Biofilm Airlift Suspension Research Articles

Approximate Models of Microbiological Processes in a Biofilm Formed on Fine Spherical Particles

This paper concerns the dynamical modeling of the microbiological processes that occur in the biofilms that are formed on fine inert particles. Such biofilm forms e.g. in fluidized-bed bio-reactors, expanded bed biofilm reactors and biofilm air-lift suspension reactors. An approximate model that is based on the Laplace–Carson transform and a family of approximate models that are based on the concept of the pseudo-stationary substrate concentration profile in the biofilm were proposed. The applicability of the models to the microbiological processes was evaluated following Monod or Haldane kinetics in the conditions of dynamical biofilm growth. The use of approximate models significantly simplifies the computations compared to the exact one. Moreover, the stiffness that was present in the exact model, which was solved numerically by the method of lines, was eliminated. Good accuracy was obtained even for large internal mass transfer resistances in the biofilm. It was shown that significantly higher accuracy was obtained using one of the proposed models than that which was obtained using the previously published approximate model that was derived using the homotopy analysis method.

Polyacrylamide Wastewater Treatment in a Nested Biofilm Airlift Suspension Reactor

Polyacrylamide has been widely used in tertiary oil recovery. Oilfield produced water in a large scale contain polyacrylamide, leading to oilfield environment pollution. In this paper, the nested loops biofilm airlift suspension reactor was used in polyacrylamide wastewater treatment. In the reactor, wastewater can alternately flow through the hypoxic environment fixed light carriers and aerobic environment suspended walnut shell biological carriers, achieving simultaneous removal of organic matter and nitrogen. The influencing factors on the organic compound degradation and denitrification performance were studied. Biological and hydrodynamic model of nitrogen and carbon removal was established. Also, the biological phase structure of the carrier biofilm was observed. The results show that polyacrylamide degradation and ammonia nitrogen removal rate are around 30% and 95%, respectively when the experimental hydraulic retention time is 24h. Due to poor denitrification efficiency; nitrate removal rate is only 20%. The carrier biofilm thickness is appropriate, and filamentous bacteria occupy the dominant position.

A wastewater treatment using a biofilm airlift suspension reactor with biomass attached to supports: a numerical model

A mathematical model of the biological process occurring in a modified biofilm airlift suspension reactor is presented. When compared with a traditional wastewater treatment plant, a biofilm airlift suspension process has major advantages, such as higher oxygen levels in the bulk fluid and lower space requirements. The limited volumes obtained with this technique generally do not allow to reach the high times of contact required for an efficient removal of nitrogen that normally are characterized by a slower kinetics than carbonaceous compounds. To avoid this problem, supports for attached biomass growth were inserted in the reactor. Both physical and biological aspects were incorporated into the presented model to simulate the removal processes of the substrates. A sensitivity analysis was performed, and the model was validated using experimental results obtained at a lab-scale plant. This model can accurately estimate the removal rate in different boundary conditions providing the details of the water quality profiles through the reactor and in the attached biomass. The model thus represents a valid aid for design purposes and for the management of treatment plants that use these uncommon reactors. The model also provides the required hydraulic retention time for a complete nitrification and the appropriate recirculation ratio. The results have shown the full-scale applicability of this treatment due to its efficiencies coupled to the advantages of its low impact, low space requirement and low sludge production.

An integrated wastewater treatment system using a BAS reactor with biomass attached to tubular supports

This paper describes laboratory experiments aimed to develop a new wastewater treatment system as an alternative to a conventional domestic wastewater plant. A modified Biofilm Airlift Suspension reactor (BAS), with biomass attached to tubular supports, is proposed to address low organic loads (typical of domestic sewage) and low residence time (typical of compact reactors technology). Attached and suspended biomasses, coupled to the high dissolved oxygen (DO), allow high removal efficiencies (90% and 56% for COD and N–NH4+ removal respectively) and high effluent quality to be reached. The experimental activity, divided into three parts, demonstrates the good efficiency of the process, and the reduction of the removal kinetics for the high operating pressure used in the technology. The occurrence of simultaneous nitrification–denitrification (SND) was also observed. When compared with the conventional BAS system, the present treatment shows comparable removal efficiencies and higher specific removal rates (80 mg COD/g VSS and 2.60 mg N–NH4+/g VSS). The experimental results were coupled with the development of a numerical model to aid in designing a full-scale treatment plant in Italy.

