Airlift Reactor Research Articles

System construction based on a wire-mesh sensor for flow analysis

Wire-mesh sensor (WMS, mesh sensor) is a device for invasive imaging of vertical and horizontal flows of liquids and gases. Visualisation of the measurement results does not require any complicated software reconstruction. The device consists of two parts: the wire-mesh acquisition module and the wire-mesh sensor. The device allows for testing of multiphase flows as well as air bubbles in air-lift reactors. The sensors are also suitable for testing various types of surface flows and the movement of bulk materials along the bottom of a pipeline. This paper describes the goals and results of construction of the system for flow analysis based on a wire-mesh sensor.

Esterase production by Aureobasidium pullulans URM 7059 in stirred tank and airlift bioreactors using residual biodiesel glycerol as substrate

Aureobasidium pullulans URM 7059 produced esterase using residual glycerol from biodiesel as the sole carbon source. The culture medium containing residual glycerol (0.1 % v/v), (NH4)2SO4 (4 g/L), and yeast extract (8 g/L) resulted in the highest esterase production using shake-flasks. The enzyme exhibited a molar mass of 50 kDa and was stable at neutral pH and temperatures below 30 °C. The cations Cu2+ and Al3+ did not affect the esterase activity, while Ca2+ promoted the highest activity loss. The enzyme kinetic parameters were determined using different substrates (p-nitrophenylcaprylate and p-nitrophenylbutyrate). Km and Vmax were 1.4 mM and 218 μmol min−1 for p-NPC, and 1.55 mM and 76.7 μmol min−1 for p-NPB. The esterase production was further evaluated using stirred tank and 2-L airlift bioreactors. The airlift reactor operating at the highest air flow rate (8 L/min) increased the enzyme productivity 3-fold compared to the shake-flasks experiments. However, the crude enzymatic extract showed 3 active protein bands by zymography with molecular masses of 172 kDa, 66 kDa, and 40 kDa approximately, suggesting that the pattern of enzyme production changed due to aeration. The crude enzyme degraded the MACO-Sty biopolymer in 14 days, being stable in a wide range of pH (7.0–9.0) and temperatures (40 °C – 80 °C). The results suggest that this enzyme is a promising catalyst in remediation processes.

A high-rate and stable nitrogen removal from reject water in a full-scale two-stage AMX® system.

This paper reports long-term performance of a two-stage AMX® system with a capacity of 70 m3/d treating actual reject water. An air-lift granulation reactor performed partial nitritation (PN-AGR) at an average nitrogen loading rate (NLR) of 3.1 kgN/m3-d, producing an average effluent NO2--N/NH4+-N ratio of 1.04. The average nitrogen removal rate of the system was 3.91 kgN/m3-d following an anaerobic ammonium oxidation (Anammox) stage moving bed biofilm reactor (A-MBBR). Although the total nitrogen concentrations in the reject water fluctuated seasonally, overall nitrogen removal efficiency (NRE) of the two-stage AMX® system was very stable at over 87%. The two-stage AMX® system, consisting of a PN-AGR followed by an A-MBBR, operated at a stable NLR of 1.86 kgN/m3-d (1.64 kgN/m3-d including the intermediate tank), which is 1.8 times higher (1.6 times including the intermediate tank) than other commercialized single-stage partial nitritation/Anammox (PN/A) processes (which operate at a NLR of about 1 kgN/m3-d). The PN-AGR was affected by high influent total suspended solids (TSS) loads, but was able to recover within a short period of 4 days, which confirmed that the two-stage PN/A process is resilient to TSS load fluctuations.

