Culture dependent and independent analyses of bacterial communities involved in copper plumbing corrosion.

AIMS: This study used culture-dependent and culture-independent approaches to characterize bacterial communities in copper plumbing corrosion and to assess biofilm formation and copper resistance of heterotrophic bacteria isolated from copper pipes. METHODS AND RESULTS: Water and copper pipes were collected from a cold-water household distribution system affected by 'blue water' corrosion and presenting biofilm formation. Corrosion-promoting ageing experiments were performed with conditioned unused copper pipes filled with unfiltered and filtered sampled water as nonsterile and sterile treatments, respectively. During 8 weeks, stagnant water within the pipes was replaced with aerated fresh water every 2 or 3 days. Total copper and pH were determined in sampled water, and copper pipe coupons were cut for microscopic analyses. Biofilms were extracted from field and laboratory pipes, and total DNA was isolated. Bacterial communities' composition was analysed by terminal restriction fragment length polymorphism (T-RFLP) and clonal libraries of 16S rRNA genes. Heterotrophic bacterial isolates were obtained from water and biofilm extracts and characterized in terms of biofilm formation capacity and copper minimum inhibitory concentration. The results indicated that copper concentration in stagnant water from nonsterile treatments was much higher than in sterile treatments and corrosion by-products structure in coupon surfaces was different. Multivariate analysis of T-RFLP profiles and clone sequencing showed significant dissimilarity between field and laboratory biofilm communities, and a low richness and the dominant presence of Gamma- and Betaproteobacteria in both cases. Several bacterial isolates formed biofilm and tolerated high copper concentrations. CONCLUSIONS: The study demonstrates microbially influenced corrosion (MIC) in copper plumbing. Gamma- and Betaproteobacteria dominated the corroded copper piping bacterial community, whose ability to form biofilms may be important for bacterial corrosion promotion and survival in MIC events. SIGNIFICANCE AND IMPACT OF THE STUDY: The characterization of micro-organisms that influence copper plumbing corrosion has significant implications for distribution system management and copper corrosion control.

Comparing biofilm models for a single species biofilm system.

A benchmark problem was defined to evaluate the performance of different mathematical biofilm models. The biofilm consisted of heterotrophic bacteria degrading organic substrate and oxygen. Mathematical models tested ranged from simple analytical to multidimensional numerical models. For simple and more or less flat biofilms it was shown that analytical biofilm models provide very similar results compared to more complex numerical solutions. When considering a heterogeneous biofilm morphology it was shown that the effect of an increased external mass transfer resistance was much more significant compared to the effect of an increased surface area inside the biofilm.

Two-dimensional cellular automaton model for mixed-culture biofilm.

Structural and microbial heterogeneity occurs in almost any type of biofilm system. General approaches for the design of biofilm systems consider biofilms as homogeneous and of constant thickness. In order to improve the design of biofilms systems, models need to incorporate structural heterogeneity and the effect of inert microbial mass. We have improved a 2D biofilm model based on cellular automata (CA) and used it to simulate multidimensional biofilms with active and inert biomass including a self-organizing development. Results indicate that the presence of inert biomass within biofilm structures does not change considerably the substrate flux into the biofilm because the active biomass is located at the surface of the biofilm. Long-term simulations revealed that although the biofilm system is highly heterogeneous and the microstructure is continuously changing, the biofilm reaches a dynamic steady-state with prediction of biofilm thickness and substrate flux stabilizing on a delimited range.