Perchlorate Degradation in Acetate-fed Bioreactors

Transcription

1 Perchlorate Degradation in Acetate-fed Bioreactors Yanguang Song Kijung Kim, Bruce Logan Department of Civil & Environ. Eng. Penn State University Perchlorate (mg/l) Effluent Influent EBCT Time (day) EBCT (min) Contaminated water source ATTRIBUTES: Continuous perchlorate removal Clogging avoided by intermittent backwash Biofilm regeneration by side process Sand Sand media filter Supplemental carbon source with (optional) N, P addition Perchlorate respiring culture (optional) Backwash with chlorate, N, P, acetate Perchlorate free water

2 PERCHLORATE FIXED-BED REACTOR [Penn State Patent/Invention Disclosure No. 1887] Contaminated water source ATTRIBUTES: Continuous perchlorate removal Clogging avoided by intermittent backwash Biofilm regeneration by side process Sand filter Sand media Supplemental carbon source with (optional) N, P addition Perchlorate respiring culture (optional) Backwash with chlorate, N, P, acetate Perchlorate free water

3 Perchlorate Degradation: Topics Bacterial isolate used in tests: KJ Bench-scale acetate-fed reactors Mixed culture Pure culture (KJ) Effect of O 2 exposure on perchlorate reduction

4 Perchlorate Reducing Pathway ClO 4 - kp ClO 3 - Acetate CO 2, H 2 O, Biomass Chlorite and chlorate do not accumulate in water: kc Acetate kd>> kc > kp CO 2, H 2 O, Biomass ClO 2 - kd Acetate Cl - + O 2 CO 2, H 2 O, Biomass

5 Are perchlorate-respiring bacteria abundant in nature? One milliliter (1 ml) of water (about one teaspoon) contains: ~ 10 6 bacteria ~1 perchlorate-degrading bacterium

6 PRM Abundance: observations PRMs present in natural waters at ~1000/10 9 PRMs in pristine soils, that have no evidence of perchlorate contamination: ~1/10 9 At sites where perchlorate is present, have a more abundant perchlorate reducing population, ~100/10 9

7 Several Perchlorate Respiring Bacteria Isolated in Our Laboratory Dechlorosoma sp. KJ: isolated from a perchloratedegrading packed bed bioreactor; Dechlorosoma sp. PDX: isolated from primary digester wastewater; Dechloromonas sp. JM: isolated from a hydrogenoxidizing consortium in a autotrophic packed-bed biofilm reactor; Dechloromonas sp. HZ: isolated from a gas-phase anaerobic packed-bed biofilm reactor.

8 Phylogentic analysis of KJ (courtesy of Dr. Ian Head, Univ. of New Castle) % Isolate KJ Isolate PDX "Dechlorosoma" sp. str. SDGM "Dechlorosoma" sp. str. Iso2 "Dechlorosoma suilla" str. PS2 "Dechlorosoma" sp. str. Iso1 96 "Dechloromonas" sp. str. CL 100 "Dechloromonas" sp. str. NM "Dechloromonas agitata" str. CKB Isolate JM Ferribacterium limneticum str. cda-1 "Dechloromonas" sp. str. SIUL "Dechloromonas" sp. str. MissR Rhodocyclus purpureus DSM 168 T Rhodocyclus tenuis str Classification: Dechlorosoma sp. KJ Zoogloea ramigera ATCC T Azoarcus sp. str. BH72 Thauera aromatica DSM 6984 T Azoarcus indigens str. VB32 T Thauera selenatis ATCC T Azoarcus denitrificans str. Td -15 Azoarcus denitrificans str. Td -1 From: Logan et al. (2001)

9 KJ Perchlorate kinetics: K s =33 mg/l (lactate grown cell suspensions) 4 Rates (mg/ug-hr) KJ1 PDX Perchlorate Concentration (mg/l) From: Logan et al. (2001)

10 Substrate kinetics: acetate Growth Rate (h -1 ) Acetate (mg/l) oxygen From: Logan et al. (2001)

11 Substrate kinetics: acetate Growth Rate (h -1 ) Acetate (mg/l) oxygen chlorate From: Logan et al. (2001)

12 Substrate kinetics: acetate Growth Rate (h -1 ) Acetate (mg/l) oxygen chlorate perchlorate From: Logan et al. (2001)

13 Kinetic constants for growth of KJ on acetate Electron Acceptor μ m (h -1 ) K S (mg/l) Oxygen 0.27 ± ± 1 Chlorate 0.27 ± ± 25 Perchlorate 0.14 ± ± 290 From: Logan et al. (2001)

14 Cell yield- KJ Cell yield (g-dry weight/g-acetate) oxygen chlorate perchlorate From: Logan et al. (2001)

15 Overall Epifluorescent micrograph (1000 ) of KJ stained with acridine orange Stoichiometry Without biosynthesis: acetate/perchlorate = 1:1 (mol/mol) CH 3 COO - + ClO 4-2HCO 3- + H + + Cl - With biosynthesis: acetate/perchlorate = 2.9:1 (mol/mol) CH 3 COO ClO NH H C 5 H 7 O 2 N (cells) + 0.7HCO Cl H 2 O