Carbon availability shifts the nitrogen removal pathway and microbial community in biofilm airlift reactor

This study investigated the response of nitrogen removal performance and microbial community to different carbon composites in biofilm airlift reactors for wastewater treatment. Three reactors were filled with poly (butylene succinate) and bamboo powder composite at the blending ratio of 9:1, 1:1 and 1:9. Increasing the component of bamboo powder in the carrier reduced the carbon availability and had an adverse effect on nitrate removal efficiency. However, bamboo powder improved the ammonia removal rate which mainly through autotrophic nitrification. Three reactors exhibited distinct microbial compositions in both bacterial and fungal diversity. High inclusion of bamboo power decreased the relative abundance of denitrifiers Denitromonas and increased the relative abundance of nitrifiers, including Nitromonas, Nitrospina and Nitrospira. Moreover, correlation network revealed a competitive interaction between the taxa responsible for ammonia removal and nitrate removal processes. Those results indicated the feasibility of steering nitrogen removal pathway through carrier formulation in wastewater treatment.

Investigation of hydrodynamics and mass transfer in an internal loop airlift slurry reactor integrating mixing and separation

Based on newly invented internal loop airlift slurry reactor integrating mixing and separation, hydrodynamics and mass transfer under different solid loadings and superficial gas velocities were systematically investigated, and mixing and mass transfer characteristics were studied. Additionally, some empirical models for these critical parameters are proposed. A phenomenon of internal fluid relay circulations in the riser of the internal loop airlift reactor at the high superficial gas velocity was firstly discovered by visual observation and was then verified both by the picture sequences and theoretical analysis, and some new thoughts for structural optimization were also proposed. It was found that the axial solid concentration deviation can be more than 30% and the solid particles were inclined to exist near the wall. Surprisingly, the particle size distributions were found to be the same in the whole reactor. This slurry reactor will be popular in industry with a further structural optimization.

Biological decolorization of Amaranth dye with Trametes polyzona in an airlift reactor under three airflow regimes

In the present work, a strain of the basidiomycete fungus Trametes polyzona was used to decolorize the Amaranth dye. The decolorization was carried out in an Airlift reactor with three flow regimes: 1, 2, and 3 vvm. The results showed that the decolorization was a function of the flow regime. The decolorization times for the regimes of 1, 2, and 3 vvm were 30, 25, and 19 days, respectively. The COD (Chemical Oxygen Demand) decreased from 1600 to 72 mg COD/L. The enzymatic activity kinetics of laccase (Lcc), lignin peroxidase (LiP), and manganese peroxidase (MnP) were determined. In all the treatments, the enzyme LiP was expressed during the first 6 days, at which point 80% decolorization was observed, whereas Lcc and MnP enzymes were produced from day 6 until the end of the decolorization process. The effluent generated showed no inhibitory effects on the growth of the algae Nannochloropsis salina. T. polyzona showed great versatility in the decolorization of synthetic effluents containing the Amaranth dye, and the fungus was able to use this dye as its only carbon source starting at the beginning of the process. LiP was the enzyme that contributed the most to the decolorization process, and on average, 95% decreases in color and the COD were observed.

Experimental and Numerical Study of Gas-Liquid Flow in a Sectionalized External-Loop Airlift Reactor

The external loop airlift reactor (EL-ALR) is widely used for gas-liquid reactions. It’s advantage of good heat and mass transfer rates compared to conventional bubble column reactors. In the case of fermentation application where a medium is highly viscous and coalescing in nature, internal in riser helps in the improvement of the interfacial area as well as in the reduction of liquid- phase back mixing. The computational fluid dynamic (CFD) as a tool is used to design and scale-up of sectionalized external loop airlift reactor. The present work deals with computational fluid dynamics (CFD) techniques and experimental measurement of a gas hold-up, liquid circulation velocity, liquid axial velocity, Sauter mean bubble diameter over a broad range of superficial gas velocity 0.0024 ≤ UG ≤ 0.0168 m·s−1. The correlation has been made for bubble size distribution with specific power consumption for different plate configurations. The effects of an internal on different mass transfer models have been completed to assess their suitability. The predicted local mass transfer coefficient has been found higher in the sectionalized external loop airlift reactor than the conventional EL-ALR.

