Aeration Basin Research Articles

Performance and life cycle assessment of moving-bed biofilm and integrated fixed-film reactors to upgrade activated sludge systems

Upgrading the capacity of existing wastewater treatment plants (WWTPs) is hindered by the limited space for extension. This matter is particularly crucial in developing countries where dense urban areas experience unexpectedly growing populations. Herein, we study the capacity upgrading of a WWTP working by a conventional activated sludge (CAS) system from 180,000 m3/d to 240,000 and 300,000 m3/d. The WWTP case study focuses on a large plant in Mansoura, Egypt, requiring capacity upgrades to accommodate population growth. For this purpose, we used mathematical modeling to simulate current and suggested WWTP designs. Moving bed biofilm reactor (MBBR) and integrated fixed film-activated sludge (IFAS) systems were designed to increase the WWTP capacity to 240,000 and 300,000 m3/d by the addition of plastic biofilm carrier to 25% and 50% of the aeration basins, respectively. IFAS outperformed conventional and MBBR systems in terms of BOD, COD, TSS, NH4, TP, and PO4, in addition to increased capacity. We moreover used life cycle assessment (LCA) to comprehend the environmental favorability of upgrading scenarios. The most affected environmental categories are global warming and eutrophication due to the operation stage (especially electricity). Global warming potential for CAS, MBBR, and IFAS (300,000 m3/d) are 2.19, 1.69, and 1.73 kg CO2 eq respectively. Eutrophication potential for CAS, MBBR, and IFAS (300,000 m3/d) are 0.0025, 0.0022, and 0.0017 kg PO4- eq respectively. We also estimated the amortization and running costs for various upgrading scenarios, providing an integrated analysis for decision-making purposes.

Removal of per- and polyfluoroalkyl substances from wastewater via aerosol capture

The widespread use of per- and polyfluoroalkyl substances (PFAS)-containing products in numerous commercial and industrial applications has resulted in their occurrence in wastewater treatment plants (WWTPs). Herein, proof-of-concept bench-scale experiments were performed to measure the extent to which PFAS could be removed from a WWTP if aerosols generated during aeration were captured. Experiments were designed to mimic the aeration rate:water volume ratio, the water volume:surface area ratio, and aeration bubble size applicable to the full-scale aeration vessel. Results showed that substantial (75%) removal of perfluorooctane sulfonate (PFOS) was observed under these operating conditions in the bench-scale system; up to 97% PFOS removal was observed if the aeration rate was increased 3-fold. PFAS removal generally increased with increasing aerosol capture and with increasing PFAS surface activity. Analysis of semi-quantified PFAS showed that the semi-quantified PFAS accounted for approximately 93% of the identified PFAS in the raw wastewater, dominated largely by the presence of 2:2 fluorotelomer carboxylic acid (2:2 FTCA). This preliminary study suggests that aerosol capture in aeration basins has potential for mitigating PFAS in WWTPs. Further testing is needed to assess the feasibility of this approach at the field scale.

Some Chemical Properties of Wastewater from the Pharmaceutical Production Processes in the State Company for Drug and Medical Appliances Samarra

The study was conducted during six months, from September 2022 to February 2023, in the General Company for the Industry of Medicines and Medical Supplies in Samarra, one of the companies affiliated to the Ministry of Industry and Minerals. For the purpose of evaluating the efficiency of the biological treatment units for the liquid waste disposed by the company, the water discharged to the treatment units was divided into four sampling stations. : Primary collection basin water or equalization basin (water resulting from industrial processes), aeration basin water (water treated in the treatment unit), sedimentation basin water (water leaving the treatment plant) and liquefaction water (water entering the company). The study includes two aspects: the first is related to the measurement of the chemical properties of the water of the four stations, while the second aspect is that some water determinants were studied and local and international standards and classifications were adopted to compare them. The chemical parameters included pH, dissolved oxygen, biological oxygen requirement, total alkalinity, total hardness, and chloride. The results showed that the pH values tended to be low alkaline with a limited range of variation, as it ranged between 7.1-8.3, while the dissolved oxygen value ranged between 7.0-4.0 mg/l, and the biological oxygen requirement ranged between 1.0-95 mg/l. The results indicate that the values of BOD5 increased in the stations (St.1, St.2, and St.3), in contrast to the station (St.4) for the liquefied water, as it recorded very low values, with significant temporal and spatial differences in most stations within months. the study. As for the total alkalinity, it ranged between 110-200 mg/l in terms of CaCO3 and showed significant temporal and spatial differences in most stations during the months of the study. While the chloride values ranged between 38-255 mg/l. The results of the current study showed a significant variation in the chloride values from one month to the next. The study also confirmed that the chloride values increased during the winter compared to the summer.

