Ch Changing Hydraulic Properties i H d li P i in Horizontal - - PowerPoint PPT Presentation

Ch i H d li P i Changing Hydraulic Properties 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,

h l b i d di heavy metals, bacteria and sediment

• 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? A d d ll hi ff h ffi i f h

• And does all this affect the efficiency of the

wetland?

Theory Theory

• Removal efficiency requires controlled water

Removal efficiency requires controlled water flow

• Overtime soils clogs due to solids and

bi l i l h biological growth

• Solids and biological growth may change

hydraulic conductivity y y

Darcy’s Law

Guiding Equation

q = -K(θ)▼H q ( ) K = Cr2(L/L )2

D ’ l ld b f ti f di t d

K = Cr2(L/Le)2

Darcy’s law could be function of sediment and biological growth, because K is essentially a f nction of radi s and L function of radius and Le

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 P i l d b d lid h i

• Particle adsorbed to solids have varying

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 Le

• Leads to decrease in K
• Leads to decrease in K

K = Cr2(L/Le)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. Bi fil l f h i d b

• Biofilms are also often characterized by

surface attachment, complex community i i d ll l i f interactions, and an extracellular matrix of polymeric substances.

Wiki di

• Wikipedia

Bioclogging Bioclogging

• Results from the growth

Results from the growth

• f biofilm
• The aging of a biofilm

causes a decrease in void space

K = Cr2(L/Le)2

Results of Sedimentation Results of Sedimentation

• Sediment Load
• Hydraulic Conductivity

Sediment Load

• Kg per square meter

Hydraulic Conductivity

• 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 d10 between 0.3 and 1.0mm are suitable for intermittent wastewater loading, while a d10 between 1 and 1.5mm are suitable for long operation without resting.” (F. li l) Suliman et al). In LWA, clogging increases retention time and hence improves the system treatment efficiency

Are there any Questions? Are there any Questions?