Surface Aeration Research Articles

Enhanced gas-liquid mass transfer coefficient by bulk nanobubbles in water

Liquid-gas operation explores the widespread applications in multiple chemical processes industries. For an instance, the inclusion of fermentation, dissolved air flotation, paper and pulp processing, sludge decomposition, aeration, ozonation, etc. are majorly covered. Liquid-gas contacting devices are primarily employed to perform their mixing, and the conventional contacting devices envelopes the fine bubble diffusers, jet aerators, surface aerators, static mixers, ejectors, etc. The gas transfer into the liquid is done by bubble formation, and the bubbles furthermore diffuses into the bulk liquid. The bubble size plays an important role in the transfer of gas, lower the size of bubbles, more is the rate of gas transfer, such as the mass transfer coefficient is remarkably enhanced by microbubbles when compared with milli-bubbles. In this work, we created O2 nanobubbles by sparging oxygen gas into nanopores, and during the production of nanobubbles, we examined the oxygen gas volumetric mass transfer coefficient (kLa) into the water. Nanoparticle tracking analysis was used to determine the population and size of nanobubbles, and we found that the population of nanobubbles is in the order of 107 bubbles/mL, with a mean diameter of 100–200 nm. The gassing out technique determines the volumetric mass transfer coefficient (kLa), and the influence of gas flow rate on the volumetric mass transfer coefficient (kLa) has been demonstrated to be positive. The volumetric mass transfer coefficient (kLa) in the case of nanobubbles is found significantly larger than that of microbubbles, ranging from 2.2 to 3.8 min−1.

Research on the optimal submergence depth of the surface aerator in an oxidation ditch by computational fluid dynamics method

Research on the optimal submergence depth of the surface aerator in an oxidation ditch by computational fluid dynamics method

Performance and Sustainability Assessment of Full-Scale Sewage Treatment Plants in Northern India Using Multiple-Criteria Decision-Making Methods

In this study, an intensive performance assessment of 36 sewage treatment plants (STPs) is carried out. The STPs were based on the process technologies: moving-bed bioreactor (MBBR), sequencing batch reactor (SBR), waste stabilization pond (WSP), and upflow anaerobic sludge blanket reactor (UASB) with posttreatment technologies of extended aeration (EA), surface aeration, and polishing ponds, with treatment capacities of 3 to 40 million L per day. The pollutant removal performance of the STPs was ranked using the gray relational analysis method, which revealed that the SBR systems ranked higher, followed by UASB with EA, whereas MBBRs, UASB with other posttreatment options, and WSP performed satisfactorily to poor. Further, the preference ranking organization method for enrichment evaluation (PROMETHEE) multiple-criteria decision-making (MCDM) approach using the fuzzy analytic hierarchy process followed by preference ranking organization method for enrichment evaluation method evaluated the major wastewater treatment technologies using three sustainability criteria: environmental, economic, and technical aspects. The MCDM method evaluation revealed that the UASB + EA method, with its lower greenhouse gas emissions, energy requirement, sludge generation, and energy and resource recovery characteristics, outranked other treatment technologies, followed by SBR. The MCDM results were later confirmed using geometrical analysis for the interactive aid method. Hence, this study summarizes that the anaerobic process followed by microaerobic technologies still possesses the capability to achieve stringent disposal standards almost equivalent to intensive aerobic technologies.

Controlling Eutrophication via Surface Aerators in Irregular-Shaped Urban Ponds

Surface aerators have often been introduced in urban ponds for esthetics, but their roles in remediating water quality are less understood. Effects of surface aerators on controlling eutrophication were examined in two urban ponds, in which anaerobic odors and cyanobacterial blooms had occurred and several aerators had been installed. In one of the ponds, a dramatic improvement in dissolved oxygen (DO) (from 1.8 to 8.1 mg L−1) and total phosphorus (TP) (from 1.6 to 0.4 mg L−1) was evident based on the comparison before and after the aeration. Although cyano-bloom did not occur, phytoplankton was dominated by cyanobacteria Microcystis species in both periods. Chlorophyll a (Chl-a) increased (from 29 to 51 μg L−1) and water transparency decreased (from 81 to 27 cm) after the aeration. In the other pond with an irregular shape, water quality was monitored two years after the installation to examine seasonal variation in trophic state and its spatial variation associated with aerator distribution. The water was mixed vertically well for the whole pond, as indicated by small surface-to-bottom differences in temperature. DO decreased in summer after rainfall but was always >5.7 mg L−1. Total nitrogen (TN) and TP were 0.8–2.3 and 0.03–0.07 mg L−1, respectively, and no cyano-blooms were observed across sites throughout the year. Phytoplankton was dominated by green algae and diatom species, which may be favored by the lower phosphorus level of the pond. Chl-a was higher and transparency was lower in the north side, which had more aerators and less shade from trees and buildings. These results suggest that surface aerators increased DO by vertical and horizontal mixing of water, reduced phosphorus release from sediment, and prevented cyano-bloom occurrence, but they did not improve Chl-a level and transparency. Rather, aeration can promote algal growth, and thus, additional purifying measures such as filtration and contact oxidation are required to further improve the trophic state of these ponds.

