(Chapra, L22 & L23) David Reckhow CEE 577 #18 1 Nitrogen - PowerPoint PPT Presentation

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