Transcript Biofilms and Drinking Water

Jurnal Sains dan Teknologi Lingkungan
ISSN: 2085‐1227
Volume 1, Nomor 1, Januari 2009, Halaman 55‐62
Biofilms and Drinking Water
Ursula Obst
Forschungszentrum Karlsruhe, Institut für Technische Chemie, Bereich Wasser- und Geotechnologie (ITC-WGT)
Abt. Mikrobiologie natürlicher und technischer Grenzflächen
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen
e-mail: [email protected]
Abstract
The preferred and dominant life forms of environmental microorganisms are biofilms adherent to
surfaces. Thus, biofilm-forming bacteria are present in any source water for drinking water treatment
such as soil bacteria in groundwater and mat-forming and fecal bacteria in river water. Biofilms may
colonize and clog water transporting pipes in wells but can also support cleaning of water during natural
(bankment) and technical filtration steps. Treatment and disinfection do not completely eliminate but only
reduce the number of biofilm-forming bacteria. Surviving bacteria are often able to express enhanced
persistence and form again biofilms shortly after water treatment steps. Thus, biofilms are transported
into the pipes, are always present in the distribution net and cannot be completely avoided. They can act
as a shelter for pathogens and may induce corrosion of pipe material or smell and taste problems. The
manipulation of biofilms by special processing or construction materials during drinking water treatment
and distribution is one of the big challenges in water industry.
Keywords: biofilm, dringking water, bacteria, water treatment.
1. Introduction
Biofilms are the preferrred life form of environmental mircroorganisms, esp. of bacteria. Biofilmforming bacteria adhere on surfaces, grow to microcolonies and subsequently develop a more or
less thick layer consisting of different microbial species, organic material and material gained from
the environment. Bacteria settling on a surface and developing a biofilm change their characteristics
from planktonic to adhesive life. By down- and up-regulation of certain gene expressions they lose
their motility and synthesize specific adhesion molecules and a slime matrix called extracellular
polymeric substances (EPS) (fig. 1). They may also start with enhanced metabolic reactions and
form metabolic chains with other members of the population (Costerton, 2007).
The members of biofilm population savour a series of advantages. Nutrients adsorbing at the
biofilm matrix may be used intensely. Moreover, the biofilm bacteria form metabolic consortia
using the products of the neighbours as substrates. E.g. nitrifyers use the product nitrite of the
ammonium oxidizers as a substrat to nitrate production. Reciprocally ammonium oxidizers cannot
be toxified by their own product. Thus, nitrifyers can only live in a close biofilm consortium. Living
in a biofilm also protects against hostile environmental conditions such as desiccation, changes of
acidity or alkinity, salt concentration and even against biocides. In summary, biofilms are an
important part of the natural self-cleaning of water, however also may cause severe problems with