The role of the schmutzdecke in Escherichia coli removal in slow sand and riverbank filtration

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Unger, Michael C
Engineering; Environmental; Civil
thesis / dissertation description
A series of studies was conducted on laboratory scale sand columns under varying operational and design conditions with spiked concentrations of E. coli to investigate the role of the schmutzdecke, a biologically active layer that develops at the interface of the water and filter in slow sand filtration (SSF) and riverbank filtration (RBF). Results confirmed that E. coli removals in slow-rate biological filters occur primarily at the interface and are related to schmutzdecke ripening state, empty bed contact time, biological activity, temperature, and protistan abundance. Using a suite of analyses characterizing the biofilm growing on the schmutzdecke, no connection was found between the preexisting extent of biological ripening and a filter's ability to recover from a scouring or scraping event that removed the schmutzdecke. Biological activity, as measured by CO2 respiration in the top 2.5 cm, as well as protistan abundance in the top 0.5 cm of the schmutzdecke did, however, correlate positively to E. coli removal. The role of predation deserves further investigation, and filters should be operated in such a way as to enhance biological activity and protistan abundance in the schmutzdecke.