Ch Changing Hydraulic Properties i H d li P i in Horizontal Subsurface Flow Constructed Wetlands Angelina Cernick BAE 558 BAE 558
Introduction Introduction • Constructed wetlands can be part of a system Constructed wetlands can be part of a system to treat stormwater and wastewater • Contaminants such as nitrogen, phosphorus, heavy metals, bacteria and sediment h l b i d di • The flow through wetland soils plays important role in removing contaminants p g
Purpose Purpose • How does sedimentation affect hydraulic How does sedimentation affect hydraulic conductivity? • How does biological growth affect hydraulic • How does biological growth affect hydraulic conductivity? • And does all this affect the efficiency of the A d d ll hi ff h ffi i f h wetland?
Theory Theory • Removal efficiency requires controlled water Removal efficiency requires controlled water flow • Overtime soils clogs due to solids and bi l biological growth i l h • Solids and biological growth may change hydraulic conductivity y y
Darcy’s Law Guiding Equation q = -K( θ ) ▼ H q ( ) K = Cr 2 (L/L e ) 2 K = Cr 2 (L/L ) 2 D Darcy’s law could be function of sediment and ’ l ld b f ti f di t d biological growth, because K is essentially a f nction of radi s and L function of radius and L e
Sedimentation Sedimentation • Sedimentation is the process in which solids Sedimentation is the process in which solids are removed from the water column • Solids settle and/or attach to vegetation and • Solids settle and/or attach to vegetation and soil • Particle adsorbed to solids have varying P i l d b d lid h i properties that may affect conductivity
Clogging Due to Sedimentation Clogging Due to Sedimentation • Decrease in pore radius Decrease in pore radius • Increase in L Increase in L e • Leads to decrease in K • Leads to decrease in K K = Cr 2 (L/L e ) 2 ( e )
Biofilm Biofilm • A biofilm is a community of microorganisms A biofilm is a community of microorganisms within a self-developed polymeric matrix and adherent to a surface adherent to a surface. • Biofilms are also often characterized by Bi fil l f h i d b surface attachment, complex community interactions, and an extracellular matrix of i i d ll l i f polymeric substances. • Wikipedia Wiki di
Bioclogging Bioclogging • Results from the growth Results from the growth of biofilm • The aging of a biofilm causes a decrease in void space K = Cr 2 (L/L e ) 2
Results of Sedimentation Results of Sedimentation • Sediment Load Sediment Load • Hydraulic Conductivity Hydraulic Conductivity • Kg per square meter • Meters a day Figures from Caselles-Osorio et al.
Results of Bioclogging Hydraulic Conductivity Tables from Suliman et al.
Results of Bioclogging Other Parameters • Change seen in • Change seen in • Retention time • Dispersivity • Pore water velocity Tables from Suliman et al.
Conclusion: Sedimentation Conclusion: Sedimentation In the study, no wetlands lost pollutant removal In the study, no wetlands lost pollutant removal efficiency over time “The main consequence of solids accumulation in SSF CWs is a reduction in either the in SSF CWs is a reduction in either the hydraulic retention time and the hydraulic conductivity (K)” (Caselles-Osorio et al). y ( ) ( ) Be careful of too high pollutant load Be careful of too high pollutant load
Conclusion: Bioclogging Conclusion: Bioclogging In SS, clogging increases pore velocity and decreases In SS, clogging increases pore velocity and decreases retention time and may decrease efficiency. “Soils or filter materials with d 10 between 0.3 and 1.0mm are suitable for intermittent wastewater loading, while a d 10 between 1 and 1.5mm are suitable for long operation without resting.” (F. Suliman et al). li l) In LWA, clogging increases retention time and hence improves the system treatment efficiency
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