Pathogen Indicator (Fecal Coliform) Regrowth In Biosolids Cake Update

Transcription

1 Pathogen Indicator (Fecal Coliform) Regrowth In Biosolids Cake Update by Todd O. Williams, BCEE, P.E. CH2M HILL Richmond, Virginia Presented at the 33 rd Annual Spring Biosolids Symposium Central States WEA Stevens Point, Wisconsin March 17, 2015

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3 Sudden Increase & Regrowth Class A Pre-pasteurization with Mesophilic Digestion 8 7 Class B Limit 6 Regrowth Mean log (FC/g DS) Class A Limit Reactivation or Sudden Increase 1 <12 <4 0 Raw Influent Sludge Pre-past. Effluent Digester Effluent Centrifuge Cake 24 hr. Stored Cake 3

4 Sudden Increase/Regrowth Definitions Sudden Increase Sudden increase immediately after dewatering More prevalent with thermophilic processes with centrifuge dewatering Not a major issue for mesophilic processes Regrowth Increases during cake storage More prevalent with centrifuge dewatering Occurs with thermophilic and mesophilic processes Source: Higgins et al., 2011, WEFTEC 4

5 Why Does SI Occur? Possible explanations: 1. Floc breakup releases bacteria 2. Regrowth of coliforms after dewatering 3. Contamination 4. Presence of non-culturable organisms that are reactivated after dewatering Source Higgins et al., 2011, WEFTEC 5

6 Contamination of E. coli Digester effluent or cake could become contaminated during dewatering process Sources of Contamination Polymer Makeup and Dosing System Water used for Polymer Make-up Dilution or Carrier Water Growth within the Centrifuge Cake Conveyance Systems Storage Site Source: Higgins et al., 2011, WEFTEC 6

7 Contamination at EEH Plant 7 6 Final Effluent Used for Polymer Potable Water Used for Polymer E. coli Density log(cfu/g DS) Reduced/eliminated SI Still Large Regrowth 1 0 Centrifuge Feed Cake Cake + 24 hrs Adapted from Baddeley et al., 2009, European Biosolids Conference 7

8 Contamination Issues For Plants with SI, contamination should be ruled out first We ve sampled polymer systems and other sources of contamination at several plants, and not seen contamination, but still get large SI Other possibilities for SI? Source: Higgins et al., 2011, WEFTEC 8

9 Non-culturable hypothesis Bacteria can become reversibly non-culturable during thermophilic treatment In other words, they are still present, and potentially viable, but we are not enumerating them with our standard culturing method Dewatering reactivates these bacteria, making them culturable and able to grow Source: Higgins et al., 2011, WEFTEC 9

10 Regrowth Regrowth appears to be due to growth of bacteria fueled by available substrate and good growing conditions Greater amounts of shear and higher cake solids are associated with greater regrowth (centrifuges vs belt filter press) Occurs with both thermophilic and mesophilic processes Source: Higgins et al., 2011, WEFTEC 10

11 Regrowth for Mesophilic with Centrifuges Mesophilic 1 Mesophilic 3 Mean log 10 (FC/g DS) Storage Time (d) Source: Higgins et al., 2011, WEFTEC 11

12 Effect of Advanced Digestion Processes 1. Enhanced Enzymic Hydrolysis (EEH) 2. Multi-stage thermophilic digestion 3. Temperature Phased Anaerobic Digestion (TPAD) 4. Two stage advanced digestion (ATAD/TPAD) 5. Pre-pasteurization followed by mesophilic anaerobic digestion 6. Cambi thermal hydrolysis (THP) followed by mesophilic anaerobic digestion Source: Higgins et al., 2011, WEFTEC 12

13 Indicator Results E. coli in the Cake 5.00 E. coli Density (log 10 E. coli/g DS) All Plants with Centrifuge Dewatering Class A Limit <0.94 <0.86 <0.92 < EH EEH Pre- Past. Thermo TPAD THP 1 THP 2 THP 3 4-Stage Thermo

14 Overview Summary and Conclusions 1. Sudden increase associated with thermophilic plants that have centrifuge dewatering 2. Regrowth and more odors associated with most digestion processes with centrifuge dewatering 3. Belt filter press cakes have lower odors and lower incidences of sudden increase and regrowth 4. Advanced digestion can reduce odors, but not always sudden increase and regrowth Source: Higgins et al., 2011, WEFTEC 14

15 HRSD Experience with Pathogen Indicator (FC) Regrowth at the Atlantic Plant CASE STUDY

16 HRSD Political Subdivision of Southeast Virginia Owns and Operates 13 Treatment Plants 9 major (> 15 MGD), 4 small (<1 MGD) Treat 231 MGD Diverse Biosolids Management - Incineration - Composting - Land application WEFTEC 2008 Chicago, IL 16

