Low Aeration Research Articles

Startup and stable operation of advanced continuous flow reactor and the changes of microbial communities in aerobic granular sludge.

In this study, the granular sludge was operated under low aeration condition in sequencing batch reactor (SBR) and advanced continuous flow reactor (ACFR), respectively. Through increasing the sludge retention time (SRT) from 22 days to 33 days, the ACFR was successful startup in 30 days and achieved long term stable operation. Under SBR operation condition, the aerobic granular sludge (AGS) showed good nitrogen (60%), phosphorus (96%) and COD removal performance. During stable operation of continuous-flow, the nitrogen removal efficiency was increasing to 70%, however, the phosphorus removal efficiency could only be restored to 65%. Meanwhile, the sludge discharge volume from ACFR was about half of that in SBR. Results of high-throughput pyrosequencing illustrated that methanogenic archaea (MA), ammonia oxidizing archaea (AOA), denitrifying bacteria (DNB), denitrifying polyphosphate-accumulating organisms (DPAOs) played an important role in the removal of nutrients in ACFR. This study could have positive effect on the practical application of AGS continuous flow process for simultaneous biological nutrient removal (SBNR).

Influence of food concentration and abiotic parameters on population density growth of the ciliated marine protozoan Euplotes sp. under controlled conditions

High mortality is common when culturing most marine fish larvae, especially during the transition from endogenous to exogenous feeding. In aquaculture, many species of marine fish are not able to survive when only fed enriched rotifers and Artemia spp. nauplii. Ciliates are a potential alternative live food organism for first-feeding larvae, because they can grow to high population densities, accept inert diets, and are natural prey organisms of marine fish larvae. The range of culture parameters to optimize population growth of the ciliate Euplotes sp. are unknown. Five experiments were conducted to determine the effects of food concentration and abiotic factors including salinity, aeration rate, temperature and photoperiod on population growth of the ciliate Euplotes sp. Results indicated the optimal ranges for population growth of Euplotes sp. was a temperature between 26 and 32°C, salinities from 20 and 35 g/L, food (Protein Selco®) concentrations of 250 and 500 mg/million ciliates, absence of or low aeration (8.5 cm3/min) and the photoperiod 0L:24D. Euplotes sp. can tolerate high ammonia and very low dissolved oxygen concentrations, and population growth can occur in these conditions for at least 7 days.

Aeration effects on water-structure impacts: Part 1. drop plate impacts

Current offshore engineering design codes for wave loading are based on pure water, but wave impacts often involve aerated flow, either as a result of air entrapment as the wave overturns or due to impact with a wave that is already broken. Therefore, it is necessary to develop a new understanding of how design codes should incorporate water-air mixture for wave impact. This experimental study investigates aeration effects on wave impacts by means of slamming impacts of a square flat plate onto a pure and aerated water surface, with zero degree dead-rise angle. The (low) aeration level between 0% and 1.6% was applied and the drop velocity varied from about 1 m/s to 7 m/s. There was a significant reduction in the peak impact loads (both pressure and force) for impact in aerated water compared to that in pure water. There was also a significant reduction in the first phase of the pressure and force impulse for aerated water. The variation in impulsive loadings is less sensitive than peak loadings for impacts. The implication for design is that maximum instantaneous loads may be conservative in the presence of aerated water.

Do wastewater pollutants impact oxygen transfer in aerated horizontal flow wetlands?