Drug biotransformation process favored by fungal biofilms formed on a proposed fixed bed‐airlift hybrid reactor

AbstractBACKGROUNDFungi have the great ability to biotransform drugs, making it possible to direct their application to obtaining new molecules. Our group developed a hybrid fixed bed‐airlift reactor (FB‐ALR) model that allows the formation of Cunninghamella elegans (or other fungi) biofilm and biotransformation of diclofenac (DCF).RESULTSHydrodynamic and rheological parameters [(mixing time (tM), linear gas velocity (UG), liquid linear velocity (UL), gas hold‐up (εG), viscosity (v)], mass transfer (kLa) and biomass formation were superior than those obtained in conventional airlift reactor (ALR) and bubble column reactor. The higher performance of FB‐ALR is a result of the improvement in the oxygenation process, in addition to the reticulate baffle used by the fungus as a support for adhesion and proliferation as biofilm. The formation of fungal biofilms, in addition to reducing the viscosity of the system, favored the retention of DCF, thus facilitating the processes of biotransformation. High‐performance liquid chromatography analyses confirmed such theory.CONCLUSIONFungal biofilms present considerable biotransforming activity, making FB‐ALR the highest yielding biotransformation system amongst those tested herein. © 2020 Society of Chemical Industry (SCI)

Continuous Neutralization of NaOH Solution with CO2 in an Internal‐Loop Airlift Reactor

AbstractThe neutralization of NaOH with CO2 in a continuously operated airlift reactor with gas flow rates up to 10 NL min−1 and gas phase recycle was investigated. Neutralization experiments were performed at 25 °C and the amount of absorbed CO2, as well as the NaOH feed rate, were recorded. The reaction rate was calculated based on the two‐film theory and empirical equations for several parameters. The calculations of the volumetric mass transfer coefficient, the liquid phase circulation velocity, and the gas holdup were experimentally validated. The reaction rate and the process efficiency were modeled with a deviation of 5 %.

Sequencing batch airlift reactors (SBAR): a suitable technology for treatment and valorization of mineral oil wastewaters towards lipids production

Produced water (PW) and spent oil-based wastewaters are some of the largest mineral oil wastewaters produced. Due to the high toxicity of hydrocarbons, several countries set stringent discharge limits and its treatment is compulsory before discharge. In this work, biological treatment of mineral oil wastewaters coupled with the production of bacterial lipids is demonstrated in sequential batch airlift reactors (SBAR). Two SBAR (2 L working volume) were used for treatment of PW and lubricant-based wastewater (LW), inoculated with Alcanivorax borkumensis SK2 (SBARAb+PW) and Rhodococcus opacus B4 (SBARR.o+LW), respectively. A total petroleum hydrocarbon removal (TPH) efficiency up to 96% and 80% were achieved for SBARAb+PW and SBARR.o+LW, respectively. Intracellular lipids production in SBARAb+PW increased when lower TPH/N ratios and higher feast stage duration were applied (up to 0.74 g g-1 cell dry weight (CDW)), whereas in SBARR.o+LW higher lipids production was observed for higher TPH/N ratios (0.94 g g-1 in CDW). Triacylglycerols (TAG) were the main intracellular lipid accumulated in both SBARAb+PW and SBARR.o+LW operations, while wax ester (WE) production was only observed extracellularly in the SBARAb+PW.

Semi-continuous production of volatile fatty acids from citrus waste using membrane bioreactors

In the production of volatile fatty acids (VFAs) from citrus waste, organic loadings rates (OLR) from 1 to 8 g VS/L·d were applied in semi-continuous anaerobic fermentation using a tubular membrane bioreactor (MBR). Filtration fluxes of the membrane were in the range of 7.9–8.5 L/m2·h. trans-Membrane pressure (TMP) revolved around 24.1–67.5 mbar. No obvious fouling and clogging occurred. The highest yield of VFAs 0.67 g VFA/g VS (volatile solids) was achieved at OLR 4 g VS/L·d. When citrus waste was pretreated to remove d-limonene using an airlift reactor, the highest yield of VFAs 0.84 g VFA/g VS was also obtained at OLR 4 g VS/L·d. A further increase in OLR of up to 8 g VS/L·d caused a sharp decrease in yield for the untreated citrus waste and only marginal changes were observed for the pretreated citrus waste. The main composition of VFAs was acetate, butyrate, caproate, and propionate.

