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. (c) 1995 John Wiley & Sons, Inc.     

Modeling of biofilm reactors with consecutive reactions

Modeling of biofilm reactors has been carried out by several authors. Most of the models use first-order or zero-order kinetics, because of the simplicity of the solution of the mathematical problem. However, the reaction kinetics for many practical situations is a non-linear Monod kinetics, which requires numerical solutions. This paper deals with the modeling of biofilm reactors and effectiveness factor calculations for a biofilm particle with Monod kinetics and two consecutive reactions. The model is applied to biological denitrification in a fluidized bed bioreactor, in which the liquid phase is assumed to be in plug flow. Effectiveness factors of biofilm are numerically calculated by solving the system of ODES by orthogonal collocation. Axial concentration profiles of nitrate and nitrite species are calculated and compared with experimental results.     

Mathematical modelling of biofilm structures

The morphology of biofilms received much attention in the last years. Several concepts to explain the development of biofilm structures have been proposed. We believe that biofilm structure formation depends on physical as well as general and specific biological factors. The physical factors (e.g. governing substrate transport) as well as general biological factors such as growth yield and substrate conversion rates are the basic factors governing structure formation. Specific strain dependent factors will modify these, giving a further variation between different biofilm systems. Biofilm formation seems to be primarily dependent on the interaction between mass transport and conversion processes. When a biofilm is strongly diffusion limited it will tend to become a heterogeneous and porous structure. When the conversion is the rate-limiting step, the biofilm will tend to become homogenous and compact. On top of these two processes, detachment processes play a significant role. In systems with a high detachment (or shear) force, detachment will be in the form of erosion, giving smoother biofilms. Systems with a low detachment force tend to give a more porous biofilm and detachment occurs mainly by sloughing. Biofilm structure results from the interplay between these interactions (mass transfer, conversion rates, detachment forces) making it difficult to study systems taking only one of these factors into account. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anammox enrichment from reject water on blank biofilm carriers and carriers containing nitrifying biomass: operation of two moving bed biofilm reactors (MBBR)

The anammox bacteria were enriched from reject water of anaerobic digestion of municipal wastewater sludge onto moving bed biofilm reactor (MBBR) system carriers-the ones initially containing no biomass (MBBR1) as well as the ones containing nitrifying biomass (MBBR2). Duration of start-up periods of the both reactors was similar (about 100?days), but stable total nitrogen (TN) removal efficiency occurred earlier in the system containing nitrifying biomass. Anammox TN removal efficiency of 70% was achieved by 180?days in both 20?l volume reactors at moderate temperature of 26.0°C. During the steady state phase of operation of MBBRs the average TN removal efficiencies and maximum TN removal rates in MBBR1 were 80% (1,000?g-N/m(3)/day, achieved by 308?days) and in MBBR2 85% (1,100?g-N/m(3)/day, achieved by 266?days). In both reactors mixed bacterial cultures were detected. Uncultured Planctomycetales bacterium clone P4, Candidatus Nitrospira defluvii and uncultured Nitrospira sp. clone 53 were identified by PCR-DGGE from the system initially containing blank biofilm carriers as well as from the nitrifying biofilm system; from the latter in addition to these also uncultured ammonium oxidizing bacterium clone W1 and Nitrospira sp. clone S1-62 were detected. FISH analysis revealed that anammox microorganisms were located in clusters in the biofilm. Using previously grown nitrifying biofilm matrix for anammox enrichment has some benefits over starting up the process from zero, such as less time for enrichment and protection against severe inhibitions in case of high substrate loading rates.     

Optimisation of support medium for particle-based biofilm reactors

The aim of this study was to propose a method to improve the biofilm growth on different polymer materials by modifying their surface properties. The ability of two aerobic bacteria strains: Pseudomonas aeruginosa O1 and Bacillus subtilis CIP 5265 to grow on various non-coated and coated polymer materials were investigated. A layer of polymethylmethacrylate and powdered activated carbon (PMMA/PAC) was used to improve the microbial adhesion dynamics. The substratum and cell surface properties were characterized using contact angle measurements. Fluorescent microscopy and SEM were used to observe the support and the biofilm growth. It was determined that better results can be obtained increasing the difference between the surface free energies of the support and the bacteria. It was found that supports with modified surface show higher biofilm development rate and better surface colonization. The influence of the surface free energy on the detachment force and correspondingly on the biofilm formation was demonstrated.     

