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Unformatted text preview: Announcements Prelim 1 review sessions in HO366: Friday at 4pm Monday at 5pm The net effect of dispersion is mass transfer to other fluid elements. This lowers the maximum concentration observed and changes reaction rates for nonconservative materials (Ex . BOD). [More on dispersion soon!] II. Other O 2 sources and sinks are neglected. Even if Q and A are constant (they aren't) and dispersion is negligible (it isn't) the model can get very messy if we include other sources and sinks of D.O. The general form of the equation we have used is: dC = udC + r i where r i = reaction terms dt dX net mass in and out by transport So far, our reaction terms include reaeration and microbial assimilation of O 2 , but in general: r i = t , X S oxidation where = source or sink which is a function of distance and/or time. t , X S so S(x,t)= +k 2 D (X) [reaeration]k 1 L (X) [BOD]k' N C N1(X) [NOD] +P (X,t) [photosynthesis]R (X) [algal respiration]B (X) [benthic uptake] Covered, and in our model Covered, but currently not in our model Coming attractions! Acts like a nonpoint source of BOD PHOTOSYNTHESIS This is carried out by green plants and algae (single celled photosynthetic autotrophs) and bacteria. C 106 H 181 O 45 N 16 P + 150 O 2 106 CO 2 + 16 NO 3 + PO 43 + 19 H + + (163/2) H 2 O The presence of algae affects D.O. since growth (photosynthesis) produces O and respiration consumes it. Photosynthesis requires algae This works out to 2 g O 2 / g algae Photo synthesis algal respiration (dark reaction) 2 sunlight, while respiration occurs both in light and dark. A simple model for lightlimited algal growth: let = rate of O 2 produced by photosynthesis (mg/L* time) = rate of O 2 consumed by respiration (mg/L * time) then d[O 2 ] = dt P R P R me interval sun is out Net rate for change in D.O. by photosynthesis only does not include bacterial respiration or reaeration. R P P m = maximum rate of P time interval sun is out time sunrise sunset P & R vs. time (+) () 2 dO dt 6 am 6 pm 24hr Net effect of P and R on D.O. concentration let = period of sunlight (days) = max. rate of photosynthesis P m 24 hours a diurnal variation in D.O....
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This note was uploaded on 04/13/2010 for the course CEE 3510 taught by Professor Lion during the Spring '10 term at Cornell University (Engineering School).
 Spring '10
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