Aerated treatment wetlands are an increasingly recognized nature-based technology for wastewater treatment that relies heavily on mechanical aeration. Although aeration-mediated oxygen transfer into the wastewater can be impeded by wastewater pollutants, little is known about the link between the volumetric oxygen mass transfer coefficient kLa and the organic carbon concentration of the wastewater in aerated wetlands. In this study, oxygen transfer experiments were carried out in a lab-scale gravel column using clean water and wastewater from a pilot-scale horizontal flow (HF) aerated wetland treating domestic sewage. The α-factor, which describes the ratio of the volumetric oxygen mass transfer coefficient kLa in wastewater to clean water, was reduced by increasing soluble chemical oxygen demand (CODs). The derived regression equation α=1.066-1.372E-3mgCODsL-1 was incorporated into a numerical process model to simulate the impact of the reduced oxygen transfer on a hypothetical HF aerated wetland. The simulations revealed that α and treatment efficacy for nitrogen were substantially reduced by CODs at low aeration (kLa of 1 h−1) and high influent wastewater strength (CODs of 300 mg L−1). At the same kLa and influent CODs concentration, longitudinal gradients of α and concentrations for dissolved oxygen (DO), NH4-N and NOx-N in the simulated wetland were shifted up to 21% of wetland length downstream. These effects decreased with increasing kLa and were found to be negligible at kLa > 3 h−1, which corresponds to an air flow rate of approximately 400 L m−2 h−1. Following this, higher organic carbon concentrations can reduce oxygen transfer in HF aerated wetland systems, thus resulting in decreased treatment efficacy.

The Characteristics of Carbon, Nitrogen and Sulfur Transformation During Cattle Manure Composting-Based on Different Aeration Strategies.

This study aimed to investigate the characteristics of gaseous emission (methane—CH4, carbon dioxide—CO2, nitrous oxide—N2O, nitric oxide—NO, hydrogen sulfide—H2S and sulfur dioxide—SO2) and the conservation of carbon (C), nitrogen (N), and sulfur (S) during cattle manure composting under different aeration strategies. Three aeration strategies were set as C60, C100, and I60, representing the different combinations of aeration method (continuous—C or intermittent—I) and aeration rate (60 or 100 L·min−1·m−3). Results showed that C, N, S mass was reduced by 48.8–53.1%, 29.8–35.9% and 19.6–21.9%, respectively, after the composing process. Among the three strategies, the intermittent aeration treatment I60 obtained the highest N2O emissions, resulting in the highest N loss and greenhouse gas (GHG) emissions when the GHG emissions from power consumption were not considered. Within two continuous aeration treatments, lower aeration rates in C60 caused lower CO2, N2O, NO, and SO2 emissions but higher CH4 emissions than those from C100. Meanwhile, C and N losses were also lowest in the C60 treatment. H2S emission was not detected because of the more alkaline pH of the compost material. Thus, C60 can be recommended for cattle manure composting because of its nutrient conservation and mitigation of major gas and GHG emissions.

Engineering Pseudomonas putida KT2440 to convert 2,3-butanediol to mevalonate

Biological production of 2,3-butanediol (2,3-BDO), a C4 platform chemical, has been studied recently, but the high cost of separation and purification before chemical conversion is substantial. To overcome this obstacle, we have conducted a study to convert 2,3-BDO to mevalonate, a terpenoid intermediate, using recombinant Pseudomonas putida and this biological process won’t need the separation and purification process of 2,3-BDO. The production of mevalonate when 2,3-BDO was used as a substrate was 6.61 and 8.44 times higher than when glucose and glycerol were used as substrates under the same conditions, respectively. Lower aeration contributed to higher yields of mevalonate in otherwise identical conditions. The maximum mevalonate production on the shaking flask scale was about 2.21 g/L, in this study (product yield was 0.295, 27% of theoretical yield (1.10)). This study was the first successful attempt for mevalonate production by P. putida using 2,3-BDO as the sole carbon source and presented a new metabolic engineering tool and biological process for mevalonate synthesis.

Aeration-induced CO2 stripping, instead of high dissolved oxygen, have a negative impact on algae–bacteria symbiosis (ABS) system stability and wastewater treatment efficiency

