A-01 Desclorinacion de Tricloroetano Tpc

8/3/2019 A-01 Desclorinacion de Tricloroetano Tpc

1/8

Paper A-01, in: V.S. Magar and M.E. Kelley (Eds.), In Situ and On-Site Bioremediation2003. Proceedings of the SeventhInternational In Situ and On-Site Bioremediation Symposium (Orlando, FL; June 2003). ISBN 1-57477-139-6, published byBattelle Press, Columbus, OH, www.battelle.org/bookstore.

CONSTRUCTION OF A SEQUENTIAL ANAEROBIC/AEROBIC

IN SITU BIOREMEDIATION SYSTEM

Benjamin L. Porter([email protected]) and Daniel P. Leigh(Shaw Environmental & Infrastructure, Inc., Concord, California, USA)

Christian D. Johnson and Michael J. Truex(Battelle Pacific Northwest Division, Richland, Washington, USA)

Steve Granade (Naval Base Ventura County, Point Mugu, California, USA)

ABSTRACT: A pilot-scale test was conducted to evaluate in situ bioremediation (ISB)

of chlorinated solvent-contaminated groundwater at Naval Base Ventura County, Point

Mugu, California. Initially the pilot-scale ISB test was for anaerobic dechlorination of

trichloroethene (TCE). TCE and its daughter product, dichloroethene (DCE), wererapidly dechlorinated. However, the DCE dechlorination product, vinyl chloride (VC),

was transformed at a much slower rate. With the intent of accelerating destruction of theremaining VC, a pilot-scale demonstration of cometabolic aerobic in situ biodegradationwas performed and was successful in destroying VC. This paper discusses the selection

and implementation of the equipment required for operation, monitoring, and control of

this sequential treatment process.The anaerobic ISB pilot-scale test used a two-well groundwater recirculation cell

to distribute periodic high concentration pulses of lactic acid to stimulate anaerobicmicrobial activity. An automated process control/data collection system was used to

operate the nutrient injection pumps, collect data from sensors, and to operate a sample

collection system during anaerobic operations. Aerobic in situ bioremediation wassubsequently applied using cometabolic methanotrophic metabolism in anin situ biofilter

approach to treat the residual VC. The separate aerobic system was designed to amendgroundwater from four extraction wells with methane and oxygen prior to injection in a

central injection well. The aerobic system relied on two eductors and downstreammixing tanks to saturate the groundwater with the gaseous nutrients without any offgas.

A process control system collected data and insured safe operation of the aerobic system.

INTRODUCTION

A site at the Naval Base Ventura County's Point Mugu facility had trichloroethene

(TCE) releases to groundwater from an underground oil/water separator that was used aspart of paint stripping operations. An evaluation of in situ bioremediation (ISB) of the

TCE [Johnson et al., 1998] concluded that accelerated anaerobic ISB should be

implemented. Thus a pilot-scale demonstration of anaerobic ISB was conducted,beginning in December 1998. Lactic acid was distributed throughout the portion of thecontaminated aquifer with the highest concentration of TCE using a single cell (2-well)

recirculation system to stimulate anaerobic biotransformation of the contaminants. It was

thought (based on laboratory microcosm results and literature information) thatdechlorination would occur mainly under methanogenic conditions; hence, the naturally

high sulfate (~ 700 mg/L) would need to be removed from the system before

methanogenic conditions would be established. The lactic acid was distributed in


2/8

periodic, high concentration pulses to stimulate sulfate reduction. To promote

chloroethene biodegradation, a final large pulse of lactic acid was injected when sulfatein the flow field had been reduced to less than 20 mg/L. Recirculation was halted at day

64 and long-term monitoring began, continuing through April 2002. Upon removal of

the sulfate, TCE and dichloroethene (DCE) were rapidly dechlorinated to vinyl chloride

(VC), which slowly declined over the next 2 years while the dissolved etheneconcentration increased (although not stoichiometrically) [Johnson et al., 1999; Leigh et

al., 2000; Granade et al, 2003]. The rate of VC dechlorination in the field (as calculated

from ethene production) was at least two orders of magnitude slower than the ratemeasured in lactate-fed laboratory microcosm tests with site sediments and groundwater

The plume characterization in the summer of 2001 (some 31 months after

initiation of nutrient injection for the anaerobic ISB pilot-scale test) indicated thatessentially all of the TCE in the original plume was gone, as was the majority of the

DCE. Given these facts (slow anaerobic VC degradation and no TCE present), it was

proposed that the full-scale anaerobic treatment not be performed and instead that aerobicin situ treatment be applied. In situ cometabolic aerobic biodegradation had the potential

to accelerate destruction of the residual VC and DCE.A pilot-scale demonstration of cometabolic aerobic ISB was performed beginning

in April 2002. The aerobic ISB design was based on methanotrophic cometabolicdestruction of VC (and DCE) implemented as an in situ biofilter [Truex et al., 2002].

