HomeMy WebLinkAboutHowaSoilAbsorptionSystemTreatsWastewaterRobert L. Uebler, Ph. D.
Soil Scientist
Reported in August of 2002
“3.4 million people, mostly children, die
annually from water related diseases”
The most prominent reason for these
deaths is that “2.4 billion people have
inadequate sewage disposal facilities”
Protection of public health is a primary
goal of your job.
Requires water using fixtures to dispose
of waste generated in every house
This water carried waste must in turn be
treated by either an on-site or central
disposal system if Public Health is to be
protected.
Combined wastewater stream from the house is first discharged to a septic tank thru a
single pipe at the inlet of the tank.
1.)Water - 98%
2.)Suspended Solids
3.)Oil and Grease
4.)Nitrogen
5.)Phosphorus
6.)Virus and Disease Organisms
7.)Fecal Coliform
Suspended solids(mg/l) - 250
Oil and Grease(mg/l) - 60
Total Nitrogen(mg/l) - 70
Total Phosphorus(mg/l) - 24
Fecal Coliform/ 100 ml - 10E6
Virus and Disease - present
Biochemical Oxygen Demand
(BOD)
Def.-The amount of oxygen used during the decomposition of organic material contained
in the wastewater.
Household Wastewater - 250 mg/l
Primary Treatment
-Settling
-Anaerobic Digestion
Required Detention Time
- 2 days
House Tank
Suspended solids (mg/l) 250 100
Oil and grease (mg/l) 60 20
Total Nitrogen (mg/l) 70 40
Total Phosphorus (mg/l) 24 12
Fecal Coli (org / 100ml) 10E6 10E6
Virus and Disease pres pres
The sewage enters a distribution devise
The sole function of this device is to spread
the effluent equally to trenches in the soil of
the yard.
The trenches store the sewage until it
infiltrates the soil.
The soil must treat the remaining
concentration of contaminants in the effluent.
Suspended Solids
1.) Filtration
2.) Digestion by Organism
> aerobic
> products of digestion
- carbon dioxide
- water
3.) Aerobic soil, allows aerobic organisms to digest the solids & prevent clogging of the trenches
Grease and Oil
1.) Filtration
2.) Digestion
> aerobic
> products - water and CO2
3.) BOD - Higher for grease and
oil than most other O. M.
Nitrogen
1.) Most nitrogen converts to ammonia in the
tank.
2.) Positively charged and attracted to
negatively charged soil.
3.) Aerobic nitrifying bacteria - NO3
4.) 40 mg/l nitrate dilutes to <10 mg/l
5.) 40 mg/l nitrate must be diluted to <10
mg/l, if it is to be safe for reuse
Phosphorus
1.) Chemically bonds to soil.
2.) Concentration increases
3.) Precipitates as combines
with- Al, Fe, Ca
4.) Insoluble
5.) Fixation
Fecal Coliform Disease Organisms
1.) Anaerobes.
2.) Filtered by the soil and attracted to
negatively charged sites.
3.) Cannot compete in aerobic environment
4.) Die off.
5.) Virus is small travels furthest.
6.) Fecal coliform are indicators of human
contamination
Simple
Reasonable in cost
Treatment effective
Responsible for treating half of the sewage in
our state
1.) The volume of sewage produced in the
house
2.) The long-term acceptance rate, LTAR,
that the soil maintains for absorption of
the sewage.
Many studies have shown the average household occupant generates 60 gallons of
wastewater in a day.
- we assume 2 people per bedroom
- 2 x 60 = 120 gal/bedroom/day
- 3 bedrooms x 120 = 360 gal/day
* Smallest design flow for any house = 240 gal/day*
Design flow in gallons per day
Divided by
LTAR in gallons per square foot per day
Match the assimilative
capacity of the soil to treat
wastewater to the amount of
water coming from the house
so that the septic system does
not fail
Surfacing of untreated waste
-direct exposure to disease
Contamination of Groundwater
Contamination of Surface Water