Biofilm Surface Area Research Articles

Performance of rotating perforated tubes biofilm reactor in biological wastewater treatment

A novel biofilm reactor named as ‘rotating perforated tubes biofilm reactor (RPT)’ was developed and used for biological treatment of synthetic wastewater. Effects of major process variables such as COD loading rate, specific biofilm surface area, number of tubes and the rotational speed (rpm) on COD removal performance of the reactor was investigated. COD removal efficiency increased with the specific biofilm surface area and the rotational speed, but decreased with increasing COD loading rate. Kinetics of COD removal was investigated and kinetic constants were determined by using the experimental data. An empirical design equation was developed to quantify the system’s performance as a function of the operating variables.

Modeling the removal of VOC mixtures in biotrickling filters

A mathematical model was derived for describing removal of mixed VOC vapors in biotrickling filters (BTFs). The model accounts for potential process rate limitation by the availability of oxygen as well as for potential kinetic interactions among pollutants during their biodegradation. Without using any fitted parameter, the model was found capable of predicting experimentally obtained removal rates of mono-chlorobenzene (m-CB) and ortho-dichlorobenzene (o-DCB) vapors. Experimental results reported here show that m-CB removal is better than that of o-DCB. The two compounds were known to be involved in a kinetic cross-inhibition interaction when degraded in suspended culture. However, model sensitivity studies showed that cross-inhibition does not affect BTF performance due to the low pollutant concentrations involved. For the same reason, the influence of oxygen on BTF performance was found to be minimal under the conditions tested. The model was found to predict experimentally obtained values with less than 10% error in the majority of cases. Computations with an earlier model describing VOC removal in conventional biofilters showed that, for the model mixture used in this study (m-CB/o-DCB), removal rates obtained with BTFs are one to more than two orders of magnitude higher than those obtained with conventional biofilters. This is attributed to the larger active specific biofilm surface area in BTFs, obtained through the creation of favorable growth conditions for the biomass, and better moisture control.

Biofiltration of toluene vapors using a model support

Vermiculite was used as biofiltration model support to study the degradation of toluene vapors. Thermal Gravimetric Analysis, cell respirometry, microcosms tests and qualitative data from Scanning Electron Microscopy (SEM) were used to estimate all the parameters (biofilm surface area, biofilm thickness, active and total biofilm density and maintenance coefficient) involved in a steady state biofiltration model. A global error of 9.7% between experimental data and the mathematical model for three different Empty Bed Residence Time (EBRT) was obtained.

Evaluation of kinetic parameters of biochemical reaction in three-phase fluidized bed biofilm reactor for wastewater treatment

This study evaluates the kinetic parameters of biochemical reaction in three-phase fluidized bed biofilm reactor from the steady state values of the response of the system to step changes in inlet concentration. It was observed from the outlet biological oxygen demand (BOD 5) plot of the response of the system that as the inlet BOD 5 was increased, the outlet BOD 5 also increased, reached a peak value and then decreased until it leveled to a new steady state value corresponding to the new inlet concentration level. The increase in BOD 5 was attributed to the accumulation of substrate within the reactor as well as the decrease in biofilm substrate consumption rate as the microorganisms adjusted to the new environment. Using the substrate balance at steady state and assuming Monod kinetics, an equation relating the substrate consumption rate to substrate concentration (BOD 5) and total biofilm surface area had been established. Monod kinetic parameters were found to be K=2.20 g/m 2/day, K m=17.41 g/m 3 and K/ K m=0.13 m/day. The ratio K/ K m can be taken as the indicator for biofilm substrate degradation effectiveness at low substrate concentrations.

Biofilm characteristics as affected by sand size and location in fluidized bed vessels

Biofilm structure was quantitatively analyzed to detect differences in biofilm structure due to sand size (effective diameter D 10 of 0.23 and 0.60 mm) and location within a fluidized-sand filter vessel. Laser scanning confocal microscopy and 3D image analysis were used to quantify biofilm volume per unit sand area, biofilm surface area per unit sand area, and biofilm surface area per biofilm volume. Biofilms from reactor vessels using 0.60 mm sand size had thin, smoother biofilms which was attributed to higher shear environments, in contrast to the thick, rough, porous films that were measured on the 0.23 mm sand samples. The thicknesses of the biofilms in the small sand reactors were affected by their location within the reactor vessel, i.e. films from the base of the reactor in the more highly turbulent zone had thinner biofilms than films on sands that were taken from a higher less turbulent location in the reactor vessel. A major finding of this study was that biofilm surface area per biofilm volume remained fairly constant regardless of sand size and sampling location.

