Biological Reductive Dechlorination of Chlorinated Compounds. Barry Molnaa WSW Remediation Practice Manager ARCADIS

Transcription

1 Biological Reductive Dechlorination of Chlorinated Compounds Barry Molnaa WSW Remediation Practice Manager ARCADIS 1

2 Presentation Outline What are we trying to do? How is it supposed to work? What are the benefits? What are the unique challenges? 2

3 What Are We Trying to Do? - By Modifying In Situ Conditions we can Enhance Ongoing Degradation of CVOCs Important because: Natural Degradation Rates are Often Not Sufficient for Remediation Goals. Natural Rates are Generally Limited By: Absence of anaerobic groundwater environment, Lack of cometabolic substrate (organic carbon source). 3 3

4 Industrial Site, New Jersey Reactive Zone Bulk Attenuation Rates 1000 Natural Rate ug/l PCE Trendline Enhanced Rate Time 4

5 PCE Degrades to TCE Cl Cl C=C Cl Cl H Cl H Cl C=C Cl Cl PCE TCE Full Degradation PCE TCE DCE VC ETHENE ETHANOL CO 2 CCl 2 =CCl 2 CHCl=CCl 2 CHCl= CHCl CH 2 = CHCl CH 2 = CH 2 C 2 H 6 O CO 2 Reductive Dechlorination of Tetrachloroethene 5

6 TREATMENT PROCESSES DISCHARGE REAGENT(S) MICROBIAL CHEMICAL PHYSICAL PROCESSES IN SITU REACTIVE ZONE 6

7 How Is It Supposed to Work? Addition of easily degradable carbohydrate provides: Source of Organic Carbon Depletion of oxygen Creation of anaerobic reduced environment Carbohydrate added through periodic solution injections. Zone of enhanced CVOC degradation. 7

8 Required Elements Carbon Source (Electron Donor) Natural, Supplemental (Molasses) Electron Acceptors Nitrate, Iron, Sulfate, Etc. Reducing Environment Low Redox Potential (< -100 mv) Demonstrated End-Products 8

9 9 Carbohydrate Solution Injection

10 IN SITU REACTIVE ZONE Reactive Zones Injection Wells Contaminant Plume

11 11 Creating a Biological Reactive Zone

12 Redox Microbial Respiration Processes & Redox Regimes - Respiration e Acceptor By-Products mv Aerobic O 2 CO 2 Denitrification NO 3 2- NO 2 -, N 2, NH 3 Manganese Mn 4+ Mn 2+ Reduction Iron Reduction Fe 3+ Fe 2+ Sulfidogenesis SO 4 2- H 2 S mv Methanogenesis CO 2 CH 4 12

13 Source Area Methanogenic SO 4 Reduction Fe /Mn Reduction NO 3 Aerobic Reduction Zone O Groundwater Flow Direction Encroachment of the Aerobic Fringe 1 - Aerobic Zone 2 and 3 - Transient Anaerobic Zones 4 and 5 - Core Anaerobic Zones Geochemical Mapping (Baseline Analysis): Conceptualization of the Dominant Terminal Electron Acceptor Process (TEAP) in Advancing Plume 13

14 Reductive Dechlorination Hydrogenolysis Cometabolic Pathways Dehalorespiration 14

15 Hydrogenolysis Production of H Atoms Influence the Rate 15

16 Supply and Demand of NAD Species Glucose Fermentative loss: NADH + pyruvate Lactic acid NADH + acetyl CoA ATP Glu-6P ADP pyruvate NAD+ Acetyl- Oxidoreductase CoA Krebs NADH H: redox (mv) defines the active couple acetaldehyde H: ethanol CO 2 16

17 17 Hydrogen Production

18 Cometabolic Degradation Fortuitous Degradation of CVOCs 18

19 Dehalorespiration C 6 H 12 O 6 + Fe 3+ CO 2 + H 2 O + Fe 2+ 19

20 What are the Benefits? Often takes advantage of existing site conditions. Uses readily available reagents. Degradation not mass-transfer. Proactive & aggressive in situ treatment. Low site impact. Flexible - immediate scale-up with minimal effort. Proven technique. Less costly & more reliable than pump & treat. 20

21 What Are the Unique Challenges? Can treatment achieve clean up standards? Is there a potential for toxic by-products? Will you mobilize CVOCs? Do you need to add bacteria? What if the site has fine-grained soils? 21

22 micrograms per liter 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 Pilot Study In-Situ Reductive Zone Technology MW Apr-95 Sep-95 Dec-95 Mar-96 Jun-96 Sep-96 Dec-96 Apr-97 Jun-97 Oct-97 Dec-97 Mar-98 Jul-98 Oct-98 Feb-99 May-99 Oct-99 Mar-00 Remediation Injection Events PCE TCE cis-1,2-dce VC Can Treatment Achieve Clean up Standards? California Site: CAH Data

23 Is There a Potential for Toxic By-Products Superfund Site - Pennsylvania Concentration (ug/l) TCE DCE VC 0 Jan-99 Oct-98 Aug-98 May-98 Mar-98 Dec-97 Oct-97 Aug-97 May-97 Mar-97 Dec-96 Oct-96 Year

24 Will You Mobilize CVOCs? Source Area Results (Molar Basis) Concentration (umoles/l) Aug-01 Sep-01 Nov-01 Dec-01 Jan-02 Mar-02 Apr-02 May-02 Jul-02 PCE TCE DCE VC Ethene Sum umoles/l 24

25 Effect of Koc on Mass sorbed /Mass total Graph of sorbed vs total mass K oc = 265 (PCE) Percent Sorbed K oc = 94 (TCE) K oc = 36 (cis-1,2-dce) Organic Carbon Fraction (foc)

26 Do You Have to Add Bacteria? Microbial Conditioning Electron Donor (only) Amendment Bioaugmentation (Microbe and Donor Amendment)

27 Remediation in Fine-grained Material Site Layout

28 Geologic Cross Section

29 Initial Carbon Injection

30 Initial Carbon Injection

31 Fixed Injection Well System

32 Groundwater Remediation Results Monitoring Well MW-13

33 PCE Transformation Over Time Monitoring Well MW-13

34 Tetrachloroethylene Plume

35 Summary Low levels can be achieved. Toxic by-products can be controlled or mitigated. Mobilization of CVOCs can be controlled. Bacteria present in subsurface. Properly engineered systems can address complicated hydrogeology. 35