Determination of Bodenstein number and axial dispersion of a triangular external loop airlift reactor

In this research, the residence time distribution (RTD) approach was used for the downcomer of the special-shaped triangular external loop airlift reactor (EL-ALR) by applying a modified downcomer to describe the flow pattern and dispersion behavior. Moreover, the effects of the three parameters of the superficial gas velocities of the downcomer and riser (Vgs1 and Vgs2, respectively), and the angle of the hypotenuse (α) were studied. Response surface methodology (RSM) was applied to analyze the results statistically and also to optimize the mixing conditions. In addition, the Bodenstein number (Bo), liquid velocity (UL), and axial dispersion coefficient (Dax) were determined. A mathematical relationship with a high accuracy was developed for the prediction of Bo number in the reactor downcomer. Also, it was shown that the reactor configuration was the most significant factor among all the studied parameters that affected the reactor performance. As a result of the RTD analysis, the flow pattern had been tended to be perfectly mixed. In this regard, the obtained values of Bo number were within the range 7.18–11.21 that confirmed this finding. The predicted optimum conditions (α = 60°, Vgs1 = 0.005 m/s, and Vgs2 = 0.019 m/s) were validated using the experimental control test, indicating a small deviation of ±0.39.

Analysis of Rapid Start-up and Mixed Nutritional Nitrogen Removal Performance of Complete Autotrophic Granular Sludge

A rapid start of the completely autotrophic nitrogen removal over nitrite (CANON) process based on granular sludge and efficient nitrogen removal under mixotrophic conditions are important steps in a continuous flow reactor for CANON engineering applications. In this study, an aged CANON granular sludge was mechanically crushed to 0.3 mm as inoculum in an airlift internal-loop reactor (AIR) to achieve simultaneous COD removal and mixotrophic denitrification of the single-stage granular sludge. The system achieved stable partial nitrification by controlling DO after 26 days of startup. Granulation and anaerobic ammonia oxidation were then promoted by shortening the HRT to increase the ammonia nitrogen load to 5.65 kg ·(m3 ·d)-1. The total nitrogen removal rate reached 58% on the 68th day. Subsequently, the C/N ratio of influent was increased from 0 to 0.25 and 0.5, which promoted the synergistic growth of AOB, AMX, and heterotrophic microorganisms. The removal rates of ammonia and total nitrogen were 95% and 85% respectively, and the removal of COD reached approximately 80%. The activity of NOB such as Nitrospira was effectively inhibited as the COD concentration was increased. q(NH4+-N) and q(TN) were stable at 0.4 g ·(g ·h)-1 and 0.34 g ·(g ·h)-1, respectively, while q(NO3--N) was approximately 0.02 g ·(g ·h)-1. Microbial diversity was observed using MiSeq high-throughput sequencing. It showed that organic carbon had no significant effect on the abundance of Nitrosomomas and Candidutus_Kuenenia, while increasing the abundance of Candidutus_Brocadia and Denitratisoma in the sludge. This study provides ideas for the rapid start of continuous flow CANON granular sludge process to treat wastewater with low C/N ratio.

A new kinetic model to predict substrate inhibition and better efficiency in an airlift reactor on deammonification process

A collection of kinetic models to explore the bacteria pathway inhibition by high-ammonia during deammonification process was fitted. The main goal was to determine the substrate concentration to operate the deammonification with efficiency, performance and low impact to ANAMMOX and ammonia-oxidizing bacteria (AOB) by substrate. A new mathematical model was created to describe the deammonification behavior, since the empirical theoretical models showed inconsistent parameters to describe the process. The proposed model showed significant prediction to the estimable parameters and according to it, until 550 mg NH3-N L−1 no inhibitions by ammonia and nitrite were observed. However, concentrations higher than this promote the decrease on specific bacterial activity and nitrite accumulation, since it was not quickly consumed by the bacteria. The proposed model can be applied to predict microorganism affinity and inhibition by substrate over a wide range of ammonia concentrations (<900 mgNH3-N L−1) in reactors treating high-ammonia concentration swine wastewater.