The biofilter approach used a recirculation cell to move groundwater through a treatment

zone that is established in situ in the area surrounding the injection well. Groundwatercontaining VC and DCE was extracted from the formation through multiple (4 or 5)

extraction wells, amended with nutrients, and re-injected into an injection well.

Operation of the in situ aerobic biofilter required injection of dissolved methane, oxygen,and nitrate to stimulate the methanotrophic bacteria that are used for destroying VC.

After a period of injection with excess stoichiometric oxygen, recirculation was halted toallow the bacteria to consume the methane and subsequently for VC to be destroyed by

available methane monooxygenase enzyme. The pilot-scale aerobic ISB test

demonstrated successful destruction of VC and (to a lesser extent) DCE.This paper discusses the assembly of equipment required for operation,

monitoring, and control of sequential anaerobic/aerobic ISB. Proper design and

construction of the treatment system is important for minimizing the cost of the treatment

and obtaining the demonstration objectives. Although the equipment discussed wasdesigned and constructed as two systems (anaerobic and aerobic), they could be readily

combined into a single mobile treatment system.

ANAEROBIC IN SITU BIOREMEDIATION SYSTEM

The anaerobic ISB system was designed to volumetrically deliver lactic acid tothe region of highest TCE concentration. The two-well recirculation cell was set up as

shown in Figure 1, with an extraction well (EW-1), an injection well (IW-1), and

monitoring wells (MW-1 to MW-5). Three monitoring wells were in line between IW-1and EW-1 and two monitoring wells were offset.

The anaerobic ISB equipment had to satisfy the needs of the system design,

providing operational flexibility, simplicity, and automation. There were three main sub-

systems: the recirculation equipment (both down-hole and aboveground), the nutrientinjection equipment, and the groundwater sampling system. The process control system


3/8

tied together the data collection and automation of operations. Figure 2 depicts the major

equipment for the recirculation and nutrient injection systems.A Process Control Trailer was designed and built for a demonstration of in situ

bioremediation of carbon tetrachloride under denitrifying conditions at the U.S.

Department of Energy's Hanford site in Washington state [Hooker et al., 1998]. The

trailer is a 35 ft (10.6 m) long semi-truck van that is divided into two sections. The frontsection houses a process control system, a sample collection manifold, and laboratory

NutrientInjection

Line

Direction ofRecirculation Flow

Process Control Trailer

IW-1 MW-1 MW-2 MW-3 EW-1

Clay

Sand &Gravel (fill)

Sand

Direction ofGroundwater

Flow

Water Table

SedimentFilter

FlowControlValve

Potentiometric

Surface

10 ft

5 ft

MSL

-5 ft

-10 ft

-15 ft

-20 ft

-25 ftElevation(ftrelativetoMeanSe

aLevel,NGVD)

FIGURE 1. Section view of the Point Mugu demonstration site showing the general

approach for volumetric anaerobic ISB.

Direction ofAboveground Flow

Sediment

Filter(with bypass)

FlowControlValve

FT

DiversionValve

ShutoffValve

FT

StockSolution

Tank

ExtractionWell

(submersible pump)

InjectionWell

(inflatable packer)

Ball Valve

Check Valve

Union

Flow

Sensor(with bypass)

StrainerGearPump

SolenoidValve

FlowSensor

Signals to/fromProcess Control System

Signal to ProcessControl System

FIGURE 2. Schematic drawing showing major equipment for the anaerobic ISB

recirculation and nutrient injection systems. Down-hole equipment is noted in

parentheses by the corresponding well.


