Effect of wall shear rate on biofilm deposition and grazing in drinking water flow chambers

Abstract

The effect of four-wall shear rates (34.9, 74.8, 142.5, and 194.5 s(-1)) on bacterial deposition on glass slides in drinking water flow chambers was studied. Biofilm image acquisition was performed over a 50-day period. Bacterial accumulation and surface coverage curves were obtained. Microscopic observations allowed us to obtain information about the dynamics and spatial distribution of the biofilm. During the first stage of biofilm formation (210-518 h), bacterial accumulation was a function of the wall shear rate: the higher the wall shear rate, the faster the bacterial deposition (1.1 and 1.9 x 10(4) bacterial cells . cm(-2) for wall shear rates of 34.9 and 142.5 s(-1), respectively). A new similarity relationship characteristic of a non-dimensional time and function of the wall shear rate was proposed to describe initial bacterial deposition. After 50 days of exposure to drinking water, surface coverage was more or less identical under the entire wall shear rates (7.44 +/- 0.9%), suggesting that biofilm bacterial density cannot be controlled using hydrodynamics. However, the spatial distribution of the biofilm was clearly different. Under low wall shear rate, aggregates were composed of bacterial cells able to "vibrate" independently on the surface, whereas, under a high wall shear rate, aggregates were more cohesive. Therefore, susceptibility to the hydraulic discontinuities occurring in drinking water system may not be similar. In all the flow chambers, significant decreases in bacterial biomass (up to 77%) were associated with the presence of amoebae. This grazing preferentially targeted small, isolated cells.

Accumulation of MS2, GA, and Qβ phages on high density polyethylene (HDPE) and drinking water biofilms under flow/non-flow conditions

“…In our experiments, we allowed two-month-old drinking water biofilms to develop on HDPE. It had a standard cell density of 1.7 Â 10 7 cells/cm 2 in accordance with previous studies (Manuel et al, 2007;Mathieu et al, 2009) and covered up to 10.8% of the surfaces (considering clusters over 300 nm thick with a 4 mm 2 surface area) whatever the wall shear rate applied, as expected from previous work (Paris et al, 2007). We showed that two-month-old biofilms modified the attractiveness of HDPE as they led to a significantly lower number of attached viruses for MS2 and Qb, but to an increase in GA bacteriophage count, and consequently caused the adhesion sequence to change to MS2 < Qb < GA.…”

Role of Force-Sensitive Amyloid-Like Interactions in Fungal Catch Bonding and Biofilms

“…Seven Listeria monocytogenes strains had initial adhesion rates that were significantly greater for shear stress at 11 dyne/cm 2 than at 1 dyne/cm 2 on stainless steel (34). Biofilms of marine bacteria and water-supply bacteria show increased cohesion and durability as the shear stress is raised (35,36). Thus, the behavior of the fungal biofilms under flow was similar to that of bacterial biofilms.…”

Spacer geometry and particle deposition in spiral wound membrane feed channels

“…Previous experimental studies report increased deposition at low cross-flow assumingly due to lower shear (Subramani and Hoek, 2008;Chong et al, 2008), while in other works higher cross-flow and shear stress is associated with enhanced deposition (Paris et al, 2007;Li et al, 2006). Koutsou et al (2009) also concluded that observed regions of more fouling with humic acids can be related to simulated areas of higher shear stress.…”