Updated: 30 October 2017 Print version Lecture #18 Streeter-Phelps: Distributed Sources & Nitrogen (Chapra, L22 & L23) David Reckhow CEE 577 #18 1
Nitrogen (Chapra L23) Nitrification/Denitrification nitrification: oxygen consuming denitrification: anaerobic, form N 2 Eutrophication stimulates plant growth Nitrate pollution from fertilizers and nitrification Ammonia toxicity (NH 3 form) David Reckhow CEE 577 #18 2
Nitrogen Cycle Atmospheric N Organic N (animals) Organic N (plants) Decomposition N in sediments or soils Aqueous N David Reckhow CEE 577 #18 3
Nitrification/Denitrification Nitrification: will satisfy NBOD and NH 3 toxicity + − + + → + + Nitrosomonas 3 NH O NO H O 2 H 2 4 2 2 2 − − + → Nitrobacter 1 NO O NO 2 2 2 3 Can be combined with traditional activated sludge so that NBOD is removed along with CBOD; occurs naturally in surface waters Denitrification: will remove nitrate, nutrient control − + → ↑ + + NO organic N CO H O 3 2 2 2 Requires an anaerobic environment David Reckhow CEE 577 #18 4
Modeling Nitrification ( ) S − − = + − D k t k t L L e 1 e n n N N o k n Point Distributed L N = 4.57*TKN David Reckhow CEE 577 #18 5
In-class problem I A poorly treated municipal wastewater is discharged into Evergreen Brook at milepoint zero. In addition there is a continuous discharge of soluble BOD from a series of hog farms extending from milepoint zero to mile 25. The WWTP discharges sufficient BOD such that there is 12 mg/L BOD at the point of mixing, 30% of which is particulate The hog farms release 5 g-BOD/d for every foot of stream length The stream can be considered to have a uniform depth of 4 ft, a width of 22 ft and a rocky bottom. Velocity is 3 mi/d. Assume a BOD settling rate of 1.2 d -1 What is the BOD concentration 10 miles downstream and how much originates from each source (WWTP vs hog farm)? David Reckhow CEE 577 #18 6
In-class problem II First determine distributed loading term ) ( ) ' ' ' g 5 S S mg − = = = 3 = ft d 1 ft d d S 2 . 0 ( − d 28 . 3 L A H 4 ft 22 ft L d c Next estimate deoxygenation rate − − 0 . 434 0 . 434 H 4 − = = = 1 k d C 0 . 3 0 . 405 d 8 8 Then formulate BOD model ( ) S deoxygenation only, no settling − − = + − k t k t D L L e 1 e r r o k r ( ) 2 − − − = + + − x x x 1 . 605 0 . 405 0 . 405 12 ( 0 . 3 ) 12 ( 0 . 7 ) 1 e e e U U U 0 . 405 David Reckhow CEE 577 #18 7
In-class problem II 5.86 mg/L @10 mi 14 2.19 mg/L from WWTP 3.67 mg/L from hog farms 12 Essentially all is dissolved 10 BOD (mg/L) 8 6 4 Dissolved Distributed Source Dissolved Point Source 2 Particulate 0 0 5 10 15 20 25 David Reckhow CEE 577 #18 8 Distance Downstream (miles)
( ) k L − − − = + − k t k t k t d o D D e e e a a r − o k k a r ( ) Full k L − − + − Point NBOD k t k t n No e e n a − k k Equation a n ' S − + + P R B ( ) H − + − k t 1 e a k a ( ) ) ( ) k S k S − − − + − − − k t k t k t d d d d 1 e e e a a r ( − k k k k k r a r a r ( ) ) ( ) k S k S − − − + − − − k t k t k t n Nd n Nd 1 e e e a n a ( − k k k k k n a n a n Distributed NBOD David Reckhow CEE 577 #18 9
Sample Problem (T&M, pg.309) Problem Determine the maximum allowable ultimate oxygen demand (UOD) in the effluent entering the stream if the DO concentration is to equal or exceed 5 mg/L. Assume the effluent DO is equal to the stream’s DO saturation concentration. Q u = 20 cfs c u = c s k a = 0.80/d @ 20 o C L u = N u = 0 k r =k d = 0.40/d @ 28 o C k N = 0.40/d @ 28 o C Q e = 4 MGD CBOD 5 = 30 mg/L, f=2.0 NH 3 -N = 10 mg/L David Reckhow CEE 577 #18 10
Problem (cont.) Analysis of existing conditions Loading BOD and NBOD may be treated as one UOD load since the decay rates are the same in the stream. Assume only the ammonia is significant in the NBOD. ( ) = + − UOD ( mg / L ) fxCBOD 4 . 57 x NH N 5 3 = + = 2 . 0 x 30 4 . 57 x 10 105 . 7 mg / L = = mg W ( UOD ) 4 MGDx 105 . 7 x 8 . 34 3530 lb / d L W ( UOD ) 3530 lb / d = = L ( ( ) ) + + o Q Q 20 cfs 4 1 . 548 cfs 5 . 4 u e = mg 25 . 0 L David Reckhow CEE 577 #18 11