4/8

bench space. The back section holds the nutrient injection system, comprised of four

250-gallon (946-liter) polypropylene tanks with stand mixers, 6 gear pumps (two pertank, with one spare tank not used for nutrient injection), plus associated plumbing, all of

which is within an 8-inch (20 cm) deep stainless steel containment pan. The Process

Control Trailer was designed to be a mobile system that could provide the process control

and nutrient pumping flexibility to do everything from pilot-scale ISB demonstrations tofull-scale ISB. The Process Control Trailer was used in just that manner at Point Mugu

to plug into the recirculation system and sampling lines.

Recirculation Equipment. Recirculation equipment consisted of a submersible

centrifugal pump in the extraction well (Grundfos, Olathe, KS), aboveground piping, andinjection well equipment. The aboveground piping was placed in a 0.5 m (1-2 ft) deep

trench that was covered with steel plating to allow for third party vehicle access to the

site while the equipment was operating. The aboveground recirculation plumbingincluded a 5-micron sediment filter (Pall Corp., Timonium, MD) to avoid injecting

sediment into the injection well, a turbine flow sensor/transmitter (Omega Engineering,

Stamford, CT), and inlets for the nutrient injection lines. An inflatable packer (TamInternational, Houston, TX) was placed in the injection well to avoid excess stagnant

water above the well screen and to allow the injection to continue even with pressure build-up. The groundwater recirculation flow rate was adjusted manually with a gate

valve placed downstream of the flow sensor. Bypasses on the flow sensor and sediment

filter provided a means for maintenance while the system continued to operate.

Substrate Injection Equipment. Lactic acid was the nutrient selected to stimulate

anaerobic microbial activity. The lactic acid was stored in a Process Control Trailer tankas an 88-wt% solution to inhibit microbial growth in the tank. Gear pumps (Micropump,

Vancouver, WA) were used with variable speed magnetically coupled pump drives to

deliver lactic acid (or bromide tracer solution) to the recirculating groundwater. Avariety of gear pump capacities are available for mounting on the same drive, providing

flexibility and easy maintenance. The process control computer was used to control

lactic acid injection intervals, duration, and flow rate by manipulating in-line solenoidvalves and the variable speed gear pump drive. The nutrient injection system had

feedback inputs to the process control computer, including line pressure and flow rate.

An in-line check valve at the connection of the nutrient injection lines to the groundwaterrecirculation line provided back-pressure against the static groundwater head and

prevented the lactic acid from draining out of the injection line. The gear pump was

selected to provide the positive pressure necessary to open this check valve. A pressure

relief valve was placed downstream of the gear pump to vent excess pressure back to the bulk storage tank if normal operating pressures were exceeded. A level switch in the

stock solution tank provided a low level alarm as an indication of either a leak into thecontainment pan or siphoning of the feed solution into the well.

Sampling Equipment. Sampling equipment was designed to obtain representativesamples of groundwater for analysis of chloroethenes and anions. Dedicated in-well

Redi-Flo2 pumps (Grundfos, Olathe, KS) were used to pump groundwater to the sample

manifold in the front section of the Process Control Trailer. Groundwater from wellEW-1 was also sampled from a port in the groundwater recirculation piping (upstream


5/8

from the nutrient injection inlets). All sample lines were connected to an automated

sampler for computer-controlled collection of anion samples for specific tests during thedemonstration. Manually collected groundwater samples (i.e., for VOCs) were also

obtained from the sampling manifold, with the process control computer being used to

select which well to pump and to time the well purging.

Process Control and Data Acquisition. Operation of the anaerobic in situ

bioremediation system required process control for unmanned nutrient injection and

sample collection, as well as data acquisition of process measurements. The processcontrol system consisted of an IBM-compatible personal computer running the AIMAX

software (TA Engineering, Moraga, CA) and several I/O Plexers (duTec, Jackson, MI) to

interface with process equipment. The process control system was used to turn on andoff the nutrient injection gear pumps and to adjust the nutrient injection flow rate as

needed. The injection line pressure and injection flow rate were monitored (and

recorded) to determine that (1) the proper amount of nutrient was being delivered to thewell, (2) there was no plugging of the feed lines, and (3) there were no leaks in the feed

lines. The process control software was used to control the autosampler system duringthe intensive sample collection required by in situ tracer tests. The process control

system was used to collect data on groundwater levels and process flowrates. Pressuretransducers were placed in each well to monitor the hydraulic head. Of particular interest

was the injection well pressure, a rise in which could signal well plugging (although such

an increase was not seen during the test). The groundwater recirculation flow rate wasrecorded, as were the times and flow rates for the nutrient injections.

