Oxidation ditch process is used to treat the municipal and domestic sewage. The untreated sewage generates fouling smell, harmful bacteria, etc. which is hazardous for public health and degrades the environment by librating noxious gases. This paper examines the use of curved blade aerator for oxidation ditch process. The rotor, which controls the aeration, is the main component of the aeration process. Therefore, the objective of this study is to find out the variations in overall oxygen transfer coefficient and aeration efficiency for different configurations of aerators by varying the parameters like speed of aerator, depth of immersion and blade tip angles so as to yield higher values of overall oxygen transfer coefficient and aeration efficiency. Four aerators of different configuration were developed and fabricated in the laboratory and were tested for above mentioned parameters. A mathematical model is developed for predicting the values of kLa and aeration efficiency which has R2 values of 0.97 and 0.99 for experimentally determined and calculated values. In laboratory studies, the optimum value of overall oxygen transfer coefficient and aeration efficiency were observed to be 10.33/h and 2.269 kg O2/kWh for aerator speed of 48 rpm, 5.5 cm depth of immersion and 47o blade tip angle for curved blade aerator.

Soil aeration by imported machines were reportedly unsatisfactory due to creation of shallow holes, taking off some patches of the turf and time consuming work needed for collecting the excavated cores. Considering these problems, a machine was developed to suit Iran’ s lawn spaces. To develop an appropriate aerator, the shape of the plugs was studied at the first step and for this purpose six types of plugs with conical and cylindrical cross section (with and without slot) with tips cut diagonally and perpendicularly were built. The plugs were compared in an experiment based on complete randomized blocks design with 3 replication in an urban lawn space with clay soil in terms of the required static force for cutting the thatch and penetrating to the soil as well as the length of projected cores. The results showed that the conical plugs with beveled tips had a 28 millimeter longer cores than the cylindrical plugs with similar tip using approximately equal forces for insertion. Having chosen the appropriate shape of plug, a split roller with a relatively large diameter were constructed for installing plugs around it and the whole device attached to a walking tractor. Comparing the developed machine with a commercial self-propelled aerator revealed that the developed aerator improved the length of the cores and depth of the holes. The split roller in the machine which windrowed the cores also caused a 65% decrease in labor requirement for collecting the cores and did not have dug patches of turf.

Dam Weirs are used to regulate the water level. About 33 percent of dam failures have occurred due to insufficient capacity of weirs. One way to prevent is to use weir with nonlinear crest, such as labyrinth weir. In this study, the effect of dentate and orifice as well as a combination of both in the weir and in three magnification ratios of 2, 3 and 4 were investigated. The experiments were performed in a rectangular laboratory channel 15 meters long, 0. 8 meters wide and 1 meter high with a flow rate of 10 to 90 liters per second. Nine physical models of weirs were used in this study, which were 3 mm thick, 15 cm high and 40, 60 and 80 cm long. Also, quarter cylinders with a radius of 1. 5 cm were installed as aerators on the simple weir models. The results showed that aerators increase the discharge coefficient up to 13% compared to simple labyrinth weir. But with the increase in flow as well as the magnification of the labyrinth weir, this effect will be very small. Studies showed for L/W= 2 and H/P= 0. 2, the discharge coefficient of orifice-dentate weir and dentate weir are 75. 6 and 17. 5 percent, respectively, more than the simple labyrinth weir. However, dent and orifice may lose their efficiency in high heads and the discharge coefficient will be close to simple labyrinth weir. The reason for these changes is the flow interference in downstream of weir which will be more by creating dentate and orifices. Also, increasing the magnification of labyrinth weir reduces the discharge coefficient, but this reduction in orifice-dentate labyrinth weir is much greater than the other two types of weirs and reaches up to 40%. Therefore, the orifice-dentate labyrinth weir performance at high magnification ratios does not seem appropriate.