Improvements in Biofilm Processes for Wastewater Treatment

2 Abstract: This review paper intends to provide an overall vision of biofilm technology as an alternative method for treating waste waters. This technology has been gaining popularity through the years, mainly because many wastewater treatment plants, which are still used Activated Sludge Process (AS) are present some shortcomings when exposed to increased hydraulic and organic loads. Fundamental research into biofilms is presented in three sections, Biofilm Types and Characterization, Advantages and Drawbacks and Design Parameters. The reactor types covered in this review are: un-submerged fixed film systems (trickling filters and rotating biological contactors) and submerged fixed film systems (biological aerated flooded filters, submerged aerated filters, biofilm up-flow sludge blanket, fluidized bed, expanded granular sludge blanket, biofilm airlift suspension, internal circulation, moving bed biofilm and membrane biofilm) reactors.

Biological oxidation of hydrogen sulfide in mineral media using a biofilm airlift suspension reactor

Hydrogen sulfide (H 2S) removal in mineral media using Thiobacillus thioparus TK-1 in a biofilm airlift suspension reactor (BAS) was investigated to evaluate the relationship between biofilm formation and changes in inlet loading rates. Aqueous sodium sulfide was fed as the substrate into the continuous BAS-reactor. The reactor was operated at a constant temperature of 30 °C and a pH of 7, the optimal temperature and pH for biomass growth. The startup of the reactor was performed with basalt carrier material. Optimal treatment performance was obtained at a loading rate of 4.8 mol S 2− m −3 h −1 at a conversion efficiency as high as 100%. The main product of H 2S oxidation in the BAS-reactor was sulfate because of high oxygen concentrations in the airlift reactor. The maximum sulfide oxidation rate was 6.7 mol S 2− m −3 h −1 at a hydraulic residence time of 3.3 h in the mineral medium. The data showed that the BAS-reactor with this microorganism can be used for sulfide removal from industrial effluent.

Simultaneous nitrification/denitrification in a biofilm airlift suspension (BAS) reactor with biodegradable carrier material

Simultaneous nitrification and denitrification in one reactor has been realized with different methods in the past. The usage of biodegradable biocompounds as biofilm carriers is new. The biocompounds were designed out of two polymers having different degradability. Together with suspended autotrophic biomass the biocompound particles were fluidized in an airlift reactor. Process water from sludge dewatering with a mean ammonium nitrogen concentration of 1150 mg L −1 was treated in a two stage system which achieved a nitrogen removal of 75%. Batch experiments clearly indicate that nitrification can be localized in the suspended biomass and denitrification in the pore structure of the slowly degraded biocompounds. Images taken with CLSM prove the concept of the pore structure within the biocompounds, which provide both a heterotrophic biofilm and carbon source.

N2O Production by Nitrifying Biomass Under Anoxic and Aerobic Conditions

The capacity of nitrifying biomass, grown in biofilms or in suspension, to reduce NO(2) (-) and NO(3) (-) under anoxic conditions was tested in batch experiments. The estimated reduction rates were 5 and 25 mg N per gram volatile suspended solids (VSS) per day for nitrate and nitrite, respectively, in the case of the nitrifying biofilms. Activity tests carried out with successive feedings indicated that no acclimation of the biomass to the tested conditions occurred, as the obtained reduction rates remained almost constant. Another series of activity assays was carried out with nitrifying suspended biomass, and the reduction rates for nitrate and nitrite were 30.4 and 48.9 mg N per gram VSS per day, respectively. N(2)O and N(2) were the final gaseous products, and their percentages depended on the source of nitrogen feed. The specific production of nitrous oxide during nitrification was investigated during continuous experiments in a biofilm airlift suspension reactor. Specific production rates up to 46 mg N(2)O-N per gram VSS per day were measured. The percentage of N(2)O produced represented up to 34.4% of the ammonia oxidized. Nitrite accumulation, low dissolved oxygen concentrations, and the presence of organic matter favored the production of nitrous oxide. N(2)O gas was not detected during the oxidation of nitrite even when organic matter was present. To prevent N(2)O gas production in nitrifying systems, the operation at low dissolved oxygen concentrations, nitrite presence, or organic matter content should be avoided.

