accounting for large displacements by using differential geometry for the curvature estimation. Gravity and pressure effects are also contemplated in the proposed formulation. The obtained equations can be numerically integrated for each wavelength, hence resulting in different growth rates and allowing computation of the free surface roughness wavelength distribution. Application to a prototype scale spillway (at the Aviemore dam) revealed that most unstable wavelength was close to the Taylor lengthscale. Amplitude distributions have been also obtained observing different scaling for perturbations stabilized by gravity or surface tension. The proposed theoretical framework represents a new conceptualization of self-aeration which explains the characteristic rough surface at the non-aerated region as well as other previous experimental observations which remained unresolved for several decades. [ABSTRACT FROM AUTHOR]

In this study, a novel aerated surface flow constructed wetland (SFCW) using exhaust gas from biological wastewater treatment was investigated. Compared with un-aerated SFCW, the introduction of exhaust gas into SFCW significantly improved NH 4 + -N, TN and COD removal efficiencies by 68.30 ± 2.06%, 24.92 ± 1.13% and 73.92 ± 2.36%, respectively. The pollutants removal mechanism was related to the microbial abundance and the highest microbial abundance was observed in the SFCW with exhaust gas because of the introduction of exhaust gas from sequencing batch reactor (SBR), and thereby optimizing nitrogen transformation processes. Moreover, SFCW would significantly mitigate the risk of exhaust gas pollution. SFCW removed 20.00 ± 1.23%, 34.78 ± 1.39%, and 59.50 ± 2.33% of H 2 S, NH 3 and N 2 O in the exhaust gas, respectively. And 31.32 ± 2.23% and 32.02 ± 2.86% of bacterial and fungal aerosols in exhaust gas were also removed through passing SFCW, respectively. [ABSTRACT FROM AUTHOR]

Physical and mechanical changes in concrete continue in subsequent days of heating since some chemically active products in concrete give reactions with water and carbon dioxide in air and new formations determine the fate of concrete. Therefore, this study was conducted to understand the effects of mineral admixtures, fiber reinforcement, air entrainment and different re-curing regimes (after heating) on residual properties of concrete. Concrete specimens were heated to 1000 °C then water and air re-curing processes were applied on heated specimens and further deterioration and recovery of concrete were evaluated. New cracks occurred on the heated surfaces during air re-curing period and reduction in mechanical properties was observed while water re-cured specimens kept their stabilities and regain in their mechanical properties was obtained. Moreover, micro level investigations were conducted on heated surfaces of air re-cured and water re-cured concrete specimens for understanding the reasons of changes observed in mechanical properties. [ABSTRACT FROM AUTHOR]

Aerated flow is a complex hydraulic phenomenon that exists widely in the field of environmental hydraulics. It is generally characterised by large deformation and violent fragmentation of the free surface. Compared to Euler methods (volume of fluid (VOF) method or rigid-lid hypothesis method), the existing single-phase Smooth Particle Hydrodynamics (SPH) method has performed well for solving particle motion. A lack of research on interphase interaction and air concentration, however, has affected the application of SPH model. In our study, an improved multiphase SPH model is presented to simulate aeration flows. A drag force was included in the momentum equation to ensure accuracy of the air particle slip velocity. Furthermore, a calculation method for air concentration is developed to analyse the air entrainment characteristics. Two studies were used to simulate the hydraulic and air entrainment characteristics. And, compared with the experimental results, the simulation results agree with the experimental results well. [ABSTRACT FROM AUTHOR]

Huge amounts of produced water are generated in offshore oil production. The Compact Flotation Unit (CFU) is an excellent pretreatment technology of produced water with high separation efficiency, low residence, and small split ratio. The Computational Fluid Dynamics-population balance model (CFD-PBM) method is used in the present work to study the oil–water separation characteristics in the self-developed Beijing Institute of Petrochemical Technology Compact Flotation Unit (BIPTCFU) at both micro-scale and macro-scale, which would help us gain more insights into the mechanism and the influence of flow field on the oil–water separation process such as the oil droplets’ diameter distribution and separation efficiency. The effects of the inlet diameter, the height of the preliminary separation zone, and the width of the annular space on the oil–water separation characteristics of CFU were discussed systematically. It is illustrated that the appropriate increase of inlet velocity, decrease of annular gap width, and increase of the height in the preliminary separation zone can effectively promote the collision and coalescence process of oil droplets. However, the overlarge height of the preliminary separation zone and the too narrow width of the annular space will both have a significant negative effect on the migration and separation of oil and water and lead to the decrease of separation efficiency. [ABSTRACT FROM PUBLISHER]