Biofilm thickness variability investigated with a laser triangulation sensor.

Measurement of the surface roughness and thickness of biological films is laborious and usually destructive, thus hampering research in this area. We developed a laser triangulation sensor (LTS) set-up for the fast and nondestructive measurement of these biofilm parameters during growth. Using LTS measurements, the morphological development of a dichloromethane-(DCM) degrading biofilm cultured on a wetted-wall column was studied. The measurements show that the biofilm develops faster at the entrance of the reactor. The biofilm consisted of a base film in which microbial colonies were embedded. The biofilm-surface area gradually increased by 23% compared to the bare surface due to the formation of a large number of these colonies. The number and shape of these colonies were followed in time. Using LTS measurements, biofilms distinctly different in surface roughness could be distinguished in a laboratory trickling filter removing DCM from a waste gas. The consequences of the observed surface characteristics for the reaction-diffusion process in the biofilm and for the falling film hydrodynamics are discussed.

Speciation and Chemical Interactions in Nitrifying Biofilms. II: Sensitivity Analysis

Steady-state models of nitrifying biofilms have been developed that take into account the mass transfer of neutral and ionic species, electroneutrality, pH-dependent Monod kinetics, chemical equilibrium, and the presence of a boundary layer. Under the conditions investigated, the models predict significant changes in the biomass speciation and percent conversions in nitrifying biofilms as functions of pH, buffer capacity [in terms of total inorganic carbons], and, for the reactor models, volumetric flow rate per unit surface area of biofilm and total ammonium loading. To a lesser extent, the models also predict sensitivity to biofilm thickness, total ammonium, total nitrite, dissolved oxygen concentration, and total biomass density. Nitrogen conversions are only a very weak function of boundary layer thickness, total nitrate concentration, and the ratio of the chemical species' diffusivity in the biofilm to its diffusivity in water.

Biological pretreatment of a chemical plant wastewater in high-rate moving bed biofilm reactors

The Moving Bed Biofilm Reactor (MBBR), where the biomass is attached to small plastic carrier elements that move freely along with the water in the reactors, has been tested for biological pretreatment of a complex chemical industry wastewater. The MBBRs were tested at organic loads up to 53 g BOD5/m2d and always removed the easily biodegradable BOD fraction, ranging from about 60 to 80%. At organic loads from 10 to 20 g BOD5/m2d slowly biodegradable organic matter was also metabolized, sometimes removing more than 95% BOD5. After polishing in an activated sludge unit, the final effluent had an average concentration of only 3.4 mg filtered BOD5/l. With a very high specific biofilm surface area, MBBRs followed by activated sludge offer a compact process combination for complete biological treatment of chemical industry wastewaters.

Biological pretreatment of a chemical plant wastewater in high-rate moving bed biofilm reactors

The Moving Bed Biofilm Reactor (MBBR), where the biomass is attached to small plastic carrier elements that move freely along with the water in the reactors, has been tested for biological pretreatment of a complex chemical industry wastewater. The MBBRs were tested at organic loads up to 53 g BOD5/m2d and always removed the easily biodegradable BOO fraction, ranging from about 60 to 80%. At organic loads from 10 to 20 g BOD5/m2d slowly biodegradable organic matter was also metabolized, sometimes removing more than 95% BOD,. After polishing in an activated sludge unit, the final effluent had an average concentration of only 3.4 mg filtered BOD5/l. With a very high specific biofilm surface area, MBBRs followed by activated sludge offer a compact process combination for complete biological treatment of chemical industry wastewaters.

Kinetics of biological treatment of phenolic wastewater in three-phase fluidized bed containing biofilm and suspended sludge

Phenolic wastewater was treated in complete mixing type three-phase fluidized bed which contained both biofilm and suspended sludge. By considering the contributions of biofilm and suspended sludge to biodegradation of phenol separately, phenol removal rates with biofilm and with suspended sludge were evaluated both theoretically and experimentally. As a result, biodegradation of phenolic wastewater by biofilm process could be treated as a zero-order reaction. The volumetric biological removal rates with biofilm was proportional to the specific surface area of the biofilm with biodegradation coefficients (K) of 1.25×10−2 kg-PhOH/m2-biofilm/d. At a lower suspended sludge concentration, bioparticle diameter and bioparticle hold-up in the three-phase fluidized bed reactor were decisive factors for the efficiency of phenol treatment, and it was also proved that almost 100 % of phenol removal could be attained at a larger specific biofilm surface area per volumetric phenol loading rate than 80 m2/(kg-PhOH/d) without suspended sludge.

