Aerobic Fluidized Bed Reactor Research Articles

Designing bacterial consortia for the complete biodegradation of insensitive munitions compounds in waste streams.

Insensitive munitions compounds (IMCs), such as 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), are replacing conventional explosives in munitions formulations. Manufacture and use of IMCs generate waste streams in manufacturing plants and load/assemble/pack facilities. There is a lack of practical experience in executing biodegradation strategies to treat IMCs waste streams. This study establishes a proof-of-concept that bacterial consortia can be designed to mineralize IMCs and co-occurring nitroaromatics in waste streams. First, DNAN, 4-nitroanisole (4-NA), and 4-chloronitrobenzene (4-CNB) in a synthetic DNAN-manufacturing waste stream were biodegraded using an aerobic fluidized-bed reactor (FBR) inoculated with Nocardioides sp. JS 1661 (DNAN degrader), Rhodococcus sp. JS 3073 (4-NA degrader), and Comamonadaceae sp. LW1 (4-CNB degrader). No biodegradation was detected when the FBR was operated under anoxic conditions. Second, DNAN and NTO were biodegraded in a synthetic load/assemble/pack waste stream during a sequential treatment comprising: (i) aerobic DNAN biodegradation in the FBR; (ii) anaerobic NTO biotransformation to 3-amino-1,2,4-triazol-5-one (ATO) by an NTO-respiring enrichment; and (iii) aerobic ATO mineralization by an ATO-oxidizing enrichment. Complete biodegradation relied on switching redox conditions. The results provide the basis for designing consortia to treat mixtures of IMCs and related waste products by incorporating microbes with the required catabolic capabilities.

Determination of the zeolite optimal diameter for the settlement of nitrifying bacteria in an aerobic bed fluidized reactor to eliminate ammonia nitrogen

In this work, the determination of the diameter of zeolite as a support for a microbial aerobic fluidized bed reactor is performed. The design of the reactor is recommended by Navarro and Palladino [1]. For the present study, the zeolite is crushed and classified granulometrically. Subsequently, the diameters of 0.5, 1 and 2 mm are arbitrarily chosen for the study of microbial adhesion. After the study of adherence of nitrifying bacteria, the obtained adhesion values for each diameter are not significantly different from each other. However, 1 mm is chosen to achieve higher adhesion values. Subsequently the aerobic fluidized bed reactor proposed by Navarro and Palladino [1] is built with the 1 mm-diameter zeolite. This presented an inlet flow of 1.35 mL.min-1 and a capacity of 8 L. The optimized quantity of zeolite for proper fluidization is 500 g, which is an 8% of total volume of the column. During operation, a good efficiency of reduction of the organic material is observed (50%).

Laundry greywater treatment using a fluidized bed reactor: a proposed model based on greywater biodegradation and residence time distribution approach

The increasing demand for water and the decrease in global water resources require research into alternative solutions to preserve them. The present study deals with the optimization of a treatment process, i.e. an aerobic fluidized bed reactor and the modelling of the degradation that takes place within it. The methodology employed is based on the hydrodynamics of the treatment process linked to the biodegradation kinetics of greywater coming from a washing machine. The residence time distribution (RTD) approach is selected for the hydrodynamic study. Biodegradation kinetics are quantified by respirometry and dissolved organic carbon (DOC) analysis on several mass quantities of colonized particles. RTD determinations show that there are no dysfunctions in the fluidized bed. Its hydrodynamic behaviour is similar to the one of a continuous stirred-tank reactor. A first-order reaction is obtained from the DOC biodegradation study. A model describing the degradation that takes place into the reactor is proposed, and from a sensitive study, the influence of the operating conditions on DOC biodegradation is defined. The theoretical results calculated from the first-order equation C(t)=0.593×C0×e−kt are compared with the experimental results and validated by a Student test. The value of the kinetic constant k is 0.011 h−1 in the presence of a biomass carrier. The results highlight that it is possible to design a reactor in order to obtain a carbon content lower than 15 mg C L−1 when the characteristics of raw greywater are known.