Introduction: To protect hydraulic structures like spillways, chutes, and bottom outlets against damage caused by cavitation, the air is usually pumped into the regions with a cavitation index below the critical value. Using the aerators, the erosion of the spillway surfaces caused by cavitation can be eliminated. The aerators are usually mounted on the bottom or the lateral walls of the spillway and cause the separation of high speed flows from the spillway surface and prevent erosion on the rigid surfaces. Most of the experiments have focused on the average air concentration of flow, while the amount of the air and the way it comes out the flow must be determined. Therefore, in the present study, the experimental data presented by Pfister (2007) for numerical simulation of flow over the aerator was used to investigate variations of the air concentration along the chute bottom. FLUENT software was used for the simulation of the two-phase air-water flow. Jump length has been considered as an important and effective factor in entering air into the flow and a criterion for verification. Methodology: According to the importance of the determination of the minimum volume of required air to prevent cavitation damages, the numerical effects of the air concentration during chute has been studied in this research. Eulerian and K-ɛ (RNG) models have been selected for two-phase simulation and for studying the turbulence effect respectively. The structured and unstructured mesh has been reviewed for the meshing model, finally, the use of structured mesh has been considered. As mentioned, the result of Pfister (2007) model has been utilized for validation and the length of the jet in crossflow was the criteria of validation. Therefore, parameters affecting the length of jet flow include the ramps with angels of 5. 7, 8. 1, and 11. 3 degrees, the steps with the heights of 23, 25, 44, 45, and 100 millimeters, the combination of the ramp and the steps, various Froude numbers in the range of 5. 8 to 10. 4, different ramp heights include 0, 6. 7, 13. 3, and 26. 7 millimeters and the chute slopes of 12, 30, and 50 degrees have been studied. The proper estimate of the jump length from the aerators has been simulated for 93 models. Additionally, the bed air concentration during chute and the air concentration at the depth, in the downstream of the impact point, has been modeled using Computational Fluid Dynamics and FLUENT software that can be employed in determining the distance of aerators. Results and Discussion: In this research, the effects of Froude number, the slope of the ramp, the initial height of the flow, the height of the step, and the ramp height on coefficient m has been studied considering the equation of changes in the bed air concentration ( (( / ) 1) m x L jet C C e ). In this equation, Cx/Ljet-1 represents the bed air concentration in the ( / 1) b x L jet point of impact to the chute bottom and m is a coefficient for which sensitivity has been tested. According to the result, air outflow decreases by increasing the Froude number. This shows a reverse trend for aerators with the ramp. Increasing the height of the step speeds up the increasing amount of m as well. The air outflow gradient goes up with the increasing the slope of the ramp so that the air outflow gradient has a significant rise by increasing the step height. The result does not show the specific trend for air outflow gradient as a function of the initial height of the flow. An increase in the step height results in increasing the length of the jump and increases the amount of the air entering the flow and the growth of air outlet from flow also increases. The air outlet gradient rises by increasing the ramp height. After determining the jump length of jet, the rate of the air entering the flow and the variability of the bottom airflow can be investigated by the equations suggested by the authors, accordingly, the appropriate distance between two aerators can be defined. The location of the first aerator is the initial point of cavitation and the distance of the second aerator can be affected by factors as follows: 1. The rate of the air coming out of the downstream of the first aerator 2. Natural aeration of the flow from the free surface. Conclusion: A comparison of the results indicates the numerical and experimental models are compatible. According to the importance of the point of the impact, where the flow collides at the chute bottom (sudden outlet of air due to collision), the point was considered as the reference point for the calculations in the equation. Generally, the results showed that the air concentration downstream of the aerators increases with an increase in Froude Number, ramp height, steps height, and ramp angle. This decreases as the height of water upstream of the aerator increases.

Purpose In soil-based nursery media, topsoil, poultry droppings and sawdust conventionally provide anchorage, nutrientsand aeration, respectively. Considering poultry droppings’ scarcity and sawdust’ s inertness nutrient-wise, more readily availableorganic wastes should be explored as substitutes. Here, we evaluated the effect of such substitution on media fertility, aimed at seeking alternatives to the conventional practice. Methods In a topsoil-manure-aerator volume ratio of 3: 2: 1, poultry droppings was substituted with pig slurry (slurry) orcattle dung (dung) as manure and sawdust with rice-husk dust (huskdust) as aerator, giving seven soil-based media includingreference medium (topsoil+droppings+sawdust) and the control (topsoil+topsoil+topsoil). They were watered regularly andanalysed for fertility parameters 4 months later. Results Reference had the highest pH (8. 60) and topsoil + dung + huskdust/control the lowest (6. 83). Substituting sawdustwith huskdust enhanced pH, organic matter and Mg2+in droppings/dung-amended media (topsoil+droppings+huskdust/topsoil+dung+huskdust) unlike slurry-amended ones where it too reduced total nitrogen (0. 19 vs 0. 11%). The substitution alsoenhanced available phosphorus in topsoil+droppings+huskdust (117. 50 mg kg− 1) and topsoil+dung+huskdust (71. 50 mg kg− 1)but reduced K+in the latter where it too had moderating effects on Na+. Reference surpassed topsoil+slurry+huskdustfor Ca2+, but was surpassed by topsoil+droppings+huskdust for Mg2+. Reference/topsoil+droppings+huskdust andtopsoil+slurry+huskdust/control showed highest and lowest CEC, respectively. Excluding pH, topsoil+dung+huskdust andtopsoil+slurry+sawdust were, notably, consistently similar. Overall, droppings-amended > dung-amended > slurry-amendedmedia and, for available phosphorus only, sawdust-aerated < huskdust-aerated media. Conclusion Based on fertility status 4 months after blending, topsoil+droppings+huskdust could serve as alternative tothe conventional nursery medium, or topsoil+dung+huskdust where near-neutral pH is preferred to increased phosphorus/cations release.

