CEE 670 TRANSPORT PROCESSES IN ENVIRONMENTAL AND WATER RESOURCES - PDF document

12/8/2011 Updated: 8 December 2011 CEE 670 Kinetics Lecture #10 1 Print version CEE 670 TRANSPORT PROCESSES IN ENVIRONMENTAL AND WATER RESOURCES ENGINEERING Kinetics Lecture #10 Surface Reactions: Pipe walls & degradation in Distribution Systems Primary Literature Surface Reactions David A. Reckhow Seasonal Variability & Biodegradation 2  Chen & Weisel study  JAWWA, April 1998  Intensive study of Elizabethtown, NJ system  125 MGD conventional plant  4.9 mg/L DOC (raw water average)  pH 7.2 CEE 670 Kinetics Lecture #6 David A. Reckhow 1

12/8/2011 Elizabethtown, NJ: THMs 3 CEE 670 Kinetics Lecture #6 David A. Reckhow Elizabethtown, NJ: TCAA 4 CEE 670 Kinetics Lecture #6 David A. Reckhow 2

12/8/2011 HAA Degradation 5  Biodegradation:  dihaloacetic acids degrade more readily than trihaloacetic acids  On BAC  MHAA>DHAA>THAA  Wu & Xie, 2005 [JAWWA 97:11:94]  In distribution systems  DHAA>MHAA>THAA  Many studies CEE 670 Kinetics Lecture #6 David A. Reckhow Degradation in Dist. Systems Town Hall; Norwood, MA Pier 1; Norwood, MA 120 120 TTHM TTHM 100 100 HAA5 HAA5 Concentration (  g/L) Concentration (  g/L) 80 80 60 60 40 40 20 20 0 0 9 0 1 2 3 4 5 6 9 0 1 2 3 4 5 6 9 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 1 2 2 2 2 2 2 2 1 2 2 2 2 2 2 2 / / / / / / / / / / / / / / / / 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 / / / / / / / / / / / / / / / / 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Date Date Example: Norwood, MA 6 CEE 670 Kinetics Lecture #6 David A. Reckhow 3

12/8/2011 Degradation of HAAs 7  Norwood, MA example 1.2 Town Hall 1.0 Pier 1 HAA/THM Ratio (  g/  g) 0.8 0.6 0.4 No Degradation Degradation 0.2 0.0 0 20 40 60 80 100 CEE 670 Kinetics Lecture #6 Percentile David A. Reckhow Why the loss of HAAs? 8  Homogeneous Chemical Decomposition ?  Decarboxylation  What is half-life  Is it too slow to be very important?  Dehalogenation  Probably too slow for chlorinated HAAs  Reaction with reduced pipe materials?  Abiotic reductive dehalogenation not likely either, especially for DCAA  Biodegradation? CEE 670 Kinetics Lecture #6 David A. Reckhow 4

12/8/2011 A few recent studies 9  Modeling HAA Biodegradation in Biofilters and Distribution Systems  Alina S. Grigorescu and Ray Hozalski, University of Minnesota at Minneapolis Journal AWWA, July 2010, 102(7)67-80 CEE 670 Kinetics Lecture #10 David A. Reckhow Background conclusion? 10  “Thus aerobic biodegradation is believed to be the dominant HAA degradation process in ….…..water distribution systems”  Citing: Tung & Xie, 2009; Zhang et al., 2009a; 2009b; Bayless & Andrews, 2008 CEE 670 Kinetics Lecture #10 David A. Reckhow 5

12/8/2011 Objective/hypothesis 11  Not really stated, but they did end the intro with:  “In this work, computer simulations were performed to predict the fate of three HAAs (MCAA, DCAA, and TCAA) along a distribution system and within a biologically active filter. Sensitivity analyses were performed to investigate the effects of physical parameters (e.g., fluid velocity) and biological parameters (e.g., biodegradation kinetics, biomass density) on HAA removal” CEE 670 Kinetics Lecture #10 David A. Reckhow Transport Model 12  Loss of HAAs in a pipe  One dimensional plug flow     k x C C e overall U 0  Overall rate is a combination of rate of biodegradation (k ra ) and mass transfer (k ma ) 1  k  overall 1 1 k k ma ra CEE 670 Kinetics Lecture #10 David A. Reckhow 6

12/8/2011 Biodegradation model 13  Monod model dC kXC   M  dt K C  Simplified for low C dC k     XC k XC r dt K M CEE 670 Kinetics Lecture #10 David A. Reckhow Biodegradation model II 14  Biodegradation rate (k ra ; in day -1 ) is the pseudo- first order biodegradation rate constant (k r ; in L/day/µg-protein) times the biofilm density (X; in µg-protein/cm 2 ) and the specific surface area (a; in m -1 )     4 k X   2 2 r k k Xa 10 cm m 10 cm m ra r L L d Where d is the pipe diameter in meters CEE 670 Kinetics Lecture #10 David A. Reckhow 7