Comparative assessment of different scenarios for upgrading activated sludge wastewater treatment plants in developing countries

Improvement of current wastewater treatment plants (WWTPs) to accommodate the growing influent flow rate and cope with the increasingly stringent regulations is hindered by the allowed space and the difficulty of changing the design parameters. Mathematical modeling is a useful tool for assessing the performance of WWTPs in light of broadening objectives. We herein explore the utilization of mathematical modeling to improve effluent quality in conventional activated sludge systems. BioWin was used to model Mansoura WWTP, one of the largest WWTPs in Egypt. Lab records, design reports, and additional analyses were conducted through site visits and a comprehensive sampling campaign. The wastewater was characterized, and the plant-wide model was calibrated following the protocol of the Dutch Foundation for Applied Water Research STOWA. Important kinetic and stoichiometric parameters were identified and adjusted during the calibration process. The model validity was assessed using different validation periods considering average relative deviation (ARD) values below 20 % as acceptable. The optimized nitrification and denitrification processes involved 16 scenarios with different operational conditions. By changing some zones in the aeration basin from aerobic to anoxic and increasing the return activated sludge, the average ammonia and nitrate concentrations were significantly reduced from 23.06 and 0.5 mg/L to 4.64 and 0.07 mg/L respectively. Furthermore, phosphorus removal optimization was carried out through biological and chemical processes. Chemical phosphorus removal was 85.76 % by using a coagulant dosage of 25 mg/L, resulting in an effluent concentration of 1.04 mg P/L. Biological phosphorus removal was increased to 85.43 % by modifying the volume of anaerobic and aerobic zones with lower power consumption. Overall, this study demonstrates the effectiveness of mathematical modeling in enhancing effluent quality and reducing energy consumption to meet stringent wastewater treatment regulations.

Adsorption process modeling to reduce COD by activated carbon for wastewater treatment

Investigations have been carried out on the utilization of Activated Carbon (AC) in adsorption processes for the wastewater treatment of industry and municipal. Sulfides materials, phenols and furfural is a toxic compounds in wastewater from refineries can adversely affect the performance of biological aeration basins in reducing COD levels. This work aims to provide the effectiveness of AC in reducing the COD level of the effluent from the Dissolved Air Flotation (DAF) unit to meet standards of environments protecting and pass the design of wastewater treatment plants. A dynamic adsorption model was developed based on the dispersion of axial in the AC packed bed, assuming that the LDF (linear driving force) model in to the adsorbents is agreed to mass transfer. The model's predictions of chemical oxygen demand breakthrough curve concentrations showed excellent agreement with experimental data. The sensitivity analysis of operational conditions such as flow rate, inlet concentration of COD and bed length was used to gain a better understanding of the optimal design of an AC fixed bed. The results suggest that an AC fixed bed can complement biological treatment of wastewater and address the challenges faced by biological basins in oil refineries.

Production, Application, and Efficacy of Biodefoamers from Bacillus, Aeromonas, Klebsiella, Comamonas spp. Consortium for the Defoamation of Poultry Slaughterhouse Wastewater

Activated sludge (AS) treatment systems’ major limitation is the nuisance foaming at the surface of the aeration basin in wastewater treatment plants (WWTPs). This foam can be stabilized by biofoamers and surfactants in the wastewater to be treated. In order to control foam, synthetic defoamers are used; however, these defoamers are toxic to the environment. This study aimed to optimize the production of biodefoamers by quantifying foam reduction efficiency and foam collapse by the isolate pervasive to poultry slaughterhouse wastewater (PSW). Before their identification and characterization, nine bacterial isolates were isolated and assessed for foam reduction efficiency. These organisms produced minute biodefoamers under various conditions generated on the response surface methodology (RSM). The isolates that produced biodefoamers with high foam reduction efficiency and at a lower foam collapse rate were Bacillus, Aeromonas, Klebsiella, and Commamonas spp. consortia. At 4% (v defoamer/v PSW), the crude defoamers produced by the consortium had 96% foam reduction efficiency at 1.7 mm/s foam collapse rate, which was comparable to 96% foam reduction efficiency and 2.5 mm/s foam collapse rate for active silicone polymer antifoam A/defoamer by Sigma-Aldrich, a synthetic defoamer. At 2.5 mm/s, all of which were achieved at pH 7 and in less than 50 s. The application of the biodefoamer resulted in sludge compacted flocs, with filament protruding flocs observed when a synthetic defoamer was used. The biodefoamer showed the presence of alkane, amine, carboxyl and hydroxyl groups, which indicated a polysaccharide core structure. The 1H NMR analysis further confirmed that the biodefoamers were carbohydrate polymers. This study reports for the first time on the efficiency and comparability of a biodefoamer to a synthetic defoamer.

