Traditional Aeration Research Articles

Use of Nanobubbles to Improve Mass Transfer in Bioprocesses

Nanobubble technology has emerged as a transformative approach in bioprocessing, significantly enhancing mass-transfer efficiency for effective microbial activity. Characterized by their nanometric size and high internal pressure, nanobubbles possess distinct properties such as prolonged stability and minimal rise velocities, allowing them to remain suspended in liquid media for extended periods. These features are particularly beneficial in bioprocesses involving aerobic strains, where they help overcome common obstacles, such as increased culture viscosity and diffusion limitations, that traditionally impede efficient mass transfer. For instance, in an experimental setup, nanobubble aeration achieved 10% higher soluble chemical oxygen demand (sCOD) removal compared to traditional aeration methods. Additionally, nanobubble-aerated systems demonstrated a 55.03% increase in caproic acid concentration when supplemented with air nanobubble water, reaching up to 15.10 g/L. These results underscore the potential of nanobubble technology for optimizing bioprocess efficiency and sustainability. This review delineates the important role of the mass-transfer coefficient (kL) in evaluating these interactions and underscores the significance of nanobubbles in improving bioprocess efficiency. The integration of nanobubble technology in bioprocessing not only improves gas exchange and substrate utilization but also bolsters microbial growth and metabolic performance. The potential of nanobubble technology to improve the mass-transfer efficiency in biotechnological applications is supported by emerging research. However, to fully leverage these benefits, it is essential to conduct further empirical studies to specifically assess their impacts on bioprocess efficacy and scalability. Such research will provide the necessary data to validate the practical applications of nanobubbles and identify any limitations that need to be addressed in industrial settings.

Research on development and quantitative control preparation technology of array-type microfine bubbles generator

In traditional wastewater treatment, ozone injection efficiency is low. There is a need for the quantitative preparation of ozone-based microfine bubbles to balance bubble stability and ozone reactivity. To address this, we developed coaxial and T-type ozone-based microfine bubble generators and conducted experiments to compare their bubble production effects. The more effective generator was then compared with the traditional aeration method. The results indicate the following: 1. The coaxial type is more effective in producing ozone-based microfine bubbles. 2. The bubbles produced by the coaxial type have an average diameter of 0.2–0.4 mm and a residence time of ∼2 min, meeting microfine bubble standards. Experimental data analysis shows compliance with the force process and bubble growth mechanism under coaxial flow, meeting the requirements for quantitative and controllable ozone-based microfine bubble production. 3. Ozone bubbles from the coaxial method surpass those from traditional aeration in volume and concentration. More than 99.73% are microfine bubbles, with an ozone concentration of ∼84.5%. 4. The coaxial method more effectively reduces COD values in water, contributing to efficient wastewater treatment. This research presents new avenues for efficient sewage treatment.

Removal efficiency and mechanism of geosmin by modified micro-nano bubbles in drinking water treatment process

The problem of odor and taste caused by geosmin had been widely discussed globally. While existing water treatment processes were difficult to remove geosmin cleanly and efficiently, and the traditional aeration method of micro-nano bubbles (MNBs) led to low removal efficiency due to the low probability of collision between the bubbles and the contaminants. In this study, micro-nano bubble modification technique was used to improve the removal efficiency. Three surface modifiers, hexadecyl trimethyl ammonium bromide (CTAB), chitosan (CTS), and poly dimethyl diallyl ammonium chloride (PDADMAC), were selected for this study. The effects of the surface modifiers on the properties of MNBs and the effects of these changes on the removal efficiency of GSM were explored. The experimental results showed that when all three modifiers were dosed at 5 mg/L, the PDADMAC-modified MNBs had the best GSM removal effect of 70.9 %, while the Zeta potential of the effluent was lower at 4.17 mV, which had less influence on the downstream process, and was an ideal modifier. The contribution of various removal pathways to GSM removal was also explored through intermediate product analysis combined with variable control experiments. The experimental results showed that the enhanced removal of GSM was attributed to the enhanced capture of GSM by PDADMAC-modified MNBs and the enhanced oxidation of GSM by PDADMAC-modified MNBs. At the same time, the removal efficiency of this process in natural waters decreased by <5 % only. This study could provide data and theoretical support for the enhanced removal of olfactory compounds by modified MNBs for application in practical engineering.

