Feridun DEMIR Department of Chemical Engineering, Osmaniye Korkut Ata University,

1. Numerical prediction of the reaction rate constant of chlorine disinfection process at a wastewater treatment plant. Experimental model validation and simulation studies Feridun DEMIR Department of Chemical Engineering, Osmaniye Korkut Ata University, Osmaniye 80000, Turkey 3rd World Congress on Petrochemistry and Chemical Engineering, November 30 –December 2, 2015 Atlanta, USA

2. Outline • Objectives • Process description • Water Reclamation Facility • Kinetics of chlorine with ammonia and chlorine disinfection • Modeling challenges • Complex reactions with ammonia • Too many partial differential equations (PDEs) • Dynamic behavior of wastewater • Dynamic model development • Approach (Mathematical transformation techniques) • Method of characteristics • Odometric transformation • Simulation results • Model validation

3. Objectives • Develop and validate a model for the entire chlorine disinfection process of wastewater treatment plant • Overcome PDEs of chlorine reactions that occur with wastewater using the method of characteristics • Overcome the highly variable flow rate using Odometric transformation • Overcome large and variable ˝ Time Delays ˝ that occur as a result of the transport time required for the wastewater to flow through contact basins • Numerically determine the reaction rate constant for the entire disinfection process

4. Process description • KanapahaWater Reclamation Facility is an advanced wastewater treatment plant in Gainesville, Florida, and uses chlorine for disinfection. • Treats 14.9 million gallonwastewater to drinking waterstandards per day, and then reuses the water for innovative irrigation. • Performs the disinfection process in two chlorine contact basins that are open to the atmosphere

5. Process description • A schematic representation of the disinfection process Sampling points for the chlorine measurements

6. Process description Water parameters of the KWRF at the chlorine contact basin

7. Chlorine-ammonia breakpoint reactions Chlorine chemistry Cl2 + H2O→ HOCl + HCl HOCl ↔ OClˉ + H+ pH dependent Breakpoint reactions

8. Reaction kinetics • Proposed kinetics equations at a wastewater reclamation plant • kDisinfection represents the rate constant for the entire disinfection process in the contact basin

9. Modeling challenges • Too long disinfection contact basin ( ≈ 200 m) • Significant flow rate changes relative to daily water usage and thereby large and variable ˝ Time Delays ˝ • Quality changes in wastewater • Exposure of water to sunlight • Complex reactions with ammonia • Many partial differential equations and the difficulties of their solution • Difficulty to develop an appropriate dynamic model for the process system

10. Development of simulation model Disinfection contact basin Dynamic model for the disinfection process Assumptions:Plug flow reactor, no diffusion exists along the reactor Influent Effluent

11. Transformation techniques Overcome PDEs of chlorine reactions using the method of characteristics

12. Transformation techniques • Overcomethe highly variable flow rate, and thereby˝ Time Delays ˝ usingOdometric Transformation () •  is the cumulative distance travelled by wastewater in the contact basin • This new variable replaces time with 

13. Applying transformation techniques • First-order partial differential equations (PDEs) with variable Time Delays • First-order ordinary differential equations (ODEs) with constant Time delays • Use of the transformation techniques produced efficient ODEs for numerical integration

14. Simulation of the model • The model was coded in Matlab programing language • A step change in the chlorine dosing was performed at the chlorine injection point, and its effect was observed along the entire contact basin • The chlorine concentrations used for the simulation and model validation were measured online at the chlorine injection point and at the effluent, and recorded approximately for 8 hours • The flow rate of the wastewater was obtained online, and recorded during the investigation • To fit the simulation results to the experimental data, various trial values of kDisinfectionwere used in the simulation model changing from 0.006 to 0.0085 h-1

15. Comparison of results Comparison of the simulation results with experimental measurements Chlorine concentration at • the chlorine injection point (red dashed line) • the effluent (blue solid line) • the simulated results (black circles)

16. Model validation • To determine the kDisinfectionmore precisely, model validation was performed • The model was validated by the comparison of the simulated responses with the experimentally measured chlorine concentrations using Matlab software packages (2013b) • The Matlab codes: Experimental_Results = iddata(y,[ ],Ts) Simulation_Results = iddata(sys,[ ],Ts) Ts = 120 compare(Experimental_Results,Simulation_Results) compare(Experimental_results, k_006,'--b', k_0065,'--g', k_007,'-- r', k_0071, '--c')

17. Modelvalidation Comparison of the simulated responseswith the experimental measurements

18. Modelvalidation Comparison of the simulated responseswith the experimental measurements

19. Modelvalidation Comparison of the simulated responseswith the experimental measurements

20. Fit (%) for the various reaction rate constants The results suggest that the value of 0.0074 h-1 yields the highest fit (%)

21. Conclusions • The joint application of the transformation techniques • successfully transformed the dynamics of the system into the ODEmodels with constant time delay • made the solution of the resulting equations numerically feasible • The numerical solutions of the resulting equations • were validated using Matlab software packages • provided the highest fit (%) value for different trial values of reaction rate constant • According to the simulation results; • kDisinfection was found to be 0.0074 h-1 , and confirmed by the experimental data • first-order kinetic model is able to describe chlorine consumption by microorganisms in the ammonia-free part of the contact basin.