Biological pretreatment of poultry processing wastewater

A biological pretreatment plant for poultry processing wastewater was designed, using an aerated equalization tank followed by two high-rate moving bed biofilm reactors (MBBRs) in series. No solids separation and sludge handling was installed. The solids from the pretreatment plant were discharged to the municipal sewer together with the pretreated wastewater. The pretreatment plant performed well, even at organic loads significantly higher than the design values. With a specific biofilm surface area of 250 m2/m3 and a total volumetric organic load of 30–45 kg COD/m3 × d on MBBR1, the removal of filtered COD was as high as 80% over MBBR1 and 90–95% over MBBR1 plus MBBR2.

Kinetics of biological treatment of phenolic wastewater in three-phase fluidized bed containing biofilm and suspended sludge

Phenolic wastewater was treated in complete mixing type three-phase fluidized bed which contained both biofilm and suspended sludge. By considering the contributions of biofilm and suspended sludge to biodegradation of phenol separately, phenol removal rates with biofilm and with suspended sludge were evaluated both theoretically and experimentally. As a result, biodegradation of phenolic wastewater by biofilm process could be treated as a zero-order reaction. The volumetric biological removal rates with biofilm was proportional to the specific surface area of the biofilm with biodegradation coefficients (K) of 1.25x10-2 kg-PhOH/m2biofilm/d At a lower suspended sludge concentration, bioparticle diameter and bioparticle hold-up in the three-phase fluidized bed reactor were decisive factors for the efficiency of phenol treatment, and it was also proved that almost 100 % of phenol removal could be attained at a larger specific biofilm surface area per volumetric phenol loading rate than 80 m2/(kg-PhOH/d) without suspended sludge.

Biological pretreatment of poultry processing wastewater

A biological pretreatment plant for poultry processing wastewater was designed, using an aerated equalization tank followed by two high-rate moving bed biofilm reactors (MBBRs) in series. No solids separation and sludge handling was installed. The solids from the pretreatment plant were discharged to the municipal sewer together with the pretreated wastewater. The pretreatment plant performed well, even at organic loads significantly higher than the design values. With a specific biofilm surface area of 250 m2/m3 and a total volumetric organic load of 30–45 kg COD/m3 × d on MBBR1, the removal of filtered COD was as high as 80% over MBBR1 and 90-95% over MBBR1 plus MBBR2.

Simulation of citric acid production by rotating disk contactor

A simple model was presented to describe the time courses of citric acid production by a rotating disc contactor (RDC) using Aspergillus niger. The model is expressed by Monod-type cell growth, Luedeking-Piret-type citric acid production rate equations, and the diffusion equation for oxygen in the biofilm. The model contains five parameters which were determined by the nonlinear least squares method by fitting the numerical solution to the experimental data. In solving the equations, the cell density of the biofilm was estimated from the value of cellular mass per unit of biofilm area using an empirical equation. The experimental time courses in citric acid production period were well simulated with this model. The relation between the specific biofilm surface area and the rate of citric acid production was also explained by the simulation using the average values of five parameters of twelve runs. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 689–696, 1997.

Simulation of citric acid production by rotating disk contactor

A simple model was presented to describe the time courses of citric acid production by a rotating disc contactor (RDC) using Aspergillus niger. The model is expressed by Monod-type cell growth, Luedeking-Piret-type citric acid production rate equations, and the diffusion equation for oxygen in the biofilm. The model contains five parameters which were determined by the nonlinear least squares method by fitting the numerical solution to the experimental data. In solving the equations, the cell density of the biofilm was estimated from the value of cellular mass per unit of biofilm area using an empirical equation. The experimental time courses in citric acid production period were well simulated with this model. The relation between the specific biofilm surface area and the rate of citric acid production was also explained by the simulation using the average values of five parameters of twelve runs. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 689-696, 1997.

