Use of ph Tolerant Bioaugmentation Cultures For Bioremediation at Low ph

Transcription

1 Use of ph Tolerant Bioaugmentation Cultures For Bioremediation at Low ph Jeff Roberts, Phil Dennis, Sandra Dworatzek and Peter Dollar 24 February 2016

2 Enhanced Bioremediation Injection of KB-1 at a site in Florida Each liter of KB-1 has 100 Billion Dhc cells Biostimulation: The addition of nutrients to stimulate microbial activity (e.g., electron donors lactate/veg. oils etc.) Bioaugmentation: the addition of beneficial microorganisms to improve the rate or extent of biodegradation KB-1 : Commercial Dehalococcoides culture used to bioaugment sites

3 Biodegradation of Chlorinated Ethenes By Reductive Dechlorination Geobacter Sulfurospirillum Dehalobacter Dehalospirillum Desulfitobacterium Desulfuromonas +Dehalococcoides Only Dehalococcoides Ethene (aka. ethylene) is non-toxic, produced by many fruit to stimulate ripening

4 LOW PH BIOREMEDIATION

5 ph Biological Perspective ph = -log [H + ] - ph 6.0 is 10 times more acidic (H + ) than ph 7.0, ph 5.7 is twice as acidic as ph 6.0 What appear to be relatively small changes in ph can have significant biological impacts on microbial: o o o o cell membranes enzyme activity DNA stability energy metabolism Dechlorination of PCE 4 fold slower at ph 6.0 than 7.0 (Young and Gosset, 1997)

6 Impact of ph on Dechlorination No Dechlorination Complete Dechlorination No Dechlorination 5.0 Incomplete/Slow Dechlorination Optimal Dechlorination 10 Incomplete/Slow Dechlorination ph of is generally required for dechlorination to ethene* ph is considered optimal range, 7.5 is best* Sites with low ph more likely to accumulate cdce/vc *Rowlands, 2004

7 Acidic Groundwater Common on Atlantic Coastal Plane Acid- sulfate soils high in pyrite (FeS 2 ) make groundwater acidic via generation of sulfuric acid upon exposure to oxygen Images courtesy of USGS Some sites particularly in the Southeast have intrinsic groundwater ph in the range

8 Declines in ph during Bioremediation (1) Reductive dechlorination produces hydrochloric acid (2) Fermentation of many electron donors produce acidic byproducts such as acetic acid: Acid Generation During Bioremediation Glucose 4 H Acetate + 2 CO 2 CO 2 dissolves in water forming carbonic acid

9 ph and Bacterial Cell Membrane bacteria pump protons across cell membrane via electron transport chain proton gradient is maintained; locally alkaline inside, acidic outside ph extremes disrupt electron transport and ph gradient

10 Correcting Low ph Inhibition with Neutralization in Microcosm PCE TCE cis-1,2-dce 1,1-DCE VC Ethene Chlorinated Ethenes and Ethene (mmoles/bottle) Bioaugmented with KB-1 ph ~4.0 ph neutralized with bicarbonate ph ~7.0 Ethene Time (Days)

11 Natural Aquifer Buffering Depending on the geology, buffering may be limited Sand = poor buffer Limestone = good buffer Moraine clay = good buffer Natural aquifer buffering reactions: Cation exchange with clays Calcite Dissolution CaCO 3 (s) + H 2 O Ca 2+ + HCO 3- + OH - Reduction of Iron Oxide 2FeOOH (s) + H 2 2Fe OH - Reduction of SO 2-4 (or NO 3- ) SO H 2 H 2 S + 2OH - + 2H 2 O If acid generation from bioremediation exceeds the buffering capacity of the aquifer, the ph will drop

12 ph Modeling: Buchlorac Model predicts the acidity generated by reductive dechlorination and associated buffer requirements CaCO 3 (s) does not provide sufficient buffering to prevent acidic conditions from developing under certain conditions Acidity generation varies by type of electron donor Robinson et al., 2009

13 Aquifer ph Neutralization ph neutralization using sodium bicarbonate, KOH NaOH and MgOH are used to buffer aquifers Challenges include: Volume requirements/cost may be high -e.g. many tons of sodium bicarbonate Keeping ph elevated is often difficult Distribution challenges can lead to alkaline conditions at injection point, acidic further out

14 Buffer Options K or NaHCO 3 Soluble, require periodic addition Potential clogging issues (calcium sulfate precipitation) Upper ph limit may not be high enough K or Na 2 CO 3 Greater buffering capacity than HCO 3 - More difficult to control ph CO H 2 O HCO 3 + H 2 O + OH H 2 CO 3 +2 OH H 2 CO 3 +2 H 2 O HCO 3 + H 3 O + + H 2 O CO H 3 O + MgOH, NaOH ph control without buffering capacity ZVI generates OH during corrosion by water Fe 0 + H 2 O Fe OH - + H 2

15 Alternatives to Aquifer Neutralization Due to challenges of aquifer ph modification, strategies to reduce acidification or to stimulate dechlorination at lower ph are worth considering; TCE Electron donor dosing and type - don t make aquifer any more acidic than required to supply necessary electrons (H 2 ) ph tolerant bioaugmentation cultures-use bacteria that can handle lower ph

