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.

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.