Membrane bioreactors (MBRs) are high-tech systems for water recycling and reusing of unconventional water resources such as municipal wastewater. However, the fouling of polymeric membranes is the main impediment to the market development of MBR. The polyolefin-based membranes are subjected to more severe organic fouling than other hydrophilic membranes due to their inherent strong hydrophobic properties, therefore, proposing efficient, fast, and economic fouling mitigation methods is vital for durable and long-standing performance. In this research, the hydrodynamics of a lab-scale membrane bioreactor with different configurations of aerators and nozzle sizes were used to investigate the air scouring efficiency. It was gained that aerators with higher air flow rates, e.g., 5.5 m/s can produce slug bubbles which are capable of foulant removal from the membrane surface. In comparison with a non-central aerator, the satisfactory scouring zone of the central aerator is narrow and the edge nozzles on both sides of the aerator are blocked. Under constant air flow rate, when the inlet air is injected into the aerator from two and three points, not only the end nozzles are blocked but also the liquid is penetrated into the aerator and the shear stress on the membrane surface decreased to 0.765 Pa. In the case of the non-central aerator, the satisfactory scouring zone becomes wider and neither nozzle blockage nor liquid penetration down to the aerator has occurred. The distribution of bubbles was optically evaluated by video imaging through the transparent plexiglass tank using aerators with different inlet flow rates and various configurations. Numerical simulations and related experimental analyses demonstrated that air inlet velocity has an important role in creating larger slug bubbles. It was shown that a non-central aerator in which the central nozzle in front of the inlet air stream is blocked, produces slug bubbles and sufficient air scoring on the flat sheet membrane. Configuration of a non-central aerator with 4 nozzles not only increased the satisfactory zone of each aerator without blockage of edge nozzles and liquid penetration into the aerator but also provided a higher shear rate over 1.104 Pa under a constant flow rate, which consequently removed the foulant from the membrane surface.

Flow aeration downstream of normal gates in bottom outlet conduits has been found to be an effective and cheap way to eliminate cavitations damages. Studies on aerators have been focused on the question of how much air is entrained into the flow for different geometry of aerators and flow conditions. Designers of the aerators use empirical equations to calculate the quantity of air required by the aerators. The area of the aerator is determined using empirical relationships assuming the air velocity not exceeded a certain values. This paper is based on the results of hydraulic model studies of new bottom outlets recently constructed and examined at Water Research Center of Iran. The results consist of Jareh Karkheh Kosar Dasht-e-Abbas and Eilam bottom outlet dams in Iran. The model studies showed two different mechanism of flow aeration. These mechanisms depend on the geometry of conduits downstream of the gates with respect to the upstream geometry. It is hopped that this information provides a better understanding of the process of aeration for the designers of such structures.

In the present research, the flow on a free dam is modeled in 3D environment of Flow-3D software, then the software results were validated in comparison with results obtained from the physical model. Finally, the effect of various types of ramps on effective factors of vacuum creation was scrutinized. The results for vacuum creation index and air concentration existing within the flow revealed that a spillwaywith ramp at the bed and a wall equipped with duct, and a spillway with ramp at bed and wall, leads to %22, %22 and %19 increase in vacuum creation index, respectively...

The increase of population and demand for water, agriculture and energy cause rapid increase construction of the dam has been. Moreover, the increase of dam height to increase storage and estimate the need for water cause increase the velocity of water over the spillway has been. Spillways, chutes and bottom outlets are important hydraulic structures for dam safety. Due to high velocities combined with low pressures, cavitation damages may occur on chute bottom and cause major damages or endanger the dam stability. Damage experience for flows in spillway tunnels and chutes indicates that damage becomes significant when water velocities exceed 30m/s, this velocity or head can be considered as the borderline for high velocity or high head flows. Introducing air to high-speed flow is necessary to prevent pressure reduction and its events such as cavitation. It is possible to protect spillway surfaces from cavitation damages using aerator devices. Usually, the air entering the flow is not reached to the bed chute. It is necessary to install the first aerated according to topographic conditions and cavitation index at the appropriate location. By determining the process of changing the air concentration of the bed, the distance between the two aerators can be determined. The air in the flow causes the compression and damping that cause Bursting bubbles. In result, the damage caused by cavitation is reduced. So cavitation investigations will be necessary and need to reduce and prevent cavitation damages. The length of the flow jet has a fundamental role in determining the distance between two aerators. With increases the length of the jump, the contact surface of the upper and lower layers of the jet is in more contact with the air and affects the amount of air entering the flow. The absorbed air is removed from the flow after the Jet collision. By determining the minimum concentration of air in the bed, an optimal distance between the two aerations can be selected to prevent cavitation damage. Select the minimum air concentration of bed is based on the relationship provided by Wood (1983). It means that the concentration of average air in the stream is higher, which causes the flow of bulking and requires taller walls for the sides of the shut Which is not economically feasible. The variation in the air concentration of the bed can only be considered as a function of the length of the jump flow and the upstream heights. Creating a suitable duct for providing A negative cavity pressure Lead to better performance that causes increases the distance between aeration. So use of aerators in suitable places and the entrance of air to water flow is a most effective way to reduce this damage, therefore in this study, an equation has been derived to estimate the distance between two aerators base on 1200 data of 90 experiments with R2 more than 0. 84. Results of the present study with distance aerators of the Azad dam based on the minimum air concentration of bed have been compared and investigated.