Enhancing resource recovery via cranberry syrup waste at the Wisconsin Rapids WRRF: An experimental and modeling study

The Wisconsin Rapids Wastewater Treatment Plant (WRWWTP) is faced with a more stringent effluent phosphorus requirement that will drive capital investment between 2020 and 2025. The facility will need to achieve a monthly average value of 0.36 mg L−1 of total phosphorus (TP). While the facility has sufficient influent carbon to drive a conventional enhanced biological phosphorus removal (EBPR) configuration, the existing infrastructure makes the addition of influent selector zones cost prohibitive. Underutilized aeration basin capacity was repurposed for testing return activated sludge (RAS) fermentation. The WRWWTP began pilot testing of RAS fermentation in April 2021. The facility moved through a series of operational setpoints to optimize phosphorus removal in a sidestream RAS (SSR) configuration, including RAS diversion, decrease of DO in aeration basins and chemical dosing shutoff. One of the key implementations was the addition of cranberry syrup waste to provide additional carbon for RAS fermentation, converting the process to a SSR plus carbon (SSRC) configuration. By the end of the testing period, effluent total phosphorus was averaging less than 0.4 mg L−1 with no chemical addition. A model was developed in the SUMO platform and was used to capture orthophosphate trends during the testing period. The model investigated microbial population dynamics and found that the operational changes including RAS diversion, chemical dosing shutoff and cranberry syrup waste addition impacted the enrichment of phosphorus accumulating organisms (PAO). After performing a sensitivity analysis on hydrolysis parameters, the predicted hydrolysis rate around 1.8–1.9 mg COD g VSS−1 hr−1 was found to match the batch rate testing data. This is the first study where cranberry syrup waste was used to successfully enhance EBPR performance, resulting in 90% TP removal. While further research is needed regarding the composition of the waste matrix and the microbial community composition, this expands the routes for resource recovery in the field of wastewater treatment.

Jet flow in hydraulic-jump-stepped spillways: experimental study

Abstract A hydraulic-stepped spillway was designed using an aeration basin to provide aerated flow to the stepped spillway utilizing a hydraulic jump. However, the flow through the entrance of the stepped spillway might separate from the first step top and impact the downstream steps at a large unit discharge, causing a so-called jet flow. A new experimental study was conducted to better understand the jet flow in the hydraulic-jump-stepped spillway with comparisons with conventional stepped spillways. The results showed that the critical condition required for the formation of the jet flow was close to the geometric parameters of the upstream aeration basin. Among these parameters, the height of the reverse step had a more significant effect on the local flow pattern, thus lowering the risk of jet flow. The relationships between the critical condition and the geometry of the aeration basin suggested that the Froude number at the entrance of the stepped spillway was the key parameter forming the jet flow. Compared with conventional stepped spillways, the hydraulic-jump-stepped spillway could effectively extend the practical application for large unit discharges by providing a better understanding of jet flow conditions.

Activated sludge bio-aerobic process to treat sugar industry effluent

Abstract The sugar industry effluent (SIE) is characterized as high organic load. The aim of this study is to treat SIE by bio-aerobic process in batch and continuous mode in bio-aeration reactor. In batch process, effect of hydraulic retention time (HRT) in terms of effluent fill volume, and in continuous process, effect of HRT in terms of effluent feed rate was studied. In batch process, HRT of 2.5 d (fill volume = 0.8 dm3) was found to be the best and in continuous process, HRT of 1.37 d (feed rate = 133 mL/h) was found to be the best. The chemical oxygen demand (COD) reduction by bio oxidation followed first order kinetics with respect to COD and the rate constant (K) was evaluated as 5.197 d−1. The sludge yield coefficient (a) and sludge endogenous oxidation coefficient (b) were also evaluated from sludge formation studies, which are 0.4 (gm VSS produced/g COD removed) and 0.1 (g VSS oxidized/day. g MLVSS in the aeration basin), respectively. In continuous process, the COD reduction of 83.12% of 4800 mg/dm3 and BOD reduction of 88.70% of 1240 mg/dm3 were obtained at HRT = 1.37 d. The results of the experiments show the SBR process to be an effective process for the treatment of SIE.