Utilizing additional aeration to enhance the pollutants removal in the ABS system has been extensively studied. It is widely accepted that that higher aeration rate poses limitations in algae growth. However, this phenomenon is always attributed the phenomenon to the high dissolved oxygen (DO), and the CO2 blow-off that results in inorganic carbon (IC) deficiency is often ignored. In this research, different aeration rates were set under the same DO condition to prove that CO2 stripping, and not DO, is the main cause of algae growth limitation. It was apparent that ideal algae growth conditions, at an aeration intensity of 100 mL/min, was deteriorated due to CO2 stripping, leading to a large amount (15.62 mg/L) of unused NO2− and NO3−. Meanwhile, algae death caused by CO2 stripping damaged the phosphate assimilation process. Furthermore, insufficient IC resulted in competition between autotrophic bacteria and algae, inducing the drastic decline of nitrifying bacteria (whose growth cycle is especially long) numbers. For the relatively lower aeration rate (20 mL/min), the ABS system presented a more stable condition and higher pollutants removal efficiency than both the non-aerated group (0 mL/min) and the high-aeration group (50 mL/min and 100 mL/min). This finding demonstrates that CO2 stripping in the aeration process is the main cause of damage to the ABS system, which guides the ABS application.

High-Level Production of 4-Hydroxyvalerate from Levulinic Acid via Whole-Cell Biotransformation Decoupled from Cell Metabolism

γ-Hydroxyvalerate (4HV) is an important monomer used to produce various valuable polymers and products. In this study, an engineered 3-hydroxybutyrate dehydrogenase that can convert levulinic acid (LA) into 4HV was co-expressed with a cofactor (NADH) regeneration system mediated by an NAD+-dependent formate dehydrogenase (CbFDH) in the Escherichia coli strain, MG1655. The resulting strain produced 23-fold more 4HV in a shake flask. The 4HV production was not dependent on ATP and required low aeration; all of these are considered beneficial characteristics for the production of target compounds, especially at an industrial scale. Under optimized conditions in a 5 L fermenter, the titer, productivity, and molar conversion efficiency for 4HV reached 100 g/L, 4.2 g/L/h, and 92%, respectively. Our system could prove to be a promising method for the large-scale production of 4HV from LA at low-cost and using a renewable biomass source.

Optimization of operations for nitrous oxide production and mitigation in aerobic and Aerobic-Anaerobic landfill method on MSW degradation

N2O is a potent greenhouse gas, induced by aeration coupled with leachate recirculation in Municipal Solid Waste (MSW) landfills. In this study, N2O emission was measured in the aerobic and Aerobic-Anaerobic Landfill Method (AALM) with or without leachate recirculation at two aeration rates in synthetic MSW. The experiment was carried out for six Plexiglass® landfill simulation reactors. Low aeration (1.6 l/kg-DM/h) was supplied in RLA, RLAA (Recirculatory) and LAA (non-recirculatory) reactors, while an aeration rate three times higher (4.8 l/kg-DM/h) was performed for RHA, RHAA, and HAA reactors. Based on the supplied leachate quantity, leachate recirculation was performed in five different phases. The results showed that a significant amount of N2O was produced in all reactors. The largest N2O emission of 0.11 and 0.13 g/kg-DM were observed in the RHA and RHAA reactors, respectively. Higher N2O and cumulative GHG was produced in high aeration reactors compared to the low aeration reactors. Recirculated leachate promoted waste stabilization, as reflected in the diminishing CH4 production and other leachate pollutant parameters, especially NH4+-N. It has been evaluated that in the operative or newly placed waste landfill, in-situ aeration with leachate recirculation exhibits the significant N2O production. However, lower amount of leachate in the later stage beneficial to inhibit the N2O production. It is recommended that in-situ aeration will become more effective after the recovery of CH4 from newly placed waste in an operative landfill for net GHG reduction, especially N2O reduction and early stabilization of landfills.

The role of turbulence models in the modeling of membrane bioreactors

In membrane bioreactors (MBRs), aeration mitigates fouling by creating turbulence and increasing shear stress on the membrane surface. To study the hydrodynamics of MBRs, several researchers have been using computational fluid dynamics (CFD). However, the literature lacks papers on the sensitivity of the CFD predictions for MBRs to the modeling choices related to the different phenomena involved in MBRs, including turbulence. This work evaluates the bubbly flow in an immersed MBR with the most common turbulence models (k-ε with two different wall functions and SST k-ω) at two aeration rates (5 and 15 m3 h−1). Predictions of velocities near the membranes and of local and spatially averaged shear stresses on the membrane modules were compared between the models and to literature data. The predictions were highly sensitive to the turbulence modeling approach, and their sensitivity was position dependent. The differences between the models reached 21.6% and 86.1% considering spatially averaged and local values of shear stress, respectively. The SST k-ω model exhibited the best prediction at the low aeration rate, indicating the relevance of the wall region for this condition. These findings show that more attention must be given to the choice of turbulence model in MBR simulations.

