Modeling of chlorine contact chamber at West Lafayette treatment plant

1. Modeling of chlorine contact chamber at West Lafayette treatment plant In-term project presentation by Kanish Jindal

2. Problem Statement • Modeling of chlorine disinfection contact chamber and predicting the effluents residence time distribution (RTD) curve

3. Model : FLUENT • CFD : Computational fluid dynamics • Dynamics of things that flow • Computational model that represents a system or device that you want to study • Fluid flow behavior • Insight Foresight Efficiency

4. Fluent • Provides numerical solution for given domain under given flow conditions • Graphic user inter phase for generation of model • Can write your own codes (User defined functions) • Solver to converge solution • Post processing to analyze results • Gives a foresight to flow physics Blending time

5. Solution method • Divides the domain into discrete control volumes using a computational grid • Solve the governing integral equations for the conservation of mass and momentum • Solves for energy, turbulence and chemical species if appropriate

6. Solution contd…. • Integration of the governing equations on the individual control volumes • Linearization of the discretized equations and solution of the resultant linear equation system to yield updated values of the dependent variables

7. West Lafayette Wastewater Treatment Plant • Originally constructed in 1958 • Expanded in 1970, upgraded in 1997 • Treats 9 millions gallons of waster water every day (3.3Billions/year) • Chlorination –before discharging into Wabash river Located at 500 South River Road, the Wastewater Treatment Utility serves 29,000 residents, plus 38,000-student Purdue University and the old regional sewer district.

8. Approach • EPA determines effectiveness of contactors by CT method • Residence time distribution (RTD) is used to predict the overall microbial inactivation level • Contactor can be modeled as a box system and its RTD can obtained using FLUENT • The RTD obtained from the model is compared with the actual results

9. Model Description Chlorine Chlorine & Treated Effluent Treated Effluent Chamber I Chamber I Hydraulic Jump Hydraulic Jump Chambers II/III Chambers II/III • Length 41.41m • Depth of water = 2.58m • Width = 1.93 m Disinfected Effluent Disinfected Effluent

10. Model Outline • Boundary conditions • Inlet • Flow = 9.91 MGD • Velocity Inlet = 0.096m/s • k = 2.3E-5 • € = 9.50E-8 • Domain default fluid • Mass Balance

11. Numerical Analysis • Preprocessing: Gambit • Geometric model: From top down approach • Interval Size = 0.4 • Hex/wedge elements • Cooper Meshing

12. Method • Segregated Model • RNG k- € Model • Based on Navier-Stokes equation • k = kinetic energy = 0.0025(vel)2 * • € = Energy dissipation rate = 0.1643 (k)3/2/(0.1 * entrance width)* Outlet Inlet Point of injection * Source : Modeling of Disinfection contactor

13. Results Mean residence time = 1628sec 27.13 min Mean residence time = 55.5min

14. Contd.. Turbulence 0.5% Length 0.025m Min time 1476 sec Max time 1626 sec Mean time 1556 sec Std Dev 54.53 sec From actual 2400 sec data (1st observation) Mean value 56.2 min = 3360 sec

15. Velocity profile Velocity decreases at corners Velocity in x direction

16. Sensitivity Analysis • Effluent RTD was insensitive to uncertainty in the influent turbulent intensity and turbulence length scale • The variation was consistent with respect to variation in turbulence intensity and turbulent length scale

17. Conclusion • There is some variation in the effluent RTD curve due to input parameter uncertainties • RNG k- € model was used which might not represent the true flow regime inside the contactor • The assumptions for mixing condition of chlorine to treated influent might have caused some deviations • The deviations between the modeled and experimental results might be due to narrow thickness between the boundary walls resulting in a plug flow regime