Heterogeneity of Rapid Sand Filters and Its Effect on Contaminant Transport and Nitrification Performance
Publication: Journal of Environmental Engineering
Volume 137, Issue 4
Abstract
Laboratory and full-scale experiments were conducted to investigate the development and effect of heterogeneity caused by filter media nonuniformity, biofilm, particles, precipitates, and gas bubbles in rapid sand filters used for drinking-water treatment. Salt tracer experiments were conducted in laboratory columns and in a waterworks, where a new tracer method for rapid sand filters was developed. Pore-water velocities and dispersivities were estimated by fitting an analytical solution to the measured breakthrough curves. Results of the column experiments showed an increase in average longitudinal dispersivity of more than 33% in the 116 h after the start of filtration with a constant pore-water velocity and a zero-order nitrification rate of . The full-scale experiments showed that the rapid sand filter was heterogeneous with pore-water velocities ranging from 2.2 to for the same inlet flow. A first-order nitrification reaction with spatially variable pore-water velocity could be interpreted as a zero-order reaction with a constant pore-water velocity. A model demonstrated that filter heterogeneity could result in higher filter outlet ammonium concentrations.
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Acknowledgments
This study was supported in part by Grontmij|CarlBro and the Urban Water Tech Research School. We acknowledge the support of the municipality of Gentofte, particularly of the employees of Sjælsø Waterworks who allowed us to perform the experiments in the rapid sand filters and provided the necessary data. We are grateful to Dr. Morten Riemer (Grontmij|CarlBro) for fruitful discussions and comments. We thank Bent Skov for his precious assistance in the laboratory and at the waterworks.
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Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 137 • Issue 4 • April 2011
Pages: 248 - 257
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Oct 26, 2009
Accepted: Nov 1, 2010
Published online: Nov 3, 2010
Published in print: Apr 1, 2011
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