Biofilms oxidizers

Biocorrosion of stainless steel is caused by exopolymer-producing bacteria. It can be shown that Fe is accumulated in the biofilm [2.62]. The effect of bacteria on the corrosion behavior of the Mo metal surface has also been investigated by XPS [2.63]. These last two investigations indicate a new field of research in which XPS can be employed successfully. XPS has also been used to study the corrosion of glasses [2.64], of polymer coatings on steel [2.65], of tooth-filling materials [2.66], and to investigate the role of surface hydroxyls of oxide films on metal [2.67] or other passive films. 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

Table 6 Performance of equivalent bromine antimicrobial treatments against biofilms in well-controlled laboratory experiments to simulate industrial applications % Removal % Decrease in Fluid Biofilm Disinfection Oxidizing of Biomass Frictional Resistance (Log Reduction in...

Templeton AS, Trainor TP, Spormann AM, Brown GE Jr (2003b) Selenium speciation and partitioning within Burkholderia cepacia biofilms formed on a-Al203 surfaces. Geochim Cosmochim Acta 67 3547-3557 Templeton AS, Trainor TP, Traina SJ, Spormann AM, Brown GE Jr (2001) Pb(II) distributions at bio film-metal oxide interfaces. Proc Natl Acad Sci USA 98 11897-11902... 

Reactive brilliant red X-3B Activated sludge Activated sludge generated a heterogeneous biofilm of several bacterial species. Biomass was increased after ozonation. Combination of ozone oxidation and upflow biological aerated filter technique to treat azo dyes [8]... 

General descriptors may be related to the metabolism responses in the biofilm. Biofilm algae have several mechanisms to counterbalance the damage caused by the toxicants. Environmental stress produces oxidative damage in the cells, which can be tracked down by means of the analysis of many enzymes (superoxide dismutase, catalase, peroxidase, etc.) that function as effective quenchers of reactive oxygen species (ROS). 

The oxidation of sulfide to elementary sulfur (S) or sulfate (SO4-) may take place when aerobic conditions exist. If sulfide is produced in the deep part of a biofilm in a gravity sewer, it may be oxidized in an aerobic upper layer of the biofilm or in the water phase (Figure 6.2). The details of the oxidation are not well known and may be due to chemical and biological processes. The final step of this process is sulfate, although sulfur in an oxidation step of 0 may be temporarily generated. Oxidation of sulfide that is released into the sewer atmosphere will be dealt with in Section 6.2.6. 

Sulfate is typically found in all types of wastewater in concentrations greater than 5-15 gS nr i.e., in concentrations that are not limiting for sulfide formation in relatively thin biofilms (Nielsen and Hvitved-Jacobsen, 1988). In sewer sediments, however, where sulfate may penetrate the deeper sediment layers, the potential for sulfate reduction may increase with increasing sulfate concentration in the bulk water phase. Under specific conditions, e.g., in the case of industrial wastewater, it is important that oxidized sulfur components (e.g., thiosulfate and sulfite) other than sulfate may act as sulfur sources for sulfate-reducing bacteria (Nielsen, 1991). 

When designing sewer networks, particularly gravity sewers, reaeration is the major process that should be focused on to reduce sulfide formation and the formation of organic odorous substances (cf. Section 4.4). A number of hydraulic and systems characteristics can be managed to increase the reaeration rate and avoid or reduce sulfide-related problems. The hydraulic mean depth, the hydraulic radius, the wastewater flow velocity and the slope of the sewer pipe are, in this respect, important factors that are dealt with in Section 4.4. It should be stressed that it is not necessarily the objective to avoid sulfide formation (in the sewer biofilm), but the sulfide that occurs in the bulk water phase should be at a low concentration level. Therefore, the DO concentration in the bulk water phase should not be lower than about 0.2-0.5 g02 m-3, sufficiently high to oxidize sulfide before a considerable amount is emitted to the sewer atmosphere. 

Injection of air the oxygen in the injected air will prevent sulfate-reducing conditions in the sewer. The DO concentration in the wastewater establishes an aerobic upper layer in the biofilm, and sulfide produced in the deeper part of the biofilm or the deposits that may diffuse into the water phase will be oxidized (cf. Figure 6.2). The oxidation of sulfide will mainly proceed as a chemical process, although microbial oxidation may also take place (Chen and Morris, 1972). Factors that affect the oxidation rate of sulfide include pH, temperature and presence of catalysts, e.g., heavy metals. 

Addition of nitrate the addition of nitrate will establish anoxic conditions when DO is depleted and will, thereby, suppress the sulfate reduction. The theoretical details of the anoxic processes in the bulk water phase and in the biofilm on the suppression of sulfate-reducing conditions and the presence of sulfide in the water phase are not well understood (Abdul-Talib et al., 2001). However, nitrate should be sufficiently active to oxidize sulfide (Einarsen et al., 2000). 

It is expected that in the very near future, the application of closed water loops will show an intensive growth, strongly supported by the further development of separate treatment technologies such as anaerobic treatment, membrane bioreactors, advanced biofilm processes, membrane separation processes, advanced precipitation processes for recovery of nutrients, selective separation processes for recovery of heavy metals, advanced oxidation processes, selective adsorption processes, advanced processes for demineralisation, and physical/chemical processes which can be applied at elevated temperature. 

Marquis RE (1995) Oxygen metabolism, oxidative stress and acid-base physiology of dental plaque biofilms. J Ind Microbiol 15, 198-207. 

Biofiltration is the removal and oxidation of volatile organic compounds (VOC) from contaminated air by fixed beds of compost, soil, or peat. Biofiltration involves microbial populations immobilized on suitable support media to degrade or transform contaminants using biofilms. 

Effect of organic coatings and microbial biofilms on metal oxide surface reactivity - X-ray standing wave studies of metal ion partitioning between coating and surface... 

Figure 7.22. Plot of log (Pb at the metal oxide surface/Pb in biofilm) vs. log Pb concentration for the a-Al203 (0001), a-Al203 (1-102), and (0001) surfaces coated by a monolayer biofilm of the Gram(-) bacterium Burkholderia cepacia. The a-Fe203 (0001) surface is most reactive to aqueous Pb(II) and the a-Al203 (0001) surface is the least reactive, (from [180])...

Similar to the microbial biofilm preparations described above, free-floating, viable microbial mats are also successful in removal of metals from solution (Bender Phillips, 1994 Vatcharapi jarn, Graves Bender, 1994). Consisting primarily of algae, cyanobacteria and bacteria, microbial mats perform a number of activities which promote metal complexation and subsequent removal. The mat contains oxidizing and reducing zones that aid in the immobilization and precipitation of... 

The use of an immobilized biofilm system is recommended, since the oxidation products often are only slowly biodegradable. Biomass, especially slow growing microorganisms, can efficiently be kept in the system using support material. This is especially important in continuously operated systems where the liquid phase is completely mixed. In such a system suspended biomass would be washed out when the hydraulic retention time is less than or equal to the population doubling time (i. e. the reciprocal of the specific growth rate Grady, 1985). In several studies materials such as polyurethane foams (Moerman et al., 1994 Jochimsen, 1997) or quartz sand particles (Stem etal., 1995 and 1996 Heinzle et al, 1995 Saupe and Wiesmann, 1998) have been used for immobilization. 

Stern M, Heinzle E, Kut O M, Hungerbiihler K (1996) Removal of Substituted Pyridines by Combined Ozonation/Fluidized Bed Biofilm Treatment in Clausthaler Umwelt-Akademie Oxidation of Water and Wastewater, A. Vogelpohl (Hrsg.), Goslar 20.-22. Mai. 1996. 

---