Application of Fine Bubbles in Biofloc Aquaculture: Towards Environmental Sustainability

Biofloc Technology (BFT) is specifically designed to tackle critical challenges in aquaculture, including the reduction of excessive water usage, minimizing effluent discharge, optimizing nutrient utilization from feed, and strengthening overall biosecurity on farms. This innovative approach utilizes clusters of bacteria, algae, or protozoa within a matrix rich in particulate organic matter to enhance water quality, improve waste management, and control diseases. Given the system loading rates, there is a heightened need for elevated dissolved oxygen levels and optimal flow rates. Acknowledging the limitations of traditional aeration systems, this review hypothesizes employing fine bubbles as a panacea. The article, therefore, condenses information on fine bubble impacts in biofloc with a special focus on faster biofloc establishment, favorable microbial diversity, improved respiratory health, accelerated growth rates, optimized metabolism, improved feed conversion ratios, reducing costs, and enhanced overall aquatic health. The suitability of fine bubbles in diverse aquaculture environments is also explored with highlights on areas for further research to optimize and scale up fine bubble-fueled biofloc as an environmentally friendly aquaculture.

Investigating the performance of a perforated pooled circular stepped cascade aeration system for intensive aquaculture

Aeration plays a crucial role in aquaculture to maintain adequate dissolved oxygen (DO) levels in water, which is essential for supporting aquatic life. However, traditional aeration systems such as paddlewheel aerators or diffused air aerators often come with high energy consumption, frequent maintenance, and greater operational costs. To address these challenges, this research paper presents the development and evaluation of a more sustainable and cost-effective aerator, named the perforated pooled circular stepped cascade aerator (PPCSC), for intensive aquaculture. Laboratory experiments were conducted in a masonry tank to assess the performance of the PPCSC aerator with different bottom radii (Rb) and discharges (Q). The results showed that the highest standard aeration efficiency (SAE) of 4.564 ± 0.6662 kg O2/kWh was achieved with a bottom radii (Rb) of 0.75 m and a discharge (Q) of 0.016 m3/s. A developed regression model was found to effectively evaluate the standard oxygen transfer rate (SOTR) and SAE for different Rb and Q values used in the PPCSC system. Both Rb and Q were found to significantly impact the SOTR and SAE of the PPCSC aerator. Overall, the PPCSC aerator is a promising option for small-scale tank-based intensive aquaculture due to its high performance and lower operational costs.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics.

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

Nanobubble aeration enhanced wastewater treatment and bioenergy generation in constructed wetlands coupled with microbial fuel cells

Artificial aeration is a widely used approach in wastewater treatment to enhance the removal of pollutants, however, traditional aeration techniques have been challenging due to the low oxygen transfer rate (OTR). Nanobubble aeration has emerged as a promising technology that utilise nano-scale bubbles to achieve higher OTRs owing to their large surface area and unique properties such as longevity and reactive oxygen species generation. This study, for the first time, investigated the feasibility of coupling nanobubble technology with constructed wetlands (CWs) for treating livestock wastewater. The results demonstrated that nanobubble-aerated CWs achieved significantly higher removal efficiencies of total organic carbon (TOC) and ammonia (NH4+-N), at 49 % and 65 %, respectively, compared to traditional aeration treatment (36 % and 48 %) and the control group (27 % and 22 %). The enhanced performance of the nanobubble-aerated CWs can be attributed to the nearly three times higher amount of nanobubbles (Ø < 1 μm) generated from the nanobubble pump (3.68 × 108 particles/mL) compared to the normal aeration pump. Moreover, the microbial fuel cells (MFCs) embedded in the nanobubble-aerated CWs harvested 5.5 times higher electricity energy (29 mW/m2) compared to the other groups. The results suggested that nanobubble technology has the potential to trigger the innovation of CWs by enhancing their capacity for water treatment and energy recovery. Further research needs are proposed to optimise the generation of nanobubbles, allowing them to be effectively coupled with different technologies for engineering implementation.

