AWWA JAW21665

Studies were conducted to characterize the growth and composition of the schmutzdecke and the associated particle removal efficiency for a field-scale experimental slow sand filtration (SSF) system used for the biological treatment of Logan River water. A naturally occurring ammonium-selective zeolite, clinoptilolite, was added as a surface amendment to the sand bed of the SSF system as a reservoir of nitrogen for algae comprising the schmutzdecke. A predominance of filamentous algae at the surface of the filter was observed throughout the entire experimental period. Single-cell algae were observed at depths in the filter from 0.5 to 1 in. (15 to 30 mm). Particle removal was superior in clinoptilolite-amended SSF, even at filtration rates two to four times greater than conventional SSF rates. The effect of schmutzdecke maturation on the removal of Giardia lamblia cyst-size particles was also investigated. The growth of algae following the initiation of a filtration cycle, i.e., the maturation period of the schmutzdecke, was associated with an increase in the ability of the amended filter to remove Giardia lamblia cyst-size particles. The zeolite-amended SSF system treated drinking water for longer periods of time at a higher filtration rates than achievable with conventional SSF without the zeolite surface amendment. Includes 29 references, tables, figures.