Rural, Community & Onsite Wastewater & Waste Management

Role of Soil in Biological Treatment

Onsite Wastewater ManagementTreatment PlantOperatorTreatment PlantTreatment Plant

Pollutants in Wastewater

Ammonia

Organic matter

Nutrients

Pathogens

Color

Metals

Domestic Sewage

Gray & cloudy Suspended solids

Suspended solids

Reduce water clarity

Settle out & interfere with aquatic life

Clog soil & equipment

Removal of solids

Settling

Filtering

Septic System

Septic Tank

Septic Tank Pumping

•Tank size (gal) •2 •4 •6

•500 •2.6 •1.0 •0.4

•1000 •5.9 •2.6 •1.5

•1500 •9.1 •4.2 •2.6

Soil Absorption System

Soil Absorption System

Filtering out solids

How deep in soil?

A few inches to 1 foot

Wastewater will be clear

Is it fully treated?

Unsaturated Soil

Soil surface

Limiting condition

Organic Matter (BOD) & Ammonia

Microorganisms Organic matter & ammonia is their food

Create ideal environment for microorganisms Surface to attach to Air Water Food

Fixed Film Biological Reactor

Organic Matter & Ammonia Removal

How deep in soil?

2 feet of unsaturated soil

Wastewater is clear with no odor

Is it fully treated?

Bacteria & Viruses

Pathogens - cause disease

Bacteria - simple cell

Virus - protein molecule

Bacteria

Remove by Filtering action of biological film Chemical attraction to soil particles

Soil particles and bacteria both have a surface electrical charge

They attract like the opposite poles of a magnet

Bacteria Removal

How deep in soil?

1 1/2 to 2 feet of unsaturated soil

200 to 400 feet in saturated soil

Wastewater is clear, has no odor and is free of bacteria

Is it fully treated?

Viruses

Too small for filtration

Removed by adsorption onto soil particles

Organic matter interferes with adsorption

Must remove the organic matter from wastewater first

Viruses Removal

How deep in soil?

1/2 to 2 feet after organic matter is removed

Depth of Soil

Ohio Code - 4 feet above Ground or perched water table Bedrock Compacted soil layers Sand and gravel layers

Soil Absorption Systems

Soil too Shallow?

Environmental impact?

Layer of sand on top of soil Sand allows for flow of air & water Substrate for biofilm No surface chemistry for adsorption of bacteria

or viruses

Removal in Sand

Suspended solids, BOD and Ammonia

Widrig, Peeples & Mancl (1996) After 24 inches of sand

BOD - 12 mg/l SS - 10 mg/l Ammonia - 0.5 mg/l

Removal in Sand

Bacteria Travel 6 feet through sand

Viruses Few sorption sites in sand Poor removal

Disinfection of Sand Treated Wastewater

Through a layer of soil Called a mound system 2 feet of soil under 2 feet of sand

Mound System

Soil too Shallow for Mound?

Environmental Impact?Filter through sand SS, BOD & ammonia removal

Disinfection system Bacteria & virus removal Classes 15 & 16

Disperse through irrigation Class 17

Sand Bioreactor System

Sand Bioreactor System

Water tight container of sand

Wastewater applied in doses

Collected and disinfected

Dispersed in soil 1 foot deep

Soil too Shallow for Irrigation?

Hydric soil - wet soil Saturated several months each year Within 1 foot of surface

Environmental Impact?

Readings

Burks & Minnis 133-140, 173-186

Suitability of Ohio Soils for Wastewater Treatment Bull 896

AEX 740 Septic Tank Maintenance

AEX 743 Septic Tank - Soil Absorption Systems

AEX 744 Septic Tank Mound Systems