Optimizing Power Reclamation of Micro Hydro Turbines in WWTPs Aeration Basins

Abstract This study investigates the optimum operating conditions and design configurations that can optimize the power reclaimed by small hydro turbines derived by the rising water-bubble current. The rising current is generated by the compressed air introduced by the diffusers at the bottom of aeration basins of Wastewater Treatment Plants (WWTPs). While optimizing the power production, the standard oxygen transfer efficiency (SOTE) is monitored since it is a significant parameter that cannot be sacrificed in the operation of WWTPs. Using one set of turbine blades, it was found out that the highest velocity is obtained in the upper half of the water column (70% - 80%). In contrast, the lowest velocities were obtained just above the air diffuser and at the water surface. Testing started with using a single turbine (ST) to determine the location of the optimum power reclaimed at each tested airflow (1.18, 1.42, 1.65, and 1.89 L/s). Then using double turbine (DT) and triple turbine (TT) to compare their performance to the ST’s maximum power increased power reclamation. The maximum percentage of increase in power reclamation for DT is 19.59%, while it is 20.24% in the case of TT. At a commonly used airflow in WWTPs (1.42 L/s), the optimum configurations of DTs and TTs were selected to investigate the effect of having the proposed setup on the SOTE. For membrane diffusers, DTs and TTs limited the dispersion of the air bubbles in the tank, therefore, reducing the SOTE (8.3% for DT and 3.7% for the TT). The ceramic and sharp-nub diffusers were also tested versus rubber membrane ones to determine the effect of using the ceramic and sharp-nub diffusers on the power reclamation and SOTE. Ceramic diffusers neither achieve higher power reclamation than the membrane nor increases the SOTE. In contrast, sharp-nub diffusers increase the SOTE for all configurations compared to membranes, but this came into account of power reclamation, where sharp-nub diffusers cause a DT and a TT to produce less power than ST does.

Comparative Study of the Biological Degradation of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) Microbeads in Municipal Wastewater in Environmental and Controlled Laboratory Conditions.

From April to June 2019, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3(HA)) microbead samples were exposed to an operational wastewater reclamation facility (WWRF) in an aerobic aeration basin in Athens, Georgia. Samples were withdrawn from the facility over a 13-week timeframe, and the particles were examined by Raman microscopy and thermogravimetric analysis/mass spectroscopy (TGA/MS) coupled with differential scanning calorimetry (DSC). The activated sludge from this facility was also used as an inoculum to examine carbon mineralization under controlled respirometry experiments to corroborate biological degradation rates determined from both the environmental and laboratory approach. Respirometry, Raman microscopy, and TGA/MS-DSC methods all measured similar biodegradation timelines for microbeads bound to an epoxy substrate, indicating that the three methods are temporally comparable and may be used to measure material biological degradation. Samples of epoxy-bound P3(HA) microbeads, free microbeads, the P3(HA) film, and poly(lactic acid) (PLA) film demonstrated carbon mineralization of 90.0, 89.4, 95.0, and 8.15%, respectively, relative to the cellulose positive control. Using a modified Gompertz growth model, the biological degradation rate coefficients (Rm) were determined for cellulose, P3(HA) film, epoxy-bound P3(HA) microbeads, and free P3(HA) microbeads and found to be 31.6, 30.2, 17.5, and 18.7 mL CO2·g-1·day-1, respectively. Moreover, P3(HA) microbeads can efficiently mineralize in WWRF infrastructure at a rate comparable to cellulose.

Experimental Investigation of the Hydraulic Performance of a Hydraulic-Jump-Stepped Spillway

For a traditional stepped spillway, low energy dissipation and cavitation damage may occur when the unit discharge is larger than a limit due to reduced air entrainment in the flow. In the present work, a new type of stepped spillway called hydraulic-jump-stepped spillway (HJSS) was developed, and the air was efficiently entrained into the flow by means of a hydraulic jump in the aeration basin, which was an aeration element of this stepped spillway. Compared with the traditional stepped spillway, various aspects of the hydraulic performance of the HJSS were experimentally investigated, including the flow pattern, energy dissipation, air entrainment characteristics and time-averaged pressure. Physical model results demonstrated that the HJSS achieved a higher energy dissipation, a more favorable air entrainment performance, and a more reasonable pressure distribution. The HJSS successfully increased the unit discharge from 50–60m2/s for a traditional stepped spillway to 101.47 m2/s.