Biocarriers facilitated gravity-driven membrane (GDM) reactor for wastewater reclamation: Effect of intermittent aeration cycle

This study investigated the performances of gravity-driven membrane (GDM) reactors integrated with granule activated carbon (GAC) biofilm process for wastewater treatment under different intermittent aeration cycles (intensity and frequency). The results showed the removal efficiencies of dissolved organic carbon, total nitrogen, ammonia were significantly improved under intermittent aeration conditions (~86–87%, ~29–37%, and ~83–99%, respectively) compared to non-aeration condition (~72% and ~18%, and ~17%, respectively). In addition, it was found that the intermittent aeration significantly reduced the cake layer resistance and therefore improved ~130–300% the permeate flux compared to control without aeration. Microbial community analysis indicated that prokaryotic and eukaryotic compositions in the cake layer biofilm were significantly influenced by aeration condition. Lastly, energy consumption analysis revealed that GAC + GDM with shorter aeration period and low aeration intensity could be promising as a decentralized wastewater treatment process in terms of water quality and operating energy.

Effect of culturing parameters on the vegetative growth of Haematococcus alpinus (strain lcr-cc-261f) and modeling of its growth kinetics.

The present study investigated the effect of different culture conditions on the vegetative growth of a new species, Haematococcus alpinus (strain LCR-CC-261f) using airlift photobioreactors. The influence of culture medium, aeration rates, CO2 concentration in air-gas mixture, temperature, light intensities, and wavelengths were investigated to achieve sustainable high cell density cultures. Growth parameters were determined by fitting the data to a form of the logistic equationthat included a lag phase. The shear-sensitive vegetative cells favored lower aeration rates in the photobioreactors. MLA medium increased to 40mM nitrate produced high density cultures. Temperatures between 12°C and 18°C, 3% (v/v) CO2 concentration and a narrow photon flux density ranging between 37 and 48μmol photons·m-2 ·s-1 were best suited for growth. The wavelength of the light source also impacted growth and a high cell density of 9.6×105 cells·mL-1 was achieved using a mixture of red and blue compared to warm white, red, or blue LEDs.

Aeration, Agitation and Cell Immobilization on Corncobs and Oak Wood Chips Effects on Balsamic-Styled Vinegar Production.

Optimum fermentor conditions are essential for desired microbial growth and activity in fermentations. In balsamic vinegar fermentation systems, the microorganisms used must endure several stressful conditions including high sugar concentration, low water activity, high osmotic pressure and high acetic acid concentration. Consequently, the present study was aimed at improving the performance of a microbial consortium of non-Saccharomyces yeast and acetic acid bacteria during balsamic-styled vinegar fermentation. Cell immobilization via adsorption on corncobs and oak wood chips in combination with aeration and agitation effects, have never been tested during balsamic-styled vinegar fermentation. Therefore, fermentations were initially conducted under static conditions without aeration with successive fermentations also being subjected to low (0.15 vvm min−1) and high (0.3 vvm min−1) aeration. The results showed improved acetification rates when cells were immobilized on corncobs under static conditions. Low aeration showed better acetification rates (1.45–1.56 g·L·day−1), while only free-floating cells were able to complete fermentations (1.2 g·L·day−1) under high aeration conditions. Overall, cells immobilized on corncobs showed higher acetification rates of 1.56 and 2.7 g·L·day−1 under low aeration and static fermentations, respectively. Oak wood chips were determined to be less efficient adsorbents due to their relatively smooth surface, while the rough surface and porosity of corncobs led to improved adsorption and, therefore, enhanced acetification rates.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor.

