Integrated Watershed Management Session 10 -- Water Quality Modeling -- Dissolved Oxygen Sinks & Nutrients BOD (Biochemical Oxygen Demand) Respiration Sediment oxygen Demand (SOD) Nitrification University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

BOD (Biochemical Oxygen Demand) OM is hard to measure, so we measure it effect Place sample of OM in bottle, shake & Stopper Measure DO over a short time -- 5 days OM + O2 ---> CO2 + NO3 + PO4 The O2 consumed is the BOD University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Typical BOD Calculation Add 10 ml sample to water up to 300 ml Initial DO = 9 mg/l 5 day DO = 6 mg/l BOD5 = 9-6 / (10 / 300) = 90 mg/l Dilution is 1:30 and DO loss is 3 mg/l therefore, 3 * 30 = 90 mg/l University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Typical BOD Values Source CBOD5 (mg/l) CBODU (mg/l) NBODU (mg/l) Org-N (mg/l) NH3 -- N (mg/l) Raw Sewage 180 220 20 28 Primary Effluent 120 150 12 Secondary Effluent 10 - 20 35 - 50 20 - 40 2 10 CSO’s 170 6 3 Storm Water 19 25 0.6 University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

A Few Observation on BOD BOD is not a substance, it is a measurement Receiving waters will feel the effect of BODU not just BOD5 BOD curves vary greatly depending on the waste Paper mill effluent has no NBOD WWTP secondary effluent NBOD does not have lag time Ethylene glycol BOD -- 800,000 mg/l University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Equation for Typical BOD Curve L = Lo (1 - e (-kt)) L = BOD (mg/l) Lo = BODU (mg/l) K = BOD Decay Rate (1/day) Typical Values for k 0.35 Raw Sewage -- Bugs love this stuff 0.2 Primary Effluent -- OK but not as good as raw 0.075 Secondary effluent -- Tough stuff to swallow University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

1st Order Kinetics Dc/dt -kc C = c0 * e –kt Board Diagram University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Photosynthesis & Respiration Aquatic Plants Affect DO Respiration: The process of breaking down food to create energy Occurs continually Diurnal DO Cycle University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

SOD (Sediment Oxygen Demand) OM, algae & solids etc. eventually end up settling to the bottom The oxidation process continue in the sediment causing an oxygen demand Two important reasons: Can be the major sink for DO Stores the pollutant history of the stream University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Nitrification 2NH3 + 4O2  2HNO3 + 2H20 Nitrification DO Demand University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Putting everything together Sources Reaeration Photosynthesis Sinks BOD from OM Respiration SOD Nitrification University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Texts & Assignments “Watershed Based National Pollutant Discharge Elimination System (NPDES) Permitting Implementation Guidance’” US Environmental Protection Agency, Dec. 2003. Section 2 University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006

Next Session Steps 1 & 2 Defining the watershed Identifying the stake holders Project problem identification University of Houston -- Integrated Watershed Mangement -- Session 10 CIVE7397 -- Spring 2006