We describe a new laboratory synthesis of the α-methyl ester sulfonates based on direct sulfonation of the methyl ester by SO3 introduced from the vapor phase. This was used to synthesize a chain deuterated sample of αC14MES, which was then used to measure the surface excess of αC14MES directly at the air/water interface over a wide range of concentration using neutron reflection. The adsorption isotherm could be fitted to an empirical equation close to a Langmuir isotherm and gave a limiting surface excess of (3.4 ± 0.1) × 10-6 mol m-2 in the absence of added electrolyte. The neutron-measured surface excesses were combined with the integrated Gibbs equation to fit the variation in surface tension with concentration (σ-ln C curve). The fit was exact provided that we used a prefactor consistent with the counterion at the surface being an impurity divalent ion, as has previously been found for sodium diethylhexylsulfosuccinate (aerosol OT or AOT) and various perfluorooctanoates. The critical micelle concentration (CMC) was determined from this fit to be 2.4 ± 0.3 mM in the absence of electrolyte. In the presence of 100 mM NaCl, this contamination was suppressed and the σ-ln C curve could be fitted using the integrated Gibbs equation with the expected prefactor of 1. The new data were used to reinterpret measurements by Danov et al. on an unpurified sample of αC14MES for which computer refinement was used to try to eliminate the effects of the impurities. [ABSTRACT FROM AUTHOR]

ABSTRACT The accumulation of dissolved and colloidal substances (DCS) and inorganic salts in the white water of papermaking circulation system will result in the abnormal runnability of paper machine and low quality of products. Contaminant adsorption on a solid adsorbent in a fluidized bed reactor has been applied for white water treatment. In this study, three kinds of hydrophilic polymers {i.e., poly[methacryloxyethyltrimethyl ammonium chloride] (poly-MAC), polyacrylamide, and poly[acrylic acid] (poly-AA)} had been grafted on the surface of the polystyrene (PS) spheres through two-step reactions. Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analysis, Zeta potential were evaluated the characteristics of modified PS spheres. The results showed that PS-poly(MAC) had good affinity to DCS. Cationic demand, total DCS, and turbidity of white water had been reduced by 79.5%, 40.0%, and 38.4%, respectively, when the amount of PS-poly(MAC) was 50 g/L. While PS-poly(AA) played an important role in removal of metal ions so as to cut down the conductivity of white water. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45169. [ABSTRACT FROM AUTHOR]

The lipophilic colloidal substances (CS) in papermaking white water mainly originate from sizing agents applied during paper manufacturing operations and wood extractives, such as resin acids and fatty acids. In this study, the aqueous dispersions of sodium resinate and sodium stearate were used to simulate the colloidal substances concentrated in white water. The aggregation process and mechanism of pitch deposits developed from soluble colloidal particles were investigated by the determination of turbidity and zeta potential of colloidal substances simulacra dispersions as a function of Ca2+ concentration, as well as through morphological observation, structural characterization, and contact angle measurement of calcium-induced pitch deposits. The results showed that the micelles with hydrophilic groups extending in the water could be formed when the colloidal substances accumulated to a certain concentration. The Ca2+ can exchange Na+ of colloidal substance micelles, and hydrophobic pitch deposits can then be produced by either particleparticle collision or "layer by layer" adsorption with addition of Ca2+, or by both of the mechanisms mentioned above. The complete destabilization of the colloidal substance simulacra occurred when the Ca2+ concentration reached 5 mmol/L. The initial contact angles of water on the surfaces of calcium resinate and calcium stearate discs were 90.2° and 96.0°, respectively. [ABSTRACT FROM AUTHOR]

Aerated lagoons are a main unit operation for wastewater treatment in the paper industry. Many such operations involve inoculation with bacterial formulations in which in situ effectiveness has not been proven; this can be translated into low efficiency in treatment and unnecessary investments. Lack of knowledge of bacterial biodiversity present in a lagoon limits the capacity to exploit the maximum degradation. To overcome such problems, various methods to identify and study these microorganisms have been developed. In this study, a PCR-DGGE analysis was performed to estimate the bacterial diversity and to verify the presence of bacteria present in a commercial inoculum in two aerated lagoons of a pulp and paper effluent. Phylogenetic affiliation of predominant member's correspondent to γ- and β-proteobacteria and Firmicutes were found. The dominant bacteria present in lagoon 2 belonged to the following genus Microbacterium sp. Rhodocyclaceae sp., Eubacterium sp. and B. subtilis. In lagoon 1 the dominant genus included Microbacterium sp., Rhodocyclaceae sp. Tepidimonas sp., Acetanaerobacterium sp., and Flavobacteria sp. The two characterized lagoons were not similar to the commercial inoculum. In addition, nondominant bacteria (less relative intensity) were composed mostly of bacteria of the commercial inoculum. [ABSTRACT FROM AUTHOR]