AEROBIC IN SITU BIOREMEDIATION SYSTEM

The aerobic ISB system operated in much the same manner as the anaerobic

system, but with the key differences that the primary nutrients injected were dissolvedgases and that the nutrient injection and groundwater recirculation systems were

integrated into skid-mounted units. The objective was to stimulate methanotrophic

bacteria, which require dissolved methane and oxygen as well as a nitrogen source [Truexet al., 2002] for growth and energy. The in situ bioactive zone also differed in the aerobic

treatment, being a biofilter instead of volumetric treatment. Figure 3 shows a conceptual

diagram of a single aerobic recirculation cell.

The aerobic ISB system was assembled on two 4 ft 8 ft (1.2 m 2.4 m)diamond-tread steel skids with forklift slots for easy transportation and placement.

Equipment on the first skid (#1) consisted of an extraction well mixing manifold, the

power distribution panel, and the process control panel. The second skid (#2) held thesubstrate amendment systems, two 240-gallon (908-liter) steel pressure tanks, one 100-

gallon (378-liter) polypropylene tank, a booster pump, a metering pump, and a sediment

filter. Two skids were used because (1) the skid dimensions allow the use of a standardfull-size truck for transportation and (2) skid #1, containing the power distribution panel

and most of the high power electrical work, could be separated from the oxygen and

methane gas sources used on skid #2. Equipment on skid #2 was either low voltage/low

amps or explosion proof because of the use of gaseous methane and oxygen. Separatingthe two skids made the system cheaper to construct, easier to move, and safer. Figure 4

shows a schematic representation of the aerobic injection system.


6/8

Biofi l ter

In ject ion W el l ( IW )Extract ion Wel l (EW)

Vadose Zone

or

Confining Layer

Biofi l ter

Groundwater

Flow

Recirculated groundwaterRecirculated groundwater

Nutr ient

Amendments

Groundwater

Flow

Plan view with subsurface

groundwater f low l ines

Packer

Pump

Pump

Extract ion W el l (EW )

EW EW

EW

EW

IW

Aquifer

FIGURE 3. Conceptual cross section and plan view of a single recirculation cell for

implementation of an in situ aerobic biofilter. Groundwater is recirculated through

an annular treatment region around the injection well (i.e., the biofilter).

FT

NitrateStockTank

PistonPump

FlowSensor

Signals to ProcessControl System

Direction ofAboveground Flow

FlowControlValveSediment

Filter(with bypass)

TypicalExtraction

Well(submersible pump)

InjectionWell

(inflatable packer)

FT

FlowSensor

FT

FlowSensor

Signalsto/fromProcessControlSystem

FlowControlValve

From otherExtraction

Wells

OxygenEductor

Mixing

Tank

Mixing

Tank

MethaneEductor

BoosterPump

OxygenGas

SupplyFTFlow

Sensor

Rota-meter

Ball Valve

Check Valve

Union

MethaneGas

Supply

FT FlowSensor

Signal to ProcessControl System

Rota-

meter

SolenoidValve

SolenoidValve

In-LineStaticMixer

FIGURE 4. Schematic drawing showing the major aerobic ISB system equipment.

Down-hole equipment is noted in parentheses next to the wells.

Groundwater sampling was not integrated into the aerobic equipment. Samples

were manually collected using a peristaltic pump (or a sample port in the combinedrecirculation stream).

Recirculation and Nutrient Amendment Equipment. Submersible pumps (Grundfos,Olathe, KS) extracted groundwater from (typically) four wells oriented in a 5-spot pattern

(the center well was the injection well). Groundwater was combined at skid #1 wheremanual gate valves were used to set the flow rate of each extraction leg to an equal value.

Readings from pressure gauges and flow sensors were recorded for the extraction legsand the combined stream. The combined stream was sent to skid #2, where nutrients

were added to the groundwater. Two separate eductor systems (Mazzei Injector

Corporation, Bakersfiled, CA) were used in series to transfer the oxygen gas (firsteductor) and methane gas into the groundwater. A 240-gallon (908-liter) mixing tank

downstream of each eductor provided residence time for the entrained gas to dissolve.