Electroactive bacteria–algae biofilm coupled with siphon aeration boosts high-salinity wastewater purification: A pilot study focusing on performance and microbial community

Constructed wetland–microbial fuel cells (CW–MFC) and aeration technology are typically used for the treatment of mariculture wastewater with a low carbon/nitrogen ratio and high-salinity. However, salt inhibition limits their efficiency. Here, based on CW–MFC, an electroactive bacteria–algae biofilm and siphon aeration technology were employed in a pilot study to validate their technical and economic feasibility. The system yielded average removal efficiencies of 80.99 % ± 1.3 %, 92.59 % ± 3.13 %, 94.03 % ± 5.11 %, 97.38 % ± 3.62 %, and 95.95 % ± 2.59 %, respectively, for chemical oxygen demand, total phosphorus, total nitrogen, sulfamethoxazole, and Cu2+, with an average voltage of 354 ± 23 mV. Nitrification and denitrification bacteria Vicingus (12.52 %), Marinobacter (7.93 %), Muricauda (10.86 %), and Xanthomarina (13.62 %); extracellular respiratory bacteria Geobacteraceae (9.47 %) and Pseudomonas (2.54 %); and microalgae bacteria Pseudooceanicola (12.45 %) and Hoeflea (7.45 %) were significantly enriched. The energy consumption per ton of sewage treatment was 0.0045 kWh·m−3, representing 47.87 % lower costs than those related to traditional aeration. These results proved the feasibility of CW–MFC coupled with electroactive bacteria–algae biofilm and siphon aeration tidal flow technology for mariculture wastewater treatment.

Energy shifting in wastewater treatment using compressed oxygen from integrated hydrogen production

Integrating renewable hydrogen production via electrolysis with wastewater treatment is an opportunity to manage environmental resources more sustainably while providing a pathway to producing sustainable hydrogen at industrial scale. The synergies of integrating oxygen production from water electrolysis and oxygen use in wastewater treatment benefit both hydrogen production and wastewater industries. However, the understanding of the most suitable integrated process configuration and scale of renewable equipment is not known. A novel energy shifting process is proposed here using compressed and stored oxygen produced by water electrolysis and used in the activated sludge process, replacing traditional aeration in the wastewater treatment plant and eliminating the high energy consuming blowers supplying air to submerged fine bubble diffusers. In the proposed energy shifting process, excess oxygen produced by water electrolysis at times of peak renewable electricity production is stored and used for wastewater treatment at times of peak oxygen demand. Wastewater treatment data from the activated sludge process was used to calculate oxygen demand in 1-h intervals over a 24-h period, and the system response of the integrated plant was simulated at hourly intervals and equipment size determined according to an optimisation algorithm that balances oxygen and electricity supply and demand over a 24-h period. Sensitivity analysis of operational parameters is assessed and the case for replacing traditional WWTP aeration with newer technologies is quantified using a high efficiency oxygen transfer system such as a Speece cone as an example that is shown to be a prerequisite for the feasibility of the process. The results produced by this study provide valuable information to the hydrogen and wastewater industries on how an integrated plant could be configured. Besides the environmental advantages of sustainably produced hydrogen, using oxygen as a biochemical energy storage medium in this configuration means WWTP powered from renewable electricity becomes more viable reducing the industries reliance on fossil fuels.

Research on oxygen transfer in an aerated flow with emergent vegetation

In the case of increasingly serious river pollution worldwide, aeration in channels is an effective way to solve water pollution. However, traditional aeration research is aimed mainly at nonvegetated channels, and there is relatively little research in vegetated channels. Aeration contributes to the absorption of pollutants by vegetation, so studying the mass transfer of dissolved oxygen in vegetated channels is of great significance. This paper innovatively studies the variation law and formula of the oxygen mass transfer coefficient in vegetated channels through an experiment and theoretical analysis. Through flume experiments, this study examines the bubble size and oxygen transfer coefficient under different vegetation densities and establishes a formula to simulate the oxygen transfer coefficient under different vegetation densities. The results show that vegetation has little effect on bubble diameter, and the main effect on bubble diameter is the aeration rate. The existence of vegetation significantly increases the mass transfer of oxygen, and the higher the vegetation density is, the greater the oxygen transfer coefficient transfer is. At the same time, a formula predicting the oxygen transfer coefficient is proven, and the simulation results are good, in which the coefficient of determination (R2) was 0.9535 and the mean absolute error (MAE) reached 0.0857. This study provides a theoretical basis for the selection and layout of aeration systems in vegetated channels.

