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CPT Joseph Hout, Assistant Professor, MSPH, REHS Winter, 2008. Wastewater. Learning Objectives. Be familiar with definitions used in class Know how a septic system works Describe the key components of a septic system
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CPT Joseph Hout, Assistant Professor,MSPH, REHS Winter, 2008 Wastewater
Learning Objectives • Be familiar with definitions used in class • Know how a septic system works • Describe the key components of a septic system • Explain the things to consider when building a waste water treatment system • Know how to determine soil permeability • Know the isolation distances associated with an onsite waste water treatment system • Know reasons for septic system failure • Know the organisms and diseases associated with sewage
Definitions • Biochemical Oxygen Demand (BOD) – The difference between the initial dissolved O2 in a water sample and the dissolved O2 in duplicate samples after a stated period of time (usually 5 days = BOD 5). Is the best single measurement of wastewater or polluted water. • Chemical Oxygen Demand (COD) – Measure of the amount of O2 chemically consumed by the oxidation of organic and oxidizable inorganic materials in a water sample. Good for industrial wastes. • COD and BOD do not necessarily measure the same types of oxygen consumption. • COD does not measure the oxygen-consuming potential associated with certain dissolved organic compounds such as acetate. However, acetate can be metabolized by microorganisms and would therefore be detected in an assay of BOD. • The oxygen-consuming potential of cellulose is not measured during BOD assay, but it is measured during a COD test.
Definitions • Domestic Sewage – used water from a home or community from toilet, bath, laundry, lavatory and kitchen sink waste. • Strength reported in BOD5, COD, and suspended solids (SS) • Black water – from toilet • Grey water – all other domestic waste water • Privy – excreta disposed without aid of water – outhouse • National Pollutant Discharge and Elimination System (NPDES) – system from issuing permits for the discharge of treated sanitary, industrial and commercial waste under the 1972 federal water pollution control act. Specifies treatment and expected outcome of effluent to protect water quality.
Definitions • Combined sewer – storm water and domestic sewage are combined in the same pipe • Separate sewer system – storm water and domestic sewage are collected separately • Suspended solids (SS) solids that are visible and in suspension in water. Test is retention on the asbestos mat in a Gooch crucible and represents the food that bacteria eat.
Septic Tank • Primary functions • Remove solids • Biological (anaerobic) txt • Sludge and Scum Storage Results in conditioned product that can be percolated into subsoil
Septic Tank • Inlet Baffle • Directs flow • Minimizes turbulence • Outlet Baffle • Clear zone guarantee • Holds scum (FOG) in tank • Can house a effluent screen
Septic Tank Cleanout every 50’ Min 4” Inlet and outlet http://extension.missouri.edu
Septic Tank • Pump System if • Scum < 3” from outlet • Scum > 12” • Sludge <12” from outlet • Scum + sludge > ½ liquid depth http://extension.missouri.edu
Drain Fields Purpose • Dispose of effluent from septic tank • Distribute so can be treated by soil before reaching groundwater
Design: Soil Permeability • Yellow, brown or red • Air and therefore water passes through • Blue or grey • Saturated for extended periods • Mottled brown or red • Fluctuating seasonal high water table • Unsuitable for subsurface absorption of wastewater • Measured using Munsell Color Chart
Design: Soil Permeability The Munsell color book is used to document color in a standard notation. Hue: Dominant spectral color. Value found in the top right-hand corner of each page. Value: The degree of light/dark of a color in relation to a neutral gray scale. Values along the left-hand side of each page. Chroma: Strength of hue. Values along the bottom of each page. The 10YR page of the Munsell color book. http://www.maenvirothon.org
Design: Soil Permeability Soil Classification • Munsell color • Structure • Texture • Content Classification yields a permeability estimate and an estimated application rate – Can also use the percolation test
Design: Soil Permeability Percolation Test A measure of the relatively constant rate at which clear water maintained At a relatively constant depth (6”) will seep out a standard sized hole
Design: Site Geography • Slope • Gradient, complexity, length and aspect • Lot Size • Gravel vs non gravel drainfield etc • Isolation distances • Vegetation • Limiting layer • Seasonal high water table OR • Soil layer with a very low percolation rate
Design: Summary • Expected flow determines tank capacity • # of bedrooms • Flow and application rate determine seepage area • # of bedrooms, percolation test, soil characterization • Depth to limiting layer, isolation distances, lot size determine • Where a system can be placed • If a system can be installed • Waste strength determines type of pretreatment • Septic tank - slower • Aerobic treatment plant (ATP) -faster
System Failure • Poor design • Hydraulic overload • Seasonal high water • Excessive water use • Leaking fixtures • System Abuse • Excessive cleaning chemicals • Flushing non digestibles • System damage • Missing or damaged baffles • Soil compaction in drain field • Improper connections • Roof gutters • Footing drains • Sub pumps • Uneven settlement • Tank • Connecting pipes • Distribution box
System Failure: Hazards • ALWAYS assume that sewage contains pathogenic organisms • Can survive in soil from days to years • Main indicator is Escherichia coli • No process other than disinfection can remove all pathogens • Pathogens of concern are bacteria, viruses, helminthes, and protozoa
Sewage Borne Bacteria NOT SALMONELLOSIS!!!!
Sewage Borne Bacteria NOT TYPHOID FEVER