Comprehensive investigation of SARS-CoV-2 fate in wastewater and finding the virus transfer and destruction route through conventional activated sludge and sequencing batch reactor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA transmission route was thoroughly investigated in the hospital wastewater, sewage collection network, and wastewater treatment plants. Samples were taken on four occasions from December 2020 to April 2021. The performance of two different wastewater treatment processes of sequencing batch reactor (SBR) and conventional activated sludge (CAS) was studied for virus destruction. For this purpose, liquid phase, solid phase and bioaerosol samples were taken from different units of the investigated wastewater treatment plants (WWTPs). The results revealed that all untreated hospital wastewater samples were positive for SARS-CoV-2 RNA. The virus detection frequency increased when the number of hospitalized cases increased. Detection of viral RNA in the wastewater collection system exhibited higher load of virus in the generated wastewater in areas with poor socioeconomic conditions. Virus detection in the emitted bioaerosols in WWTPs showed that bioaerosols released from CAS with surface aeration contains SARS-CoV-2 RNA posing a potential threat to the working staff of the WWTPs. However, no viral RNA was detected in the bioaerosols of the SBR with diffused aeration system. Investigation of SARS-CoV-2 RNA in WWTPs showed high affinity of the virus to be accumulated in biosolids rather than transporting via liquid phase. Following the fate of virus in sludge revealed that it is completely destructed in anaerobic sludge treatment process. Therefore, based on the results of the present study, it can be concluded that receiving water resources could not be contaminated with virus, if the wastewater treatment processes work properly.

PERFORMANCE EVALUATION OF LOCALLY FABRICATED MECHANICAL SURFACE AERATOR

Experimental analysis for a fabricated Low-Speed surface aerator that can be used in wastewater and water treatment is presented in this research. The designed impeller configuration was tested to determine its power consumption, standard oxygen transfer rate (SOTR), and standard aeration efficiency (SAE). Impeller oxygen transfer and power consumption in a scaled laboratory tank were measured during aeration phase. The impeller was consisting of 8 inclines flat blades with an angle of 45° from center of the disc, was operated at 3 different immersion depths and 5 different rotational speeds for examining the impact of such factors on impeller efficiency. The results recorded that the best standard aeration efficiency for this configuration is (0.206 Kg. O2/KW.hr) at 120rpm and 7cm depth of the submersion, i.e. submersion depth to impeller diameter (h/D) ratio equals 0.175. Submergence depth increase beyond this limit would result in SAE decrease and definitely result into more power consumption.

Characteristics study of ammonia-n and phosphorus in sewage wastewater effluent: a case study of Alkhumrah, Jeddah Wastewater Treatment Plant