Application of two component biodegradable carriers in a particle-fixed biofilm airlift suspension reactor: development and structure of biofilms

Two component biodegradable carriers for biofilm airlift suspension (BAS) reactors were investigated with respect to development of biofilm structure and oxygen transport inside the biofilm. The carriers were composed of PHB (polyhydroxybutyrate), which is easily degradable and PCL (caprolactone), which is less easily degradable by heterotrophic microorganisms. Cryosectioning combined with classical light microscopy and CLSM was used to identify the surface structure of the carrier material over a period of 250 days of biofilm cultivation in an airlift reactor. Pores of 50 to several hundred micrometers depth are formed due to the preferred degradation of PHB. Furthermore, microelectrode studies show the transport mechanism for different types of biofilm structures, which were generated under different substrate conditions. At high loading rates, the growth of a rather loosely structured biofilm with high penetration depths of oxygen was found. Strong changes of substrate concentration during fed-batch mode operation of the reactor enhance the growth of filamentous biofilms on the carriers. Mass transport in the outer regions of such biofilms was mainly driven by advection.

High-Rate Degradation of Aromatic Sulfonates in a Biofilm Airlift Suspension Reactor

A wastewater containing aromatic sulfonates was treated in a laboratory-scale biofilm airlift suspension (BAS) reactor. The general objective of the experiments was to assess the performance of a particle-based biofilm reactor in the biodegradation of refractory organic compounds under varying operating conditions. To this end, the reactor was inoculated with a mixed culture of biomass, adapted to grow on the leachate as the sole source of carbon, which colonized carrier particles in the reactor and formed stable and uniform biofilms. Depending on their degradation kinetics (characterized in independent experiments) and the fraction of specific degraders in the biofilms, aromatic sulfonates attain different degradation efficiencies in the BAS reactor, with more compex molecules (e.g., trisusbtituted naphthalene sulfonates and some bisubstituted naphthalene sulfonates) showing the lowest degradation efficiencies. The BAS reactor achieved high biomass concentration (12 g L -1 ) and an overall degradation efficiency of 67% based on COD measurements for loading rates up to 0.45 kg COD kg v s -1 day -1 , corresponding to a specific degradation rate of 0.3 kg COD kgvs -1 day -1 . For higher loading rates, the hydraulic retention time of leachate in the reactor proved to be insufficient for complete degradation of aromatic sulfonate with slow degradation kinetics, resulting in a decrease of overall degradation efficiency. The fast degradation rate of most aromatic sulfonates is attributed to the long biomass retention time and reactor biomass concentration, resulting in high concentrations of degraders for specific compounds.

Treatment of High-Strength Pharmaceutical Wastewater and Removal of Antibiotics in Anaerobic and Aerobic Biological Treatment Processes

Anaerobic and aerobic treatment of high-strength pharmaceutical wastewater was evaluated in this study. A batch test was performed to study the biodegradability of the wastewater, and the result indicated that a combination anaerobic-aerobic treatment system was effective in removing organic matter from the high-strength pharmaceutical wastewater. Based on the batch test, a pilot-scale system composed of an anaerobic baffled reactor followed by a biofilm airlift suspension reactor was designed. At a stable operational period, effluent chemical oxygen demand (COD) from the anaerobic baffled reactor ranged from 1,432 to 2,397mg∕L at a hydraulic retention time (HRT) of 1.25 day, and 979 to 1,749mg∕L at an HRT of 2.5 day, respectively, when influent COD ranged from 9,736 to 19,862mg∕L. As a result, effluent COD of the biofilm airlift suspension reactor varied between 256 and 355mg∕L at HRTs of from 5.0 to 12.5 h. The antibiotics ampicillin and aureomycin, with influent concentrations of 3.2 and 1.0mg∕L, respectively, could be partially degraded in the anaerobic baffled reactor: ampicillin and aureomycin removal efficiencies were 16.4 and 25.9% with an HRT of 1.25 day, and 42.1 and 31.3% with HRT of 2.5 day, respectively. Although effective in COD removal, the biofilm airlift suspension reactor did not display significant antibiotic removal, and the removal efficiencies of the two antibiotics were less than 10%.