Problem (cont.) Adjust Reaction rates to ambient temp. = θ − o T 20 k k ( 20 C ) x a a ( ) − = = − ( 28 20 ) 1 o 0 . 8 1 . 024 0 . 97 d @ 28 C Determine t crit − 1 D ( k k k − a o a r = ln 1 t crit - k L k k k a r r d o − 1 0 . 97 0 ( 0 . 97 0 . 40 = − ln 1 ( ) 0 . 97 0 . 40 0 . 40 0 . 40 25 . 0 - = 1 . 55 d David Reckhow CEE 577 #18 12
Problem (cont.) Then get x crit ( ) = = = 16 . 4 mpd x Ut 0 . 5 fps 1 . 55 d 12 . 7 mi And c s is: fps accounting for temp. & altitude = Finally the c min is: mg c 6 . 19 s L k − = − k t d c c L e r crit min s o k a 0 . 40 = − − 0 . 40 ( 1 . 55 ) 6 . 19 25 . 0 e 0 . 97 = mg 0 . 64 L David Reckhow CEE 577 #18 13
Problem (end) Determine allowable load, if WQC require 5.0 mg/L minimum D.O. Recognize that the loading:deficit relationship is linear k Also, t crit is − ≡ − = k r t d D c c L e crit independent of L crit s min o k when D o =0 a so determine allowable L D D = crit ( allowable ) crit L L o o ( allowable ) D L 1 . 19 ( 105 . 7 ) = = crit ( allowable ) o L o ( allowable ) D 5 . 55 crit = mg 23 L David Reckhow CEE 577 #18 14
Additional notes on WLA Not from Chapra Selecting a model number of dimensions usually 1, major gradients are longitudinal, very minor gradients in lateral and vertical directions sometimes 2, deep rivers or river-run impoundments; use should be justified never 3, except research and a few extraordinary cases David Reckhow CEE 577 #18 15
Additional notes on WLA (cont.) Loads, sources & sinks Categorize category I - major sources controlling water quality thorough data collection - temporal variation category II - background sources small to moderate data collection necessary data long-term BOD,with nitrification inhibition analysis of all forms of nitrogen org-N, NH 3 , NO 2 , NO 3 David Reckhow CEE 577 #18 16
Additional notes on WLA (cont.) Time scale steady state quasi-steady state const. loads, constant Q, diurnal DO variations due to photosynthesis const. loads, variable Q variable loads, constant Q others Fully time-variable analysis David Reckhow CEE 577 #18 17
Additional notes on WLA (cont.) Design Conditions 7Q10 - summer generally endorsed by USEPA Spring Floods - large event storm intensity, sequences, recessional hydrograph Ice cover - winter Spatial Extent well into the zone of recovery David Reckhow CEE 577 #18 18
Additional notes on WLA (cont.) Dispersion (is it significant?) ft ft/s * = calculate E 2 UB = − U gHS 34 10 5 E . x * HU from slope mi 2 /d ft from dye studies k E = calculate dimensionless estuary # d n 2 U use Chapra’s criteria n<0.1, advection predominates n>10, diffusion predominates or calculate reaeration/deoxygenation ratio & use O’Connor figure φ = k a k d David Reckhow CEE 577 #18 19
Figure prepared by O’Connor From: Technical Guidance Manual for Performing Waste Load Allocations: Book II, Chapter 1 David Reckhow CEE 577 #18 20
( ) k L − − − = + − k t k t k t d o D D e e e a a r − o k k a r ( ) Full k L − − + − Point NBOD k t k t n No e e n a − k k Equation a n ' S − + + P R B ( ) H − + − k t 1 e a k a ( ) ) ( ) k S k S − − − + − − − k t k t k t d d d d 1 e e e a a r ( − k k k k k r a r a r ( ) ) ( ) k S k S − − − + − − − k t k t k t n Nd n Nd 1 e e e a n a ( − k k k k k n a n a n Distributed NBOD David Reckhow CEE 577 #18 21
Additional notes on WLA (cont.) Nitrogen modeling NBOD measure and model TKN only all 4 major species org-N, NH 3 , NO 2 , and NO 3 requires separate analysis of loadings, rate coefficients, etc. David Reckhow CEE 577 #18 22
General Model Kinetics Atmosphere K 2 K 4 SOD K N 1 K 1 K 3 Dissolved Oxygen NBOD CBOD David Reckhow CEE 577 #18 23
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