生物膜の挙動に与える膜表面形態の影響

Qualitative effects of morphology of surface on behavior of biofilm were investigated by two-dimensional biofilm model with ideal rough surface which was numerically analyzed by finite element method. This model is presented by diffusion and double Monod-type microbial reactions in the biofilm and the diffusion layer can be included in the model. The biofilm was formed by acidophilic iron-oxidizing bacteria.Effect of the roughness of surface on the increase rate of flux, which is the rate of substrate removal flux of biofilm with rough surface to that of plane biofilm, is significant when surface roughness is large. This effect is changed by substrate and dissolved oxygen concentration in bulk liquid and the influence of the concentration in bulk liquid is small when the surface roughness is large. The maximum rate of increase of flux approaches to the rate of increase of surface area of biofilm. Morphology and area of biofilm domain (IMFD) which has 99% of substrate removal flux is changed by the surface roughness and the concentration in bulk liquid. The rate of increase of flux becomes large when IMFD changes around the shape of rough surface.

Formation and Detachment of Biofilms and Granules in a Nitrifying Biofilm Airlift Suspension Reactor

AbstractThe influence of the bare basalt carrier concentration on nitrifying biofilm formation in biofilm airlift suspension (BAS) reactors was studied. The time needed to develop fully covered biofilm particles strongly increased with an increasing initial carrier concentration. This was caused by the increased shear and subsequent higher detachment. During startup the diameter of the biofilm particles increased, leading to a higher biomass concentration, larger biofilm surface area, and lower surface‐specific substrate load. Eventually a “steady state” thickness is obtained, where surface‐specific growth and detachment are equal. The biofilm density decreased with a decreasing bare basalt concentration. The steady state biomass concentration was not very much influenced by the initial carrier concentration. Up to 75% of the produced biomass was retained in the reactors. Maximum biomass retention was found when the initial bare basalt concentration was in between 10 and 30 g·L−1. The continuous detachment of biofilm fragments leads, upon growth of these small fragments, to the formation of granules (biofilms without a carrier). The granules have average density and size equal to those of the biofilm particles. The granules are formed, if the detached biofilm fragments are large enough to be retained by the three‐phase separator on top of the BAS reactor. Since the superficial liquid velocity in the three‐phase separator is scale dependent, granule formation will be influenced by reactor scale, hydraulic load, and dimensions of the three‐phase separator.

Dynamics of biofilm detachment in biofilm airlift suspension reactors

The dynamic change in the overall detachment rate of spherical biofilms in a biofilm airlift suspension reactor was measured after a downshift of the substrate loading rate to zero while all other conditions remained constant. In contrast to the expectations, the overall detachment rate decreased rapidly to a nearly stable level. Correlations available from literature were not able to describe this phenomenon. Concepts were formulated which can describe the observations from this study. Research under dynamic conditions and careful monitoring of the biofilm surface area and biofilm morphology are necessary to elucidate and discriminate biofilm detachment mechanisms.

Nitrogen removal from dilute wastewater in cold climate using moving‐bed biofilm reactors

A moving‐bed biofilm reactor has been developed, where the biofilm grows on small, free‐floating plastic elements with a large surface area and a density slightly less than 1.0 g/cm3. Nitrogen removal, based on nitrification and denitrification, was studied in a pilot plant with an active, specific biofilm surface area of approximately 310 m2/m3. Temperatures ranged from 7 to 18°C, and untreated wastewater had concentrations typically less than 100 mg soluble chemical oxygen demand (COD)/L and 25 mg total N/L. Both predenitrification, using untreated wastewater as carbon source, and post‐denitrification of pre‐precipitated wastewater, using acetate as an external carbon source, were examined. The predenitrification process was carbon limited, and only 50% to 70% total N removal was obtained, at a recirculation ratio of approximately 2.0 and a total empty bed hydraulic residence time of approximately 6 hours in the biofilm reactors. With post‐denitrification and an external carbon source, 80% to 90% total N removal could easily be reached at total empty bed hydraulic residence times less than 3 hours.

Nitrification of municipal wastewater in moving‐bed biofilm reactors

A moving‐bed biofilm reactor has been developed, where the biofilm grows on small, free‐floating plastic elements with a large surface area and a density slightly less than 1.0 g/cm3. Nitrification of preprecipitated wastewater in a once‐through system and raw wastewater in a recycled system with predenitrification has been studied in a pilot plant with an active, specific biofilm surface area of approximately 310 m2/m3. Maximum nitrification rates under comparable operating conditions were 20% to 25% higher with preprecipitated wastewater in the once‐through system than with raw wastewater in the recycled system. A temperature coefficient of θ = 1.09 was found. However, under oxygen‐limited conditions, the apparent temperature effect was insignificant in the temperature range from 7 to 18°C because of increased dissolved oxygen levels at low temperatures. At 10°C volumetric nitrification rates from 300 to 400 g NH4‐N/m3·d can be expected.