Ammonia-N (NH3-N) and Phosphorus (P) pollutions remain highly challenging pollutants to the Saudi environment. The sewerage treatment plant can be one of the main contributors to NH3-N and P pollutants. The main aim of this study is to investigate the concentration of NH3-N and P released from the Al Khumrah wastewater treatment plant in Jeddah. The treatment process used in this treatment plant consists of screening, aerated grit removal chambers, surface aeration, sedimentation and sludge thickening and de-watering via belt filter presses. For this study, primary data of N and P is obtained from the Ministry of Environment & Agriculture, Kingdom of Saudi Arabia. The data is collected from the wastewater treatment plant of Al Khumrah, Jeddah. A total of 101 data is collected for NH3-N and P within a period of 6 months from September 2019 to February 2020. Descriptive statistic was used to analyse the data. It was found that the highest mean concentration of NH3-N and P in the effluent are 4.2 mg/L and 1.7 mg/L respectively. The concentration of NH3-N and PO4 3- in the influent exceeded the maximum limit of 1.0 mg/L stated in General Environmental Regulations and Rules for Implementation (2001) provided by the Kingdom of Saudi Arabia Presidency of Meteorology and Environment. A low effluent concentration is set up by the authorities to meet the requirement of water reuse and recycling. The result has shown that the removal efficiency of NH3-N during the treatment is 55%. However, the removal efficiency of PO4 3- is very inconsistent with the percentage removal varied from 0%-61.5 %. This finding demonstrated that the treatment plant will continuously not be able to comply with the standard discharge limit especially if a higher concentration of NH3-N and PO4 3- entering the treatment plant. In this case, the changes of the current treatment process or addition of tertiary treatment would be needed to ensure the discharge wastewater met the reuse and recycling requirement.

Oxygen Transfer Effects in a Two-Phase System of an Aqueous Phase and Liquid Perfluorochemical Subjected to Continuous Wave-Assisted Agitation in Disposable Bioreactor

Systems of two immiscible liquid phases—aqueous phase (i.e., distilled water (dH2O) or phosphate-buffered saline (PBS)) and liquid perfluorochemical (i.e., perfluorodecalin (PFD))—were subjected to wave-assisted agitation, i.e., oscillatory rocked, in a disposable bag-like container in a ReadyToProcess WAVETM25 bioreactor, to recognize oxygen transfer effects and effectivity of the surface aeration. According to the DoE methodology, values of the volumetric liquid-side mass transfer (kLa) coefficient for dH2O, PBS, dH2O-PFD, and PBS-PFD systems were determined for the whole range of operating parameters of the WAVE 25 bioreactor. A significantly higher maximal value of kLa was found for waving dH2O than for dH2O-PFD (i.e., 0.00460 s−1 vs. 0.00331 s−1, respectively) compared to more equal maximal values of kLa reached for PBS and PBS-PFD (0.00355 s−1 vs. 0.00341 s−1, respectively). The interface development factor (f) depended on the interfacial area a, and the enhancement factor (EPFD), depending on kLa, was introduced to quantitatively identify the mass transfer effects in the systems of waving two immiscible liquids. The phase of PFD was identified as the reservoir of oxygen. Dimensional correlations were proposed for the prediction of the kLa coefficient, in addition to the f and EPFD factors. The presented correlations, and the set of kLa values, can be directly applied to predict oxygen transfer effects reached under continuous oscillatory rocked systems containing aqueous phase and liquid perfluorochemical.

A coupled hydrodynamic‐biokinetic simulation of three‐phase flow in an oxidation ditch using CFD

AbstractCoupling the hydrodynamic and biokinetic models, was done on a lab‐scale oxidation ditch as the bioreactor of the activated sludge process and validated against the available experimental data. The simulation was carried out in three‐phase, three‐dimensional conditions with k‐є and Eulerian–Eulerian methods. A simplified activated sludge model No.1 (ASM1) has been added to transport terms to account for the biokinetic model. Rotatory speed for surface aerator was initially increased and its corresponding effects on solid volume fraction, dissolved oxygen, and velocity profile and values were observed. A 150 rpm increase in the rotational velocity resulted in 36% higher average liquid phase velocity for the one‐aerator arrangement, which was 3% more than that of the two‐aerator oxidation ditch. The 150% increase in the solid volume fraction led to a 10% reduction in the maximum liquid phase velocity. The effect of aerators number has been considered explicitly on baffle performance and liquid phase velocity profile. Finally, a new design for the aerator has been offered that provides an ordered flow field and optimal conditions for the performance of the baffle and oxidation process.

Long-term operation assessment of a full-scale membrane-aerated biofilm reactor under Nordic conditions.