A biofilm model to understand the onset of sulfate reduction in denitrifying membrane biofilm reactors

This work presents a multispecies biofilm model that describes the co‐existence of nitrate‐ and sulfate‐reducing bacteria in the H₂‐based membrane biofilm reactor (MBfR). The new model adapts the framework of a biofilm model for simultaneous nitrate and perchlorate removal by considering the unique metabolic and physiological characteristics of autotrophic sulfate‐reducing bacteria that use H₂ as their electron donor. To evaluate the model, the simulated effluent H₂, UAP (substrate‐utilization‐associated products), and BAP (biomass‐associated products) concentrations are compared to experimental results, and the simulated biomass distributions are compared to real‐time quantitative polymerase chain reaction (qPCR) data in the experiments for parameter optimization. Model outputs and experimental results match for all major trends and explain when sulfate reduction does or does not occur in parallel with denitrification. The onset of sulfate reduction occurs only when the nitrate concentration at the fiber's outer surface is low enough so that the growth rate of the denitrifying bacteria is equal to that of the sulfate‐reducing bacteria. An example shows how to use the model to design an MBfR that achieves satisfactory nitrate reduction, but suppresses sulfate reduction. Biotechnol. Bioeng. 2013; 110: 763–772. © 2012 Wiley Periodicals, Inc.     

Detachment and emission of airborne bacteria in gas-phase biofilm reactors

Three laboratory scale biofilters filled with different packing materials (peat and sieved sugarcane bagasse) and operating with different microbial cultures (allochthonous and autochthonous bacteria) were run and monitored in parallel to assess the emission rate of airborne bacteria in the biofiltration of benzene-contaminated air streams. The effect of the fluid dynamic and loading conditions on the rate of microbial emission in the air environment was investigated by performing continuous experiments at different inlet benzene concentrations and superficial gas velocities. The experiments prove that the concentration of airborne bacteria in the effluent air from lab-scale biofilters is only slightly higher than in the ambient air. The emission rate is not dependent on superficial gas velocity because of low shear stress exerted by the gas flow. On the other hand, the loading conditions have a strong effect on the emission rate, which increases with increasing growth and degradation rate, and different packing media show remarkably different behaviors.     

Advances in biofilm reactors for production of value-added products

Biofilms are defined as microbial cell layers, which are irreversibly or reversibly attached on solid surfaces. These attached cells are embedded in a self-produced exopolysaccharide matrix, and exhibit different growth and bioactivity compared with suspended cells. With their high biomass density, stability, and potential for long-term fermentation, biofilm reactors are employed for the fermentation and bioconversion, which need large amount of biomass. During the past decade, biofilm reactors have been successfully applied for production of many value-added products. This review article summarizes the applications of biofilm reactors with different novel designs. Advantages and concerns using biofilm reactors, potential uses for industrial-scale production, and further investigation needs are discussed.     

Current and future trends for biofilm reactors for fermentation processes

Biofilms in the environment can both cause detrimental and beneficial effects. However, their use in bioreactors provides many advantages including lesser tendencies to develop membrane fouling and lower required capital costs, their higher biomass density and operation stability, contribution to resistance of microorganisms, etc. Biofilm formation occurs naturally by the attachment of microbial cells to the support without use of any chemicals agent in biofilm reactors. Biofilm reactors have been studied and commercially used for waste water treatment and bench and pilot-scale production of value-added products in the past decades. It is important to understand the fundamentals of biofilm formation, physical and chemical properties of a biofilm matrix to run the biofilm reactor at optimum conditions. This review includes the principles of biofilm formation; properties of a biofilm matrix and their roles in the biofilm formation; factors that improve the biofilm formation, such as support materials; advantages and disadvantages of biofilm reactors; and industrial applications of biofilm reactors.     

