Monochloramine was used to inactivate biofilm cells of Pseudomonas aeruginosa. Experimental results indicated that the clean RotoTorque system had no monochloramine demand. The dose of 4 mg·l−1 killed in situ biofilm cells more than 99·99% within 60 min, while the dose of 3 mg·l−1 killed 80% and the dose of 2 mg·l−1 showed no significant killing. Computations of pseudo steady state surface gradient of monochloramine and the observable modulus indicated that there was no marked mass transfer resistance in the biofilm for the 4 mg·l−1 treatment, moderate mass transfer resistance for the 3 mg·l−1 treatment, and high mass transfer resistance for the 2 mg·1−1 treatment. Mass transfer resistance within the biofilm impacts the biocide performance.

Microbial biofilms containing sulfate‐reducing bacteria (SRB) and general anaerobic bacteria (GAB) were grown in a closed flow channel reactor in air‐saturated bulk liquid. The SRB proliferated within anaerobic microniches even when dissolved oxygen penetrated the entire biofilm at some locations. Corrosion of mild steel during aerobic/anaerobic biofilm accumulation was classified as aerobic corrosion and SRB‐enhanced corrosion. Aerobic corrosion dominated during the early stages of biofilm accumulation. The corrosion rate decreased as the biofilm became more uniform over the surface. SRB‐enhanced corrosion occurred after the SRB community was established within the deposits and significant amounts of iron sulfides contacted the bare steel surface. The initiation and propagation of SRB‐enhanced corrosion in an aerobic/anaerobic biofilm system was explained through the establishment of an FeS/Fe galvanic cell.

The effect of alternating oxic and anoxic conditions (12 h oxic‐12 h anoxie) on sulfate reducing activity, iron‐sulfur chemistry and the corrosion of mild steel, has been studied in biofilm reactors. During the experiment (35 d) an increasing activity of sulfate reducing bacteria was observed. A part of the produced sulfide and iron sulfide (FeS) was oxidized during oxic periods and resulted in a mixture of acid volatile sulfides (mainly mackinawite, FeS), chromium reducible sulfur (mainly pyrite, FeS2) and elemental sulfur (S°). At the end of the experiment an amount of total S corresponding to 157 umol cm−3 was found within the deposit. Corrosion rates were measured electrochemically during the experiment and were found in the range of 3–5 mpy after 7 d to 120–160 mpy after 34 d. An extended aeration of the biofilm system for 1 month without addition of any organics showed that the pools of Fe‐S compounds in the deposit and the corrosion rate remained high. Microsensor studies of dissolved oxygen penetration through the biofilm and the deposit showed that even after 1 month of aeration oxygen did not penetrate to the metal surface. The limited oxygen penetration was caused by a very high oxygen consumption rate due to oxygénation of reduced chemical species originating from the dissolution of metal by the corrosion process (approximately 66 mmol Fem−2 h−1). Measurements of in situ sulfate reducing activity revealed high sulfate reduction rates within the anoxic part of the deposit and suggested that SRB activity was important as electron carrier from the metal surface to the oxic interface.

Biofouling and microbially influenced corrosion (MIC) are mediated by micro-organisms attached to the metal surface and/or embedded in a gelatinous organic matrix (the biofilm). Microbial adhesion processes lead to an important modification of the metal/solution interface, inducing changes in the type and concentrations of ions, pH, oxygen levels, flow velocity and buffering capacity of the liqud microenvironment or the interface. This feature drastically changes the classical concept of electrochemical interface used in corrosion studies. Metal dissolution at a biofouled surface will be conditioned by two different processes occurring at the metal/solution interface: passivity, directed from the metal to the solution, and biofouling settlement, oriented towards the metal substratum. Electrochemical concepts, adapted to the characteristics of the biologically conditioned interface to interpret the corrosion process, and process analysis to interpret biofouling, are used in a unified approach for understanding biofilms, MIC and their interactions.

Biofilm research has focused on studies of undefined mixed microbial populations and, more recently, on investigations of monopopulation biofilms. In the first case, the biofilm is considered a homogeneous mass, ignoring the properties of individual species. The second case concentrates on the properties and processes of one microbial species in the biofilm. This article describes biofilm experiments conducted with monopopulations of Klebsiella pneumoniae and Pseudomonas aeruginosa and with binary populations of K. pneumoniae and P. aeruginosa. Process rates and stoichiometric coefficients were determined for the monopopulation and for the binary population biofilms and evaluated in light of the species distribution in the latter. Results indicate that neither the specific cellular product formation rate nor the glucose-oxygen stoichiometric ratio of K. pneumoniae or P. aeruginosa in the binary biofilm is affected by the presence of the other species. Consequently, species interaction was not observed. Although the specific cellular growth rate of K. pneumoniae is five times that of P. aeruginosa, the former species did not dominate the microbial population in the biofilm. Possible reasons for this unexpected behavior are discussed.

