Big Savings with Little Operational Changes

Transcription

1 Big Savings with Little Operational Changes in NPDES System at Drinking Water Plant Charlie Minter & Brandon Garner

2 DWI Plant Layout The treatment facility is a 15 MGD Super Pulsator Includes 6 dual media filters with timed sludge blowdowns Backwash water goes into a 0.5 MG holding tank Two lagoons and a gravity thickener/sludge press operation Flow measurement via V-notch weir and dechlorination Effluent goes into the Frog Pond where it mixes with runoff before final outfall to the Yadkin

3 DWI Water Treatment Facility

4 Previous Operation Backwash water essentially flowed through the 0.5 MG holding tank to the South lagoon Backwash water from the C. O. Pickle Plant (currently under renovation) went directly into the South lagoon Effluent from the gravity thickener flowed into the North lagoon Lagoons operated in parallel

5 Previous Operation Continued Combined flow from the lagoons was dechlorinated in weir box prior to flow measurement Calcium thiosulfate used to dechlorinate Dosed according to a Safe setting intended to maintain compliance of 17 ppb Free Chlorine Residual at the effluent Effluent from the weir box goes to the Frog Pond prior to final discharge

6 Operational Requirements Typical monitoring and compliance requirements for drinking water plants Flow Turbidity Chlorine Toxicity Other water quality parameters

7 Residual Free Chlorine Permit limitation of 17 ppb However, we have Footnote 2! 2. Total Residual Chlorine (TRC) The Division shall deem compliant all effluent TRC values reported below 50 µg/l. However, the Permittee shall record and submit all values detected by North Carolina-certified test methods (including field certified), even if these values are detected below 50 µg/l.

8 What Did We Do? Increase detention time Cut off Calcium Thiosulfate feed system Increase field monitoring to ensure compliance

9 Increasing Detention Time Hold water in the 0.5 MG Backwash tank by adjusting effluent valve Intentionally space out filter backwashes to maximize time between backwashes All flow into the North lagoon via the South lagoon (Series rather than Parallel Operation) Allows chlorine free water from gravity thickener to mix in the lagoons with chlorinated backwash water

10 DWI Water Treatment Facility

11 Increased Monitoring Using a DR890, samples were taken upstream of the Calcium Thiosulfate dosing point According to Hach s website, the DR890 DPD method has an accuracy range down to 0.02 mg/l This gives us a close approximation of compliance levels Does not account for potential interferences such as Manganese

12 Increased Monitoring Continued Using the DR 890 is not an approved method for compliance, but again we only wanted to approximate compliance to judge when to use dechlorination Samples taken daily for one month Over time the frequency of this special sampling was decreased as our confidence grew

13 Results Only once in over a year has dechlorination been used as a result of a plant upset requiring more frequent backwashes and then primarily as a precautionary measure DWI had previously received shipments approximately bimonthly at a cost of roughly $5,000 per shipment Total savings conservatively estimated at $25,000/annually

14 The Future Currently working with MBD Engineering and Public Water Supply to begin recycling water As the Pickle Plant rehab project is finished, DWI will begin operating 8 filters daily rather 6 With this, it may be advantageous to increase hours between filter backwashes to maintain and/or increase detention time prior to recycle/discharge

15 Wrapping Up Questions