Use of flow cell reactors to quantify biofilm formation kinetics

Summary A parallel plate flow cell reactor is introduced and used to evaluate cell adhesion and biofilm formation kinetics for four different bacterial strains of the species,E. coli. The reactor allows biofilm growth under defined, well-controlled fluid dynamics while providing continuous observations and direct sampling of biofilm for biological, chemical and physical analyses as well as immunofluorescent labeling.     

Biofluid mechanics of the human reproductive process: modelling of the complex interaction and pathway to the oocytes

Recent revelations in the human reproductive process have fuelled much interest in this field of study. In particular, the once prevailing view of large numbers of ejaculated sperms racing towards the egg has been refuted recently. This is opposed to the current views derived from numerous clinical findings that state that only a very small number of sperms will ever enter the oviduct. It is believed that these few sperms must have been guided to make the long, tedious and obstructed journey to the egg. For a mature spermatozoon, its hyperactivated swimming motility upon capacitation plays an important role in the fertilization of a mature egg. Likewise, the female genital tract also provides guiding mechanisms to complement the survival of normal hydrodynamic profile sperms and thus promotes an eventual sperm-egg interaction. Understanding these mechanisms can be essential for the derivation of assisted conception techniques especially those in vitro. With the aid of computational models and simulation, suitability and effectiveness of novel assisted conception methodology can be assessed, particularly for those yet to be ready for clinical trials. This review discusses the possible bioengineering models and the mechanisms by which human spermatozoa are guided to the egg.     

Evaluation of plastic composite-supports for enhanced ethanol production in biofilm reactors

Biofilms are a natural form of cell immobilization that result from microbial attachment to solid supports. Biofilm reactors with polypropylene composite-supports containing up to 25% (w/w) of various agricultural materials (corn hulls, cellulose, oat hulls, soybean hulls or starch) and nutrients (soybean flour or zein) were used for ethanol production. Pure cultures ofZymomonas mobilis, ATCC 31821 orSaccharomyces cerevisiae ATCC 24859 and mixed cultures with either of these ethanol-producing microorganisms and the biofilm-formingStreptomyces viridosporus T7A ATCC 39115 were evaluated. An ethanol productivity of 374g L^–1 h^–1 (44% yield) was obtained on polypropylene composite-supports of soybean hull-zein-polypropylene by usingZ. mobilis, whereas mixed-culture fermentations withS. viridosporus resulted in ethanol productivity of 147.5 g L^–1 h^–1 when polypropylene composite-supports of corn starch-soybean flour were used. WithS. cerevisiae, maximum productivity of 40 g L^–1 h^–1 (47% yield) was obtained on polypropylene composite-supports of soybean hull-soybean flour, whereas mixed-culture fermentation withS. viridosporus resulted in ethanol productivity of 190g L^–1 h^–1 (35% yield) when polypropylene composite-supports of oat hull-polypropylene were used. The maximum productivities obtained without supports (suspension culture) were 124 g L^–1 h^–1 and 5 g L^–1 h^–1 withZ. mobilis andS. cerevisiae, respectively. Therefore, forZ. mobilis andS. cerevisiae, ethanol productivities in biofilm fermentations were three- and eight-fold higher than suspension culture fermentations, respectively. Biofilm formation on the chips was detected by weight change and Gram staining of the support material at the end of the fermentation. The ethanol production rate and concentrations were consistently greater in biofilm reactors than in suspension cultures.This is Journal Paper No. J-16356 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 3253     

A comparison between the reaction rates in biofilm reactors and free suspended cells bioreactors

A theoretical equation for comparison of the bioreaction rates in a biofilm reactor and in a bioreactor with free suspended cells at different input substrate concentrations and substrate conversions is proposed. The main assumption is that there is no kinetic change after fixation of the cells. Some previously published experimental data are used for verification of this equation. It is shown that difference between the experimental and calculated data is within 19%.     

