The Use of Chlorine Dioxide to Reduce TOC at Davidson Water, Inc. Water Treatment Plant

1. The Use of Chlorine Dioxide to Reduce TOC at Davidson Water, Inc. Water Treatment Plant

2. Presentation Agenda Introduce Davidson Water, Inc. and discuss the water quality issues experienced by the system. Discuss - what is Chlorine Dioxide? What were the beneficial impacts from using Chlorine Dioxide at the DWI WTP.

3. Davidson Water, Inc. Davidson Water Inc. is located in Welcome NC Member Owned Water Utility Water system was started in 1968 with construction of a 4 MGD WTP and distribution system Original WTP was expanded several times, finally to a capacity of 20 MGD in 1995 Original treatment process included Flash Mix, Flocculation, Conventional Sedimentation Basins (later retrofitted with Tube-Settlers), and twenty – 1 MGD dual media filters

4. Davidson Water, Inc. DWI serves all of the unincorporated areas of Davidson County and parts of Randolph County. The system consists of: Service to over 58,000 customers Distribution system consisting of: 1800 miles of pipeline ranging from 36 inch to 2 inch 27 elevated and ground storage tanks with over 14 million gallons of storage 19 pump stations The DWI system developed utilizing USDA funding. During the early development, funding restricted line sizes which resulted in the need to have multiple parallel lines throughout the system. Water age within the system creates a water quality problem.

5. DWI Raw Water Source The raw water source is the Yadkin River The DWI intake is located downstream from Winston Salem. Winston Salem has a run of the river impoundment structure that can have an impact on the Yadkin during low flow periods. The Yadkin River can experience flashes in turbidity. Generally the water quality is good. The TOC in the Yadkin ranges from 2.0 to 3.0.

6. DWI Treatment Issues DWI had experienced issues with finished water quality in the past including: Discolored water in distribution system Lead and Copper TTHM (Especially with Stage 2) In order to address water quality issues in the past, DWI had changed the type of coagulant utilized: Aluminum Sulfate through June 2002 Ferric Chloride from June 2002 through September 2008 Ferric Sulfate from September 2008 to present Utilized Sodium Permanganate to control Iron and Manganese

7. DWI Treatment Goals DWI constructed a major upgrade and expansion to the WTP including raw water intake beginning in 2011 and extending through 2013. The treatment goals for the upgrade included: Stabilization of water quality – eliminate discolored water in the distribution system Reduce TTHMs in the distribution system Keep distribution system on Free Chlorine

8. DWI Upgrade – Process Before Upgrade After Upgrade

9. DWI Upgrade – Process The WTP Upgrade and Expansion included: Construction of New River Intake and PS Modification of Off Stream Storage Reservoirs Construction of New Raw Water Pump Station 30 MGD Flash Mix 15 MGD SuperPulsator 15 MGD Conventional Filters with Air Scour Granular Activated Carbon Contactors (utilize when necessary 5 MG Contact Chamber / Clearwell 40 MGD Finished Water Pump Station New Chemical Feed New SCADA

10. DWI Upgrade – Process

11. DWI Upgrade - Treatment DWI Upgrade included modifications to chemical feed systems including: Added Sulfuric Acid Used acid to control coagulation pH without having to use as much Ferric Sulfate Lowered Ferric Sulfate dosage from 40+ ppm to 18-20 ppm Eliminated Sodium Permanganate Added Chlorine Dioxide

12. Chlorine Dioxide What is Chlorine Dioxide and how is it used? Oxidant approved by EPA for Primary and Distribution Disinfection All Chlorine Dioxide is produced from one of two precursors: Sodium Chlorite (NaClO2) Sodium Chlorate (NaClO3) Chlorine Dioxide is generated on-site Two part system using Gaseous Chlorine and Sodium Chlorite Three part system using Sodium Hypochlorite, Sodium Chlorite, and Muriatic Acid

13. Chlorine Dioxide Typically applied to raw water prior to coagulation but can be used at other locations within the WTP. Pre-Filter (What about Manganese?) Can be used to achieve CT

14. CT Value of ClO2 CT Values for Inactivation of Various Microorganisms (a): EPA Guidance Manual - LT1ESWTR Disinfection Profiling and Benchmarking,May 2003 (b): LT2ESWTR Toolbox Guidance Manual, June 2003 (c): Hoff & Geldreich

15. Benefits from Chlorine Dioxide What benefits are some of the benefits from Chlorine Dioxide? Beneficial in reducing THM and HAA Beneficial in reduction of Iron and Manganese Reduces taste and odor issues Effective in pH ranges from 2 - 10 Does not oxidize Bromide to Bromate There is no reaction with Ammonia Does not chlorinate organics

16. Drawbacks to Chlorine Dioxide There are typically some drawbacks to any chemical. With Chlorine Dioxide, some drawbacks include: Cost The MCL for Chlorine Dioxide in the system is 0.8 ppm The use of ClO2 forms Chlorite. Chlorite is regulated by EPA with an MCL of 1.0 ppm. The more Chlorine Dioxide you use in the process, the more chlorite is formed Required to test for Chlorite daily Requires additional operations interface and maintenance

17. ClO2 at DWI How did we incorporate Chlorine Dioxide into the DWI facility? We received a lot of assistance and coordination from the Area WTP Specialist with NC DENR Able to install the equipment in the same building as the chlorine storage and feed equipment Equipment was installed in an existing storage room approximately 22 feet X 30 feet Equipment included ClO2 generation equipment and a bulk sodium chlorite tank Generation skid is capable of using a 2-part or 3-part system System can be monitored on SCADA

18. ClO2 at DWI How did we incorporate Chlorine Dioxide into the DWI facility? Were permitted to perform a full scale pilot study which was then converted to a permanent installation Applied the Chlorine Dioxide in the raw water main as far upstream as possible Started feeding the chemical at a low rate and gradually increased Normal feed rate is approximately 0.7 ppm

19. ClO2 at DWI How did we incorporate Chlorine Dioxide into the DWI facility? New Water Treatment plant was approved and went on-line in April 2013 Chlorine Dioxide feed system was installed and went on-line in early summer 2013 Daily testing was one challenge that had to be addressed

20. ClO2 at DWI

21. ClO2 at DWI

22. ClO2 at DWI

23. ClO2 at DWI What were the benefits from Chlorine Dioxide? (How would we know it was working?) TOC TTHM testing Chlorine Residual at Point of Entry and in the distribution system Water quality issues Manganese – Discolored Water Taste and Odor

24. ClO2 at DWI Raw and Finished TOC

25. Results from TTHM Sampling ClO2 at DWI

26. ClO2 at DWI Chlorine Residual at the Point of Entry

27. What is the take-away from DWI’s experience in feeding ClO2? Quantifiable improvement in testing parameters TOC TTHM Chlorine Residual at Point of Entry and in the distribution system Noticeable improvement in water quality Manganese – Discolored Water Taste and Odor Distribution system continues to utilize free chlorine Summary

28. What about the cost of feeding ClO2? Cost is based on: Replacement of equipment Cost of Chemical Testing Estimated cost per 1000 gallons - $0.015 You cannot credit ClO2 for all the improvements Operations Optimization of coagulation chemistry Improvements in raw water supply Summary

29. Whatever happened to the GAC Contactors? Sitting full of GAC but have not needed to be put into service yet Credits: Tom Johnson – Plant Superintendent DWI Vince Alarid – Evoqua TA Loving Construction One Final Comment

30. Questions or Comments