Phosphorus removal in different wastewater by fluidized bed airlift reactors with internal circulation

The wastewater discharge produces impacts on receiving water bodies. Nutrients as P produce implications on lentic systems because they accelerate the eutrophication processes. Several technologies for P removal from the wastewater have been used: physic chemical treatment systems with important effects by coagulant products addition; biological processes based on anaerobic and aerobic conditions with great implications on the required volume; natural systems as stabilization ponds and irrigation require bigger areas and post-treatment processes. The aerobic fluidized bed reactors with internal circulation (AFBRIC) are compact options with high concentrations of active biomass that have demonstrated their capacity for organic matter and N removal. For sewage from the wastewater pumping station of Ilha Solteira city and effluents of a recirculation aquaculture system (RAS) for semi-intensive tilapia farming, the reactive P and total P removal efficiency in three AFBRIC with 250 mm external tube diameter and different internal tube diameter (ITD), for two different support media at different concentrations was evaluated. The average reactive P removal efficiency for domestic wastewater to hydraulic retention time (HRT) of 3 hours and 125 mm ITD reactor varied from 25,6 to 38,4% and with 150 mm ITD reactor varied from 27,5 to 32,5%; the average total P removal for the RAS wastewater at a HRT of 0,19 hours and 100 mm ITD was of 32,7%.

Application of a fluidized bed bioreactor for cod reduction in textile industry effluents

The biodegradation of textile industry effluents, in an aerobic fluidized bed reactor with a working volume of 3.6 L, was investigated in this work. The system was batch fed and the biomass was adhered to small PVC cylinders acting as a support. The activation of the support was carried out with 95% concentrated nitric acid, under magnetic stirring, for 20 min at ambient temperature. Seven different effluents were tested with the aim of determining the degradability of different textile industry effluent streams using an aerobic process in a fluidized reactor with adhered biomass. The results demonstrated that the adhered biomass resists well the variation in the influent composition, since there was no sudden variation in the COD of the reactor outlet on starting feeding with a new effluent. The variation in pH at the reactor outlet remained at around 8.5, regardless of the pH of the input material, demonstrating a closed-lid system. The results show that regardless of the stream fed to the system, the final COD was around 200 mg/L; the filtered COD reduction efficiency for the different effluent inputs were: 80 and 72% for the effluents of the stabilization tank; 60 and 28% for the holding tank streams and 74% for the neutralization tank stream. This study reveals that the application of aerobic processes with biofilms is an excellent alternative for reducing COD in industrial textile effluents, without the use of chemicals compounds, which are utilized in the traditional effluent treatment processes, making this biofilm technology “environmentally friendly”.

ATP content and biomass activity in sequential anaerobic/aerobic reactors.

Specific ATP content of volatile solids was measured to characterize the sludge activity in a sequential an-aerobic/aerobic wastewater treatment system, with an upflow anaerobic sludge blanket (UASB) reactor and a three-phase aerobic fluidized bed (AFB) reactor. The wastewater COD level was 2000-3000 mg/L in simulation of real textile waste-water. The ATP content and the specific ATP contents of volatile solids at different heights of the UASB reactor and those of the suspended and immobilized biomass in the AFB reactor were measured. In the UASB reactor, the maximum value of specific ATP (0.85 mg ATP/g VS) was obtained at a hydraulic retention time (HRT) 7.14 h in the blanket solution. In the AFB reactor, the specific ATP content of suspended biomass was higher than that of immobilized biomass and increased with hydraulic retention time reaching a maximum value of 1.6 mg ATP/g VS at hydraulic retention time 4.35 h. The ATP content of anaerobes in the UASB effluent declined rapidly under aerobic conditions following a 2nd-order kinetic model.

