Biofilm operation

Table 3.1. Biofilm operation compared with floe bioprocessing.

Measuring this quantity is difficult in an operating plant. Methods involving a micrometer and phase contrast microscopy are described in the literature both for particles (Parker, Kaufmann, and Jenkins, 1971) and for films (Korne-gay and Andrews, 1968). Biofilm operation is characterized in comparison with floe operation in Table 3.1. 

An important consequence of this unified model approach is that it can be applied to all reactor configurations, since it is based on common principles for the dynamic interaction of kinetics and transports. These results demonstrate that simple loading criteria cannot predict the performance of a variety of biofilm operations because they ignore the interactions among and reactor balance. 

Babauta JT, Hsu L, Atci E, Kagan J, Chadwick B, Beyenal H. Multiple cathodic reaction mechanisms in seawater cathodic biofilms operating in sediment microbial fuel cells. ChemSusChem 2014 7 2898-2906. 

Microsensors and CV can be coupled to assess ORR in cathodic biofilms operating in aerobic environments and to investigate cathodic reaction mechanisms operating in biocathodes in SMFCs and other bioelectrochemical systems. 

Anaerobic Filter. The anaerobic filter is similar to a trickling filter ia that a biofilm is generated on media. The bed is fully submerged and can be operated either upflow or downflow. For very high strength wastewaters, a recycle can be employed. 

The particle size and porosity of the filter media, since operating efficiency is directly related to the available biofilm surface area. 

Biofihn concentrations attached onto the surface of the sands and gravels in the aerobic tank were measured at 120 different location of the constructed wetland at different times (6 months, 12 months, 18 months and 24 months). The concentrations of the biofilm increased continuously upto 6 month operation, but thereafter remained almost imchanged upto 24 months. Figure 7 and 8 show the concentrations and distributions of biofilms attached onto the the surface of the sands and gravels of the aerobic tank, respectively. The attached biofilm was well distributed over the aerobic tank, and the total volume of the attached biofilm occupied just about 0.5% of the initial void volume of the aerobic tank. 

Figure 7. The amounts and distribution of biofilm attached onto the surface of the sands after 2 year operation.

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. 

The study reported some problems regarding the data for the biofilm from the media after 3 weeks of operation, and also sludge accumulation at the bottom of the bioreactor. It was also found that an external carbon source, such as methanol, was necessary for controlling the denitrification stage. 

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, ... 

Sreekrishnan, T. R., Ramachandran, K. B., and Ghosh, P., Effect of Operating Variables on Biofilm Formation and Performance of an Anaerobic Fluidized-Bed Bioreactor, Biotechnol. Bioeng., 37 557 (1991)... 

Ong SA, Toorisaka E, Hirata M, Hano T (2006) Decolorization behavior of azo dye with various co-substrate dosages under granular activated carbon-biofilm configured packed column operation. ARPN J Engin Appl Sci 1 29-34... 

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. 

On the other hand, cell immobilization on carriers definitively improves bioreactor efficiency. Cell aggregation in a biofilm structure increases process stability and tolerance to shock loadings. A proper selection of operating conditions allows... 

Fluidized beds, both in the conventional and in the airlift configurations, require more careful operation. Proper selection of the operating conditions makes it possible to control biofilm-growth while preventing reactor clogging. Typically, the reactor is operated as a CSTR by establishing large recycle of the liquid stream [36, 37],... 

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. 

Biomass containment in continuously operated bioreactors is an essential prerequisite for the feasibility of practical industrial-scale dye biodegradation. Biofilm airlift reactors have demonstrated excellent performance for their ability to control mixing, interphase mass transfer and biofilm detachment rate. Further studies are required to further exploit the potential of this type of reactors with either aggregated cells or biofilm supported on granular carriers. 

Although the effect of nutrients and classical toxicants (e.g. heavy metals, herbicides) is well known, that of the so-called non-PS in biofilms is still largely unknown. Furthermore, the combination of effects, which operate at the basin scale, requires complex approaches. Therefore, the response of biofilms to these situations should trigger the development of new applications and higher standardisation in the use of biofilms. The standardisation of methods and procedures is a challenge for the future research on the use of natural and laboratory biofilms. 

It is important to note that the amount of oxygen needed to avoid sulfate-reducing conditions is determined by the aerobic respiration rate of the wastewater and the biofilm and not the potential amount of total sulfide production in the sewer. The relatively low solubility of oxygen (9-11 g02 m-3) in wastewater compared with the DO consumption rate typically requires that oxygen must be injected at several points of a sewer pipe to ensure aerobic conditions. This is, of course, expensive and requires manpower in terms of operation and maintenance. Furthermore, the readily biodegradable and fast hydrolyzable fractions of the organic matter may be depleted (Tanaka et al., 2000b). In the case of requirement for mechanical treatment, this is positive ... 

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