Rural, Community & Onsite Wastewater & Waste Management Role of Soil in Biological Treatment

Onsite Wastewater Management

Pollutants in Wastewater Ammonia Organic matter Nutrients Pathogens Color Metals

Domestic Sewage Gray & cloudy 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)

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 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

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 , 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