12/8/2011 15 CEE 670 Kinetics Lecture #10 David A. Reckhow Mass Transfer Model I 16  Mass transfer constant (k ma ) is the mass transfer velocity (k m ; m/s) times the specific surface area; and k m is related to the Sherwood number ShD ma  m  k k a w k m d Compare to equ  combining 7.126 in Clark ShD 4 ShD    w w k k a a ma m 2 d d  Linton & Sherwood (1950) found the following correlation for flow in pipes (fn(Reynolds and Schmidt numbers)): Sh  Eq 7.164 in Clark 0 . 83 0 . 33 0 . 023 Re Sc CEE 670 Kinetics Lecture #10 David A. Reckhow 8

12/8/2011 Mass Transfer Model II 17  The Schmidt number is the ratio of mass to viscous diffusion timescales, and calculated from the viscosity, the density and the diffusion coefficient:   w Sc Compare to equ  7.82 in Clark D w w  And the Reynolds number can be calculated from the pipe diameter, velocity, density and viscosity:  du  w Re  w CEE 670 Kinetics Lecture #10 David A. Reckhow Model Predictions 18 CEE 670 Kinetics Lecture #10 David A. Reckhow 9

12/8/2011 Impact of biomass density 19 CEE 670 Kinetics Lecture #10 David A. Reckhow Impact of flow velocity 20 CEE 670 Kinetics Lecture #10 David A. Reckhow 10

12/8/2011 Impact of Pipe Diameter 21 CEE 670 Kinetics Lecture #10 David A. Reckhow Combining 22 CEE 670 Kinetics Lecture #10 David A. Reckhow 11

12/8/2011 Conclusions 23  “Overall the model calculations suggest that biodegradation is…..not likely to play a major role in most water distribution systems”  “the conditions needed for significant HAA removals in a distribution system (i.e., total biomass densities > 10 5 cells/cm 2 over long distances of pipe) are unlikely in the US water distribution systems where total chlorine residuals typically are high and thus inhibit the development of biofilm on pipe walls” But this seems to contradict their introductory conclusion – how to reconcile? CEE 670 Kinetics Lecture #10 David A. Reckhow What could they have concluded? 24  Variability vs diurnal demand 30 25 20 Q/Qavg u (ft/s) 15 t (hr) C (ug/L) 10 5 CEE 670 Kinetics Lecture #10 David A. Reckhow 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 12

12/8/2011 Objective/hypothesis 25  Not really stated, but they did end the intro with:  “In this work, computer simulations were performed to predict the fate of three HAAs (MCAA, DCAA, and TCAA) along a distribution system and within a biologically active filter. Sensitivity analyses were performed to investigate the effects of physical parameters (e.g., fluid velocity) and biological parameters (e.g., biodegradation kinetics, biomass density) on HAA removal” CEE 670 Kinetics Lecture #10 David A. Reckhow What could they have said? 26  To determined if observed HAA loss could be attributed to biodegradation on pipe walls given known physical and microbial characteristics of distribution systems  To estimate spatial and temporal variability of HAA concentrations based on a rational physical model of biodegradation in distribution systems CEE 670 Kinetics Lecture #10 David A. Reckhow 13

12/8/2011 What could they have done? 27  Find some direct evidence for biodegradation of HAAs in distribution systems  A product of the enzymatic reaction?  Chlorohydroxyacetate?  Evidence of abiotic reactions?  Increase in MCAA? CEE 670 Kinetics Lecture #10 David A. Reckhow What else? 28  Consider mass transfer resistance within biofilm CEE 670 Kinetics Lecture #10 David A. Reckhow 14

12/8/2011 What should be done next? 29  Experimental Work  In-situ controlled study of flow velocity vs DCAA loss in a pipe segment?  Effect of biocide in above segment?  Model Refinement  Account for internal mass transfer resistance  Combine with growth model for HAA degraders CEE 670 Kinetics Lecture #10 David A. Reckhow  B1: biologically fixed bacteria  B2: adsorbed bacteria SANCHO Model 30 Input Output Internal Processes (H1, H2, B3) CO 2 BDOC H2 Cl 2 Cl 2 Free Bacteria Mortality B3 S H1 Cl 2 B2 Mortality B1 Fixed Bacteria CEE 670 Kinetics Lecture #10 David A. Reckhow 15

12/8/2011 31 CEE 670 Kinetics Lecture #10 David A. Reckhow 32 CEE 670 Kinetics Lecture #10 David A. Reckhow 16

12/8/2011 33 CEE 670 Kinetics Lecture #10 David A. Reckhow Effect of Zn on HAAs 34  Effect of Zinc on the Transformation of HAAs in Drinking Water  Wei Wang and Lizhong Zhu  Journal of Hazardous Materials 174:40-46. CEE 670 Kinetics Lecture #10 David A. Reckhow 17

12/8/2011 35  End CEE 670 Kinetics Lecture #10 David A. Reckhow 18