Formation mechanism of nitrifying granules observed in an aerobic upflow fluidized bed (AUFB) reactor

The influences of trace metals in the wastewater and shear stress by aeration were particularly examined to clarify the formation mechanism of nitrifying granules in an aerobic upflow fluidized bed (AUFB) reactor. It was found that Fe added as a trace element to the inorganic wastewater accumulated at the central part of the nitrifying granules. Another result obtained was that suitable shear stress by moderate aeration (0.07-0.20 L/min/L-bed) promoted granulation. Furthermore, it was successfully demonstrated that pre-aggregation of seed sludge using hematite promoted core formation, leading to rapid production of nitrifying granules. From these results, a nitrifying granulation mechanism is proposed: 1) as a first step, nitrifying bacteria aggregate along with Fe precipitation, and then the cores of granules are formed; 2) as a second step, the aggregates grow to be spherical or elliptical in form due to multiplication of the nitrifying bacteria and moderate shear stress in the reactor, and then mature nitrifying granules are produced. Fluorescence in situ hybridization (FISH) analysis successfully visualized the change in the spatial distribution of nitrifying bacteria in the granules, which supports the proposed granulation mechanism.

Biodegradation of MTBE and BTEX in an aerobic fluidized bed reactor

An aerobic fluidized bed reactor (FBR) was operated for the removal of methyl tert-butyl (MBE) and benzene, toluene, ethylbenzene, and p-xylene (BTEX) from water. The reactor was seeded with a mixed culture adapted to MTBE. Granular activated carbon (GAC) was used as the biological attachment medium. Influent MTBE to the reactor was 7.8 mg/L MTBE, with a flow rate of 22.7 L/day, and an empty bed contact time of 1 hour. The acclimation period required was relatively short, about 30 days before reaching an average stable effluent concentration of 18.5 +/- 10 microg/L. BTEX was introduced to the feed at an equivalent chemical oxygen demand (COD) as the MTBE at day 225 and was biodegraded spontaneously with no apparent acclimation period required. The average influent of each of the four BTEX compounds was about 2 mg/L, and the range of the average effluent concentrations wae 1.4-2.2 microg/L. After achieving 180 days of stable performance with BTEX addition, the total low rate to the reactor was gradually increased by 20% increments to 160% of the original flow (36.4 L/day). Increases by 20% and 40% had no apparent effect on reactor performance, but increase by 60% required 30 days before effluent quality returned to previous values. Composition of the culture was monitored throughout operation of the reactor using denaturing gradient gel electrophoresis (DGGE). The culture consisted of Flavobacteria-Cytophaga and organisms with high similarity to the known MTBE degrader PM1.

The Effect of Benzene, Toluene, and o-Xylene on COD Removal in an Aerobic Fluidized Bed Reactor Utilizing Acetic Acid as the Main Carbon Source

A laboratory-scale fluidized bed reactor (FBR) model was operated to examine the effect of BTX on the removal of COD in the presence of acetic acid, which was readily degradable. An activated sludge culture was taken from a petrochemical industry wastewater treatment plant and acclimated first to acetic acid (up to 2,000 mg COD/L), and then to BTX (up to 3 mg/L) as a total concentration. Microbial oxygen uptake rates are controlled during the adaptation period. Then this culture is used as inoculum in the FBR unit. The system was initially operated with a total BTX concentration of 6 mg/L, and concentrations of 12 and 18 mg/L, respectively, were tried during an operational period of 42 days, while the theoretically estimated COD concentration (due to the acetic acid in the system) was kept constant, remaining at 2,000 ± 75 mg/L. An organic loading rate of 1.3 kg/m3/day and a hydraulic retention time of 36 h are the fixed operating parameters used during this study. It was seen that the dissolved COD concentrations in the effluent were relatively low and similar for 6 and 12 mg/L influent BTX concentrations. However, the dissolved COD concentration of effluent wastewater increased significantly when the total influent wastewater BTX concentration was 18 mg/L. The BTX concentration of the effluent wastewater was less than 1 mg/L, indicating BTX was accumulated onto the GAC, or it was biodegraded by attached micro-organisms. The experiments, which were carried out under shock loads of BTX at given intervals (with the FBR operating semicontinuously), proved this result with a very low (actually undetectable) effluent wastewater BTX concentration and a tendency to increase the effluent COD concentration caused foam formation in the reactor due to the adverse effect of BTX.