A novel MABR process based on HN-AD bacteria-chlorella symbiotic system: Effects of COD/TN ratios on performance, community structure, functional bacteria and key genes

Microorganisms in heterotrophic nitrification-aerobic denitrification (HN-AD) mixed bacteria-Chlorella symbiotic system are difficult to be fixed and easily lost in continuous flow process. Meanwhile, excessive aeration in traditional aeration method might result in CO2 stripping. In this study, the membrane-aerated biofilm reactor (MABR) was employed to achieve efficient nitrogen and phosphorus removal with different COD/TN ratios based on HN-AD mixed bacteria-Chlorella symbiotic system. The results showed that compared with the HN-AD bacteria system, the symbiotic system reduced 33.3 % carbon demand and 43.6 % CO2 emission. The removal efficiency of TN and TP increased by 14.9 % and 51.2 %, respectively. The SEM, EPS and EEM analysis indicated that, the biofilm mass and intensity reached its best conditions at the optimal COD/TN ratio of 8. 16S rRNA high-throughput sequencing and functional gene prediction indicated that Chlorella increased the abundance of HN-AD functional bacteria (Acinetobacter, Pseudomonas and Paracoccus played a key role) and the expression of functional gene (Nas). This paper provides new insights for the application of the novel HN-AD mixed bacteria-Chlorella symbiotic system in MABR, which will be beneficial for future research.

ОСОБЛИВОСТІ СПУХАННЯ АКТИВНОГО МУЛУ В МЕМБРАННИХ БІОРЕАКТОРАХ

Membrane bioreactor (MBR) technology, the practical application of which is growing steadily, is a combination of classical technology of biological treatment with activated sludge with a membrane system of micro- or ultrafiltration. MBR are an alternative to the widely used method of separating activated sludge from wastewater in secondary settling tanks used in traditional biological treatment systems. MBR exclude large-scale negative consequences, as in system with traditional aeration tanks and secondary settling tanks in the "swelling of activated sludge". But "swelling of activated sludge" can affect the nitrification process and minimize the efficiency of ammonium nitrogen removal. The purpose of the work is to study the swelling of activated sludge swelling on the existing membrane bioreactor. The research was carried out by hydrochemical analysis of wastewater in MBR and determination of technological properties of activated sludge in the bioreactor. The negative effect of activated sludge swelling in MBR on nitrification activity in the system was established, which caused a decrease in the efficiency of ammonium nitrogen removal. Filamentous bacteria were identified according to the classification of D. Eickelbum, which caused swelling of activated sludge in the studied MBR, Type 021N.

Study on Aeration Optimization and Sewage Treatment Efficiency of a Novel Micro-Pressure Swirl Reactor (MPSR)

This study developed a new type of micro-pressure swirl reactor (MPSR) for treating rural domestic sewage with variable water volume in northern China. The transformation of a traditional aeration tank to MPSR was mainly divided into three steps. Firstly, the aeration device was installed on one side of the aeration tank. Secondly, most of the top cover plate was sealed. Finally, the liquid level-lifting zone was set to achieve micro-pressure. The study measured the flow velocity and dissolved oxygen (DO) distribution in the main reaction zone of MPSR, studied the effects of MPSR sewage treatment in continuous operation mode and sequential batch operation mode, and analyzed the main microbial species. The experimental results showed that a stable circular circle flow and a spatial DO gradient in MPSR were formed when the aeration rate of MPSR was 0.2 m3/h. Through the MPSR sewage treatment experiment in two operation modes, it could meet the current requirements of rural environmental pollution controlled in China. Analysis of the types of microorganisms showed that microorganisms with different functions gathered in different zones of the MPSR due to the different dissolved oxygen environment and water flow environment, which further improved the ability of MPSR to simultaneously remove nitrogen and phosphorus.