Exchange of gasses, such as O2, CO2, and CH4, over the air-water interface is an important component in aquatic ecosystem studies, but exchange rates are typically measured or estimated with substantial uncertainties. This diminishes the precision of common ecosystem assessments associated with gas exchanges such as primary production, respiration, and greenhouse gas emission. Here, we use the aquatic eddy covariance technique - originally developed for benthic O2 flux measurements - right below the air-water interface (~ 5 cm) to determine gas exchange rates and coefficients. Using an Acoustic Doppler Velocimeter and a fast-responding dual O2-temperature sensor mounted on a floating platform, the 3D water velocity, O2 concentration, and temperature are measured at high-speed (64 Hz). By combining these data, concurrent vertical fluxes of O2 and heat across the air-water interface are derived, and from the former, gas exchange coefficients. Proof-of-concept deployments at different river sites gave standard gas exchange coefficients (k600) in the range of published values. A 40 h long deployment revealed a distinct diurnal pattern in air-water exchange of O2 that was controlled largely by physical processes (e.g., diurnal variations in air temperature and associated air-water heat fluxes) and not by biological activity (primary production and respiration). This physical control of gas exchange is prevalent in lotic systems and adds uncertainty to common ecosystem assessments of biological activity relying on water column O2 concentration recordings. For example, in the 40 h deployment, there was close-to constant river flow and insignificant winds - two main drivers of lotic gas exchange - but we found gas exchange coefficients that varied by several fold. This was presumably caused by vertical temperature-density gradient formation and erosion in the surface water driven by the heat flux into or out of the river that controlled the turbulent mixing. This effect is unaccounted for in widely used empirical correlations for gas exchange coefficients and is another source of uncertainty in gas exchange estimates. The aquatic eddy covariance technique allows studies of air-water gas exchange processes and their controls at an unparalleled level of detail. A finding related to the new approach is that heat fluxes at the air-water interface can, contrary to those typically found in the benthic environment, be substantial and require correction of O2 sensor readings using high-speed parallel temperature measurements. Fast-responding O2 sensors are inherently sensitive to temperature changes, and if this correction is omitted, temperature fluctuations associated with the turbulent heat flux will mistakenly be recorded as O2 fluctuations and bias the O2 eddy flux calculation. [ABSTRACT FROM AUTHOR]

Swinewastewatermanagement is often affected by twomain issues: a too high volume for optimal reuse as a fertilizer and a too high strength for an economically sustainable treatment by classical solutions. Hence, an innovative scheme has been tested to treat swinewastewater, combining a lowcost anaerobic reactor, upflowanaerobic sludge blanket (UASB),with intensified constructedwetlands (aerated CWs) in a pilot scale experimental study. The swine wastewater described in this paper is produced by a swine production facility situated in North Italy. The scheme of the pilot plant consisted of: (i) canvas-based thickener; (ii) UASB; (iii) two intensified aerated vertical subsurface flowCWs in series; (iv) a horizontal flow subsurface CW. The influent wastewater quality has been defined for total suspended solids (TSS 25,025±9,323mg/l), organic carbon (chemical oxygen demand (COD) 29,350±16,983mg/l), total reduced nitrogen and ammonium (total Kjeldahl nitrogen (TKN) 1,783±498 mg/l and N-NH+4 735±251 mg/l) and total phosphorus (1,285± 270mg/l), with nitrates almost absent. The overall system has shown excellent performances in terms of TSS, COD, N-NH+4 and TKN removal efficiencies (99.9%, 99.6%, 99.5%, and 99.0%, respectively). Denitrification (N-NO-3 effluent concentration equal to 614±268mg/l) did not meet the Italian quality standards for discharging in water bodies, mainly because the organic carbon was almost completely removed in the intensified CW beds. [ABSTRACT FROM AUTHOR]

UV–visible spectroscopy has been shown to be a useful technique for determining dissolved organic carbon (DOC) concentrations. However, at present we are unaware of any studies in the literature that have investigated the suitability of this approach for tropical DOC water samples from any tropical peatlands, although some work has been performed in other tropical environments. We used water samples from two oil palm estates in Sarawak, Malaysia to: i) investigate the suitability of both single and two-wavelength proxies for tropical DOC determination; ii) develop a calibration dataset and set of parameters to calculate DOC concentrations indirectly; iii) provide tropical researchers with guidance on the best spectrophotometric approaches to use in future analyses of DOC. Both single and two-wavelength model approaches performed well with no one model significantly outperforming the other. The predictive ability of the models suggests that UV–visible spectroscopy is both a viable and low cost method for rapidly analyzing DOC in water samples immediately post-collection, which can be important when working at remote field sites with access to only basic laboratory facilities. [ABSTRACT FROM AUTHOR]