Cocultivation of an ultrasmall environmental parasitic bacterium with lytic ability against bacteria associated with wastewater foams.

Many wastewater treatment plants around the world suffer from the operational problem of foaming. This is characterized by a persistent stable foam that forms on the aeration basin, which reduces effluent quality. The foam is often stabilized by a highly hydrophobic group of Actinobacteria known as the Mycolata1. Gordonia amarae is one of the most frequently reported foaming members1. With no currently reliable method for treating foams, phage biocontrol has been suggested as an attractive treatment strategy2. Phages isolated from related foaming bacteria can destabilize foams at the laboratory scale3,4; however, no phage has been isolated that lyses G. amarae. Here, we assemble the complete genomes of G. amarae and a previously undescribed species, Gordonia pseudoamarae, to examine mechanisms that encourage stable foam production. We show that both of these species are recalcitrant to phage infection via a number of antiviral mechanisms including restriction, CRISPR-Cas and bacteriophage exclusion. Instead, we isolate and cocultivate an environmental ultrasmall epiparasitic bacterium from the phylum Saccharibacteria that lyses G. amarae and G. pseudoamarae and several other Mycolata commonly associated with wastewater foams. The application of this parasitic bacterium, 'Candidatus Mycosynbacter amalyticus', may represent a promising strategy for the biocontrol of bacteria responsible for stabilizing wastewater foams.

Effect of Magnetic Fields on the Sludge Properties in the Aeration Basin of the Activated Sludge Treatment Process

Purpose: Sludge management is one of the most important problems in wastewater treatment plants (WWTPs) and an activated sludge treatment process. Excessive growth of filamentous bacteria may cause, less dense floc structure, poor sludge compaction, slow settling, and wash-out solids from the final clarifiers. Sludge volume index (SVI) is an unknown method and the most appropriate parameter to express and estimate the settling characteristics of the sludge. The use of chemical materials to increase the volume of sludge is custom, but these methods are expensive and are not a green process. In recent years, the use of integrated treatment methods such as the use of magnetic fields (MFs) with biological methods, to accelerate the growth of microorganisms has become common. Methods: In this case and control study use of MFs (from 0.19 to 3.21mT) to decrease SVI (30 minutes time to settling) or enhancement of sludge, considered. Results: Based on the result of this study by increased the intensity of MFs, a decrease in SVI (0.03 to 53 percent) happened statistically. Conclusion: One of the main, physical, and practical methods to reduce the huge volume of sludge by decrease SVI in WWTPs can be used by applying MFs.

The Power Reclamation of Utilizing Micro-Hydro Turbines in the Aeration Basins of Wastewater Treatment Plants

Abstract Upgrading the aeration basin technology can improve the oxygen transfer efficiency (OTE), while keeping the energy consumption at its minimum level. Therefore, this paper introduces a new idea of installing micro-propeller turbines in the aeration basin of a wastewater treatment plant (WWTP) to extract power from the high-velocity location in the water column. This extracted power can be used to operate a mixer at the top of the membrane to induce the mixing in that region, which will drive the less oxygenated wastewater into the water column. The rest of the extracted power will rotate microturbine rotors for electric power generation. By applying the proposed microturbines to the 13 audited facilities, it was demonstrated to achieve a gross annual energy-savings of 3,836.9 MWh, a gross annual cost-saving of $260,497, and total CO2 emissions that would be reduced by 2,714 metric tons/year. Generally, the addition of the proposed microturbines can save up to 15.7% of the annual plant electricity consumption (1.3–12.8% of the plant annual electricity bills).

Energy management platform for integrated battery-based energy storage – solar PV system: a case study

This study develops an energy management platform for battery-based energy storage (BES) and solar photovoltaic (PV) generation connected at the low-voltage distribution network. The sewage treatment plant of Gujarat International Finance Tec-City located in the Gujarat state is considered as a testbed. The contribution of this case study is twofold: (i) Formulation and lab-scale implementation of an optimal scheduling algorithm to charge/discharge BES while minimising the net energy purchase cost. (ii) Development of a fuzzy logic-based speed control strategy for aeration blower to enhance the process efficiency. A stochastic optimisation problem was formulated as mixed-integer linear programming to achieve the charging and discharging schedules of BES. The simulation study on speed control of aeration blower was carried out to demonstrate the air injection control for optimal dissolved oxygen level in the aeration basin at the testbed. Simulation results of the case study and lab-scale hardware realisation (through real-time digital simulator interfaced with modular hardware) were presented to validate the demand- and supply-side energy management platform.