Biofilm formation on 304 stainless steel (S30400) does not necessarily result in an ennoblement of the corrosion potential. Instead, biofilms composed of aerobic and anaerobic bacteria from Gulf of Mexico water formed an anaerobic biofilm/metal interface and caused the corrosion potential to move in the negative direction. Biofilms from the same source containing photosynthetic diatoms in the presence of light produced aerobic biofilm/metal interfaces and a positive shift (ennoblement of the corrosion potential). Corrosion potentials of stainless steels exposed in natural seawater cannot be predicted without an understanding of the composition of the biofilm and its impact on interfacial chemistry. In this paper, measurements of corrosion potential, interfacial pH and dissolved oxygen have been correlated with SEM/EDAX surface analyses to evaluate the electrochemical behaviour of stainless steels exposed to Gulf of Mexico water. The interfacial chemistries that influence the corrosion potential are also discussed. Key words: Microorganismsseawatermarinestainless steelselectrochemistry

The nonlinear and 3 linearized forms of the integrated Michaelis-Menten equation were evaluated for their ability to provide reliable estimates of uptake kinetic parameters, when the initial substrate concentration (S0) is not error-free. Of the 3 linearized forms, the one where t/(S0−S) is regressed against ln(S0/S)/(S0−S) gave estimates ofVmax and Km closest to the true population means of these parameters. Further, this linearization was the least sensitive of the 3 to errors (±1%) in S0. Our results illustrate the danger of relying on r2 values for choosing among the 3 linearized forms of the integrated Michaelis-Menten equation. Nonlinear regression analysis of progress curve data, when S0 is not free of error, was superior to even the best of the 3 linearized forms. The integrated Michaelis-Menten equation should not be used to estimateVmax and Km when substrate production occurs concomitant with consumption of added substrate. We propose the use of a new equation for estimation of these parameters along with a parameter describing endogenous substrate production (R) for kinetic studies done with samples from natural habitats, in which the substrate of interest is an intermediate. The application of this new equation was illustrated for both simulated data and previously obtained H2 depletion data. The only means by whichVmax, Km, and R may be evaluated from progress curve data using this new equation is via nonlinear regression, since a linearized form of this equation could not be derived. Mathematical components of computer programs written for fitting data to either of the above nonlinear models using nonlinear least squares analysis are presented.

An empirical expression is presented which describes the rate of fouling biofilm development from clean surface conditions to the onset of fluid frictional resistance increase. Experiments were conducted in a CSTR with internal recycle; a system which provided control of biological activity in the bulk fluid while simulating turbulent flow conditions. Primary biofilm accumulation rate is described by a first order expression in which the rate coefficient is a function of suspended biomass concentration, Reynolds number, and suspended biomass growth rate.

Amyloid adhesins are β-sheet-rich extracellular proteins thought to contribute to bioflocculation. They are present in activated sludge to varying extent. However, it remains unclear which operational conditions promote their production. To this end, the abundance and distribution of amyloids and their potential producers were monitored in two lab-scale reactors operated in sequencing batch mode with an unaerated and aerated reaction phase. Various feeding regimes ranging from feast-famine to nearly continuous feeding were applied. Thioflavin T staining revealed more amyloids in the lab-scale reactors during all operational stages compared to the full-scale industrial and municipal inocula. Furthermore, the feeding regime impacted the distribution of produced amyloids from dense clusters during feast-famine conditions towards a dispersed distribution during nearly continuous feeding. This dispersed presence did not negatively impact the bioflocculation (towards average floc size and shear sensitivity). 16S rRNA sequencing detected several known EPS and amyloid producers. More continuous and, hence, partially aerobic feeding promoted the relative abundance of denitrifiers. Sequential Thioflavin T staining and fluorescence in situ hybridization identified Zoogloea and Ca. Competibacter as potential amyloid producers under the applied conditions. This experiment confirms that amyloid producers need to be triggered for production and that the feeding regime impacts the microbial community composition, which in turn influences the amyloid production and distribution.