Membrane-aerated biofilm reactor (MABR) technology is an exciting alternative to conventional activated sludge, with promising results in bench and pilot-scale systems. Nevertheless, there is still a lack of long-term and full-scale data under different operational conditions. This study aims to report the performance of a full-scale hybrid MABR located in the North of Europe. Influent, effluent, and exhaust data were collected for 1year (September 2019 to September 2020) using online sensors/gas-analyzers and off-line laboratory analysis. Next, oxygen transfer rate (OTR), oxygen transfer efficiency (OTE), and nitrification rates (NR) were quantified as process indicators. Finally, multivariate methods were used to find patterns among monitored variables. Observations revealed that lower airflows achieved higher OTE at the same values of OTR and OTR was strongly correlated to ammonia/um concentration in the MABR tank (NHx,eff). The dynamics between oxygen concentration in the exhaust (O2,exh) and NHx,eff indicated that a nitrifying biofilm was established within 3weeks. Average NR were calculated using four different methods and ranged between 1 and 2gNm-2d-1. Principal component analysis (PCA) explained 81.4% of the sample variance with the first three components and cluster analysis (CA) divided the yearly data into five distinctive periods. Hence, it was possible to identify typical Nordic episodes with high frequency of heavy rain, low temperature, and high variations in pollution load. The study concludes that nitrification capacity obtained with MABR is robust during cold weather conditions, and its volumetric value is comparable to other well-established biofilm-based technologies. Moreover, the aeration efficiency (AE) obtained in this study, 5.8kg O2 kW h-1, would suppose an average reduction in energy consumption of 55% compared to fine pore diffused aeration and 74% to the existing surface aeration at the facility.

Pollutants removal, greenhouse gases emission and functional genes in wastewater ecological soil infiltration systems: influences of influent surface organic loading and aeration mode.

The influences of influent surface organic loading rate (SOLR) and aeration mode on matrix oxygen, organic matter, nitrogen, phosphorus removal, greenhouse gases emission and functional gene abundances in lab-scale wastewater ecological soil infiltration systems (WESISs) were investigated. In WESISs, intermittent or continuous aeration improved oxygen supply at 50 cm depth and hardly changed anaerobic condition below 80 cm depth, which enhanced chemical oxygen demand (COD), NH4+-N, total nitrogen (TN) removal, the abundances of bacterial 16S rRNA, amoA, nxrA, narG, napA, nirK, nirS, qnorB, nosZ genes and reduced CH4, N2O conversion efficiencies with SOLR of 16.9 and 27.6 g BOD/(m2 d) compared with non-aeration. Increased SOLR resulted in high TN removal, low N2O emission in aeration WESIS, which was different from non-aeration WESIS. High average COD removal efficiency of 90.7%, NH4+-N removal efficiency of 87.0%, TN removal efficiency of 84.6%, total phosphorus (TP) removal efficiency of 93.1% and low average N2O emission rate of 12.8 mg/(m2 d) were achieved with SOLR of 16.9 g BOD/(m2 d) in intermittent aeration WESIS. However, continuous aeration WESIS obtained high average removal efficiencies of 90.1% for COD, 87.5% for NH4+-N, 84.1% for TN, 92.9% for TP and low average emission rate of 13.1 mg/(m2 d) for N2O with SOLR of 27.6 g BOD/(m2 d). Aeration could be an optional strategy for WESISs to achieve high pollutants removal and low CH4, N2O emission when treating wastewater with high SOLR.

An efficient hydrodynamic-biokinetic model for the optimization of operational strategy applied in a full-scale oxidation ditch by CFD integrated with ASM2

Oxidation ditches (ODs) are often used for wastewater treatment. However, limitations of ODs like high energy expenditure and increased sludge sedimentation hinder its wide application. In this study, the computational fluid dynamics (CFD) model integrated with Activated Sludge Model No. 2 (ASM2) was proposed and applied in a full-scale OD. The integrated model provided heterogeneous information on the characteristics of hydrodynamics and biokinetics of OD, especially with respect to the simulation of total phosphorus removal by CFD-ASM2 integration model for the first time. The simulated values of flow velocities, suspended solids (SS), dissolved oxygen, chemical oxygen demand, total nitrogen, ammonium nitrogen, and total phosphorus concentrations were well validated with the measured results, with the standard deviation errors of less than 5.56%, 0.28%, 0.74%, 7.39%, 3.17%, 5.27%, and 7.40%, respectively. Based on the integrated model, four different operational strategies were simulated. The proposed operational strategy of operating 7 surface aerators and 10 submerged impellers not only met the standard discharge requirements (GB 18918–2002) but also consumed less energy by 22.3%, compared with the original strategy of operating 9 surface aerators and 13 submerged impellers. Meanwhile, this proposed operational strategy also reduced the SS concentrations in the second and fourth channels, which was beneficial to elimination of sludge sedimentation. Moreover, the proposed operational strategy was successfully applied and validated in full-scale OD. The foregoing results collectively suggest that the CFD-AMS2 integration model is numerically capable to optimize the operational strategy of ODs.