A cost-effective production of hydrogen peroxide via improved mass transfer of oxygen for electro-Fenton process using the vertical flow reactor

This study has investigated a novel jet-type reactor (vertical flow reactor) in order to improve the oxygen utilization for enhanced production of hydrogen peroxide (H2O2). In vertical flow electro-Fenton (EF) system, the effects of current density, water flow rate, Fe2+ concentration and initial pH were investigated for the removal of tetracycline hydrochloride. The efficient removal of tetracycline hydrochloride could reach 100% within 60 min under the current density of 24 mA cm−2, water flow rate of 10 L h−1 and pH of 3. The vertical flow reactor was relatively stable and reusable for the removal of pollutants. The removal rates of tetracycline hydrochloride and total organic carbon (TOC) were maintained at about 95% and 80%, respectively in a 5-time continuous runs. Moreover, the vertical flow reactor could efficiently remove a wide type of organic pollutants, and the TOC removals of acid magenta, rhodamine B, alizarin yellow R, orange Ⅳ and diclofenacdium were 75.96, 77.90, 61.27, 72.11 and 82.89%, respectively after 3 h of reaction time. Cathodic adsorption, anodization, and H2O2 oxidation played minor roles in the removal of tetracycline hydrochloride, while the OH radicals are the most pivotal oxidizing substance in the system. As compared with the traditional aeration, the vertical flow reactor has a high-speed jet flow state, which makes the liquid-gas mixture homogeneous, and renders it high oxygen absorption rate, cost effectiveness and high power efficiency for the degradation of pollutants.

Preparation of synthetic rutile from reduced ilmenite through the aeration leaching process

The traditional aeration leaching process for the upgrading of reduced ilmenite is extremely sluggish and needs significant improvements in its efficiency. An improved aeration leaching process which comprises reduction, aeration with a catalyst, wet magnetic separation, and further leaching, was used for the preparation of synthetic rutile in the present study. The effects of NH4Cl concentration, HCl addition, 9, 10-anthraquinone-2, 6-disuifonic acid, disodium salt (catalyst AQ-2, 6) addition, temperature, stirring speed, liquid/solid mass ratio, and leaching time on the metallic iron removal rate from the reduced ilmenite were studied. The bench-scale experiment results reveals that the aeration leaching efficiency can be significantly improved by adding 2.0% HCl or 0.2% AQ-2, 6 in NH4Cl solution, and the fine magnetite (Fe3O4) particles can be steadily produced with the addition of AQ-2, 6. The pilot-scale experiment results show that the synthetic rutile can be upgraded to ∼86% of TiO2 with 0.2% AQ-2, 6 addition within 8 h of aeration leaching, and the recovery of TiO2 can be improved by 3% when replace the traditional hydrocyclones with the swet magnetic separation. The improved process can not only shorten the leaching time but also possible to improve the quality of the products by accurate classification.

Mass transfer of nanobubble aeration and its effect on biofilm growth: Microbial activity and structural properties

It is necessary to improve the performance and reduce the aeration cost is of wastewater treatment by aerobic biofilm systems. Nanobubble aeration is supposed to be a promising method to achieve these goals. Compared with coarse bubbles, dissolved oxygen profiling showed that the nanobubbles provided more oxygen to biofilms, offering superior oxygen supply capacity and 1.5 times higher oxygen transfer efficiency. Nanobubble aeration accelerated the growth of the biofilm and achieved better removal efficiencies of chemical oxygen demand and ammonia, with as maximum as six times higher dehydrogenase activity, and more extracellular polymeric substance content than when using the traditional aeration mode. This is attributed to the enhancement of metabolism and the proliferation of microorganisms. Confocal laser-scanning microscopy imaging confirmed that nanobubble aeration affected the components of biofilm by shifting the microbial community and changing its metabolic pathways of biofilms, such as carbohydrate synthesis. Nanobubble aeration resulted in an energy saving of approximately 80%. The assessment of nanobubble aerated biofilm growth suggests that this technique can offer a rapid-initiation, high efficiency, and low-cost strategy for aerobic biofilm systems in wastewater treatment.