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08cms-1, low dissolved oxygen concentration (DO) of 2.0mgL-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9μm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

Seasonal biomass production, fermentable saccharification and potential ethanol yields in the marine macroalga Ulva sp. (Chlorophyta)

Marine macroalgae (seaweeds) can accumulate high amounts of starch and cellulose in their tissues, hence, offering an attractive potential source of feedstock for bioethanol production. In this study we determined the specific growth rates (SGRs) in the seaweed Ulva sp. (Chlorophyta) during a full year cultured in a land-based facility to estimate sustainable biomass yields. We used 40 and 600 L outdoor tanks that received high and low irradiances, running seawater, aeration and external nutrients. Daily SGRs in 40 L tanks averaged 12 ± 2.04, 15.3 ± 0.8, 19.3 ± 1.8 and 10.3 ± 1.9% biomass increase per day for winter, spring, summer and autumn, respectively, while in 600 L growth averaged 2.5 ± 0.4, 2.2 ± 0.3, 9.8 ± 0.5 and 1.4 ± 0.4% d−1, respectively. In an up-scaled growth trial during summertime in larger culture units of 3400 and 27,000 L growth rates were 4.6 ± 0.8 and 8.7 ± 1.04% d−1, respectively. Altogether, the total biomass potential would yield 1.3 ton FW m−2 y−1. We also optimized enzymatic hydrolysis of dried biomass by means of time-course incubations with cellulase, amyloglucosidase and α-amylase in order to maximize the yields of total reducing sugars (TRS). We measured 163.6 ± 0.3, 179.7 ± 0.1 and 223.9 ± 0.5 mg TRS g−1 DW for summer, spring and winter months, respectively, with an average fermentation of the hydrolysate of 0.3 ± 0.06 g EtOH g−1 TRS. This work underlines the feasibility of seaweed feedstock production in land-based cultivation with respect to ethanol production.

Effect of aeration rate on the anti-biofouling properties of cellulose acetate nanocomposite membranes in a membrane bioreactor system for the treatment of pharmaceutical wastewater

In this study, the effect of aeration rate in terms of specific aeration demand per membrane area (SADm) on the anti-biofouling properties of cellulose acetate (CA) nanocomposite membranes (CA/ND-NH2) in a membrane bioreactor system was investigated. The amount of EPS and soluble EPS under high aeration rate conditions was observed to be higher than under low aeration rate conditions. The results obtained showed that either lower or higher aeration rates had a negative impact on membrane permeability. The high aeration rate resulted in a severe breakage of sludge flocs, and promoted the release of soluble EPS from the microbial flocs to the bioreactor tank. By increasing the aeration rate, the COD removal increased and decreased respectively for the membranes and the activated sludge. It was finally concluded that higher anti-biofouling properties of neat CA and nanocomposite membranes were obtained under optimal aeration rate conditions (SADm = 1 m3 m−2 h−1).

The Volume of the Product of Backward Water Splash Based on Submerged Blade Depth of Paddlewheel Aerator

The paddlewheel is a common used aeration equipment. In term of aeration mechanism and driving force, it is very good to be used. However, the paddlewheel has a slow aeration rate resulting in low aeration efficiency. One of the causes is the splash of the backward water of the paddlewheel that is already aerated, but it is splashed again so it wastes the power. The aim of this study was to determine the volume of the backward water splash production. The paddlewheel used a 1 phase motor, 1 hp power, 1400 rpm motor speed, and 2 pieces of wheels. The treatment was carried out by varying the blade of 65,85, and 105mm submerged. The test was done by collecting the backward water splash and calculating its volume. The results showed that the volume per hour of backward water splash at the blade submerged in the 65, 85, and 105mm were 10.68, 13.74, and 15.27 m3, respectively. The average of forward splash volume of water was 58.04%, while the backward was 41.96%. The results of this study indicated that the volume of backward water splash is very significant to be utilized.