Generation of aqueous foams and fiber foams in a stirred tank

Generation of fiber foams with surface aeration was studied by simultaneous mixing of pulp fibers, surfactant, air and water in a lab-scale tank. The mixing took place in either transient or turbulent conditions. The effect of impeller type (RT-6 and BT-6), mixing speed, mixing power, and surfactant dosage on air content, bubble size and half-life time of the foam was investigated. Air content increased with increasing agitation power saturating to 50–75% depending on the SDS dosage. The dependence of bubble size on power was a power law with an exponent typical for processes where coalescence plays an important role. The relation between the half-life time and air content was well described by a power law. Power number of the BT-6 impeller was almost constant, and similar to that of pure water in turbulent conditions. The power number of the RT-6 impeller varied and was similarly to gas-liquid stirred tanks, in many cases clearly below that of water. The variability of the power number of RT-6 could be explained with the variation of the mixing Reynolds number.

Evaluation of the Efficiency of Wastewater Treatment Plants in Taiz City and their Suitability for Irrigation

Abstract
 A field study was carried out for influent and effluent wastewater from Two treatment plants in Taiz city. The aim of the study is to evaluate and increase the efficiency of the treatment plants in Al-Buriahy and Nadfood factories (Al-Qurf), in order to ensure the safe and suitable use of wastewater for irrigation. Four samples of sewage were collected from influent and effluent of different locations within the areas of Al-Qurf, Al-Hawjlah, Hidran Al-Dabab and Al-Buraihy. The results of the chemical analysis showed that the samples of the partially treated wastewater compared with the untreated wastewater were higher in total dissolved solids. The values of the trace elements remained at the level of the sewage influent before and after the treatment plant in Al-Buraihy, the level of treatment did not decrease the concentration of a number of these elements. The results of the study indicate that the concentration of Biochemical Oxygen Demand (BOD5) for effluent wastewater from the treatment plants recorded a significant decrease in their values. In contrast the results were close in the concentration of the BOD5 influent from the treatment plant in Al-Buraihy with the BOD5 concentration effluent from the treatment plant in the Nadfood has, reached 457mg/l, because the influent of the sewage from the industrial processes in the treatment plant of the Nadfood was too high, reaching an average of 7791 mg / l compared with 553 mg / l in the municipal influent sewage at the treatment plant in Al-Buraihy. The results of bacteriological analyses showed that the treated wastewater recorded a significant reduction in the number of fecal coliform compared with the number of fecal coliform at influent from treatment plant at Al-Buraihy area.These indications for treatment in wastewater stabilization ponds in Al-Buraihy, and treatment plant for industrial wastewater, that include the aeration and sedimentation units in Al-Qurf Nadfood factories, indicate that the degree of treatment is below the required level and still exceeds the limit allowed for irrigation purposes according to Yemeni and International standards. This suggests an action of rehabilitation of existing sewerage system, completion of the sewerage network and the establishment of the new treatment plant by using stabilization ponds with floating surface aerator in the facultative ponds at north of Taiz City. In addition, increase the efficiency of the current treatment plant by division of wastewater stabilization ponds in Al-Buraihy, into anaerobic, facultative and maturation ponds, providing each pond with two devices/tools to measure the flows, and the establishment of the new treatment plant at the Nadfood factories. It should consist of screening, oil /fat removal, primary and secondary clarifiers, high rate trickling filters (1st and 2nd stage), sludge digester, sand drying beds, and chlorination.
 Keywords: Taiz city, sewage, biochemical oxygen demand, fecal coliform,treatment plant, efficiency, municipal, industrial.

