Septic System Basics - SAHRAweb.sahra.arizona.edu/education2/wrtt/lecs/Poe_SepticSys... · Septic...
Transcript of Septic System Basics - SAHRAweb.sahra.arizona.edu/education2/wrtt/lecs/Poe_SepticSys... · Septic...
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Septic System Basics
Kitt Farrell-PoeExtension Water Quality Specialist
Ag & Biosystems Engineering Dept.
Today’s Presentation:
• What is an “onsite wastewater treatment” system?
• Components of a septic system• Treatment & dispersal• Management
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Common Domestic Pollutants• Microorganisms
– Bacteria, viruses, protozoa, etc.• Nutrients
– Ammonia, nitrate, phosphorus• Suspended Solids• Toxics
– Heavy metals, pharmaceuticals• Organics
– pesticides
What is an Onsite Wastewater Treatment System?
Source
Pretreatment
Final treatment & dispersal
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What should an onsite wastewater treatment system do?
• Treat sewage– Public health concerns– Environmental quality concerns
• Disperse sewage• Provide acceptable level of risk – put the
“odds” on our side
Goals of Treatment• Separate solids *
• Reduce organic materials (BOD)* †• Reduce nutrients†• Reduce pathogens†• Reduce toxic discharges†
* Septic tank† Soil treatment area
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Goals of Dispersal
• Disperse effluent evenly across soil treatment area to keep soil unsaturated and aerobic.
• Provide enough time in the soil for treatment to take place.
• Percolate to groundwater so original water can be recycled back into the water cycle.
Components
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Pretreatment Final Treatment & Dispersal
Application-Distribution
OWTS Components
Source
EXCEPT: Place all water softener backwash into a separate component if possible.
Source: All Sewage!
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Conserving water helps -• Maintain retention time in septic tank• Promote oxygen levels in drainfield
Properly dispose of cooking oils
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Chemicals & Other Materials
* NOTE: Septic tanks should only receive pre-digested foods
Garbage Disposals
• Higher risk of solids carryover to drainfield• Recommend composting kitchen scraps • If used, then increase septic tank size (2X)• Expect to pump solids more often (2X)• Use an effluent screen
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Pretreatment Final Treatment & Dispersal
Application-Distribution
OWTS Components
Pretreatment – Purpose: “Pretreat” wastewater so downstream component(s) can function more reliably for longer terms.
Source
Pretreatment: Septic Tank• Functions
– Separate solids, oils, and greases from liquid– Anaerobic decomposition (some, not a lot)– Keep sewage in tank at least 24-36 hours– Store solids– Dissipate energy of wastewater
Screen
As scum and sludge layers build and come
closer together, the 2-day detention time becomes less and solids removal
efficiency drops.
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Pretreatment: Septic Tank
• Components– Sanitary tees– Compartments– Effluent screen– Inspection port– Manhole
Screen
screen
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Septic Tank - Materials
Tanks should betested for water
tightness
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Septic Tank Outlet Screens
• Functions– Helps keep solids out of
drainfield– Helps lessen energy of surge
flows
• Goes in outlet of tank or replaces it
• Variety of types of models• Will plug periodically• Needs careful periodic
cleaning
Septic Tank• Management
– Pump -- sludge & scum accumulations• 25-33% = need to pump
– Inspect• Structural soundness• All baffles/inlets/outlets, etc. are intact
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Septic Tank Additives
No published scientific evidence showing additives increase system lifespan.
“Never pump again” works against the whole purpose of the septic tank, which is to trap solids and prevent them from getting to the drainfield.
OWTS Components
Pretreatment Final Treatment & Dispersal
Application-Distribution
Source
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Soil Treatment Area
• Receives effluent & transmits to soil• Soil underneath provides treatment
– physical filtration– biological activity– chemical reactions
• Soil should remove disease-causing organisms and some chemicals of concern
Courtesy of National Assn of Wastewater Transporters
Pathogen capture
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Courtesy of National Assn of Wastewater Transporters
Pathogen removal
How effluent moves
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“Conventional” Soil Treatment Systems
• Drainfield [Soil treatment area]– Network of trenches, beds, chambers, seepage pits– Gravity distribution
Trench
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Bed
Seepage Pit
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Chamber Technology
“Alternative” Soil Treatment Systems
– Usually pressure distribution– Examples include mound and drip systems
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Alternative Soil Treatment Systems
• Allows use of septic systems in areas with poor soils, shallow bedrock, or high water table
• Operates in all climates• Higher installation cost than conventional
drainfields
• Greater space needed
• Limits on slopes
• Requires pump O&M
Distribution Media
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How are the pieces connected?
• Parallel • Serial
Distribution boxDrop box
Construction Concerns
• Compaction• Material selection
– Clean?• Soil conditions• Divert run-on
away
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Drainfield Management
• Traffic control• Surface water• Inspection pipes
– 1-½” to 4”– At the end of the
system– Connected into the
system
REMEMBER:Conventional Septic System
• Effective where lots are appropriate• Must have well-drained soils with limited
slopes• Requires regular inspection and periodic
pumping• Alternatives broaden applications and can
improve effectiveness• Avoid garbage grinders• Groundwater problems
are possible• Systems fail if forgotten
6.22
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IN SUMMARY:What conditions are important to
maximize system function?• An environment that allows bacteria to thrive
– proper temperature and pH, no deterrent to growth– anaerobic conditions in septic tank
• Watertight and structurally sound septic tank• Sufficient time in tanks and soil• 2-5 feet of slow, downward flow through dry,
aerobic soil – but not too coarse• Certain horizontal distances from wells, surface
water, etc. to soil treatment area
QUESTIONS??
http://ag.arizona.edu/waterquality/onsiteOr
http://extension.arizona.edu/water-portal/onsite-wastewater-education-program