Michael Urynowicz, Ph'D', P'E'

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On-Site Wastewater Treatment Systems

• Michael Urynowicz, Ph.D., P.E.
• Assistant Professor
• Department of Civil Architectural Engineering
• University of Wyoming, Laramie, WY 82071-3295
• Telephone [phone] Email
  murynowi_at_uwyo.edu

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Presentation Outline

• Workshop
• On-Site Wastewater Treatment Systems
• Centralized vs Decentralized Wastewater Treatment
  Systems
• Wastewater Constituents
• Conventional Septic System
• Septic Tank
• Soil Absorption System
• Importance of the Clogging Matt
• Importance of the Unsaturated Zone
• Fate and Transport of Pathogens
• Alternative On-Site Wastewater Systems
• Video and Closing Remarks

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On-Site Wastewater Treatment Systems

• Underground cesspool (France, 1870s)
• Septic tank systems (U.S.A., early 1900s)

• Designed for subsurface disposal

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On-Site Wastewater Treatment Systems

• Nearly 25 of the U.S. population is served by
  on-site and decentralized wastewater systems.
• Approximately one-third of new development is
  supported by such systems.
• Roughly 25 million existing systems.
• Approximately 0.2 million new systems being
  installed each year.

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On-Site Wastewater Treatment Systems

• Traditionally, onsite systems were viewed as
  temporary disposal solutions.
• Good enough for now (i.e., until the public
  sewer is available).

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On-Site Wastewater Treatment Systems

• Why have on-site treatment systems been
  traditionally viewed as inferior to centralized
  systems?

• Publics perception
• Less uncertainty
• Less responsibility
• Predictable costs
• More assurance regarding public heath and the
  environment

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On-Site Wastewater Treatment Systems

• On-site systems are now viewed as a necessary
  and permanent wastewater treatment approach.

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On-Site Wastewater Treatment Systems

• Why the shifting paradigm?

• Funding
• Economics (collection costs 65 80 vs lt 30 of
  total costs)
• Water management

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On-Site Wastewater Treatment Systems

• Questions and Considerations (Micro-Scale)
• Levels of purification achieved by conventional
  onsite systems
• Effects of using alternative on-site systems
• Vadose zone sampling
• Clogging zone formation affects
• Source of pathogens in water

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On-Site Wastewater Treatment Systems

• Questions and Considerations (Macro-Scale)
• Public health impacts associated with using
  decentralized versus centralized systems
• Public health impacts associated with
  catastrophic events (e.g., flooding)
• Public health impacts associated with inadequate
  design, siting and operation and maintenance
• Watershed effects

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On-Site Wastewater Treatment Systems

• Most of the areas using septic systems also rely
  on private wells for domestic supply.

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Wastewater Constituents

• Organic Compounds
• BOD, COD, TSS
• Nitrogen
• NH4-N, organic-N, NO3--N, N02N
• Anaerobic (NH4-N, organic-N)
• Aerobic (NO3--N)

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Wastewater Constituents

• Nitrogen
• Dissolved Inorganic Nitrogen (NO3--N, N02N,
  NH4-N)
• Kjeldhal Nitrogen (NH4-N and organic-N)

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Wastewater Constituents

• Phosphorous
• Organic-P, Orthophosphates
• Pathogens
• Bacteria, viruses, protozoa, helminths
• Most water borne pathogens can cause illness with
  10 to 1000 infectious units

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Conventional Septic Systems

• What is a septic system?

• Septic tank
• Gravel-filled drainfield
• Soil beneath the drainfield

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Conventional Septic Systems
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Conventional Septic Systems

• Advantages
• Can provide excellent treatment and disposal of
  wastewater
• Reliable, cost-effective method
• Least costly to maintain
• Disadvantages
• Can be used at fewer and fewer sites

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Conventional Septic Systems
Septic tank Soil Absorption
System
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Septic Tank

• Basic function is to remove solids (separates
  solids and oil/scum)
• Dissolved and suspended matter (pathogens) leaves
  the tank untreated
• Provides some degree of anaerobic digestion
• Solids and scum must be removed periodically (3
  to 5 years)

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Septic Tank

• Retention time gt 24 hours (sufficient sludge and
  scum retention)
• Gas deflectors and filter screens or
  inclined-plate settling units help to minimize
  effluent solids.
• Multiple chambers in series or baffles can
  improve sludge and scum removal.

