Biofilm reactor operation

Due to the adhesion capacity of microbes, biofilm formation must be taken into account in river analysis as well as in the chemostat or fixed beds (percolating or trickling filter). The significance of microbial films in fermenters has been extensively studied and reviewed (Atkinson, 1973, 1974 Atkinson and Fowler, 1974 Atkinson and Knights, 1975 Charaklis, 1981 Harremoes, 1978). 

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Here [g m" -h ] is the maximum mass flux through biofilm surface. The physical model used by these authors was the same as that proposed by Atkinson, extended to double S limitation (glucose and O2). Their authors case A corresponds to no S or O2 limitation, case B involves an inactive aerobic film (S limitation), and case C involves O2 limitation (partly anaerobic film). With a modified Thiele modulus and a pseudo-first-order approximation for the enzyme-catalyzed rate under the given surface conditions, Fig. 4.40 shows the result of the calculation of versus (/>j as a function of Sj /K under various conditions. For biofilm reactor operation, is more convenient in the form... 

A special advantage of biofilm reactor operation in practice comes from the fact that the performance is independent of film thickness when thick films are used. However, as in thick biofilms generally S and O2 limitations occur, which result in a loss of viability of the cells. Thereby, the adhesive bond to the support surface is weakened so that sloughing will occur, which will disturb the reactor performance. 

Another pseudohomogeneous model of biofilm reactor operation was derived by Atkinson and Davies (1972) on similar assumptions to quantify the behavior of the CMMFF (cf. Fig. 3.42). For this case of a completely mixed... 

Quantification of rg, S utilization rate, in the case of interactions between reaction and internal or external transports. This problem of solving Equs. 4.76 and 4.101 simultaneously was discussed in Sect. 4.5. These solutions give steady-state S utilization but do not consider growth or decay of the biofilm. Adequate modeling of biofilm reactor operation must incorporate this fact. 

Wilderer, P. A. 1995. Technology of membrane biofilm reactors operated nnder periodically changing process conditions. Water Science and Technology, 31, 173-183. 

Simultaneous degradation of 2,4- and 2,6-DNT has been achieved in a fluidized-bed biofilm reactor (Lendemann et al. 1998) that was successfully operated with contaminated groundwater containing 2- and 4-nitrotoluenes and 2,4- and 2,6-DNTs. The nitrite that was produced during degradation was recovered as nitrate. 

Fig. 6 Acid orange 7 and phenol concentration in the internal loop airlift reactor operated with Pseudomonas sp. 0X1 biofilm on natural pumice. (A) Aerobic phase. Gas air. Liquid continuous feeding of phenol supplemented synthetic medium. (AN) Anaerobic phase. Gas nitrogen. Liquid batch conditions, dye supplemented medium...

A dynamic model has been developed to simulate the behavior of a Pseudomonas sp. 0X1 biofilm reactor for phenol and azo-dye conversion during the aerobic-anaerobic cyclic operation. Phenol and oxygen were considered as the limiting substrates for growth kinetics. 

Fentachlorophenol is readily degraded in biofilm reactors, so bioremedi-ation is a promising option for the treatmenl of contaminated groundwater brought to the surface as part of a pnmp-and-treat operation. 

The use of continuous immobilized cell biofilm reactors eliminates downtime and hence results in superior reactor productivity (2,3). Adsorbed cell continuous biofilm reactors have been shown to favorably affect process economics (4). Application of these reactors reduces capital and operational cost, thus making the process simpler. Within these reactors, cells are immobilized by adsorption, which is a simpler technique than other techniques such as entrapment and covalent bonding (5). Adsorption is a simple technique and can be performed inside the reactors without the use of chemicals, whereas entrapment and covalent bonding are complicated techniques and require chemicals for bond formation. In anaerobic systems, such as butanol production, adsorption can be performed anaerobically within the reactor. An additional advantage of adsorption is that cells form uniform biofilm layers around the support, which lessens diffusion resistance compared to entrapped and covalently bonded cells. Hence, these reactors are called biofilm reactors. Because of reduction in diffusion resistance, the reaction rate is enhanced. For this reason, adsorption was chosen as the technique to be employed for Clostridium beijerinckii BA101 cell immobilization to produce butanol. In addition to being simple, it has the potential to be used in large-scale reactors. In the present study, clay brick was chosen as the cell adsorption support. It is available at a low cost and is easy to dispose of after use. 

