Impact on Water Distribution System Biofilm Densities from Reverse Osmosis Membrane Treatment of Supply Water (1)

By Meckes, Mark C.; Haught, Roy C. et al. | Journal of Environmental Engineering and Science, July 2007 | Go to article overview

Impact on Water Distribution System Biofilm Densities from Reverse Osmosis Membrane Treatment of Supply Water (1)


Meckes, Mark C., Haught, Roy C., Kelty, Keith, Blannon, Janet C., Cmehil, David, Journal of Environmental Engineering and Science


Abstract: The quality of potable water is such that the concentration of nutrients available for growth of microorganisms within distribution systems is limited. In such systems carbon is often the growth limiting nutrient. Research conducted in the Netherlands has indicated that low levels (<10 [micro]g/L) of available organic carbon in water is sufficient to maintain an actively growing population of heterotrophic, or organic carbon utilizing, bacteria in aquatic systems. However, the ability of commercially available and cost effective technologies to achieve such low concentrations of assimilable organic carbon in full-scale water systems is doubtful. Reverse osmosis (RO) systems have been used for many years to effectively remove contaminants from source waters. We challenged a water distribution system simulator (DSS) with water from a municipal system and water that was treated using an RO system under two concentrations of residual free chlorine to evaluate the effect of this disinfectant on biofilms in contact with low nutrient water. Our results showed that biofilm densities in the DSS carrying low nutrient RO treated water were lower than biofilm densities taken from the DSS when it carried water directly obtained from a municipal system.

Key words: water distribution systems, reverse osmosis, biofilms, heterotrophic plate count, HPC, chlorine, assimilable organic carbon.

Resume: La qualite de l'eau potable est telle que la concentration de nutriments disponibles pour la croissance de microorganismes dans les reseaux de distribution d'eau est limitee. Dans de tels systemes, le carbone est souvent le nutriment limitant la croissance. Une recherche effectuee aux Pays-Bas a indique que de faibles niveaux de carbone organique disponible (<10 [micro]g/L) dans l'eau est suffisent pour maintenir une population en croissance active de bacteries heterotrophes, ou utilisant le carbone organique, dans les systemes aquatiques. Cependant, la capacite des technologies rentables disponibles sur le marche pour atteindre de telles concentrations faibles de carbone organique assimilable dans les reseaux d'eau a pleine echelle est douteuse. Les systemes par osmose inverse sont utilises depuis de nombreuses annees pour eliminer efficacement les contaminants des eaux de source. Nous avons mis a l'epreuve un simulateur d'un reseau de distribution d'eau (DSS) en utilisant de l'eau provenant d'un reseau municipal et de l'eau qui avait ete traitee par un systeme par osmose inverse avec deux concentrations de chlore libre residuel afin d'evaluer l'effet de ce desinfectant sur les biofilms en contact avec de l'eau contenant de faibles concentrations de nutriments. Nos resultants montrent que les densites de biofilms dans les DSS transportant de l'eau traitee par osmose inverse contenant de faibles concentrations de nutriments etaient inferieures aux densites de biofilms mesurees dans les DSS transportant de l'eau provenant directement d'un reseau municipal.

Mots-cles : reseaux de distribution d'eau, osmose inverse, biofilms, numeration sur plaque des bacteries heterotrophes, chlore, carbone organique assimilable.

[Traduit par la Redaction]

Introduction

Virtually anywhere a surface comes into contact with the water in a distribution system one can find biofims. Biofilms are formed in distribution system pipelines when microbial cells attach to pipe surfaces and multiply to form a film or slime layer on the pipe (van der Wende and Characklis 1990). Probably within seconds of entering the distribution system, some particles, including microorganisms, adsorb to clean pipe surfaces.

Some microorganisms can adhere directly to the pipe surface via appendages that extend from the cell membrane; other bacteria form a capsular material of extracellular polysaccharides (EPS), sometimes called a glycocalyx, which anchors the bacteria to the pipe surface (Geldreich 1988). The organisms take advantage of the macromolecules attached to the pipe surface for protection and nourishment. …

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