Biological and electrochemical oxidation of naphthalenesulfonates

AbstractA biofilm airlift suspension (BAS) reactor and an undivided flow cell equipped with a boron‐doped diamond (BDD) anode and a stainless‐steel cathode were used to investigate the effects of varying operating conditions on process performance in the biological and electrochemical oxidation of a mixture of naphthalenesulfonates contained in the infiltration water of a contaminated industrial site. The experiments were aimed at evaluating the feasibility of process integration and the criteria for optimization (i.e. how to maximize degradation efficiency with minimum energy consumption) in combined biological and electrochemical oxidation of scarcely biodegradable compounds. Because of high reactor biomass concentration and long biomass retention time, the BAS reactor achieved a high degradation capacity (up to 6.8 kg COD m−3 d−1). On the other hand, owing to the recalcitrant character of some of the aromatic sulfonates in the leachate, the overall degradation efficiency did not exceed 70% based on COD measurements. All naphthalene‐mono‐ and ‐disulfonates (except naphthalene‐1,5‐disulfonate) were completely degraded in the BAS reactor, whereas more complex molecules (e.g. naphthalenetrisulfonates) were more recalcitrant to biological oxidation. These compounds were completely mineralized by electrochemical oxidation using a boron‐doped diamond anode. The energy consumption and the time required for the complete mineralization of the infiltration water decreased from 80 kWh m−3 and 4 h to 61 kWh m−3 and 3 h for the oxidation of raw and biologically pretreated leachate, respectively. Copyright © 2005 Society of Chemical Industry

Development of particle-based biofilms for degradation of xenobiotic organic compounds

The aim of the experiments performed in this work was to develop a biofilm airlift suspension (BAS) process for the degradation of a mixture of organic sulfonates contained in the infiltration water from a contaminated site. To achieve this goal, active biomass growing on the contaminating xenobiotic organics as the sole source of carbon was obtained by enriching a mixed microbial culture sampled from an activated sludge treatment plant. After kinetic characterisation, the enriched culture was inoculated in the BAS reactor, where it colonised carrier particles and formed stable and uniform biofilms. In spite of the slow growth and degradation kinetics ( μ max = 0.014 h - 1 ) , due to high biomass concentration (up to 12 g VS L −1) a high rate process was performed in the BAS reactor, achieving a degradation capacity of 8.7 kg COD m −3 d −1, with an overall degradation efficiency of 70% based on COD measurements.

Influence of Hydrodynamics on the Performance of a Biofilm Airlift Suspension Reactor

Five biofilm airlift suspension (BAS) reactors filled with ceramic materials as biocarriers were used to investigate the hydrodynamics, liquid mixing, and biofilm detachment kinetics in the BAS reactor. A mathematical model was developed to describe the internal liquid circulation within the BAS reactor. The Froude number was introduced to correlate the relationship between the Froude number and superficial gas velocity at different biocarrier concentrations. The validity of the empirical model was verified over a wide range of experimental conditions and the result shows that the internal liquid circulation velocity was proportional to the square root of the reactor height and the superficial gas velocity. Because the internal liquid circulation flow rate was much larger than influent flow rate, the BAS reactor had a strong capacity to resist shock loading caused by the change in influent organic matter concentration. Shock loading resistance increased with the height of a BAS reactor. Although biofilm detachment was a very complicated process which involved many mechanisms, dimensional analysis was employed to successfully analyze the biofilm detachment kinetics. It was found that the biofilm detachment rate was proportional to the first power of the superficial gas velocity and biofilm thickness, and to the 2/3 power of the number of biocarriers in the reactor, respectively. Use of the Froude number and dimensional analysis provide an effective and accurate method to study the characteristics of the BAS reactor.