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Septic Tank

• Organic Compounds
• Removes solids (scum and sludge)
• 70 TSS, 60 BOD removal, 25 to 50 COD removal
• Nitrogen
• 10 of total N removed (sludge)
• Anaerobic (NH4-N, organic-N)

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Septic Tank

• Phosphorus
• Converts most of the phosphorus into soluble
  orthophosphates
• Pathogens

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Soil Absorption System

• Underground piping network buried in trenches
  below the ground surface.
• Distributes septic tank effluent over a large
  soil area
• Purification (most pollutants and pathogens are
  removed)

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Soil Absorption System

• Organic Compounds
• Most of the remaining dissolved organics are
  removed (filtration, decomposition, incorporation
  into microbial cells)
• Nitrogen
• Aerobic (NO3--N)
• 20 of the total N removed from septic tank
  effluent (denitrification, adsorption, plant
  uptake, and volatilization)
• gt50 of N (NO3--N) reaches groundwater

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Soil Absorption System
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Soil Absorption System

• Oxidation States of Nitrogen
• N2 (0)
• NH3, NH4(-III)
• NO3- (V)
• Nitrification
• NH4 2O2 NO3- 2H H2O
• Nitrate Reduction or Denitrification
• 5CH2O 4NO3- 4H 5CO2 7H2O 2N2
• When oxygen is not available, microorganisms can
  use nitrate as the oxidant (electron acceptor).

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Soil Absorption System

• Phosphorus
• Most of the phosphates are removed (adsorption,
  precipitation, plant uptake, biological
  immobilization)
• Pathogens
• Most pathogens are removed (filtration,
  precipitation, adsorption, biological enzyme
  attack, natural die off)
• Protozoagtbacteriagtviruses (behave differently)
• Absorption vs filtration
• Virus attenuation is strongly influenced by soil
  properties (cation exchange, mineralogy, texture,
  pH, and temperature)

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Importance of the Clogging Mat

• Deposition (effluent solids, biomass,
  precipitation, etc.)
• Alters pore structure (pore blocking)
• Microbial environment
• Microorganisms degrade organics (reduction in
  BOD, SS, and fecal coliform)
• Causes unsaturated flow to occur beneath the matt

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Importance of the Unsaturated Zone

• Water travels more slowly through the unsaturated
  zone
• Slower flow ? Longer residence time (more
  opportunity for purification to occur)
• Good aeration is necessary to achieve die-off of
  bacteria and viruses

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Alternative On-Site Wastewater Treatment Systems

• Not all sites are well suited for conventional
  on-site wastewater treatment systems
• Distance from building, property line, property
  lines, potable water lines, water well, waterways
  etc.)
• Availability of perc. land

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Alternative On-Site Wastewater Treatment Systems

• Advantages
• Can provide excellent treatment and disposal of
  wastewater.
• Can be used at more problematic sites.
• Disadvantages
• Higher maintenance
• Higher cost

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Alternative On-Site Wastewater Treatment Systems

• Aerobic Treatment Units (ATUs)
• Suspended or attached Growth
• Media Filters
• Sand, Peat, Foam, Textile, etc.
• Natural Systems
• Wetland, Evapotranspiration, etc.
• Wastewater Separation and Waterless Toilets
• Disinfection Systems
• UV light, strong oxidizers, etc.

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Aerobic Treatment Units (ATU)

• Individual aerobic wastewater treatment plants
• Used as alternatives to septic tanks or in series
• Soil absorption field may still be required
• Can be used when an inadequate soil adsorption
  system is present (soil depth, properties,
  groundwater, etc.)
• Treatment is equivalent to 1 foot of the
  unsaturated zone

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Media Filters

• Sand Filters

• Single pass or recirculating
• Used in series with septic tank or ATU
• Soil absorption field may still required

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Media Filters

• Sand Filters

• Reduces BOD and TSS
• Converts nitrogen to nitrate
• Reduces phosphorus
• Reduces pathogens

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Media Filters

• Sand Filters

• Especially important in the control of
  Cryptosporidium oocysts and Giardia cysts

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Media Filters

• Mound Systems

• Can be used when an inadequate soil adsorption
  system is present (soil depth, properties,
  groundwater, etc.)

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Media Filters

• Peat Filters

• Used in series with septic tank (soil absorption
  field is still required).
• Reduces BOD, TSS, nitrogen, phosphorus, and
  pathogens (aerobic biochemical activity and
  physical filtration).

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Natural Systems

• Wetlands

• Used in combination with pre-treatment
• Treatment of dissolved and suspended solids
  (contact with active biomass)

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Wastewater Separation

• Wastewater Separation
• Gray Water (wastewater that doesnt come from
  toilets).

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Waterless Toilets

• Incinerating or Composting Toilets

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Disinfection

• UV light
• Chemical oxidizers (chlorination)
• Neither chemical disinfectants nor UV will act
  well against pathogens that are protected by
  suspended material.

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Integrated On-Site Wastewater Systems

• Wastewater Separation/Surface Application

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Integrated On-Site Wastewater Systems

• ATU/Disinfection/Surface Application

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Community Onsite Options
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Closing Remarks

• Decentralized wastewater treatment systems are
  now considered an effective and long-term
  wastewater treatment approach.
• Requires proper design, installation, and
  operation maintenance.
• Matching the system with the site is critical.
• The use of on-site wastewater treatment systems
  will continue to grow and evolve.