Figure 1. Methods of immobilization of microorganisms (E signifies the enzyme system inside the immobilized cells).

Figure 2. Kinetic model of conidial aggregation of A. niger AB 1.13 based on experimental results (Grimm et al., 2004).

Figure 3. Structures of ionic polysaccharides. (a) Alginates with d-mannuronic acid, l-guluronic acid, and mixed structural elements; (b) κ-carrageenan (R = OH) and ι-carrageenan (R = OSO ₃ ^–; (c) chitosan.

Figure 4. Mechanisms of gel formation. (a) Statistical polymer network in solution; (b) double/twin helices; (c) bundle/packet of double helices and (d) their tertiary/supramolecular structure; (e) network formation in alginates due to cross-linking by multivalent cations (filled circles).

Figure 5. Immobilization in alginate. (a) Syringe method; (b) jet cutter method with alginate-cell suspension, pressure application Δp, rotating cutter, jet nozzle, cylindrical solution leaving the nozzle, cutting to yield spherical droplets falling down into the CaCl ₂ solution for crosslinking (Prüße et al., 2000).

Figure 6. Particles (a) and particle size distribution (b) of alginate beads (with 30% (w/w) sand for improved settling properties) prepared by syringe or jet cutter(Reproduced with permission of Elsevier © 2004, from Berensmeier et al., 2004).

Figure 7. Biofilm growth cycle. Initially, free-swimming cells settle on a surface via reversible attachment (a), which triggers the production of extracellular polymeric substances for surface adhesion (b). Biofilm proliferates within the EPS matrix (c) and exhibits typical biofilm morphology on maturation (d) in a microorganism such as Pseudomonas. During biofilm dispersal (e), individual free-swimming cells are released from mature biofilms to colonize new surfaces, which completes the biofilm growth cycle(Reproduced with permission of Elsevier © 2009, from Rosche et al., 2009).

Figure 8. Processes during growth of an anaerobic mixed culture on either smooth and even or, in contrast, raw glass surfaces (Wanda et al., 1990). (a) Rate of primary adsorption (measurement of cell number per cm ²) with acetic acid as carbon source. (b) Formation of a biofilm on a glass surface (measurement via COD per cm ²) with different carbon sources (open circles, open diamonds, reactor A: acetic acid; closed circles, closed diamonds, reactor B: acetic and butyric acid). (c) Polysaccharide content of the system shown in (b).

Figure 9. Scheme of anaerobic degradation reactions.

Figure 10. Microorganisms of an anaerobic mixed culture adhering to (a) sand and (b) pumice particles at two different magnifications (scale bar = 50 µm).

Figure 11. Scheme of a biological trickling filter, with water reservoir (1), collecting trough (2), pump (3), ventilator (4), root (5), packings for droplet removal (6), water distribution system (7), bed with packings (8), outflow control (9), waste gas inflow (10), and purified gas (11).

Figure 12. Principle of substrate supply and product extraction in the biofilm tube reactor (Gross et al., 2007).

Figure 13. Identified electron transfer mechanisms in MFCs. Electron transfer via (a) cell membrane-bound cytochromes, (b) electrically conductive pili (nanowires), (c) microbial redox mediators, and (d) oxidation of reduced secondary metabolites (Rosenbaum et al., 2006).