An Innovative Approach to Retrofitting for Nitrogen Removal

Transcription

1 June 29, 2017 An Innovative Approach to Retrofitting for Nitrogen Removal OWEA 2017 TECHNICAL CONFERENCE & EXPO

2 Innovation From Wikipedia: The application of better solutions that meet new requirements. 2

3 Today s Topics Nitrogen Removal from Wastewater Principles Case Studies - A: Stabilizing Nitrification in HPO system - B: Creating an Anoxic zone - C: Denitrifying STEP ww All case studies presented include an (online) process monitoring component 3

4 Why Nitrogen Removal? Required by Discharge Permit Improve Water Quality (avoid future limit) Increase Revenue (water quality trading) Stabilize Process Save Energy 4

5 kwh / MG Energy Intensity Benchmarking 2,500 2,000 1,934 1,853 1,955 1,500 1,000 1, ,249 1,118 1,202 Typical Best Practice Basic Secondary Nitrification BNR ENR Joint WEF/WERF Webcast: Net Zero Energy Solutions for Water Resource Recovery Facilities Wednesday, October 29th, 2014

6 The Microbiological Nitrogen Cycle OHO NO 2 - NOB AOB

7 The Microbiological Nitrogen Cycle OHO NO 2 - NOB AOB

8 3 Requirements for Biological N Removal Stable nitrification to generate nitrate (NH 3 NO 3 ) Anoxic (low DO, low/negative ORP) conditions Carbon (BOD) for a source of energy 8

9 Case Study A HPO Activated Sludge Short retention time conditions change fast Caustic added to effluent to meet ph requirements Summer limit: 1.9 mg NH 3 -N / L Winter limit: 5.0 mg NH 3 -N / L (30-day average) Problems maintaining adequate nitrification, especially in Spring 9

10 Nitrification Aeration to provide DO > 1.0 Solids Retention Time > 8 days (depends on temperature) ph 6.5 to 8.5 (peak rate is around 7.5) Usually relatively easy to achieve provided DO, SRT, and ph conditions are maintained within acceptable ranges 10

11 Measuring Nitrification Better Best Good 11

12 Case Study A Innovations Relocated caustic dosing point to upstream from aeration tanks. Redirected 2 nd stage solids to 1 st stage. Installed monitoring system for ammonium, nitrate, and ph Ammonia Exceedances CAU arrives 0 Online process monitoring installed 12

13 Case Study B Extended Aeration Activated Sludge 2 x 1-pass aerated tanks (212 kgal. ea.) 1 in service for daily flow of 260 kgpd EQ, Sand filters, chlorine disinfection, post aeration, aerobic sludge storage tanks New discharge limits: 10 mg TIN / L Fully aerobic (oxic) Stable nitrification but not designed for denitrification no anoxic zones or nitrate recirculation 13

14 Typical Denitrification Flow Sheet 3-4 Q NO 3 -N Nitrate recycle WW Anoxic NO 3 N 2 Oxic NH 3 NO 3 NO 3 -N NO 3 -N Clarifier RAS NO 3 -N 14

15 Typical Denitrification Flow Sheet 3-4 Q NO 3 -N Nitrate recycle WW Anoxic NO 3 N 2 Oxic NH 3 NO 3 NO 3 -N NO 3 -N Clarifier RAS NO 3 -N 15

16 Case Study B Innovations Convert EQ tank to anoxic zone? Convert 1 of 2 aerated tanks to anoxic zone? Build anoxic zone into existing online aeration tank? 16

17 Case Study B Innovations Convert EQ tank to anoxic zone? Convert 1 of 2 aerated tanks to anoxic zone? Build anoxic zone into existing online aeration tank? 17

18 NO3-N (mg N/L) ph Case Study B Nitrate Recirculation? No nitrate recirculation Instead: Intermittent aeration of oxic zone for increased denitrification Lead blower off 3 x / day 2 blowers operated continuously for nitrification of peak morning load NO3-N ph 18

19 Case Study B - Process Monitoring System A N O H A N O H Anoxic Oxic

20 Case Study C: STEP system WWTP on new housing development / early in build-out Nitrate recycle system but no external carbon Nitrates in effluent exceed limits / nitrification stable 20

21 Troubleshooting Denitrification Oxic / effluent Anoxic Condition Remedy Low NO 3 Low NO 3 DN not limited None as long as nitrification is stable High NO 3 Low NO 3 Nitrate limited Increase nitrate recycle High NO 3 High NO 3 Carbon limited Increase carbon dosing 21

22 Case Study C Oxic NO 3 Anoxic NO 3 Nitrate Recycle Rate Anoxic Volume Carbon Initial % 1 x N/A Stop nitrate recycle pump % 1 x N/A Resume nitrate recycle / add anoxic volume New nitrate method Add mixer to 2 nd anoxic zone ? 15 / 75 2x N/A 22

23 2:33 PM 10:33 PM 6:33 AM 2:33 PM 10:33 PM 6:33 AM 2:33 PM 10:33 PM 2:11 PM 10:11 PM 6:11 AM 2:11 PM 10:11 PM 6:11 AM 3:40 PM Effluent NO 3 -N (mg/l) Case Study C: Optical Nitrate Probe

24 Case Study C Simple Carbon Dosing System Peristaltic pump off the shelf Gycerin safe alternative to methanol 24

25 Case Study C Oxic NO 3 Anoxic NO 3 Nitrate Recycle Rate Anoxic Volume Carbon Initial % 1 x N/A Stop nitrate recycle pump % 1 x N/A Resume nitrate recycle / add anoxic volume New nitrate method Add mixer to 2 nd anoxic zone Add carbon dosing system ? 15 / 75 2x N/A 25

26 Case Study C Effluent Monthly Total Inorganic Nitrogen (TIN) 26

27 Summary Innovation to provide N removal requires an understanding of the biology to cultivate and enrich critical populations. Innovation includes modifications to existing equipment, developing new ways to operate, or creating new systems from off-the-shelf materials and equipment. Online process monitoring is valuable for understanding what is limiting treatment performance and quickly evaluating viability of solutions. Case Study A: HPO system modified chemical dosing point and implemented new solids recirculation to stabilize nitrification. Case Study B: Extended Aeration constructed new zone, operational modification to aeration to create anoxic conditions. Case Study C: STEP system influent optimized nitrate recirculation, added carbon dosing system to stabilize denitrification. 27

28 Acknowledgments Jon van Dommelen, Ohio EPA Compliance Assistance Unit Delaware County RSD Wastewater Facility Operations Department 28

29 Questions? 29