Evaluation of the Efficiency of Wastewater Treatment Plants in Taiz City and their Suitability for Irrigation

Abstract
 A field study was carried out for influent and effluent wastewater from Two treatment plants in Taiz city. The aim of the study is to evaluate and increase the efficiency of the treatment plants in Al-Buriahy and Nadfood factories (Al-Qurf), in order to ensure the safe and suitable use of wastewater for irrigation. Four samples of sewage were collected from influent and effluent of different locations within the areas of Al-Qurf, Al-Hawjlah, Hidran Al-Dabab and Al-Buraihy. The results of the chemical analysis showed that the samples of the partially treated wastewater compared with the untreated wastewater were higher in total dissolved solids. The values of the trace elements remained at the level of the sewage influent before and after the treatment plant in Al-Buraihy, the level of treatment did not decrease the concentration of a number of these elements. The results of the study indicate that the concentration of Biochemical Oxygen Demand (BOD5) for effluent wastewater from the treatment plants recorded a significant decrease in their values. In contrast the results were close in the concentration of the BOD5 influent from the treatment plant in Al-Buraihy with the BOD5 concentration effluent from the treatment plant in the Nadfood has, reached 457mg/l, because the influent of the sewage from the industrial processes in the treatment plant of the Nadfood was too high, reaching an average of 7791 mg / l compared with 553 mg / l in the municipal influent sewage at the treatment plant in Al-Buraihy. The results of bacteriological analyses showed that the treated wastewater recorded a significant reduction in the number of fecal coliform compared with the number of fecal coliform at influent from treatment plant at Al-Buraihy area.These indications for treatment in wastewater stabilization ponds in Al-Buraihy, and treatment plant for industrial wastewater, that include the aeration and sedimentation units in Al-Qurf Nadfood factories, indicate that the degree of treatment is below the required level and still exceeds the limit allowed for irrigation purposes according to Yemeni and International standards. This suggests an action of rehabilitation of existing sewerage system, completion of the sewerage network and the establishment of the new treatment plant by using stabilization ponds with floating surface aerator in the facultative ponds at north of Taiz City. In addition, increase the efficiency of the current treatment plant by division of wastewater stabilization ponds in Al-Buraihy, into anaerobic, facultative and maturation ponds, providing each pond with two devices/tools to measure the flows, and the establishment of the new treatment plant at the Nadfood factories. It should consist of screening, oil /fat removal, primary and secondary clarifiers, high rate trickling filters (1st and 2nd stage), sludge digester, sand drying beds, and chlorination.
 Keywords: Taiz city, sewage, biochemical oxygen demand, fecal coliform,treatment plant, efficiency, municipal, industrial.

The impact of clearance on mixing time for interface-added substrate.

This study was carried out to find the optimum clearance (impeller to bottom distance) for Rushton and pitch-blade turbine impellers in a stirred tank bioreactor for improved substrate mixing time added at interface, taking advantage of computational fluid dynamics. In this regard, the time needed for a thin layer of liquid, resembling substrate-rich or poor part, getting homogenously dispersed within the tank was calculated. The mixing time calculated in this way is called the surface aeration related mixing time (SARMT). SARMT was calculated using two approaches and was compared with each other. For the pitch-blade turbine impeller, a criterion which guarantees accurate mixing time by simulation was not satisfied, so the SARMT profile against clearance was not achieved. For the Rushton impeller, a general descending order of SARMT against impeller-bottom clearance was observed.

Study of the generation and diffusion of bioaerosol under two aeration conditions

Given that studies on actual sewage treatment plants are often affected by environmental conditions, it is challenging to clearly understand the associated bioaerosol generation and diffusion characteristics during the aeration process. Therefore, to enhance understanding in this regard, in this study, bioaerosol generator was used to simulate bioaerosol generation and diffusion under two aeration modes, i.e., bubble bottom aeration and brush surface aeration. The total concentration range of culturable bacteria in the bioaerosol produced by bubble bottom aeration and that produced by brush surface aeration were 300–3000 CFU/m3. Under bubble bottom aeration, the generated bioaerosol was symmetrically distributed around the source point, whereas under brush surface aeration, it was primarily distributed in the forward direction of the rotating brush surface. These bioaerosols from bubble bottom aeration predominantly consisted of particles with sizes below 3.3 μm, particularly those with sizes in the range 1.1–2.1 μm. On the contrary, the bioaerosols produced via brush surface aeration predominantly consisted of particles with sizes above 3.3 μm. The distribution characteristics of population structure in the two aeration modes were consistent with the distribution characteristics of concentration in the corresponding models. Additionally, the results showed that when the aeration process is unaffected by environmental conditions (particle matters, wind direct, wind speed, etc.), the bioaerosol components originate primarily from the parent sewage or sludge, and do not diffuse far from the source point. Therefore, source reduction (capping or sealing) can be recommended as the primary control strategy for bioaerosols in sewage treatment plants. The adoption of such measures will significantly limit the diffusion of bioaerosols, thereby reducing the potential risks associated with human exposure.