Interaction between biofilm development, structure and detachment in rotating annular reactors

In biotechnology, composition of biofilms and suspended bioaggregates can be crucial for system performance or product quality. Consequently, understanding biofilm dynamics is important for any process optimisation. The aim of this study was to investigate biofilm development and detachment under different hydrodynamic conditions and varying glucose load. Confocal laser scanning microscopy proved to be a fast method providing information about structure, distribution and volume ratio of bacteria and extra cellular polymers (EPS) within biofilms and detached biomass. As a result, it could be shown that biofilm structure, in terms of density and EPS volume, was largely influenced by hydrodynamic conditions. Furthermore, it was demonstrated that the EPS:bacteria ratio and distribution was largely influenced by substrate load. Finally, the characteristics in biofilm structure and development were reflected in the composition and quantity of the detached biomass.     

Quantification of viable biomass in biofilm reactors by extractable lipid phosphate

 Lipid phosphate, which is a measure of viable biomass, was determined using biofilm samples from three different laboratory-scale reactors. The analysis procedure proposed in the literature was modified and tested for suitability in experiments with biofilm reactors. The microbial contents of the biofilms studied are compared in three types of reactor. Received: 2 November 1994/Accepted: 23 January 1995     

Biofilm development during the start-up period of anaerobic biofilm reactors: the biofilm Archaea community is highly dependent on the support material

To evaluate the impact of the nature of the support material on its colonization by a methanogenic consortium, four substrata made of different materials: polyvinyl chloride, 2 polyethylene and polypropylene were tested during the start-up of lab-scale fixed-film reactors. The reactor performances were evaluated and compared together with the analysis of the biofilms. Biofilm growth was quantified and the structure of bacterial and archaeal communities were characterized by molecular fingerprinting profiles (capillary electrophoresis-single strand conformation polymorphism). The composition of the inoculum was shown to have a major impact on the bacterial composition of the biofilm, whatever the nature of the support material or the organic loading rate applied to the reactors during the start-up period. In contrast, the biofilm archaeal populations were independent of the inoculum used but highly dependent on the support material. Supports favouring Archaea colonization, the limiting factor in the overall process, should be preferred.     

Proteomic analysis of Campylobacter jejuni 11168 biofilms reveals a role for the motility complex in biofilm formation

Campylobacter jejuni remains the leading cause of bacterial gastroenteritis in developed countries, and yet little is known concerning the mechanisms by which this fastidious organism survives within its environment. We have demonstrated that C. jejuni 11168 can form biofilms on a variety of surfaces. Proteomic analyses of planktonic and biofilm-grown cells demonstrated differences in protein expression profiles between the two growth modes. Proteins involved in the motility complex, including the flagellins (FlaA, FlaB), the filament cap (FliD), the basal body (FlgG, FlgG2), and the chemotactic protein (CheA), all exhibited higher levels of expression in biofilms than found in stationary-phase planktonic cells. Additional proteins with enhanced expression included those involved in the general (GroEL, GroES) and oxidative (Tpx, Ahp) stress responses, two known adhesins (Peb1, FlaC), and proteins involved in biosynthesis, energy generation, and catabolic functions. An aflagellate flhA mutant not only lost the ability to attach to a solid matrix and form a biofilm but could no longer form a pellicle at the air-liquid interface of a liquid culture. Insertional inactivation of genes that affect the flagellar filament (fliA, flaA, flaB, flaG) or the expression of the cell adhesin (flaC) also resulted in a delay in pellicle formation. These findings demonstrate that the flagellar motility complex plays a crucial role in the initial attachment of C. jejuni 11168 to solid surfaces during biofilm formation as well as in the cell-to-cell interactions required for pellicle formation. Continued expression of the motility complex in mature biofilms is unusual and suggests a role for the flagellar apparatus in the biofilm phenotype.     

Mathematical simulation of a biofilm process

A mathematical model has been developed for a fixed-film biological process (film flow over a flat plate) that describes bulk liquid transport, diffusional transport of oxygen and organics across a stagnant film, diffusional transport of oxygen and organics into the biofilm, biochemical reactions by the individual cells within the biofilm, biofilm growth, and cell density changes within the biofilm due to cellular decay. Simulation studies are presented to show how contact time and diffusion layer thickness affect process performance.