17 Atlantic Plant 54 MDG design Annual average flow 30 MGD Approximately 30,000 wet tons biosolids/ year land applied since 1980 s acres per year - Private Sites - HRSD Progress Farm 17

18 Biosolids Processing Conventional two stage mesophilic anaerobic digestion to achieve Class B time and temperature Centrifuge dewatering with Sharples 75,000 centrifuges 4 hour hopper storage 90 day covered pad storage Agricultural land application 18

19 HRSD Land Application Project Goals Protect Environment / Public Health Maintain 100% Regulatory Compliance Be a Good Neighbor Use Best Management Practices Operate Cost Effectively Uphold NBP Code of Good Practice (EMS)

20 WERF 2006 Study and Impact on HRSD Operations Does reactivation and regrowth occur? Does storage on pad impact reactivation and regrowth? Should HRSD test for fecal coliform even though program has always been in compliance with USEPA Class B operational standards? If test results indicate reactivation/regrowth what should be the plan of action? 20

21 HRSD Response to WERF Study Test to determine fecal coliform levels WERF report indicates storage provides reduction Test stored biosolids If fecal coliform levels are greater than 2 million MPN/gm TS what is the plan of action? Temporarily suspend land application until a solution is determined Implement new process enhancements 21

22 Initial Test Results Fecal coliform levels > 2 million MPN/gm TS in stored biosolids Determine strategy for reducing FC levels Implement strategy Ensure compliance with both standards Operational time and temperature Fecal coliform testing < 2 million MPN/gm TS 22

23 HRSD Study Plan Storage - testing over time Low lime dosing (1% - 9% dose rates) Testing biosolids after digestion Testing biosolids after centrifuge dewatering Testing biosolids after temporary (<4 hour) storage in hopper Belt filter dewatering compared to centrifuges Digester modifications (series vs. parallel) Odor evaluation Evaluate varying centrifuge speeds and torques Evaluate raising digester temperatures from 98 F to 104 F Evaluate effect of back-mixing Evaluate effect of storage temperatures Evaluate other technologies as they develop 23

24 Reactivation/Regrowth Base Conditions (2006) 3,000,000 2,500,000 Salmonella Concentration MPN/4g Dry Weight Right Axis ,000, ,500,000 1,000, ,000 Fecal Coliform Concentration MPN/g Dry Weight Left Axis FC Salmonella Primary Digester Discharge Secondary Digester Discharge Dew atered Cake Dew atered Cake After 2 hours 0.0 FC Average FC Geo Mean Salmonella Ave Salmonella Geo Mean 24

25 >50 days of Storage Needed to Control FC Regrowth in Spring Conditions (56 F) FC vs. Pile Age Test 1 FC Concentration (MPN/g) 20,000,000 18,000,000 16,000,000 14,000,000 12,000,000 10,000,000 8,000,000 6,000,000 4,000,000 2,000, Pile Age (Days) 25

26 >30 days of Storage Needed to Control FC Regrowth in Summer Conditions (77 F) FC vs. Pile Age Test 2 FC Concentration MPN/g 80,000,000 70,000,000 60,000,000 50,000,000 40,000,000 30,000,000 20,000,000 10,000, Pile Age (Days) 26

27 Field Studies with Low Level Lime Dosing Lime Feed Lime Dosed Piles Mixer 27

28 Low Level Lime Dosing Trial Results - 9% lime addition required to control FC regrowth 9% lime 6% Lime No Lime Fecal Colilform MPN/g 90,000,000 70,000,000 50,000,000 30,000,000 10,000,000-10,000,000 6,800,000 7,230,000 1,060,000 38,888 11,700, Days 82,600 28

29 BFP vs Centrifuge Trial Results FC Comparison Centrifuge and BFP Geometric Mean of 7 Samples 100,000, Belt Filter Cake Centrifuge Cake 2,000,000 Limit Hours 10,000,000 1,000, ,000 10,000 Log FC MPN/g dry wt 29

30 Fecal Coliform Levels by Centrifuge RPM (geometric mean) Fecal Coliform (geo mean MPN/g dry weight) 35,000,000 30,000,000 25,000,000 20,000,000 15,000,000 10,000,000 5,000, Tim e (hours) 2300 RPM 2100 RPM 1900 RPM 30