Performance of a Biofilm Airlift Suspension Reactor for Synthetic Wastewater Treatment

Performance stability of a biofilm airlift suspension reactor (BASR) was studied using ethanol as a substrate. The main objective of this research was to investigate the applicability of the reactor as a wastewater treatment process by examining the effects of soluble chemical oxygen demand (SCOD) loading rate and hydraulic retention time (HRT) on the performance of the reactor. SCOD removal of 90% or higher was achieved at an HRT of 45 min with loading rates from 10 to 18 kg SCOD/m3 day. Similar results were obtained at HRTs of 60 and 90 min and a SCOD loading rate of 10 kg SCOD/m3 day. Nitrification occurred in the system when the ratio of SCOD to ammonia nitrogen was changed from 10:1 to 6:1. The morphology of the biofilm in the BASR was denser and thicker when nitrifiers grew in the biofilm. Filamentous overgrowth was observed from time to time and proper chlorine dose successfully suppressed its growth. The oxygen uptake rate was an effective tool for monitoring the effect of chlorination.

Coupled BAS and anoxic USB system to remove urea and formaldehyde from wastewater

Wastewater containing formaldehyde and urea was treated using a coupled system consisting of a biofilm airlift suspension (BAS) reactor and an anoxic upflow sludge blanket (USB) reactor. The anoxic USB reactor was used to carry out denitrification and urea hydrolysis, while the BAS reactor was used to carry out nitrification. In a first step, individual experiments were carried out to investigate the effects of both compounds on the nitrifying and denitrifying biomass. The BAS reactor was fed with a synthetic medium containing 500 mg N-NH 4 + L −1 and 100 mg N-urea L −1, that were added continuously to this medium. Neither urea hydrolysis nor inhibition of nitrification was observed. Nitrification efficiency decreased when formaldehyde was fed during shocks at concentrations of 40, 80 and 120 mg C-formaldehyde L −1. The anoxic USB reactor was fed with a synthetic medium containing nitrate, formaldehyde and urea. Concentrations of formaldehyde in the reactor of 100–120 mg C-formaldehyde L −1 caused a decrease in the denitrification and urea hydrolysis rates. In a second step, the coupled system was operated at recycling ratios ( R) of 3 and 9. Fed C/N ratios of 0.58, 1.0 and 1.5 g C-formaldehyde g −1 N-NH 4 + were used for every recycling ratio. The maximum nitrogen removal percentages were achieved at a C/N ratio of 1.0 g C-formaldehyde g −1 N-NH 4 + for both recycling ratios. A fed C/N ratio of 1.5 g C-formaldehyde g −1 N-NH 4 + caused a decrease in the efficiency of the system with respect to nitrogen removal, due to the presence of formaldehyde in the BAS reactor, which decreased the nitrification. Formaldehyde was completely removed in the BAS reactor and a heterotrophic layer formed around the nitrifying biofilm.

Biofilm Airlift Suspension Reactor Treatment of Domestic Wastewater

Domestic wastewater with an influent COD of 160 to 327 mg L-1 was evaluated for treatment by the Biofilm Airlift Suspension-reactor (BAS-reactor). Ceramic materials withdiameters of 0.25–0.5 mm (for reactor (1)) and 0.5–0.71 mm(for reactor (2)) were used as carriers, respectively. Theresults show that reactor (1) with smaller carriers outperformedreactor (2) with larger carriers. At steady state, the BAS-reactors showed high COD removal efficiencies. When the HRT was kept at 0.5 hr, the mean effluent CODs were 33±4 and 58±5 mg L-1 for reactors (1) and (2), respectively, at a confidence interval of 95% (p = 95%). When HRT was extended to 1.0 hr, these values decreased to 24±2 and 30±3 mg L-1 for reactors (1) and (2), respectively (p = 95%). Biomass concentration increased whilebiofilm thickness decreased with an increase in carrierconcentration. Biomass concentrations as high as 6.16±0.12 and 5.50±0.10 g VSS L-1 (p = 0.95) were achieved at carrier concentrations of 100 g L-1 forreactors (1) and (2), respectively. Biofilm thickness had a significanteffect on reactor performance: with an increase in biofilm thickness, biomass concentration increased and the critical gas velocity to maintain carrier fluidization decreased. An oxygenation model for a BAS-reactor was proposed and the effectsof gas velocity and carrier concentration on the oxygen transfercoefficient were examined. It was found that oxygen transfer coefficient increased with gas velocity while the relationship between carrier concentration and oxygen transfer coefficient wascomplicated. During a period of more than three months of steadystate operation, carrier washout with the effluent was negligible.Comparison of the parameters of the conventional activated sludgeprocess to that of the BAS-reactor shows that the BAS-reactor isa promising wastewater treatment process with high efficiency andlow operation cost.

