Septic Systems and the Environment

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Septic Systems and the Environment
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Goals of On-Site Wastewater Systems

• Treat the effluent to minimize health risks
• Treat the effluent to minimize environmental
  health risk
• Dispose of the treated effluent

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What is in wastewater?

• Water - How much is used per capita per day?
• Pathogens - How many are produced per capita?
• Bacteria
• Viruses

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What is in wastewater?

• Nutrients - How much per capita per year?
• Nitrogen
• Phosphorus

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What is in wastewater?

• Organics
• Inorganics
• VOC and HC

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Is all wastewater the same?

• Residential
• Commercial
• Restaurant
• Industrial

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Components of On-Site Systems

• Source
• Septic Tank
• Drainfield
• Soil

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System Components
Source
Well
Tank
Drainfield
Treatment in Soil
Groundwater
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Processes occurring at the source

• Source
• wastewater generation
• initial treatment via chemical additions

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Composition of Domestic Wastewater
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The Septic Tank
Ground Surface
Riser
Riser
Influent
Effluent
Scum or
Grease Layer
Liquid
Effluent Filter
Solids/Sludge
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Characteristic Wastewater from the Septic Tank
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Processes occurring in the septic tank

• settling of solids
• floating of scum
• nutrient reduction and transformation
• pathogen reduction

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Processes occurring in the drainfield

• Filtering of solids
• Additional nutrient and pathogen removal
• Dispersal of effluent into the environment

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Processes occurring in the soil

• Nitrification Transformation of NH4 to NO3
• Nutrient reduction
• Pathogen removal
• TSS and BOD reduction
• Soil must be aerobic for order to have proper
  treatment

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Solids

• Settle in tank
• Filtered out in drainfield
• Filtered out in soil

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Organic Materials

• Biochemical Oxygen Demand
• 200 -290 mg/l
• Oil and Grease
• Amounts vary
• Source
• Feces, food, fiber, etc.

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Organic Materials Concerns

• Oxygen demand
• Potential for clogging
• Large systems
• Restaurants

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Organic Materials Reactions

• Microbial degradation
• Oxygen transfer

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Nitrogen

• Source
• Urine, undigested food, cleaning fluids
• Occurs as organic-N and NH4
• 10-16 lb. per capita per year

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Nitrogen Concerns

• Methemaglobanemia (blue baby syndrome)
• Eutrophication

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Nitrogen Reactions

• Mineralization
• Nitrification
• Denitrification
• Sorption
• Immobilization

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Denitrification

• Lack O2
• Presence of denitrifying bacteria
• Presence of NO3
• Presence of a carbon source (food)

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Respiration
O2
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Denitrification
NO3
N2 gas
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Iron Reduction
Fe3
Fe2
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Location of Denitrification

• Under drainfield
• In wetlands
• In stream bottom sediments

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N Cycle in Septic Systems
Mineralization
Immobilization
Nitrification and Sorption
Denitrification ?
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Phosphorus

• Source
• detergents etc., excreta
• Occurs as organic-P and orthophosphate
• 3-5 lb.. per capita per year

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Phosphorus Concerns

• Water Quality - Eutrophication

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Phosphorus Reactions

• Sorption
• Precipitation
• Sediment erosion

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Pathogens

• Source
• Feces, laundry
• Bacteria
• up to 1010 per 100ml
• Viruses
• up to 109 per gram

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Pathogens Concerns

• Health risk

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Pathogens Reactions

• Sorption
• Filtration
• Death
• Must have aerobic and unsaturated soil for proper
  treatment

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Wet Conditions
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Moist Conditions
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VOC and HCs

• Source
• cleaning fluids, solvents
• Variable amounts

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VOC and HCs Concerns

• Carcinogens
• Toxins

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VOC and HCs Reactions

• Sorption
• Microbial transformation
• Volatilization

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Septage

• Sludge must be removed from septic tank
• Must be properly treated and disposed
• Municipal treatment plant
• Land applied

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Conclusions

• Many choices for wastewater treatment
• In the On-site wastewater arena the first choice
  is the conventional system
• Advanced treatment system are used when
  environmental conditions demand a higher degree
  of treatment
• Combination of several technologies often results
  in the highest degree of treatment