31 Historical Results Since Operating at Lower RPM Storage Pile Testing Fecal Coliform vs. Pile Age 9,000,000 8,000,000 7,000,000 Time when Centrifuges were switched to 1900 RPM Insufficient Pile Age FC Geomean mpn/g 6,000,000 5,000,000 4,000,000 3,000, Pile Age in Weeks 2,000,000 1,000,000 0 Sample Date 11/27/2006 1/17/ /8/2007 4/2/2007 4/18/ /8/2007 6/21/ /19/ /2/2007 9/20/ /25/07 1/3/08 1/31/ 2008 FC geomean Sam ple Dates 2/14/ /13/ /27/ /10/ /8/2008 Pile age in weeks 5/22/ /19/ /2/2008 7/31/ /21/ /11/

32 Results of FC Testing in Jan-Feb 2008 Full Scale 40,000,000 35,000,000 FC Concentration (MPN/g) 30,000,000 25,000,000 20,000,000 15,000,000 10,000,000 5,000,000 3rd order polynomial of Average 2,000,000 MPN/g Target Hours Trial 1 Trial 2 Trial 3 Trial 4 Average Series6 Poly. (Average) 32

33 Historical Results Since Operating at Lower RPM Storage Pile Testing Fecal Coliform vs. Ambient Temperature 9,000,000 8,000,000 Time when Centrifuges were switched to 1900 RPM Insufficient Digester SRT AND Low Ambient Temperature ,000,000 FC Geomean mpn/g 6,000,000 5,000,000 4,000,000 3,000, Ambient Temp C 2,000,000 1,000,000 0 Sample Date 11/27/2006 1/17/ /8/2007 4/2/2007 4/18/ /8/2007 6/21/ /19/ /2/2007 9/20/ /25/07 1/3/08 FC geomean Sam ple Dates 1/31/ /14/ /13/ /27/ /10/ 2008 Ambient Temps C 5/8/2008 5/22/ /19/ /2/2008 7/31/ /21/ /11/ /18/

34 Historical Results Since Operating at Lower RPM Storage Pile Testing Fecal Coliform vs. Digester SRT 9,000,000 8,000,000 Time when Centrifuges were switched to 1900 RPM Insufficient Digester SRT AND Low Ambient Temperature 29 7,000, FC Geomean mpn/g 6,000,000 5,000,000 4,000,000 3,000, Digester SRT in Days 2,000,000 1,000,000 0 Sample Date 11/27/2006 1/17/ /8/2007 4/2/2007 4/18/ /8/2007 6/21/ /19/ /2/2007 FC geomean 9/20/ /25/07 1/3/08 Sam ple Dates 1/31/ /14/ /13/ /27/ /10/ /8/2008 Digester SRT in Days 5/22/ /19/ /2/2008 7/31/ /21/ /11/

35 Conclusions for the Atlantic Plant Solids Centrifuge cake fecal coliform reactivation occurs immediately after dewatering with regrowth within hours Storage > 50 days required for FC reduction below 2 million MPN/gm TS during winter months, 30 days or less during summer months Low lime dosing at 9% CaCO provides effective reduction of FC for stored biosolids Low lime dosing at 3% CaCO is effective only if added within 2 hours after dewatering However, low lime dosing significantly increases odors, costs and handling 35

36 Conclusions (continued) Belt filter cake did not experience reactivation Operating digesters in series decreased fecal coliform levels but regrowth still occurred above levels desired Operating digesters at higher temperatures (104 F) increases FC regrowth concentrations Decreasing centrifuge speed from 2300 rpm to 1900 rpm reduced storage time to 2 weeks to achieve target FC concentrations Higher storage pile temperatures results in higher FC concentrations in the first week, but the trend reverses between one and two weeks Cold ambient temperatures (< 8 C) results in FC concentrations above target level of 2 million even with long storage times. Reduced digester SRT (<20 days) in combination with cold ambient temperatures results in FC concentrations above target level of 2 million. 36

37 Current HRSD Mode of Operation Continue tracking time and temperature for Class B compliance in digestion Added second storage building to provide > 90 days storage Weekly batch storage for better tracking Test stored biosolids bi-weekly for FC If FC below 2 million MPN/gm TS, batch is approved for land application Clean digesters in the summer or fall months only Converting to thermal hydrolysis in the future to achieve Class A, eliminate regrowth and reduce cake odors 37

38 Acknowledgements Bucknell University Matthew Higgins, PhD Virginia Tech John Novak, PhD HRSD Staff Treatment Department Rhonda Bowen, Dave Waltrip, Mardane McLemore, Erv Bonatz, Rich Roberts, Lee West, Sam Jones and all the plant operators Technical Services Mark Feltner Laboratory Robin Parnell and the lab staff HRSD Contractors AgNutrients Jim Salmons CH2M HILL Technologists and Others Bob Forbes, Tim Shea, Chris Easter, Thomas Hahn 38

39 Pathogen Indicator Regrowth in Biosolids Cake Update QUESTIONS? Todd O. Williams, BCEE, P.E. March 17,