Wastewater treatment in the multifunctional marine transshipment complex «Bronka»

The article describes an effective method of wastewater treatment generated during the operation of the multifunctional marine transshipment complex «Bronka». The presented scheme allows to significantly increase the concentration of activated sludge in such a circuit (up to 20 g/l instead of 6 g/l in traditional aeration tanks), which ensures a more intensive biological treatment process. The most significant advantage is that during purification, water passes through the pores of ultrafiltration membranes up to 100 nanometers in size. At the indicated filtration mode, the water after purification has a turbidity of no higher than 2.5 mg/L.

Removing ammonia from skim by air stripping with rotating packed bed

Abstract Based on the effects of skim components on ammonium removal as well as the current processing technology, a new process-intensified technology of removing ammonia from skim by air stripping on rotating packed bed was proposed. The experiments were conducted on a wave-thread packed Rotating Packed Bed (RPB) under atmospheric pressure, suggesting that, in terms of order of importance, the ammonium concentration of feed-stock (xw), the average ultra-gravity factor (β), feed-stock flux (L), and gas flux (G) had significant impact on ammonium removal rate (η) and the ammonium concentration of products (xD). In the experiment, mass-transfer coefficient in gas phase (kyae) increases with the increase of β, G/L, and L. The ammonium concentration of products decreases with the increase of β, G/L and the increase of L. The ammonium concentration of products would be as low as 0.10% and the ammonia removal rate would be 63.21% when skim temperature was 25 °C, xw 0.28%, β 133.2, and G/L 15.0 m3·L− 1. Experiment results indicated that the proposed technology for removing ammonium from skim on a rotating packed bed would be a new process-intensified technique compared with traditional aeration process and centrifugal atomization method.

Study on the mechanical lifting process for membrane fouling control

ABSTRACTIn order to reduce energy consumption and control membrane fouling, a novel submerged membrane separation process was developed in this paper. In this design, the traditional aeration device was replaced by a low-power motor. Through the traction force produced by the motor, the membrane module can move up and down in the water. In this case, friction will be created between the membrane surface and the water, which can prevent the deposition of pollutants on the membrane surfaces and then control membrane fouling. After a 64-min filtration operation, compared with the aeration process, the cake-layer resistance of the lifting process reduced by about 13.6%. For a 120-min filtration operation, the transmembrane pressure (TMP) of the lifting process was 11.1% lower than that of the aeration process at the end of filtration. According to the long-time operation, the stable running time was increased from 352 min of the aeration process to 408 min of the lifting process. All these suggest that the novel lifting process can control membrane fouling more effectively than the aeration process. Therefore, the lifting process is an efficient and feasible membrane separation technology.

Wave generation in subsurface aeration system: a new approach to enhance mixing in aeration tank in wastewater treatment

Energy crises in the early 1970’s created awareness of the cost of wastewater treatment and the energy required for each stage. Aeration process was the focal point of energy saving research, due to its high power consumption, which led to change the use of coarse bubble aeration system to fine bubble aeration. Until now, all commercially existing aeration systems use continuous airflow. Meanwhile, the system investigated in this paper uses pulsation flow to reduce energy consumption in aeration tank by improving oxygen transfer efficiency (OTE). In this study, a new innovative air injection method is proposed to improve OTE in the aeration basin without extra power depletion. The suggested method is simply to inject air alternatingly from two adjacent diffusers into the aeration system. It was found that OTE was improved using this method. This improvement could be attributed to water agitation caused by transient condition operation. Timing the separation between two injections is a very important aspect of the proposed system. The optimum separation time was found by varying the timing between these injections. The highest OTE was obtained at a separation time of 1.5 s and a volumetric flow rate of 42 LPM with a 57.1% enhancement in comparison to the steady state traditional aeration system.