The COD Removal Performance of an Aerobic Fluidized Bed Reactor

Aerobic fluidized bed reactors (FBRs) are used as a new technology in wastewater treatment. In this study, an aerobic fluidized bed reactor with granulated activated carbon (GAC) as carrier material was operated under different conditions, including batch-loading, semicontinuous loading, and continuous loading. The FBR effluent was studied for changes in Chemical Oxygen Demand (COD). In this study, acetic acid was used as a carbon source. During the course of the study while the FBR was operating continuously initial COD influent concentration of the acetic acid was 1,000 ± 100 mg/L. Additional continuous flow investigations were conducted with the influent COD at 2000, 3,000 and 4,350 ± 125 mg/L. The total operation period was 5 months including a 1-month start-up process. Organic loading rate increased from 1.0 kg/day/m3 to 14.4 kg/day/m3. This was achieved by changing the influent water COD concentration and/or the hydraulic loading rate. The average effluent dissolved COD concentration was 141 ± 38 mg/L in this organic loading range. When the organic loading rate increased to 21 kg/day/m3, the effluent COD concentration sharply increased, and at the steady state the effluent COD was 928 mg/L. This can be attributed to an increase in the acetic acid concentration of the influent wastewater, because the hydraulic loading rate in the former mode of operation had remained stable. The biomass concentration in the fluidized bed was measured during continuous operation after the steady-state conditions were obtained. The total biomass concentration increased from 7500 mg/L to 17,300 mg/L during the study period.

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700 mg COD l−1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD l−1 h−1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02 mg ATP g VS−1 versus 0.85 mg ATP g VS−1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6 mg ATP g VS−1 versus 1.1 mg ATP g VS−1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.

A three-phase fluidized bed reactor in the combined anaerobic/aerobic treatment of wastewater

Aerobic degradation or polishing is an essential step in the combined anaerobic/aerobic treatment of wastewater. In this study, a type of porous glass beads was used for immobilization of microbial cells in a three-phase aerobic fluidized bed reactor (AFBR) with an external liquid circulation. The effects of superficial gas and liquid velocities on bed expansion, solid and gas hold-ups and specific oxygen mass transfer rate, kLa, were investigated. A tracer study showed that the mixing and flow pattern in the 8 dm3 reactor could be simulated by a non-ideal model of two continuous stirred tank reactors (CSTRs) in series. By treating an effluent from an upflow anaerobic sludge blanket (UASB) digester, the distribution of suspended and immobilized biomass in the reactor as well as the kinetics of COD removal were determined. The specific oxygen mass transfer rate, kLa, at a superficial gas velocity of 0.7 cm s−1 dropped by about 30% from 32 h−1 in tap water to 22 h−1 after a carrier load of 15% (v/v) was added. The measured kLa further dropped by about 20% to 18 h−1 in the wastewater, a typical value of the bubbling fermenters with no stirring. Compared with the aerobic heterotrophs under optimum growth conditions, the microbes in this reactor which was fed with anaerobic effluent plus biomass behaved like oligotrophs and showed slow specific COD removal rates. This might be attributed to the presence of a significant amount of obligate anaerobes and facultative organisms in the aerobic reactor. This was confirmed by a relatively low intrinsic oxygen uptake rate of the microbial population in the reactor, 94 mg O2 dm−3 h−1 or 19 mg O2g VS−1 h−1. © 1999 Society of Chemical Industry