Lee, H. Barnett, S.M. A predictive model for the allowable operating velocities and the biomass concentration in a three phase fluidized biofilm reactor. J. Ind. Eng. Chem. 2003, 9, 202-211. 

Intermediate periodic operation lies between both extremes and covers systems in which the response time is of the same order as the imposed function cycle time so that resonance is possible. Here the state of the mechanism changes dynamically and is not directly related to the environmental conditions at the moment considered. Intermediate periodic operations encompass semibatch periodic operations, selectivity in periodically forced CSTRs, cycled reactors with heterogeneous catalysts, and non-steady-state biofilm reactors (e.g., Rittmann and McCarty, 1981). Lag, overshoot phenomena, and oscillations can typically occur. Biological reactor operation will basically fall into this latter class of operation, and balanced growth must be distinguished from steady-state growth (Barford et al., 1982). 

The effectiveness factor varies only with the biofilm thickness and the support particle size at constant voidage of the fluidized bed. This leads to the conclusion that an optimal biofilm thickness exists for fluidized bed biofilm reactors (Kargi and Park, 1982). The effect of biofilm thickness on the performance of a fluidized bed reactor was also examined by Shieh (1981), who showed the same results. Neither maintenance of thicknesses with 10 to 100 jum nor the highest biomass will be beneficial to optimum reactor operation. 

Recently, the application of fluidized beds to bioprocessing stimulated the modeling of FBBRs. In this complex case, however, models of the hydraulics must be combined with a model of biofilm kinetics, including mass transport-affected substrate conversion. This truly heterogeneous case of reactor operation will be presented here. 

Hwang, J. H., Cicek, N. and Oleszkiewicz, J. A. 2009a. Long-term operation of membrane biofilm reactors for nitrogen removal with autotrophic bacteria. Water Science and Technology, 60,2405-2412. 

Zellner G, Eeuerhake E.H-J, Macario AJL, Conway De Macario E (1995) Denitrifying and methanogenic bacteria in the biofilm of a fixed-film reactor operated with ethanol-nitrate demonstrated by immunofluorescence and microscopy Appl. Microbiol. Biotechnol. 43(5) 566-571 Zellner G, Macario AJL, Conway De Macario E (1997) A study of three anaerobic methanogenic bioreactors reveals that syntrophs are diverse and different from reference organisms. FEMS Microbiol Ecol 22(4) 295-301 Zhang TC, Bishop PL (1994) Density, porosity, and pore structure of biofilms. Wat Res 28 2267-2277... 

To remove urea and formaldehyde from synthetic wastewater, Campos and colleagues33 operated a coupled system consisting of a biofilm airlift suspension (BAS) reactor to carry out nitrification and an anoxic USB reactor to carry out the denitrification and urea hydrolysis (Figure 19.8). 

During start-up, the microbial population distribution in the biofilm varies with time. Initial colonization of the particle may be by one or more species that alter the surface favorably for colonization by other species. For instance, in the operation of a butyrate-degrading fluidized bed bioreactor, methanogens attached to the sand particles early in the start-up process and produced a primary matrix of heteropolysaccharides that allowed attachment of other bacterial species (Sreekrishnan et al., 1991 Zellner et al., 1991 Yongming et al., 1993). This is contrary to findings in an acetate-propionate-butyrate degrading reactor, in which facultative anaerobes were found to be the initial colonizers (Lauwers et al., 1990). 

Ryhiner, G., Petrozzi, S., and Dunn, I. J., Operation of a Three-Phase Biofilm Fluidized Sand Bed Reactor for Aerobic Wastewater Treatment, ... 

Abstract This chapter embodies two sections. In the first section a survey of the state of the art of azo-dye conversion by means of bacteria is presented, with a focus on reactor design and operational issues. The relevance of thorough characterization of reaction kinetics and yields is discussed. The second section is focused on recent results regarding the conversion of an azo-dye by means of bacterial biofilm in an internal loop airlift reactor. Experimental results are analyzed in the light of a comprehensive reactor model. Key issues, research needs and priorities regarding bioprocess development for azo-dye conversion are discussed. 

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