16 Impact of Different Electron Donors? Electron donors have different acidification impacts per reducing (H 2 ) equivalent which vary significantly Lactic Acid (polymers) Glucose (e.g., Molasses) (10*) Linoleic Acid (vegetable oils) (7.5*) Ethanol (5.8*) Sodium Lactate (3.3*) Methanol (2.6*) Sodium Formate (NA) ph neutralizing donor produces sodium bicarbonate upon fermentation =HCL produced by dechlorination (McCarty et al., 2009) (*) mm bicarbonate required to neutralize 0.2 mm of dechlorination by this donor. Modified from Robinson et al., 2009 Decreasing acidification potential

17 LOW PH TOLERANT BIOAUGMENTATION CULTURE

18 ph Tolerant Dechlorinators? Acid loving microbes (acidophiles) can grow at ph as low as 1.0 Complete dechlorination to ethene at ph 5.5/5.6 by several bioaugmentation cultures suggest Dhc can tolerate moderately low ph* Cultures enriched from low ph sites (or acclimated commercial bioaugmentation cultures) may be beneficial for lower ph sites (*SiREM, 2012; Findley et al., 2011; Freidman et al., 2011.)

19 Low ph KB-1 Plus Anaerobic liquid bioaugmentation culture enriched from a wetland site with ph <5.0 Grown on TCE at progressively lower ph over a ~3 year period - started ph 6.5 currently at ph 5.6 Applied at >10 sites to date

20 Ethene Production of KB-1 versus Low ph KB-1 Plus at ph 6.0 and ph 7.0 Ethene production rate of low ph KB-1 Plus is 5X higher than standard KB-1 at ph 6.0

21 Microbial Composition KB-1 (ph 7.0) Low ph KB-1 Plus (ph 5.6) Other Archaea Synergistales Geobacter Acetobacterium Other Dhc 21.7 Geobacter Acetobacterium TCEDesulfovibrio 10.8 Treponema Dhc 49.0 Dehalococcoides Anaerolinaceae Bacteroidales Treponema Desulfovibrio Other KB-1 vs low ph KB-1 Plus (pyrotag 454 sequencing) in low ph reduced diversity, higher % Dhc and % Desulfovibrio, %Treponema lower % Geobacter and lower % Acetobacterium

22 CASE STUDIES

23 Low ph KB-1 Plus in Microcosm Study TCE cdce VC Ethene Total Ethenes Bioaugmented with KB-1 Plus ph cvocs and Ethene (mmoles/bottle) Days ph

24 Case Study Full Florida Scale Site ph Modification Industrial Facility-Florida TCE up to 5,000 µg/l plus significant sorbed mass Average ph 5.5 with some locations below 5.0 Amended with EVO/buffer products and low ph KB-1 Plus (40 liters) applied in 2 events

25 Case Study Full Florida Scale Site ph Modification ph MW3 MW4 MW8 MW10 MW11 MW Low ph KB-1 Difficult to increase and maintain optimal ph Bioaugmented with low ph KB-1 Plus

26 Case Study Full Florida Scale Higher ph Modification ph Well MW-1 TCE cis-dce VC Ethene ph ph 100,000 10,000 Donor / buffer KB-1 Plus Injection #1 KB-1 Plus Injection #2 & Donor buffer Injection # CONCENTRATION (ug/l) 1, TCE t 1/2 39 days DCE t 1/2 33 days /26/2011 9/14/2011 4/1/ /18/2012 5/6/ /22/2013 6/10/ /27/2014 7/15/2015

27 Florida- Lower ph Well 100,000 MW-11 TCE cis-dce VC Ethene ph ph 8 CONCENTRATION (ug/l) 10,000 1, DCE t 1/2 180 days TCE t 1/2 81 days /14/2011 4/1/ /18/2012 5/6/ /22/2013 6/10/ /27/2014 7/15/2015

28 Florida- Lower Mass Flux Well MW-12 TCE cis-dce VC Ethene ph ph 10,000 8 CONCENTRATION (ug/l) 1, TCE t 1/2 53 days DCE t 1/2 56 days /14/2011 4/1/ /18/2012 5/6/ /22/2013 6/10/ /27/2014 7/15/2015

29 Case Study Florida Full Scale Dhc ph Enumeration Modification 1.E+09 Dehalococoides/L 1.E+08 1.E+07 1.E+06 1.E+05 1.E+04 1.E+03 KB-1 Plus Low ph KB-1 Plus Low ph MW-1 MW-11 Lower ph well 1.E+02 1.E+01 1.E+00 1-Feb-12 1-Apr-12 1-Jun-12 1-Aug-12 1-Oct-12 1-Dec-12 1-Feb-13 1-Apr-13 1-Jun-13 Growth and attainment of high Dhc concentrations after second low ph KB-1 Plus bioaugmentation another indicator of successful bioaugmentation at ph below Aug-13 1-Oct-13 1-Dec-13 1-Feb-14 1-Apr-14 1-Jun-14 1-Aug-14 1-Oct-14 1-Dec-14

30 Conclusions Low ph is a common condition encountered in bioremediation Aquifer ph modification can be effective but challenging Need for ph modification could be reduced by use of: TCE - electron donors with lower acidification impact - use of ph tolerant bioaugmentation cultures Preliminary site data suggests that effective remediation can be performed at ph <6.0, current ph limit for complete dechlorination appears to be ~5.5

31 Questions Questions Further Information siremlab.com /