The Unexpected Consequences of Water Conservation on Water Reuse Facilities

Transcription

1 The Unexpected Consequences of Water Conservation on Water Reuse Facilities Linda Sawyer Linda Sawyer WateReuse Northern California December 8, 2017

2 Water Conservation and Water Reuse Decreased Flows and Flow Projections Treatment Process Loading Capacity Alkalinity Limitations Effluent Quality Recycled Water Flows DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 2

3 Decreased Flows and Flow Projections DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 3

4 Drought Led to Water Conservation Water conservation measures include Drought tolerant landscaping Outdoor water restrictions Low-flow toilets Low-flow shower heads Faucet aerators Water conserving appliances Greywater recycling Not flushing as often Shorter showers Gallons per Toilet Flush Before s- 1990s Low- Flow Brown and Caldwell 4

5 Water Conservation Results in Lower Wastewater Flows Summer flow is July through September Brown and Caldwell 5

6 Water Conservation Results in Lower Wastewater Flows Summer flow is July through September Brown and Caldwell 6

7 Water Conservation Results in Lower Wastewater Flows Brown and Caldwell 7

8 Water Conservation Results in Lower Wastewater Flows Brown and Caldwell 8

9 Water Conservation Results in Lower Wastewater Flows Letters indicate different plants. Flow range is permitted flow. Ratios based on summer flow (average of July through September). Brown and Caldwell 9

10 Water Conservation Results in Lower Wastewater Flows Letters indicate different plants. Flow range is permitted flow. Ratios based on summer flow (average of July through September). Brown and Caldwell 10

11 Flow Projections and Decreased Flows Often developed with collection system planning Biggest concern is conveying peak flows DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 11

12 Flow Projections Conservatively High Brown and Caldwell 12

13 Treatment Process Loading Capacity DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 13

14 Loadings Have Increased at Some Plants Brown and Caldwell 14

15 Loadings Have Increased at Some Plants Brown and Caldwell 15

16 Influent Concentrations Have Increased Brown and Caldwell 16

17 Average Flow is Typically Used to Rate Capacity Average Flow PRIMARY CLARIFIERS ACTIVATED SLUDGE SECONDARY CLARIFIERS DISCHARGE ADVANCED TREATMENT FILTRATION CHLORINE CONTACT REUSE DEWATERING DIGESTION THICKENING HAULING Brown and Caldwell 17

18 What Really Limits Plant Capacity? Peak Flow Organics Loading and Peak Flow Peak Flow PRIMARY CLARIFIERS ACTIVATED SLUDGE SECONDARY CLARIFIERS DISCHARGE ADVANCED TREATMENT FILTRATION CHLORINE CONTACT REUSE DEWATERING DIGESTION THICKENING HAULING Organics Loading Brown and Caldwell 18

19 Example of Plant Capacity Change Plant designed in the 1970s: 12 mgd at 120 gal/capita-day 20,000 lb BOD/day at 0.2 lb BOD/capita-day Population: 100,000 Brown and Caldwell 19

20 Per Capita Flows Have Decreased Brown and Caldwell 20

21 Loading Capacity Exceeded at Design Flow Treating design flow in 2015: 12 mgd at gal/capita-day 20,000 40,000 lb BOD/day at 0.2 lb BOD/capita-day Population: 100, ,000 Brown and Caldwell 21

22 Flow Capacity Reduced at Design Loading Treating design loading and population in 2015: 12 mgd 6 mgd at gal/capita-day Brown and Caldwell 22

23 Flow and Capacity Loading is key to capacity Equivalent flow capacity now is probably less than it used to be Less flow does NOT mean spare capacity Brown and Caldwell 23

24 Alkalinity Limitations DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 24

25 Alkalinity is needed for nitrification 1 g Nitrate-N (NO 3- ) Carbon O 2 1 g Nitrite-N (NO 2- ) 1 g Nitrite -N (NO 2- ) Alkalinity Carbon Alkalinity O 2 1 g Ammonia-N (NH 3 /NH 4+ ) Nitrification consumes alkalinity (7.2 g Alkalinity (as CaCO 3 ) destroyed/g N) Denitrification recovers some alkalinity Nitrogen Gas (N 2 ) Alkalinity Brown and Caldwell 25

26 Case Study El Estero Plant in Santa Barbara Process includes primary clarifiers and activated sludge Flow decreased 12% Converting to nitrification Reference: Sawyer et al, Planning for Future Droughts Lessons Learned at Water Resource Recovery Facilities, WEFTEC 2016, Brown and Caldwell 26

27 El Estero Influent Ammonia Increased 35% Brown and Caldwell 27

28 Alkalinity Concentration Only Increased 6% Brown and Caldwell 28

29 Changes in Potable Water Source May Exacerbate the Problem Brown and Caldwell 29

30 Alkalinity Supplementation Needed Projected with desalination Average alkalinity, mg CaCO 3 /L Average Ammonia, mg N/L Before drought, alkalinity was sufficient Based on 2014 data, alkalinity supplementation was needed Source water changes can exacerbate the problem Monitor alkalinity and add chemical if needed Brown and Caldwell 30

31 Effluent Quality DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 31

32 Plant C Effluent Nitrate has Increased Plant C Brown and Caldwell 32

33 Plant C Effluent Phosphorus has Increased Plant C Brown and Caldwell 33

34 Process Models Predict Nutrient Concentration Increases Influent NH3- N, mg/l Effluent TN, mg/l Effluent TN, lb/day , , ,500 Brown and Caldwell 34

35 Planning for Effluent Concentration Increases Additional chemicals or improved processes may be needed Consider loading-based limits instead of concentrationbased limits in permit negotiation Attractive if strict discharge limit, but expect reduced discharge flow due to recycling. Brown and Caldwell 35

36 Recycled Water DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 36

37 Less Water Available Due to Conservation Excess capacity (stranded assets) Insufficient water to meet demands Revenue impacts Brown and Caldwell 37

38 Planning Conservatism Highest flow is conservative PRIMARY CLARIFIERS ACTIVATED SLUDGE SECONDARY CLARIFIERS DISCHARGE ADVANCED TREATMENT FILTRATION CHLORINE CONTACT REUSE DEWATERING DIGESTION THICKENING Lowest average flow may be conservative HAULING Brown and Caldwell 38

39 Complete Reuse is Challenging Brown and Caldwell 39

40 Recycled Water Challenges Less water available for recycling Peak reuse demand is often in a different season and year than peak influent flow IPR and DPR demands are year-round, but brine disposal is required Brown and Caldwell 40

41 Planning for Water Conservation Brown and Caldwell 41

42 Planning for Future Water Conservation Expect less flow that is more concentrated Understand the conservatism of flow projections Less flow may not mean spare treatment capacity Anticipate possible alkalinity limitations Expect increased effluent concentrations Plan for variations in recycled water supply and demand DISCHARGE ADVANCED TREATMENT REUSE Brown and Caldwell 42

43 Thank You