The Ineffectiveness of Water Splash on Paddlewheel Aerator

The successful of intensive aquaculture is strongly influenced by the ability of the farmers to overcome the deterioration of water quality. The problem is low dissolved oxygen through aeration process. The aerator device which widely used in pond farming is paddle wheel aerator because it is the best aerator in aeration mechanism and usable driven power. However, the paddlewheel has a slow aeration rate resulting in low aeration efficiency. The problem is caused by the backward water splash ineffectively. The backward water of the paddlewheel that is already aerated, but it is splashed again so it wastes the power. However, only the forward splash is effectively. The aim of this study was to determine the ineffectiveness of paddlewheel aerator based on the backward water splash. The paddlewheel used an 1 phase motor, 1 hp power, 1400 rpm motor speed, and 2 pieces of wheels. The treatment was carried out by varying the blade of 65, 85, and 105 mm submerged. The test was done by collecting the forward and backward water splash and calculating its volume. The normal position of the float on the blade submerged by 85 mm was obtained that the forward and backward splash volume of water was 17.99 and 13.74 m3/hour. Only 56.70% the effectiveness of the water splash compared to 43.30% the backward water splash. In fact, the forward splash coverage volume of water was 47.83% compared to the forward was 52.17%. This result shown that the water splash of paddlewheel aerator was not effective, so the backward water splash need to optimize to the effectiveness of water splash.

Boosting productivity of heterotrophic microalgae by efficient control of the oxygen transfer coefficient using a microbubble sparger

We isolated and characterized an oleaginous Thraustochytrid microalga. Based on 18 s rRNA sequencing, we classified this strain as Schizochytrium sp. SH103. Growth of these cells in a 5 L fermentor with a microbubble-type sparger (MTS) efficiently increased the oxygen transfer coefficient (OTC), while inducing only low external stress. For fermentation under conditions of low agitation (100 rpm) and aeration (3 L/min), the OTC was 8.6-fold higher using a MTS than a general type sparger (GTS). Under these same conditions, dry cell weight (DCW) productivity (0.54 vs. 1.26 g/L·h) and total lipid productivity (0.29 vs. 0.61 g/L·h) were each about 2.2-fold higher using a MTS than a GTS. Under conditions that optimized the OTC in a MTS fermentor (876 h−1), DCW productivity, total lipid productivity and DHA productivity were each 1.3-fold greater than non-optimized condition. Fed-batch fermentation experiments indicated the maximal DCW was 100.6 g/L at 48 h, maximal DCW productivity was 2.1 g/L·h, maximal lipid content was 48.6 g/L at 48 h, and lipid productivity was 1.0 g/L·h. Additionally, the results of experiments using a 50 L MTS fermentor (96.0 g/L DCW and 44.3 g/L total lipids at 48 h) were similar to those using the 5 L fermentor. Our results suggest that use of a MTS may help to achieve the efficient fermentation of heterotrophic microalgae for high cell densities.

Full-scale comparison of N2O emissions from SBR N/DN operation versus one-stage deammonification MBBR treating reject water - and optimization with pH set-point.

To be able to fulfill the Paris agreement regarding anthropogenic greenhouse gases, all potential emissions must be mitigated. Wastewater treatment plants should aim to eliminate emissions of the most potent greenhouse gas, nitrous oxide (N2O). In this study, these emissions were measured at a full-scale reject water treatment tank during two different operation modes: nitrification/denitrification (N/DN) operating as a sequencing batch reactor (SBR), and deammonification (nitritation/anammox) as a moving bed biofilm reactor (MBBR). The treatment process emitted significantly less nitrous oxide in deammonification mode 0.14-0.7%, compared to 10% of total nitrogen in N/DN mode. The decrease can be linked to the changed feeding strategy, the lower concentrations of nitrite, a lower load of ammonia oxidized, a shorter aeration time, the absence of non-optimized ethanol dosage or periodic lack of oxygen as well as the introduction of biofilm. Further, evaluation was done how the operational pH set point influenced the emissions in deammonification mode. Lower concentrations of nitrous oxide were measured in water phase at higher pH (7.5-7.6) than at lower pH (6.6-7.1). This is believed to be mainly because of the lower aeration ratio and increased complete denitrification at the higher pH set point.