Nitrogen (Chapra L23) Nitrification/Denitrification nitrification: - PDF document

CEE 577 Lecture #18 10/30/2017 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 1

CEE 577 Lecture #18 10/30/2017 Nitrogen Cycle Atmospheric N Organic N Organic N (animals) (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           3 Nitrosomonas 2 NH O NO H O H 2 4 2 2 2        1 Nitrobacter 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       organic NO N CO H O 3 2 2 2 Requires an anaerobic environment David Reckhow CEE 577 #18 4 2

CEE 577 Lecture #18 10/30/2017 Modeling Nitrification   S      D 1 k t k t L L e 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 3

CEE 577 Lecture #18 10/30/2017 In‐class problem II  First determine distributed loading term    ' ' ' 5 g S S mg  3    1  ft d ft 2 . 0 d d S  28 . 3  d 4 22 L A H ft ft L d c  Next estimate deoxygenation rate   0 . 434 0 . 434    4  H     1   0 . 3   0 . 405 k d C d  8   8   Then formulate BOD model   S deoxygenation only, no settling      1 k t k t D L L e e r r o k r   2     1 . 605  0 . 405   0 . 405 12 ( 0 . 3 ) x 12 ( 0 . 7 ) x 1 x 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 12  3.67 mg/L from hog farms  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) 4

CEE 577 Lecture #18 10/30/2017   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      1 k t e a k a      k S k S        1 k t k t k t d d d d e e e a r a   k k k k k r a r a r      k S k S        1 k t k t k t n Nd n Nd 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 5

CEE 577 Lecture #18 10/30/2017 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.      ( / ) 4 . 57 UOD mg L fxCBOD x NH N 5 3    2 . 0 30 4 . 57 10 105 . 7 / x x mg L   ( ) 4 105 . 7 mg 8 . 34 3530 / W UOD MGDx x lb d L ( ) 3530 / W UOD lb d   L     o   20 4 1 . 548 5 . 4 Q Q cfs cfs u e  25 . 0 mg L David Reckhow CEE 577 #18 11 Problem (cont.)  Adjust Reaction rates to ambient temp.    ( 20 ) 20 o T k k C x a a     ( 28 20 )   0 . 8 1 . 024 0 . 97 1 @ 28 o d C  Determine t crit      ( 1 D k k k    ln  a 1  o a r =   t crit -  k L    k k k a r r d o      0 . 97 0 ( 0 . 97 0 . 40 1     ln 1       0 . 97 0 . 40 0 . 40 0 . 40 25 . 0   -    1 . 55 d David Reckhow CEE 577 #18 12 6

CEE 577 Lecture #18 10/30/2017 Problem (cont.)  Then get x crit     16 . 4  0 . 5 mpd 1 . 55 12 . 7 x Ut fps d mi  And c s is: fps  accounting for temp. & altitude   Finally the c min is: 6 . 19 mg c 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  0 . 64 mg 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 Also, t crit is k     k r t d D c c L e crit independent of L min crit s o k when D o =0 a  so determine allowable L D D ( )  crit allowable crit L L ( ) o o allowable 1 . 19 ( 105 . 7 ) D L  ( )  crit allowable o L ( ) o allowable 5 . 55 D crit  23 mg L David Reckhow CEE 577 #18 14 7

CEE 577 Lecture #18 10/30/2017 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 8

CEE 577 Lecture #18 10/30/2017 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 9

CEE 577 Lecture #18 10/30/2017 Additional notes on WLA (cont.)  Dispersion (is it significant?) ft ft/s  calculate E 2 *  UB   U gHS 3 4 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   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 10