Successful OWTS Treatment

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Successful OWTS Treatment

• Siting
• Site Evaluation
• System Location
• Design
• System Sizing
• System Selection and Design
• Installation
• Operation/Maintenance

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Failure

• A condition that threatens public health by
  failure to adequately treat sewage or creating
  potential for direct contact
• Examples
• Pooling on ground surface
• Back up into structure
• Leaking tanks, pump chamber or collection system
• Impacted water quality (surface or ground)

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Factors Affecting OWTS Performance

• Soil system performs multiple tasks in typical
  OWTS
• Treat the water to remove contaminants
• Dispose of treated water
• Factors that affect these tasks
• Soil Wastewater Characteristics
• Loading Rates Users Lifestyle
• O M Temperature
• Rainfall Surrounding Development

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Soil

• Texture
• Structure
• Depth
• Compaction
• Landscape Position

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Soil Profiles Typical Layers
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Soil Horizons Soil Properties According to Depth

• Distinct soil horizons or layers form from
  weathering processes
• Layers have distinct chemical compositions
  determines
• amounts and state of organic matter
• amounts of nutrient elements
• Each layer supports varying amounts and types of
  microbial communities
• Surface layers of soils (O layers) are organic
• Dominated by organic matter (e.g. leaves, twigs,
  etc.) ( O1 layer)
• Dominated by unrecognizable organic matter in
  next lower layer
• some decomposition has occurred (O2 layer)
• Sub-surface soil layers (A layers) various
  combinations of organic and mineral materials
  which experience increasing amounts of leaching
  ( eluvial layers)
• Lower layers (B layers) experience leaching and
  horizontal movement of materials ( illuvial
  layers)
• Lowest soil layers (C layer) experience least
  weathering in contact with bedrock

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Loading Rates

• Hydraulic overloading is one of leading causes of
  OWTS failure
• Design flow typically based on number of people
  in house (assumption generally 2 per bedroom)
• 60 gpd/person (common assumption in design)
• Loading rates determined by type of soil

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Loading Rates

• Clogging Mat
• Gravitational potential
• Matric Potential

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Users Lifestyle

• Low-flow devices (toilet, faucets, shower heads,
  etc.)
• Rainfall collection
• Use of garbage disposals
• Excessive use of FOG
• Laundry habits
• Time in Residence

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Wastewater Characteristics

• BOD5 (above 230mg/L will reduce life of system
  and level of treatment)
• Biologically active chemicals (bleach,
  antibiotics, etc.)
• FOG
• Other chemicals (Cleaners, solvents, degreasers,
  etc.)

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Operation and Maintenance (OM)

• Pump Tanks every 3 to 5 years (plan on every 4)
• Actual time period should depend on active
  monitoring of system
• Conduct at least biannual monitoring of tank
  levels, baffles, and drainfield
• This is the minimum, more frequent monitoring
  recommended (required for advanced systems)
• Pump tank when sludge layer thickness exceeds 25
  of working liquid capacity of the tank, or if
  scum layer is within three inches of bottom of
  outlet baffle

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Septic Tank
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Temperature and Rainfall

• Temperature
• Affects flow and mixing in septic tank
• Soil treatment relies on biological activity
• Cold slows down biological processes
• 50 loss in activity for 10ºC drop in temp
• Activity effectively stops at 2 ºC
• Rainfall
• Additional hydraulic load on soil
• Reduction in vertical separation
• Benefit-dilute nitrates, however also increase
  transport rate

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Alternative Waste Treatment

• Stabilization Ponds
• Wetlands
• Composting Toilets
• Separation of Waste Streams
• Greywater Sytstems
• Primitive Systems

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Facultative Oxidation (Waste Stabilization) Pond
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Stabilization Ponds or Lagoons

• Aerobic and Facultative Ponds
• Biologically Rx by complementary activity of
  algae and bacteria.
• Used for raw sewage as well as primary- or
  secondary-Rxd. effluent.
• Bacteria and other heterotrophs convert organic
  matter to carbon dioxide, inorganic nutrients,
  water and microbial biomass.
• Algae use CO2 and inorganic nutrients, primarily
  N and P, in photosynthesis to produce oxygen and
  algal biomass.

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Stabilization Ponds or Lagoons

• Many different pond designs have been used to
  treat sewage
• facultative ponds upper, aerobic zone and a
  lower anaerobic zone.
• Aerobic heterotrophics and algae proliferate in
  the upper zone.
• Biomass from upper zone settles into the
  anaerobic, bottom zone.
• Bottom solids digested by anaerobic bacteria.

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Constructed Wetlands and Enteric Microbe
Reductions

• Surface flow (SF) wetlands reduce enteric
  microbes by 90
• Subsurface flow (SSF) wetlands reduce enteric
  microbes by 99
• Greater reduction in SSF may be due to greater
  biological activity in wetland bed media (porous
  gravel) and longer retention times
• Multiple wetlands in series incrementally
  increase microbial reductions, with 90-99
  reduction per wetland cell.

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Primitive Systems

• Outhouses
• Privy
• Throne
• Palace
• Comfort station
• Castle
• Post office
• Johnny

• Stool
• Doolie
• White house
• Hut
• WC
• Ajax
• Bog House
• Defacatorium

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Mr. Turdley Says-Dont be a fecaphobe