Degradation of polymers in a biofilm airlift suspension reactor

The effect of degradation of polymeric substrates (starch and soy proteins mixture) on the structure of biofilms has been studied. The characteristics of the obtained biofilms were compared to those obtained on corresponding monomeric substrates (glucose and aspartic acid). Based on literature suggestions it was hypothesized that the polymeric substrates, which have a low diffusion rate in the biofilm matrix, would affect the biofilm structure if hydrolytic activity occurs in the biofilm. The obtained biofilm could be expected to present properties like low density and rough surface, facilitating transport and conversion of large polymeric molecules. From the present study it was concluded that the structure of the formed biofilms was influenced by the substrate degraded, however no unequivocal effect of degradation of a polymer on the biofilm structure could be observed. The hydrolytic activity with soy protein and starch as substrate was under stable conditions found to be mainly associated to the biofilm (more than 95% of the total activity). During unstable conditions or start-up significant hydrolytic activity occurred outside the biofilm.

Aerobic granulation in a sequencing batch airlift reactor

Aerobic granular sludge was cultivated in an intensely mixed sequencing batch airlift reactor (SBAR). A COD loading of 2.5 kg Acetate-COD/(m 3 d) was applied. Granules developed in the reactor within one week after inoculation with suspended activated sludge from a conventional wastewater treatment plant. Selection of the dense granules from the biomass mixture occurs because of the differences in settling velocities between granules (fast settling biomass), and filaments and flocs (slow settling biomass). At ‘steady state’ the granules had an average diameter of 2.5 mm, a biomass density of 60 g VSS/l of granules, and a settling rate of >10 m/h. The biomass consisted of both heterotrophic and nitrifying bacteria. The reactor was operated over a long period during which the granular sludge proved to remain stable. The performance of the intermittently fed SBAR was compared to that of the continuously fed biofilm airlift suspension reactor (BASR). The most importance difference was that the density of the granules in the SBAR was much higher than the density of the biofilms in the BASR. It is discussed that this could be due to the fact that the SBAR is intermittently fed, while the BASR is continuously fed.

Simultaneous urea hydrolysis, formaldehyde removal and denitrification in a multifed upflow filter under anoxic and anaerobic conditions

A multifed upflow filter (MUF), working under anoxic or anaerobic conditions, coupled with an aerobic biofilm airlift suspension (BAS) reactor was operated in order to treat a wastewater with high formaldehyde (up to 1.5 g L −1) and urea (up to 0.46 g L −1) concentrations. In the MUF, formaldehyde removal, denitrification and urea hydrolysis took place simultaneously. The MUF was operated at 37°C, at a hydraulic retention time (HRT) ranging from 1 to 0.3 d. An organic loading rate (OLR) of 0.5 kg-formaldehyde m −3 d −1 was efficiently eliminated during anaerobic operation and transformed into methane, while a much higher OLR (up to 2 kg-formaldehyde m −3 d −1) was oxidised under anoxic conditions by the nitrite or nitrate from the nitrifying airlift. However, only 80% of urea was hydrolysed to ammonia in an anoxic environment while complete conversion occurred under anaerobic conditions. Moreover, formaldehyde concentrations higher than 50 mg L −1 provoked a loss of efficiency of urea hydrolysis, decreasing to 10% at formaldehyde concentrations above 300 mg L −1. Methane production rate during the anaerobic stage was adversely affected by accumulations of formaldehyde in the reactor causing lower formaldehyde removal efficiency. However, denitrification proceeded properly even at a formaldehyde concentration of 700 mg L −1 in the reactor, although nitrous oxide appears in the off-gas. The COD/N ratios required for complete nitrite and nitrate denitrification with formaldehyde were estimated at 2.1 and 3.5 kg-COD/kg-N, respectively.