TY - JOUR
T1 - Temporal changes in hydraulic conductivity of sand porous media biofilters during wastewater infiltration due to biomat formation
AU - Beach, Deborah N.H.
AU - McCray, John E.
AU - Lowe, Kathryn S.
AU - Siegrist, Robert L.
N1 - Funding Information:
This work was sponsored in part by Infiltrator Systems, Inc., and by the US Department of Education through a GAANN graduate-student fellowship to Ms Beach. The Alexander Deussen professorship in the Jackson School of Geosciences at The University of Texas at Austin supported manuscript preparation. Colorado School of Mines researchers John Albert, Sheila Van Cuyk, and Abigail Wren are acknowledged for their assistance with the laboratory experiments. The reviewers would also like to thank Dr Karen Salvage (State University of New York at Binghamton) and one anonymous reviewer for suggestions that significantly improved the manu-script.
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2005/9/15
Y1 - 2005/9/15
N2 - Porous media biofilters (PMBs) are commonly used to treat domestic wastewater. Biomats develop at the infiltrative surface of PMBs due to continued wastewater application and create an impedance to flow. The goal of this research is to quantify the temporal evolution of normalized biomat hydraulic conductivity (Kbm/bbm) and effective hydraulic conductivity (Ke). Ke is the overall hydraulic conductivity of the infiltrative zone, including biomat and unsaturated media below the biomat. Research was conducted using eight one-dimensional (1D) sand columns with gravel-free and gravel-laden infiltrative surfaces. The columns were loaded at design rates of 100-200 cm/d for 20 weeks of column operation. The Ke values for these continuously loaded columns were determined from analyses of bromide-tracer tests, falling-head permeability tests, and volumetric water content measurements during biomat development. The reduction in the Ke due to biomat formation is due to two factors: reduced hydraulic conductivity of the thin biomat, and a reduced hydraulic conductivity of the subsoil due to development of a biomat-induced unsaturated flow regime. Unsaturated hydraulic conductivities of the subsoil below the biomat (K ss) were estimated from capillary curves and water content measurements. For observed final biomat thicknesses (less than 1 cm), the biomat hydraulic conductivity, Kbm, is three orders of magnitude smaller than the unsaturated hydraulic conductivity (Kss). However, the relatively large thickness of the vadose zone causes the Kss to be an important contributor to the overall Ke value. For these columns, the final Ke values were approximately two orders of magnitude smaller than the original value. Because the exact thickness of the biomat (bbm) is unknown during the flow experiments, the hydraulic conductance of the biomat zone is presented using a normalized hydraulic conductivity function (Kbm/bbm). A similar K bm/bbm is reached regardless of wastewater loading rate. An exponential relationship exists between the volume of wastewater applied to the column and both Ke and Kbm/bbm.
AB - Porous media biofilters (PMBs) are commonly used to treat domestic wastewater. Biomats develop at the infiltrative surface of PMBs due to continued wastewater application and create an impedance to flow. The goal of this research is to quantify the temporal evolution of normalized biomat hydraulic conductivity (Kbm/bbm) and effective hydraulic conductivity (Ke). Ke is the overall hydraulic conductivity of the infiltrative zone, including biomat and unsaturated media below the biomat. Research was conducted using eight one-dimensional (1D) sand columns with gravel-free and gravel-laden infiltrative surfaces. The columns were loaded at design rates of 100-200 cm/d for 20 weeks of column operation. The Ke values for these continuously loaded columns were determined from analyses of bromide-tracer tests, falling-head permeability tests, and volumetric water content measurements during biomat development. The reduction in the Ke due to biomat formation is due to two factors: reduced hydraulic conductivity of the thin biomat, and a reduced hydraulic conductivity of the subsoil due to development of a biomat-induced unsaturated flow regime. Unsaturated hydraulic conductivities of the subsoil below the biomat (K ss) were estimated from capillary curves and water content measurements. For observed final biomat thicknesses (less than 1 cm), the biomat hydraulic conductivity, Kbm, is three orders of magnitude smaller than the unsaturated hydraulic conductivity (Kss). However, the relatively large thickness of the vadose zone causes the Kss to be an important contributor to the overall Ke value. For these columns, the final Ke values were approximately two orders of magnitude smaller than the original value. Because the exact thickness of the biomat (bbm) is unknown during the flow experiments, the hydraulic conductance of the biomat zone is presented using a normalized hydraulic conductivity function (Kbm/bbm). A similar K bm/bbm is reached regardless of wastewater loading rate. An exponential relationship exists between the volume of wastewater applied to the column and both Ke and Kbm/bbm.
KW - Biomat
KW - Hydraulic conductivity
KW - Infiltration
KW - Porous media biofilters
KW - Wastewater
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U2 - 10.1016/j.jhydrol.2005.01.024
DO - 10.1016/j.jhydrol.2005.01.024
M3 - Article
AN - SCOPUS:22244438851
SN - 0022-1694
VL - 311
SP - 230
EP - 243
JO - Journal of Hydrology
JF - Journal of Hydrology
IS - 1-4
ER -