Deicing Fluid Treatment in Batch-Loaded Aerobic Fluidized Bed Reactor

This study demonstrates the feasibility of treating storm water contaminated with airport deicing fluid (ethylene glycol) in a batch-loaded aerobic fluidized bed reactors. In addition, the removal rates were measured for batch-loaded and continuously loaded fluidized bed reactors. These values were compared with each other and with more conventional wastewater treatment processes. Treating the contaminated storm water in batches eliminated the operational problems common to a continuously loaded aerobic fluidized bed reactor. Most significantly, excess biofilm growth and the accompanying maintenance and operational problems were controlled through endogenous respiration. Ethylene glycol and chemical oxygen demand removal rates of 710 and 2,200 g/m{sup 3}/day, respectively, were achieved in the batch-loaded reactor. The resulting batch-loaded full-scale installation is expected to be two to three times larger than a continuously operated fluidized bed reactor; however, it is expected to be equal to or much smaller than more conventional activated sludge and fixed film process installations. An additional benefit of the batch-loaded process is the low quantity of sloughed biofilm, which results in a low level of effluent solids (16 mg/L total suspended solids). As a result, secondary clarification and associated sludge treatment might not be required.

EFFECTS OF TEMPERATURE ON CHLOROPHENOL BIODEGRADATION KINETICS IN FLUIDIZED-BED REACTORS WITH DIFFERENT BIOMASS CARRIERS

Groundwater contaminants including 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP), and pentachlorophenol (PCP) were mineralized in three aerobic fluidized-bed reactors (FBRs) employing sand, volcanite, and diatomaceous earth as biomass carriers. The effect of temperature on chlorophenol degradation kinetics was studied in FBR batch tests at temperatures ranging from 4 to 16.5°C. TCP and TeCP degradation was modeled using the Michaelis-Menten kinetics. Specific maximum degradation rates for TCP and TeCP varied with temperature from 0.46 × 10 −3 to 31 × 10 −3 mg mgVS −1 h −1 and K s varied from zero to 7.1 mg l −1. Degradation of PCP was affected by the presence of TCP and TeCP and followed competitive inhibition kinetics. Specific degradation rates for PCP degradation varied with temperature from 0.24 × 10 −3 to 1.7 × 10 −3 mg mgVS −1 h −1 and were always lower than for other chlorophenols. The Arrhenius equation described the temperature effects on biodegradation of chlorophenols. The activation energies (kJ mol −1) for TCP and TeCP varied from 126 to 194, and for PCP from 59 to 130. In the studied temperature range, a 10°C decrease in temperature generally resulted in over seven times slower degradation rates. The volcanite reactor had the highest and the sand reactor the lowest biomass accumulation. © 1998 Elsevier Science Ltd. All rights reserved

Operating strategies for aerobic fluidized bed reactors

This research demonstrated that an aerobic fluidized bed reactor can be operated either to maximize substrate removal, to minimize solids production or to treat intermittently produced wastewater. The operational mode is controlled by the quantity of biomass attached to the media. A thinner biomass encourages endogenous respiration and minimizes excess sludge production. Increasing biofilm thickness increases substrate removal efficiencies up to the point at which the diffusion of substrate, nutrients or oxygen becomes limiting. A thick biofilm was found to remain active even after an extended non-loading period, most likely because of endogenous respiration. Upon the introduction of substrate after the non-loading period, the substrate was immediately removed. This indicates the potential of using a fluidized bed reactor for applications that produce only intermittent wastewater flows, such as those found in many industries and hazardous waste remediation systems.

5487829 Internal media cleaning device for aerobic fluidized bed reactors : Safferman Steven I; Bishop Paul L Cincinnati, OH, United States assigned to The United States of America as represented by the Administrator of the United States Environmental Protection Agency; The University of Cincinnati

5487829 Internal media cleaning device for aerobic fluidized bed reactors : Safferman Steven I; Bishop Paul L Cincinnati, OH, United States assigned to The United States of America as represented by the Administrator of the United States Environmental Protection Agency; The University of Cincinnati