16 Perchlorate Degradation: Topics Bacterial isolate used in tests: KJ Bench-scale acetate-fed reactors Mixed culture Pure culture (KJ) Effect of O 2 exposure on perchlorate reduction

17 Acetate-Fed Sand Packed-bed Column Experiments Sampling from the side ports of the column

18 Acetate-fed Bioreactors Columns: 14 cm or 28 cm long. Mixed cultures: enriched on perchlorate (activated sludge samples) Feed: Artificial groundwater (AGW) containing 20 mg/l perchlorate and nutrients

19 Mixed cultures (14 cm sand column) Critical EBCT was 34 minutes. Effluent Perchlorate (ug/l) EBCT (min) Detection Limit series 1 series 2 From: Kim and Logan (2000)

20 Mixed cultures (28 cm sand column) Critical EBCT was ~40 minutes. Startup Perchlorate (ug/l) Influent Effluent EBCT EBCT (min) Time (day) 0 From: Kim and Logan (2000)

21 Perchlorate Degradation: Topics Bacterial isolate used in tests: KJ Bench-scale acetate-fed reactors Mixed culture Pure culture (KJ) Effect of O 2 exposure on perchlorate reduction

22 Acetate-fed Bioreactors Columns: 14 cm or 28 cm long. Pure culture: Dechlorosoma sp. KJ Feed: Artificial groundwater (AGW) containing 20 mg/l perchlorate and nutrients; water from the City of Redlands

23 Pure culture: KJ (28 cm-sand column) Critical EBCT was ~2.1 minutes. 1 Perchlorate (ppm) Minimum EBCT 2.1 min <--Startup--> Empty Bed Contact Time, EBCT (min) From: Kim and Logan (2001)

24 As EBCT decreased: Pure culture: KJ (28 cm-sand column) Perchlorate was nondetectable for 84% of samples (n=147) Perchlorate (mg/l) Effluent Influent EBCT Time (day) EBCT (min) From: Kim and Logan (2001)

25 Pure culture: KJ (28 cm-sand column) Reliability: After start up, perchlorate removal was stable at: 95% of time: <23 ppb 84% of time: <4 ppb % of samples less than the concentration perchlorate (mg/l) From: Kim and Logan (2001)

26 Redlands Water Pure culture KJ, (28 cm-sand column) Perchlorate is completely removed using Redlands water (containing NO 3- ) for detention time >11 min Redlands Effluent Detention Time Redlands Influent 60 Perchlorate (ug/l) Detention Limit (4ug/L) Detention time: 9 min Detention Time (min) Redland Water Time (day) 0 From: Kim and Logan (2001)

27 Control w/o Nitrate Pure culture KJ, (28 cm-sand column) Perchlorate is completely removed using artifical groundwater (no NO 3- ) for detention time >8 min Control Effluent Detention Time Control Influent 60 Perchlorate (ug/l) Detention Limit (4ug/L) Detention time: 27 min Detention time: 7.4 min Detention Time (min) Time (day) 0 From: Kim and Logan (2001)

28 Effect of Nitrate Pure culture KJ, (28 cm-sand column) Perchlorate degradation is more stable for groundwater with nitrate Redlands Effluent Redlands Influent Control Effluent Control Influent Perchlorate (ug/l) Detention Limit (4ug/L) 1.0 Redland Water Time (day) From: Kim and Logan (2001)

29 Perchlorate Degradation: Topics Bacterial isolate used in tests: KJ Bench-scale acetate-fed reactors Mixed culture Pure culture (KJ) Effect of O 2 exposure on perchlorate reduction

30 Problem... When a reactor is shut down (either for maintenance or due to mechanical problems), perchlorate respiring bacteria can be exposed to high concentrations of DO. High DO concentrations inhibit perchlorate reduction. Our question was: How long can an anaerobic culture be exposed to oxygen before losing the ability to reduce perchlorate?

31 Oxygen Exposure [ClO4-]. (ppm) Time (hr) Anaerobic Control Ana-aer Control

32 Oxygen Exposure [ClO4-]. (ppm) Time (hr) Anaerobic Control Ana-aer Control T=12h

33 Oxygen Exposure [ClO4-]. (ppm) Time (hr) Anaerobic Control Ana-aer Control T=1h T=2h T=4h T=8h T=12h

34 Oxygen Exposure [ClO4-]. (ppm) Time (hr) Anaerobic Control Ana-aer Control T=1h T=2h T=4h T=8h T=12h T=22h T=28h T=32h

35 Solution... There should be no problems for short exposure times (<12 h) of the bacteria to oxygen. Avoid oxygen exposure for longer shut down times Do not drain the reactor. This will keep air out of the system to maintain the culture under anaerobic condition. Stop feeding the electron donor (this will lower ph) and nutrients (N, P).

36 CONCLUSIONS It is possible to obtain high perchlorate removal rates, with EBCT as low as 2.1 min, in packed bed reactors inoculated with pure culture (KJ). Mixed cultures require longer times (>11 min). Perchlorate removal was achieved in the laboratory using groundwater from the Redlands site, containing dissolved oxygen and nitrate. Perchlorate reduction by strain KJ can be recovered after exposure to oxygen for less than 12 hours.

37 ACKNOWLEDGMENTS Funding AWWARF: Project manager Frank Blaha National Science Foundation Penn State University

38 Thank You! Q s and A s