title: Bacterial colonization of pellet softening reactors used during drinking water treatment.
abstract: Pellet softening reactors are used in centralized and decentralized drinking water treatment plants for the removal of calcium (hardness) through chemically induced precipitation of calcite. This is accomplished in fluidized pellet reactors, where a strong base is added to the influent to increase the pH and facilitate the process of precipitation on an added seeding material. Here we describe for the first time the opportunistic bacterial colonization of the calcite pellets in a full-scale pellet softening reactor and the functional contribution of these colonizing bacteria to the overall drinking water treatment process. ATP analysis, advanced microscopy, and community fingerprinting with denaturing gradient gel electrophoretic (DGGE) analysis were used to characterize the biomass on the pellets, while assimilable organic carbon (AOC), dissolved organic carbon, and flow cytometric analysis were used to characterize the impact of the biological processes on drinking water quality. The data revealed pellet colonization at concentrations in excess of 500 ng of ATP/g of pellet and reactor biomass concentrations as high as 220 mg of ATP/m(3) of reactor, comprising a wide variety of different microorganisms. These organisms removed as much as 60% of AOC from the water during treatment, thus contributing toward the biological stabilization of the drinking water. Notably, only a small fraction (about 60,000 cells/ml) of the bacteria in the reactors was released into the effluent under normal conditions, while the majority of the bacteria colonizing the pellets were captured in the calcite structures of the pellets and were removed as a reusable product.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland. frederik.hammes@eawag.ch
authors.forename: Frederik
authors.initials: F
authors.lastname: Hammes
authors.forename: Nico
authors.initials: N
authors.lastname: Boon
authors.forename: Marius
authors.initials: M
authors.lastname: Vital
authors.forename: Petra
authors.initials: P
authors.lastname: Ross
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Magic-Knezev
authors.forename: Marco
authors.initials: M
authors.lastname: Dignum
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000235:genetics / Q000254:growth & development*; D018533:Biomass; D019149:Bioreactors / Q000382:microbiology*; D001709:Biotechnology / Q000379:methods; D002119:Calcium Carbonate / Q000737:chemistry*; D002244:Carbon / Q000032:analysis; D004326:Drinking; D014867:Water / Q000737:chemistry; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods*; D014880:Water Softening / Q000379:methods*; D014881:Water Supply
chemical_list: D014867:Water; D002244:Carbon; D002119:Calcium Carbonate