Mathematical Modelling of OnSite Soil Absorption System OSAS Performance

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Mathematical Modelling of On-Site Soil Absorption
System (OSAS) Performance

• Ruwan Jayarathne

• SUPERVISORS
• Dr. Sam Yuen, Dr. Mike Connor, Dr. Peter
  Pivonka

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Overview
- Introduction - Literature review - Gaps -
Methodology - Expected Outcomes
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What is domestic wastewater?

• Water generated from kitchen, bath rooms,
  laundries, toilets, etc.
• - Types of Domestic wastewater
• Black water
• Grey water

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What is an OSAS?
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OSAS in use

• Australia 13 of population
• USA - 25 of population

• - OSAS failure
• Hydraulic failure
• Treatment failure

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Cause of Failure

• Flow rate
• Hydraulic loading rate,
• Organic loading rate
• Soil type
• Vadose zone conditions
• Degree of saturation
• Hydraulic conductivity
• Groundwater level

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Modelling work done to date on OSAS

• Watershed based modelling
• Individual system modelling
• -Watershed based modelling
• Weintraub et al.(2004) WARMF
• Carroll et al.(2004) -MODFLOW-2000

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Modelling work done to date ... Contd...

• - Modelling on individual system
• Biofilm modelling using HYDRUS-2D
• Beach and McCray (2003)
• Beal et al.(2004)
• Chemical transport
• Lee et.al. (1998) 1D model
• McAvoy et al.(2002) Laundry detergent
  surfactants
• Shutter et al. (1994) - Impact on
  groundwater

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Gaps in modelling work

• Probability of contamination of groundwater from
  an individual system
• Movement of N,P to groundwater through vadose
  zone
• Suitability of installing an OSAS in particular
  type of soil

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Methodology
- Selecting a suitable modelling software
FEMLAB, VADOSE/W CTRAN/W - Laboratory column
tests Determine the parameter values
required to incorporate into the model -
Field work To assess the extent of
propagation of the contaminant plume, and to
validate the model
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Expected Outcomes

• Prediction of contaminant plume propagation N,
  P
• Suitability of the site
• Optimum Hydraulic loading rate
• Area required to install OSAS optimum trench
  dimensions
• Life span of OSAS

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Thank you.