Significance of biofilm structure on transport of inert particulates into biofilms

Abstract

Evolutional changes in interior structures of mixed population biofilms grown on domestic wastewater were quantitatively analyzed using a cryosectioning technique and an image analysis. Meanwhile, transport of particulates into the biofilms was also experimentally investigated using fluorescent microbeads as tracers to relate the biofilm structure and particulate transport into the biofilm. Microscopic observation of the cryomicrotomy biofilm sections indicated the biofilms were very porous and consisted of interwinded filamentous biomass acting as a framework of the biofilm. A honeycomb structure was often found, which would make the biofilm more resistant to water flow. There were micropores with the diameter of about 10 μm microcolony aggregates attached to filamentous biomass and macropores with the diameter of 20–200 μm in the biomass matrix. These pores did not clog during two months of cultivation. Areal porosity was about 30% in the bottom biofilm and more than 90% in the surface. Significant difference in transport efficiency was not observed for various sizes of microbeads due to the presence of macropores. Therefore, even 10 μm tracer beads could quickly traverse throughout a biofilm 640 μm thick via water channels or macropores and then penetrated into the micropores. Convective transport from the bulk to the bottom biofilm, rather than molecular diffusion, was responsible for this rapid transport. Based on experimental results, it can be concluded that the biofilm structure seems to be well designed to maximize the transport efficiency of substrates and products and the strength of biofilm structure.

Accumulation and Fate of Microorganisms and Microspheres in Biofilms Formed in a Pilot-Scale Water Distribution System

“…The inference here is that the physicochemical properties of both the microspheres and the substratum influenced the accumulation of the hydrophobic spheres to a greater degree than biofilm density. Similar results have been reported, where no correlation between biofilm thickness and incorporation of fluorescent microspheres has been found (6,23,24,29).…”

“…To investigate this, a novel pilot-scale water distribution system representative of the Stockholm drinking-water distribution system was constructed within the Lovö Waterworks, Sweden. Naturally grown biofilms were exposed to hydrophobic and hydrophilic fluorescent polystyrene microspheres, Salmonella bacteriophage 28B, and Legionella pneumophila bacteria, and their accumulation and persistence in biofilms were measured over a 38-day experimental period.Fluorescent microspheres have been used as surrogate particles in a variety of applications to examine and quantify the accumulation and fate of particulate material within microbial biofilms and are favored for their similarity to bacteria in size and cell surface properties as well as their resistance to biodegradation and disinfection (4,6,10,19,23,24,29). The latter two properties were exploited in this investigation to allow the separation of biological, i.e., loss in culturability, grazing from physical phenomena such as detachment.…”

“…Fluorescent microspheres have been used as surrogate particles in a variety of applications to examine and quantify the accumulation and fate of particulate material within microbial biofilms and are favored for their similarity to bacteria in size and cell surface properties as well as their resistance to biodegradation and disinfection (4,6,10,19,23,24,29). The latter two properties were exploited in this investigation to allow the separation of biological, i.e., loss in culturability, grazing from physical phenomena such as detachment.…”

Seasonal Retention and Release of Cryptosporidium parvum Oocysts by Environmental Biofilms in the Laboratory

“…This persistence of oocysts in the water supply was attributed to the release of oocysts trapped in biofilms on the interior surface of the distribution pipes and may have contributed to additional infections. Several studies have examined pathogen transport dynamics in biofilms using glass or latex beads of various sizes as surrogates for pathogens (5,8,16,17). A few studies examined the attachment of C. parvum oocysts to biofilms but did not use natural microbial assemblages to make the biofilms (3,23) or quantify how many oocysts attached or sloughed (9,22).…”

The role of biofilms in subsurface transport processes

“…Biofilm structure appears to be of three main types: planar structures; stacks of microcolonies of microbes held together by EPS; or mushroom or tulip shaped formations (Wimpenny et al 2000;Beyenal et al 2004). However, laboratory grown biofilms often comprise interwoven filamentous biomass with micropores of 20-200µm diameter (Okabe et al 1998). …”