Process Design of Ammonia Separation for Nitrification Control in Aeration Basins at an IKORC’s Oily Wastewater Treatment Unit

In the current decades, water shortage is well understood as one of the main limiting factors for oil industry development all over the world. One of the available and reasonable solutions is reusing wastewater. The oily wastewater treatment unit of the IKORC oil refinery provides a portion of the makeup water for cooling towers, applying physical, biological, and chemical treatments. Ammonia shocks are the only crisis that disrupts the nitrification process. This condition eventuates in destroying the microorganisms of aeration basins and leads to a high ammonia containing effluent. In order to protect the aeration process, it is mandatory to apply a suitable system for removing excess ammonia. In this study, at first, ammonia removal history is reviewed. Then quantity and quality of the oily sewer are investigated. Because of high volatility of ammonia contamination and high TDS, a stripping tower with air is selected among diverse solutions. Taking into account the principles of project econometrics, operating parameters such as stripping factor, pressure drop, tower volumetric flow rate, and number of towers are determined. Then, the process is designed and its environmental survey is conducted. Finally, calculating indices proved that this project is economically profitable in addition to its environmental benefits.

Impact of Ammonia-Based Aeration Control (ABAC) on Energy Consumption

An Ammonia-Based Aeration Control (ABAC) system is installed in the primary aeration basins of a regional wastewater treatment facility. The energy consumption of the system of air blowers, measured in kilowatts per hour by an existing meter, is analyzed for seven months after the installation of the ABAC system and compared to system performance prior to commissioning of the ABAC system. Processed data, including volume flow rate, ammonia loading, and treatment equipment efficiency, are evaluated for periods before and after the ABAC system installation. Ammonia mass loading and air transfer ratio in the aeration basins are determined to be the leading factors affecting the performance of the ABAC system and thus impacting the metered energy consumption. The metered energy consumption data are normalized by the two calculated ratios, which reflect the change in ammonia loading and air transfer ratio. The normalized and metered energy consumption data are compared, and the results show a reduction in energy consumption since the installation of the ABAC system. A yearly savings of approximately 9 ± 1% in energy costs is estimated with the installation of the ABAC system. The savings in energy consumption calculated as well as the improvements in nitrification efficiency confirm the benefit of an ABAC system in reducing operation costs and enhancing process control.

Uniform flow and energy dissipation of hydraulic-jump-stepped spillways

Abstract In skimming flow, a uniform flow can be achieved and the flow depth, velocity and air concentration remain constant if a stepped spillway is sufficiently long. In this study, physical model experiments were performed to investigate the uniform characteristics and energy dissipation of a hydraulic-jump-stepped spillway, which is a new type of stepped spillway for increasing the unit discharge capacity and energy dissipation. Based on the redefinition of uniform flow, experimental results show that at a given stepped spillway slope, a smaller height for the beginning of the uniform flow region, a greater uniform aerated flow depth and a greater uniform equivalent clear water flow depth can be obtained as compared with the traditional stepped spillway due to strong aeration in the aeration basin. Under the condition of uniform flow, the energy dissipation rate of stepped spillways can be estimated by the equivalent clear water flow depth with given inflow conditions. Compared with the traditional stepped spillway, the uniform flow over the hydraulic-jump-stepped spillway has a smaller specific energy, revealing that the hydraulic-jump-stepped spillway is more advantageous for dissipating energy, especially at large unit discharges.

Hydraulic characteristics of the aeration basin in a ski-jump-step spillway

AbstractThe ski-jump-step spillway was designed using a ski-jump and an aeration basin to effectively pre-aerate flow in a stepped spillway. A new experimental study of the hydraulic characteristics of aeration basins was conducted to better understanding their pre-aeration properties and mechanisms. The plunge-pool patterns of aeration basins were classified into partially aerated, fully aerated, and vortex expelled, with increasing unit discharge. Relations between the distributions of the time-averaged pressure and the air concentration of the plunge-pools suggested that the ski-jump jet impact and the recirculating vortices are the main causes of plunge-pool air entrainment. Based on the export cross-section of the aeration basins, the bottom air concentrations remained greater than 3.0%. The sidewall air concentrations were greater than 7.5% and followed a logarithmic distribution in the vertical direction, demonstrating that the export flow attains a completely aerated state without any blackwater zones. In addition, increasing the aeration basin length was found to prevent the occurrence of a vortex expelled plunge-pool, thus promoting the appropriate pre-aeration effect under large unit discharges.