Date of Award

Winter 2009

Project Type


Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

M Robin Collins


The organic layer that forms on top of the sand bed in slow sand filters, known as the schmutzdecke, is vital for bacterial removal. The schmutzdecke consists of abundant bacteria and protists, and is where suspended particles can be strained, organic matter compounds broken down, and microorganisms are entrapped.

Some varieties of protists prey upon bacteria. Their role in bacterial removal is not well quantified. The goal of this study was to confirm the relationship between filter run time and protistan abundance, to determine the significance of protistan predation on E. coli, and whether protists can be "seeded" onto filters to improve SSF startup times.

Results from a series of bench- and full-scale experiments confirmed a relationship between increased ripening time and increased biomass, protistan abundance, and E. coli removals. The "seeding" studies showed increased protistan populations in some filters, and a strong correlation between protistan abundance and CO2 respiration.