Hydroxyapatite crystallization-based phosphorus recovery coupling with the nitrogen removal through partial nitritation/anammox in a single reactor

For digestion effluent treatment, while the anammox-based process has been successfully applied for nitrogen removal, in most cases, phosphorus (P) represents another major concern. In this study, a novel process, integrating the partial nitritation/anammox and hydroxyapatite crystallization (PNA-HAP) in a single airlift reactor, was developed for the simultaneous nitrogen removal and P recovery from synthetic digestion effluent. With a stable influent P concentration of 20.0 mg/L, an HRT of 6 h, and alternating increases of influent calcium and ammonium, the final achieved nitrogen removal rate was 1.2 kg/m3/d and the P removal efficiency was 83.0%. The settleability of sludge was desirably enhanced with the calcium addition and a high biomass concentration was achieved in reactor. Quantitative and qualitative analyses confirmed that HAP was the main inorganic content in sludge, which could be harvested for P recovery. According to the Scanning Electron Microscope observation and the Energy Dispersive X-ray spectrometry analysis, the microbes were mainly distributed on the outer layer of the sludge aggregate, while the HAP mainly in the interior. The relevant theoretical calculation also revealed that the sludge discharge manipulation has direct effect on the sludge composition and aggregate structure. In sum, the results are evidence of the feasibility of simultaneous nitrogen removal and P recovery through one-stage PNA-HAP process for digestion effluent.

Free ammonia resistance of nitrite‐oxidizing bacteria developed in aerobic granular sludge cultivated in continuous upflow airlift reactors performing partial nitritation

Free ammonia (FA) inhibition has been taken advantage as a strategy to suppress the growth of nitrite-oxidizing bacteria (NOB) in aerobic granules stabilized in a continuous upflow airlift reactor to achieve partial nitritation. However, after nearly 18months of continuous exposure of aerobic granules to FA in the reactor, the FA inhibition of NOB was proven ineffective, and the partial nitritation gradually shifted to partial nitrification even though the long-term granule structural stability remained excellent under the continuous-flow mode. The extent of NOB resistance to FA inhibition was quantified based on the kinetic response of NOB to various FA concentrations in the form of an uncompetitive inhibition coefficient. It was confirmed that the NOB immobilized in larger granules under longer term exposure to FA tend to become more resistant to FA. Thereby, it was concluded that NOB can develop strong resistance to FA after continuous exposure, and thus, FA inhibition is not a reliable strategy to achieve partial nitritation in mainstream wastewater treatment. PRACTITIONER POINTS: Nitrifying aerobic granules can remain structurally stable in continuous-flow bioreactors. NOB developed free ammonia resistance after 6-month continuous exposure. Larger aerobic granules tended to develop stronger free ammonia resistance. Free ammonia inhibition is not a reliable strategy for mainstream anammox.

Start-up of PN-anammox system under low inoculation quantity and its restoration after low-loading rate shock

Partial nitritation (PN)-anaerobic ammonium oxidation (anammox) is a promising pathway for the biological treatment of wastewater. However, the destruction of the system caused by excessive accumulation of nitrate in long-term operation remains a challenge. In this study, PN-anammox was initialized with low inoculation quantity in an air-lift reactor. The nitrogen removal rate of 0.71 kgN/(m3 · d) was obtained, which was far higher than the seed sludge (0.3 kgN/(m3 · d)). Thereafter, excess nitrate build-up was observed under low-loading conditions, and recovery strategies for the PN-anammox system were investigated. Experimental results suggest that increasing the nitrogen loading rate as well as the concentration of free ammonium failed to effectively suppress the nitrite oxidation bacteria (NOB) after the PN-anammox system was disrupted. Afterwards, effluent back-flow was added into the reactor to control the up-flow velocity. As a result, an aggressive discharge of sludge that promoted the synergetic growth of functional bacteria was achieved, leading to the successful restoration of the PN-anammox system. The partial nitritation and anammox activity were in balance, and an increase in nitrogen removal rate up to 1.07 kgN/(m3 · d) was obtained with a nitrogen removal efficiency of 82.4% after recovery. Besides, the proportion of granular sludge (over 200 µm) increased from 33.67% to 82.82%. Ammonium oxidation bacteria (AOB) along with anammox bacteria were enriched in the granular sludge during the recovery period, which was crucial for the recovery and stable operation of the PN-anammox system.