Image processing for hydraulic jump free-surface detection: coupled gradient/machine learning model

High-frequency oscillations and high surface aeration, induced by strong turbulence, make water depth measurement for hydraulic jumps a persistently challenging task. The investigation of hydraulic jump behaviour continues to be an important research theme, particularly with regards to the stilling basin design. Reliable knowledge of time-averaged and extreme values along a depth profile can help develop an adequate design of a stilling basin, improve safety, and aid the understanding of the jump phenomenon. This paper presents an attempt to mitigate certain limitations of existing depth measurement methods by adopting a non-intrusive computer vision-based approach to measuring the water depth profile of a hydraulic jump. The proposed method analyses video data in order to detect the boundary between the air–water mixture and the laboratory flume wall. This is achieved by coupling two computer vision methods: (1) analysis of the vertical image gradients, and (2) general-purpose edge detection using a deep neural network model. While the gradient analysis technique alone can provide adequate results, its performance can be significantly improved in combination with a neural network model which incorporates a ‘human-like’ vision within the algorithm. The model coupling reduces the likelihood of false detections and improves the overall detection accuracy. The proposed method is tested in two experiments with different degrees of jump aeration. Results show that the coupled model can reliably and accurately capture the instantaneous depth profile along the jump, with low sensitivity to image noise and flow aeration. The coupled model presented fewer false detections than the gradient-based model, and offered consistent performance in regions of high as well as low aeration. The proposed approach allows for automated detection of the free-surface interface and expands the potential of computer vision-based measurement methods in hydraulics.

Performance of Closed Loop Venturi Aspirated Aeration System: Experimental Study and Numerical Analysis with Discrete Bubble Model

In wastewater treatment plants, aeration plays a significant role as it encourages aerobic respiration of microbes, which are necessary to break down carbonaceous matter in the waste stream. This process can account for the majority of energy use in wastewater treatment plants. The aeration process is also necessary in odor control in lagoons and in the aquaculture industry. Generally, the aeration process is accomplished with compressors or blowers which can be of low efficiency due to ideal gas laws. This study introduces the idea of increasing aeration efficiency by looping water from a reservoir through a piping network which includes a venturi aspirator at its inlet. For this purpose, an experimental study has been conducted in a laboratory setup with a pump which pulls water from a tank, passes it through a Venturi aspirator and a helical piping network intended to increase bubble residence time, before depositing it back into the bulk fluid tank. This same process is modeled computationally, using a discrete bubble method (DBM), with good agreement with experiments. The overall purpose here is to determine the optimal configurations for standard aeration efficiency (SAE) and the standard oxygen transfer rate (SOTR). A parametric study has been implemented using the DBM based on different hydraulic and flow parameters. The model is also used to predict the SAE of a hypothetical aeration system. Results indicate that it is possible to achieve SAE values in the range of surface aerators or submersed jet aerators using the proposed aeration system with less complex components, thereby decreasing overall costs.

Real-time dissolved carbon dioxide monitoring II: Surface aeration intensification for efficient CO2 removal in shake flasks and mini-bioreactors leads to superior growth and recombinant protein yields.

Mass transfer is known to play a critical role in bioprocess performance and henceforth monitoring dissolved O2 (DO) and dissolved CO2 (dCO2) is of paramount importance. At bioreactor level these parameters can be monitored online and can be controlled by sparging air/oxygen or stirrer speed. However, traditional small‐scale systems such as shake flasks lack real time monitoring and also employ only surface aeration with additional diffusion limitations imposed by the culture plug. Here we present implementation of intensifying surface aeration by sparging air in the headspace of the reaction vessel and real‐time monitoring of DO and dCO2 in the bioprocesses to evaluate the impact of intensified surface aeration. We observed that sparging air in the headspace allowed us to keep dCO2 at low level, which significantly improved not only biomass growth but also protein yield. We expect that implementing such controlled smart shake flasks can minimize the process development gap which currently exists in shake flask level and bioreactor level results.