5487829 Internal media cleaning device for aerobic fluidized bed reactors

5487829 Internal media cleaning device for aerobic fluidized bed reactors

Aerobic Fluidized Bed Reactor with Internal Media Cleaning

An aerobic fluidized bed reactor process with internal media cleaning to control attached biomass thickness was developed. Biomass control was achieved by the periodic creation of a turbulent zone within a specially designed cylindrical screened region surrounding the effluent port. A screen washer aided in keeping the cylindrical screen clean. A bed lifter produced turbulence throughout the bed to allow individual media particles to enter the cleaning zone for the removal of excess biofilm. The reactor system operated continuously without excessive biomass buildup on the support media and without the need for external media cleaning or recovery. Four analytical methods—systematic scanning electron microscope (SEM) analyses, granular activated carbon drained density, phospholipid analyses, and fluorescein diacetate activity (FDA) measurements —were modified/developed for use in characterizing the microbial population attached to the media of the fluidized bed. The SEM analyses was valuable for monitoring changes and cleaning cycle caused to the biofilm. Phospholipid and FDA analyses were found to have potential for use as design and monitoring tools of the process.

Biological cyanide degradation in aerobic fluidized bed reactors: treatment of almond seed wastewater

The continuous aerobic transformation of synthetic cyanide waste-water, amygdalin solutions and almond seed extract containing cyanide was investigated in several fluidized bed reactors. Various inocula consisting of activated sludge or soil slurry were used. Successful inoculation was achieved with simple soil slurry. No significant influence was found between the performance of the systems inoculated with a cyanide contaminated soil and a garden soil. The performance and stability of the reactors with respect to degradation rate were tested for a range of cyanide loading conditions, with feed containing only cyanide, and with different additional carbon sources, as well as various C∶N ratios at a hydraulic retention time of 24 h. No growth with cyanide as the sole source of carbon and nitrogen was observed. The system with lactate as the organic C-source was capable of operating at cyanide concentrations of 160 ppm cyanide with a conversion rate of 0.125 kg cyanide/m3 d. Ammonia was the end product and the effluent concentration was 0.5 ppm CN−. The systems with ethanol as the organic C-source could degrade only 0.05 kg cyanide/m3 d, whose feed concentration was 60 ppm cyanide. Amygdalin, an organic cyanide-containing compound present in stone fruit seeds, was fed as a model substrate. Degradation rates up to 1.2 kg COD/m3 d could be measured with no free or organically bound cyanide in the effluent. These rates were limited by oxygen transfer, owing to the large amount of degradable COD. The further investigations with almond seed extracts, confirmed the applicability of the aerobic process to treat food-processing waste streams having low concentrations of cyanide with high COD content.

Laboratory‐scale evaluation of aerobic fluidized bed reactors for the biotreatment of a synthetic, high‐strength chemical industry waste stream

ABSTRACT: Laboratory‐scale fluidized bed reactors (FBRs) containing either sand or granular activated carbon (GAC) as biocarriers for immobilized bacteria were evaluated for biotreatment of chemical industry wastes. The FBRs were fed high levels of a synthetic waste stream containing aniline (ANL), methyl ethyl ketone (MEK), p‐nitrophenol (PNP) and sodium formate (FRM) at concentrations increasing from approximately 3 600 mg/L total chemical oxygen demand (COD) up to 17 000 mg/L COD. Microbial biomass attached to the GAC increased from 15 000 mg/L at a COD loading of 3.2 Kg COD m‐3 d‐1 to over 40 000 mg/L at a maximum COD loading of 16.0 Kg COD m‐3 d‐1. The sand was colonized slower during start‐up but supported biomass levels of 2 600 to 20 000 mg/L at COD loadings up to 9.6 COD m‐3 d‐3. Scanning electron microscopy confirmed biomass measurements and showed that high levels of bacteria were retained on GAC after a toxic surge in COD loading, but were significantly reduced in the sand reactor resulting in diminished performance. Specific chemical analyses showed over 99% removal of organic feed components by both reactors throughout the study. The sand reactor study was terminated early due to its inability to handle an accidental surge in COD loading. Biological solids production from the GAC reactor ranged from 0.056 to 0.184 g solids/g COD removed. The GAC reactor demonstrated a greater ability to handle rapid increases in COD loading (for adsorbable chemicals) than the sand reactor. This study has increased fundamental understanding of the operation and performance of FBRs treating a representative chemical industry waste stream and has demonstrated some advantages of GAC over sand as a biocarrier.