Development and application of Sequencing Batch Airlift Reactor for Domestic Sewage Treatment

Aiming at the demand of decentralized domestic sewage treatment in rural areas, Sequencing Batch Airlift Reactor (SBAR) for domestic sewage treatment was developed and applied for sewage disposal of an office building in shenjiadun village, Deqing, Zhejiang Province. The device doesn’t need to set up sedimentation tank and sludge reflux system. It has a good precipitation effect and only occupies a small area. In the aspect of control, it adopts the self-researched embedded software system. And it integrates GPRS/GSM/SMS/CDMA/Internet communication technology and high-precision electrical parameter measurement technology. The actual operation results show that the device can ensure sufficient contact between sludge and waste water. It can effectively remove BOD5, CODCr, ammonia nitrogen and total nitrogen from domestic sewage. And it has the advantages of low investment, low energy consumption, high automation and simple operation. Therefore, this device has important popularization value in the field of distributed treatment of rural domestic sewage.

Startup of granulation of sludge in sequencing batch airlift reactor for simultaneous removal of nitrogen and organic carbon from tannery wastewater

The transition from flocculent to granular sludge process was investigated in Sequencing Batch Airlift Reactor (SBAR) for the treatment of synthetic tannery wastewater. Chemical Oxygen Demand (COD) loading rate of 6.3 kg/m3.d and nitrogen loading rate of 0.425 kg/m3.d were applied to the reactor for 105 days using simulated tannery wastewater. The flocculent sludge was transformed to granular sludge when the operating settling time was reduced sequentially. Based on the current findings of the study, the aerobic granules formed had a MLSS concentration of 12.3 g/L, biomass density of 6.1 g /L granule, settling velocity of 30−40 m/h, SVI of 16−20 ml/g TS and size distribution in the range 1.8–3.2 mm. Evaluation of the performance of the reactor showed a very good quality effluent with average COD, NH4-N and TN removal of 97.7 ± 1.5 (%), 87.1 ± 11.8 and 74.43 ± 11.7 (%) respectively. The effect of granulation on the existence and relative abundance of selected bacteria gene involved in nitrogen cycle was analyzed by PCR and qPCR. The result confirmed the existence of AOB-amoA, nirK and PLA46+Amx820 gene. The results for qPCR also confirmed that the relative abundance of AOB-amoA and PLA46+Amx820 was higher in the reactor compared to the control.

Improving laccase production from Trametes versicolor using lignocellulosic residues as cosubstrates and evaluation of enzymes for blue wastewater biodegradation

Biocatalytic degradation of recalcitrant pollutants employing ligninolytic enzymes is a promising approach for wastewater treatment. However, enzymes production must be improved to make biodegradation a more cost-effective treatment. In this research, laccase production from Trametes versicolor using lignocellulosic residues (agave bagasse, coconut fibers and wheat bran) as cosubstrates was improved using a central composite face-centered design, and the application of the enzymes-rich culture supernatant was evaluated for blue wastewater biodegradation. Findings revealed that the optimal conditions for laccase production were found at 35 °C and 5 g/L of wheat bran as cosubstrate, reaching about 200 U/mL in 11 days in a batch submerged fermentation. These conditions were scaled up for a submerged fermentation using an airlift reactor, and a maximum enzymatic activity of 1200 U/mL was achieved in 9 days at 30 °C. This enzymes-rich culture supernatant was tested for the degradation of blue wastewater from aircraft in an airlift reactor. Results showed a COD removal efficiency of 43% and an increase of the biodegradability index from 0.64 to 1.36, both results applying an enzymatic activity of supernatant of 300 U/mL. In conclusion, the enzymatic biodegradation becomes a viable strategy for the pretreatment of a real effluent such as the blue wastewater collected in public transportation.