Thin-plate weirs are the simplest and least expensive devices, which frequently have been employed in many water projects. In this research, a unique type of Sharp-Crested V-notch weir, entitled SCVW, has been introduced. The hydraulic characteristics of the present weir were investigated theoretically and experimentally under free aerated and non-aerated flow conditions in an open channel for large physical models. To investigate the variations of the discharge coefficient of SCVW versus weir height and vertex angle, a comprehensive laboratory experiments were conducted by measuring the discharge and the water head over the crest of weir. Possibility of different formulations for the head- discharge relationship of SCVW was examined and suitable analytical equation was proposed. The computed discharge using the suggested equation was within 0–10% of the observed ones. According to the experimental observations, the SCVW showed better performance in comparison with normal wire. [ABSTRACT FROM AUTHOR]

Artificial supercavitation is a promising technology for the drag reduction of high-speed underwater vehicles, whereby a cavity is generated through air entrainment to encompass the entire vehicle. Supercavitation experiments are conventionally conducted in closed wall water tunnels. In order to properly extend these results to the operation of underwater vehicles in the ocean, it is imperative to understand the underlying physics governing these processes. The current study focuses upon the factors that govern the ventilation demand of a supercavitating vehicle operating under artificial supercavitation mode. Systematic artificial supercavitation experiments are carried out in a high-speed water tunnel with two different experimental models and high-speed visualization and measurements of air entrainment are carried out at different stages of supercavity formation, sustenance and collapse. Our measurements suggest a marked difference between the two experimental models for formation, sustenance and critical air entrainments of supercavities. Such differences are explained based on the understanding of fundamental physical factors governing the process, such as bubble breakup, coalescence and the effect of the presence of a body inside the supercavity. [ABSTRACT FROM AUTHOR]

Air can be entrapped in water and wastewater systems under a variety of conditions, and if such air is not managed properly, it can impose considerable operational penalties. To avoid these problems and the dangers associated with air pockets, several air management strategies have been routinely suggested. However, the devastating consequences of air pockets frequently documented in the literature imply the need for further development in this area. Improving air management obviously requires a thorough understanding of the current strategies and their shortcomings. This paper overviews the sources of air in pipes and key consequences associated with its presence. Current measures for managing air in water pipes are reviewed and critiqued. Finally, knowledge gaps that limit the efficient application of current air management strategies to real world problems are identified, and suggestions for future development are presented. [ABSTRACT FROM AUTHOR]

Chute aerators separate the flow of water from the bottom of a chute, and air bubbles generated in the cavity zone must go through the impact zone as they travel downstream. In this study, the air concentration and air bubble characteristics along the chute were investigated systematically by a series of model tests that eliminated the effect of the upper aeration region. It was found that the large amount of air entrained in the cavity zone was only partially entrained into the final flow. Based on the lower air discharge properties, the chute downstream of the aerator was partitioned into four reasonable zones: the cavity zone (0 < x < L ), the impact zone ( L ≤ x ≤ L m ), the equilibrium zone ( L m ≤ x ≤ L D ), and the far zone (x > L D ). The details of the bubble chord length and bubble frequency distributions in each zone were measured. In the cavity zone, the bubble frequency distribution was related to the air concentration by a parabolic law. In the impact zone, the air concentration decreased sharply while the bubble frequency decreased to a lesser extent. Due to the turbulent fluctuation effect, the probability of smaller bubbles increased while the probability of larger bubbles decreased as they progressed down the chute. In the equilibrium zone, the bubble frequency decreased slightly. At the cross section, the range of probability of bubble chord lengths tended to increase from the bottom to the upper surface. The distributions of the mean chord lengths followed approximately a power low distribution. A formula was provided to predict the maximum air bubble frequency in the impact and equilibrium zones. [ABSTRACT FROM AUTHOR]

In urgent situations, the intake gates of a hydroelectric power generating station must be closed to stop the inflow of water to the station's penstock. During the course of gate closure, the air pressure in the penstock can drop drastically, posing safety risks. This paper aims to develop reliable methods for predicting pressure drop. The methods consider time-dependent water inflow, air entrainment in the penstock, air-water outflow from the penstock, and airflow down the air vent system. The methods are used to calculate time-dependent flow and pressure drop for two stations in Quebec, producing results in good comparison with field measurements. In the penstock, water jet intensifies in the first half of the closure time period, whereas air pressure drops in the last one third of the time period. Air entrainment is an important cause of pressure drop. The methods are useful for planning air-vent upgrades and safe closure operations. [ABSTRACT FROM AUTHOR]

