Comprehensive Approaches To Maintain Disinfection and THMs Compliance

Transcription

1 Comprehensive Approaches To Maintain Disinfection and THMs Compliance Town of Englehart Water Treatment Plant Study Presented by: Zirui (Ray) Yu, Ph.D., P.Eng. Co-authors: Bruce McMullan, Simon Breese, AECOM Sue Renaud, Glen Milton, Town of Englehart 2014 OWWA Annual Conference May 5, 2014

2 Town of Englehart, Ontario ~550 km north of Toronto Population: 1,514 in 2011 One WTP serves: Residents in Town 351 peoples in small communities Georgia-Pacific Plant (25% demand)

3 Town of Englehart Water Treatment Plant - 1 Two production wells Well #2: 1,205 m 3 /d Well #3: 1,591 m 3 /d Water Treatment Plant Treatment capacity: 2,998 m 3 /d Treatment process chlorination - filtration Reservoir Total volume 1,564 m 3 Provide volume for primary disinfection

4 Town of Englehart Water Treatment Plant - 2 SBS Cl 2 monitor at POE Cl 2 Cl 2 monitor at filter eff. NaClO May 5, 2014 Page 4 SBS

5 WTP Study Objectives

6 WTP Study Objectives THMs approaching the regulatory limit Confirm THMs Issue Identify probable causes Recommend solutions Future Demand Forecast future water demand Review infrastructure upgrade and expansion needs May 5, 2014 Page 6

7 Confirmation of THMs Issue RAA LRAA May 5, 2014 Page 7

8 Probable Causes

9 High TOC/DOC in Raw Waters - Main Cause #1 historical May 5, 2014 Page 9

10 High Chlorine Demand Ave. 9.5 mg/l Ave. 6.9 mg/l Ave. 2.7 mg/l May 5, 2014 Page 10

11 High Chlorine Dose Iron background: Well #2: 409 μg/l Well #3: 291 μg/l Combined: 336 μg/l Year Average Fe oxidation requires: Theoretical: 0.22 mg/l Typical: 5 mg/l for organically bound Fe Chlorination Fact: 2012 Cl 2 dosing average: ~ 15 mg/l May 5, 2014 Page 11

12 Excessive Chlorine Dosing Main Cause #2 THMs approach 80 μg/l when Cl 2 is dosed above 13 mg/l May 5, 2014 Page 12

13 High ph Probable Cause #3 High ph increases THMs formation May 5, 2014 Page 13

14 Can Chlorine Dosages be Lowered? Reduce Cl 2 dosing: Reduce THMs formation Maintain residual Cl 2 above O.Reg. Lower ph O.Reg. 170/03 requires at all points in distribution system: Min mg/l Cl 2 Max. ph mg/l req d at POE May 5, 2014 Page 14

15 Manual Control further Complicates THMs Issue The plant was originally designed to compound loop control chlorine dosing Automatic control is not implemented as the issues with instrumentation Dechlorination by SBS is also not implemented due to operational difficulty Current chlorine dosing is in the fix-speed feed mode based on the estimate of daily water production May 5, 2014 Page 15

16 Potential Hydraulic Issues in Reservoir - 1 Baffling Factor: 0.1 Fill and Draw: 0.27 m May 5, 2014 Page 16

17 Potential Hydraulic Issues Probably Increase THMs Formation Probable Cause #4 Completely Mixed Flow Reactor (CMFR) Model General Guideline: 72 hours (3 days) Non-ideal situation exacerbates THM formation May 5, 2014 Page 17

18 Deficiencies in CT Calculation Two primary disinfection segments exists in the WTP, but only one is considered A portion of volume in Reservoir is reserved for primary disinfection, but possible errors was identified in calculating the volume (~ 25% volume not considered) May 5, 2014 Page 18

19 Solutions and Recommendations and Implementation

20 Operation Optimizations Reduce Chlorine Dose Correct CT calculation error in reservoir volume (lower POE Cl 2 target) Reduce chlorine dose as much as possible Maintain 2-log virus inactivation and minimum Cl 2 residue in distribution system Optimize Reservoir Operation Guarantee minimum volume for primary disinfection and emergency uses Facilitate Fill and Draw operation to minimize water age Restore Control System Automation May 5, 2014 Page 20

21 Process Improvements Change Disinfection Profile Revise to two segment primary disinfection model Change Disinfectant Change reservoir only as a part of distribution system Use chloramination for secondary disinfection Require primary disinfection completed in first segment Decrease ph Improve Reservoir Hydraulics Use multiple inlets and outlets configuration Aeration in Reservoir May 5, 2014 Page 21

22 Water Source GUDI Investigation The first step would be to establish whether a GUDI study is necessary. If a further GUDI study is necessary, groundwater monitoring, and hydrogeological studies shall be performed. Water table (or potentiometric) drawdown profiles shall be established for the Town s wells under the current and future conditions. May 5, 2014 Page 22

23 Implementation Approaches Probable Costs Operational Optimization Reduce Chlorine Dose 0 Optimize Reservoir Operation 0 Restore Control System Automation $70,000 Process Improvement Change Disinfection Profile $15,000 Change Disinfectant $100,000 Decrease ph $100,000 Improve Reservoir Hydraulics $100,000 - $150,000 Provide Aeration in Reservoir $200,000 - $300,000 Water Source GUDI Investigation Desktop Assessment $5,000 GUDI Study $15,000 - $25,000 May 5, 2014 Page 23

24 Implementation Approaches Probable Costs Operational Optimization Reduce Chlorine Dose 0 Optimize Reservoir Operation 0 Restore Control System Automation $70,000 Process Improvement Change Disinfection Profile $15,000 Change Disinfectant $100,000 Decrease ph $100,000 Improve Reservoir Hydraulics $100,000 - $150,000 Provide Aeration in Reservoir $200,000 - $300,000 Water Source GUDI Investigation Desktop Assessment $5,000 GUDI Study $15,000 - $25,000 May 5, 2014 Page 24

25 Implementation Approaches Probable Costs Operational Optimization Reduce Chlorine Dose 0 Optimize Reservoir Operation 0 Restore Control System Automation $70,000 Process Improvement Change Disinfection Profile $15,000 Change Disinfectant $100,000 Decrease ph $100,000 Improve Reservoir Hydraulics $100,000 - $150,000 Provide Aeration in Reservoir $200,000 - $300,000 Water Source GUDI Investigation Desktop Assessment $5,000 GUDI Study $15,000 - $25,000 May 5, 2014 Page 25

26 Thank You! Zirui (Ray) Yu, Ph.D., P.Eng. Process Specialist, Project Engineer

27 Town of Englehart Water Treatment Plant - 3 May 5, 2014 Page 27

28 Potential Hydraulic Issues Probably Increase THMs Formation Probable Cause 4 General Guideline: 72 hours (3 days) Plug Flow Reactor Model Completely Mixed Flow Reactor Model May 5, 2014 Page 28