Sustainability of Bioremediation

Transcription

1 Enhanced Bioremediation of Chlorinated Solvents at Brownfield Sites Making the Most of our Biological Resources Florida Brownfields Conference, November 1-4, 2009, Tampa, FL Phil Dennis and Sandra Dworatzek-SiREM, Guelph, ON Leading Science. Lasting Solutions Sustainability of Bioremediation Benefits: Uses food grade nutrients and natural microbial cultures Degrades contaminants to non-toxic end products (doesn t just move them) Carbon footprint is low Challenges: Potential for methane production- greenhouse gas May be slower than some alternative technologies If site conditions or microbial population not optimal potential for accumulation toxic daughter products 1

2 Applicability of Bioremediation for Chlorinated Solvents at Brownfield Sites Low cost, may be 1/3 rd the cost of other technologies Less subject to contaminant rebound-microbial processes often continue long after active remediation phase No extensive above ground footprint required Compatible with the built environment Often sufficiently rapid to meet remedial goals Comparison of CO 2 Footprint of Bioremediation to Physical Extraction Approaches Bioremediation Pump & Treat (10 hp) Air Sparge (15 hp) CO 2 Equivalents [Metric Tons/Year] Multi-Phase Extraction (25 hp) 5 to to To 100 Notes: Electricity Emission Factors Source: U.S. EPA egrid2006 Version 2.1 Sub-region FRCC (Florida) Bioremediation: Based upon ranges of CH 4, biomass, and CO 2 production. Does not include potential CO 2 tied up in carbonate cycle Pump and Treat included 3 recovery wells Air Sparge (45 air sparge wells) & Multi-Phase Extraction (15 extraction wells): Range represents 50 to 100% operational cycle 2

3 Common Factors Limiting Effective Bioremediation of Chlorinated Solvents Site Conditions: - Not sufficiently anaerobic (ORP >-100 mv) Solution: add electron donor - ph too low or too high (<6.0->8.5) Solution: add buffering agent -Low groundwater temperature (<10 ºC) Solution: in situ heating/allow more time -Comingled plumes/inhibitory compounds (Chloroethenes +1,1,1-TCA/chloroform,CFCs) Solution: degrade to non-inhibitory products Microbial Limitations: -Site lacks the microorganisms for effective bioremediation Solution: Add beneficial microorganisms (bioaugmentation) Dehalococcoides (Dhc) Our Closest Ally in Bioremediation Dehalococcoides are: Only known complete degraders of chlorinated ethenes Found throughout the world but absent from many sites or not evenly distributed Dehalococcoides FL2 (Courtesy of He et al., 2005) 3

4 Biodegradation of Chlorinated Ethenes Can accumulate if Dhc are absent wrong strain Other Common Microbes Only Dehalococcoides +Dehalococcoides Vinyl Chloride Reductase (vcra) and Essential Enzyme for Effective Bioremediation TCE-reductase VC-reductases (vcra) Slow fast vcra (or similar enzymes ) common in Dhc but absent in a subset of Dhc- if absent can lead to vinyl chloride stall 4

5 How Common are Sites Lacking Suitable Microbes for Effective Bioremediation? Percentage of Locations Testing Negative for Dehalococcoides In (*at least) 37% of locations Dhc not detected =high potential for cis-dce accumulation (SiREM unpublished data) n=2840 samples *overestimate of indigenous Dhc as survey included post-bioaugmentation samples 5

6 How Common is Vinyl Chloride Reductase (vcra) ~ ¼ of Dhc positive locations lacked vcra, =high potential for VC accumulation (n=980) vcra testing of Dhc positive locations indicated that 24% were vcra negative (SiREM unpublished data) Implications of Dehalococcoides Survey The combination of Dhc negative Sites (>37%) and vcra negative (~24%) means ~50% of locations have microbial limitations that impact the applicability of bioremediation Lack of Dhc or vcr A typically leads to incomplete dechlorination (cis-dce or vinyl chloride stall) Bioaugmentation is often the solution for sites lacking of Dhc or the right kind of Dhc 6

7 Bioaugmentation Bioaugmentation: the addition of beneficial microorganisms to improve the rate or extent of biodegradation KB-1 : a commercial Dhc culture used to introduce Dhc to sites where they are absent or the wrong type Bioaugmentation at a Site in Florida Bioaugmentation and Complete Dechlorination (Post-bioaugmentation Survey) n= 58 sites After KB-1 bioaugmentation-95% of sites had detectable ethene, indicating bioremediation effective at most sites with previous microbial limitations 7

8 Speed of Bioremediation (Post-bioaugmentation Survey) More than ½ of sites reported complete dechlorination (i.e., ethene production) within 3 months of KB-1 bioaugmentation * n= 52 sites After bioaugmentation 6 months-3 years (average 16 months) were required to reach remedial objectives (typically MCLs) Case Study: Enhanced Bioremediation Brownfield Application Former Industrial Site, California 8

9 Site Background Former Manufacturing Facility Re-development slated as mixed residential/business Baseline conditions TCE ranged from 5 µg/l to ~10,000 µg/l cis-dce up to 500 µg/l vinyl chloride typically < 20 µg/l, sparse distribution ethene not detected generally aerobic (oxidizing) groundwater Dehalococcoides not detected Remediation/ Redevelopment Timeline Regulatory Approval-Regional Water Quality Board (2002) Pilot Tests (three areas) (2002/2003) Full-Scale Remediation (two pilot areas expanded) (2005/2006) No Further Remediation Status granted for one area (2006) Site redevelopment begins (2008) Redeveloped site residential/commercial 9

10 Bioremediation Costs Emulsified Vegetable oil (EVO) Electron donor and Bioaugmentation (KB-1 ) applied to ~ 175 wells Materials on a Unit Basis EVO ~ $2,000 per well (KB-1 ) ~$750 per well (at current KB-1 price ~$570 per well ) Overall cost of bioremediation program was ~$3.5M Bioremediation Results Increases in ethene within 3 months (PTA1) to 9 months (PTA2) TCE reductions of at least 50% after 9 months Injection Wells-TCE <50 µg/l after 2 years Anaerobic conditions persisted at least 22 months Dehalococcoides were detected in all wells at the completion of the study 10

11 Conclusions Bioremediation is a sustainable remediation option compatible with brownfields redevelopment Approximately ½ of all sites have microbial deficiencies that limit the applicability of bioremediation Bioaugmentation provides an effective solution increasing the number of sites where bioremediation is feasible Improved (slow-release) electron donors and commercial ph buffering agents have also increased bioremediation feasibility Efficient bioremediation is sufficiently rapid/dependable to meet site redevelopment time-lines Acknowledgements Geosyntec Consultants: Michaye McMaster, Guelph Natasha Barros, Guelph Dr. Rebecca Deprato, Titusville Jim Langenbach, Titusville SiREM: Jeff Roberts, Ximena Druar, Jennifer Wilkinson, Elizabeth Ney 11

12 Questions/Comments Further Information Toll Free: Phil Dennis extension