The wider scale use of aerated water for irrigation has been limited by dis-uniformity of aeration in the field, limited longevity of oxygen in irrigation water and lack of knowledge of what oxygen concentration brings optimal growth. Two options are presented for increasing dissolved oxygen (DO) in irrigation water: Venturi (VT) and fluidic oscillator (FO) aeration systems. Sweet corn was grown in pots to evaluate the effect of aerated water. Compared to the control treatment (CK), VT and FO showed an increase in irrigated water DO in the irrigation tank and feeding pots after aeration. Incorporation of surfactant in the irrigation water significantly improved DO level for the VT and FO treatment. Typically the DO levels reached a peak when the pump is turned off and then decline to a minimum after 24 h. The VT and FO systems had a higher magnitude and duration of the DO level in the water in all treatments compared to the CK system. The FO aeration maintained the longest duration of elevated DO in the water by a factor of two compared to the VT aeration. Compared to the CK, the best result on longevity and DO concentration was achieved using 4 ppm of a non-ionic surfactant. The corn biomass was significantly greater for the VT compared to both the FO and CK treatments. [ABSTRACT FROM AUTHOR]

The oxidation process of dissolved iron particles in water changes the iron into red-brown solid particles (particulate), which settle down in the water. Those large particles that settle down in the water can be handled. Nevertheless, iron that does not procedure large enough particles to settle down remains suspended (colloidal iron) and thus leaves the water with red tint. Unfortunately, these particles threat the industry and the municipal of water supplies. This is due to formation of scales as well as blockage of water pipes that lead to economic problems. Numerous studies have been conducted to study the effect of using oxidation processes followed by the filtration process only for the removal of iron from water. This study introduces a comparison of filtration of aerated raw water though a filter of sand bed with and without Alum as a coagulant prior to filter. A synthetic iron dozes are added to tap water to represent a pre-determined different concentrations of iron as 2 and 3 mg/L which result in 14 and 32 NTU, respectively, after aeration of raw water. The effluent of water was taken at regular time intervals to monitor the progressive rate of removal of these elements for different values of filtration rates 120, 180 and 240 m3 /m2 /day. A single layer gravity rapid sand filter was used with sand bed of 70 cm thickness, effective diameter of 0.7 mm and uniformity coefficient of 1.57. During the experiments, the iron concentration and turbidity in the effluent were recorded at all the used filtration rates. The results show that the low limit of the removal efficiency of iron is 89% and the high limit is 97% without coagulation and 78% to 97% with coagulation. Also, the higher the concentration of iron and turbidity, in the influent, the higher the efficiency removal of filter for all filtration rates takes place. For all tested parameters of influent iron concentrations and filtration rates, the effluent iron concentrations and effluent turbidities within the allowable limits of Egyptian drinking water specifications (0.3mg/l for iron and 1.0 NTU for turbidity), except for filtration rates exceeds the 180m3/m2/day the turbidity was above these allowable limits for both cases using coagulant or not. It obvious, also, from experiments that at low concentration of influent iron (below 3 mg/l) and filtration rates up to 180m3/m2/day there is no need to coagulation process. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of a complete stirred and aerated reactor for deliberate phosphate precipitation as struvite from anaerobic sludge in a domestic wastewater treatment plant and, to achieve the optimum operational conditions in order to reduce the potential formation of struvite downstream of the digester and decrease the phosphate (P) and nitrogen (N) load on the treatment plant. The reactor was fed with anaerobic sludge and operated at different hydraulic retention times (HRT) and aeration rates. Theoretical calculations indicated that a minimum pH of 7.5 would be necessary to attain struvite precipitation to its potential. To reach this pH value, a minimum HRT of 1.0 h with aeration flow rate of 46.7 m3air/h/m3reactor was necessary. Struvite precipitation kinetics were observed to be much faster than other minerals that can precipitate and a decrease in HRT promotes a precipitate richer in struvite. An increase in the HRT to 2.0 h, for the same aeration rate led to a higher phosphate precipitation with calcium. However, for all HRT and air flows studied, the precipitate obtained can be considered to be poor in struvite (maximum 0.72 mmol/l) and it was responsible for around only 4 and 0.5% decrease in the phosphate and ammonia load on the plant, respectively. [ABSTRACT FROM PUBLISHER]