Schmutzdecke Characterization of Clinoptilolite‐Amended Slow Sand Filtration

Abstract

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 higher filtration rates than achievable with conventional SSF without the zeolite surface amendment.