7/8

The whole system was operated under a pressure of nominally 40 psi (276 kPa) to

increase the gas solubility. A booster pump was used downstream of the first mixingtank to insure the pressure in the second mixing tank was high enough and to provide

sufficient fluid velocity for proper operation of the eductor. Downstream of the two

eductors, an aqueous solution of nitrate (stored in the 378-liter polypropylene tank) was

amended to the groundwater using a manually set piston-drive metering pump (LiquidMetronics Incorporated (LMI, Milton Roy), Acton, MA) connected to the recirculation

line via a check valve. An in-line static mixer downstream of the nitrate injection insured

complete mixing. A bag filter was used downstream of the in-line mixer to remove anysediment or precipitates that might have formed (i.e., iron oxides) so that material would

not be injected into the injection well. A gate valve at the injection well head was used to

control the injection flow rate.Oxygen and methane gases were introduced into the recirculated groundwater

through an eductor (venturi tube with an inlet at the flow restriction). Five standard

oxygen cylinders (1,685 SCF, 47.7 standard m) were combined through a manifold tosupply sufficient oxygen to the system over a 2-week period. The oxygen line passed

through a normally closed solenoid valve, a rotameter, and a mass flow meter. Themethane assembly was similar except that only one gas cylinder could be used at a time.

The normally closed solenoid valve acted as a safety feature. In the event that the systemlost power or shut down, the valve automatically closed to insure that the system failed

safe. The rotameter was used to control the gas flow rate and the mass flow meter was

used to record the gas flow rate.

Process Control and Data Acquisition. To improve the productivity and safety of

process operations, the aerobic equipment used a process control and data acquisition(SCACA) unit (phonetics, Aston, PA). The SCADA unit had programmable logic

control that allowed it to start automatically with the push of a single button or from aremote computer. The startup routine of the SCADA unit insured the proper order of

equipment operation and would not allow operations if water levels in mixing tanks, flow

rates, or pressures were out of the specified operational limits. To improve reliability ofdata collection and productivity of site personnel, the SCADA unit recorded groundwater

flow rates (each extraction leg and the combined stream), pressure in the mixing tanks,

and mass flow rates of oxygen and methane gas amendment, of the system every 10

minutes while groundwater was recirculating.A common alarm was programmed to trip if certain events occurred, whereupon

the SCADA unit would automatically shut down the groundwater pumps and call project

personnel via fax, pager, or phone. Several conditions could cause the common alarm totrip. Five analog (4-20 mA) flow sensors corresponding to the extraction well legs and

the combined stream of the recirculation system were monitored. An extraction flow rate

less than the set point of 1.5 gpm (5.7 lpm) was programmed to cause system shutdownand notification of project personnel. This alarm condition was designed to detect a

break in an extraction well line or failure of a groundwater pump. The system was also

equipped with four digital pressure switches with a high and low settings and one analog

pressure switch that would shut the system down in the event that the pressure wentbeyond the set point. A low-pressure alarm would indicate a break in the line and a high

pressure would indicate a blockage or closed valve. If the system turned off due to an


8/8

alarm, all pumps would be shut down immediately, and the solenoid valves on oxygen

and methane gas lines would fail closed. After the system shut down, the unit would calland report the cause of the alarm.

CONCLUSIONS

The constructed anaerobic and aerobic equipment systems had sufficientrobustness and flexibility to allow the ISB demonstrations to achieve their goals. As a

result of successful deployment, the mobile skids containing the aerobic ISB equipment

will be used on projects currently being planned by Shaw E & I at Hunters Point Navalshipyard, CA and Treasure Island, CA for the United States Navy. Similarly the Process

Control Trailer will be used on future ISB projects. These new projects will also use

sequential anaerobic/aerobic in situ bioremediation, as site conditions require.

REFERENCES

Granade, S., D.P. Leigh, and C.D. Johnson. 2003. "Chlorinated Solvent Bioremediation:

3 Case Studies." In: Proceedings of the Seventh In situ and On-Site BioremediationSymposium (Orlando, Florida; June 2-5, 2003). Battelle Press, Columbus, OH. In

press.Hooker, B.S., R.S. Skeen, M.J. Truex, C.D. Johnson, B.M. Peyton, and D.B. Anderson.

1998. "In situ Bioremediation of Carbon Tetrachloride: Field Test Results."Bioremediation Journal, 1(3):181-193.

Johnson, C.D., R.S. Skeen, D.P. Leigh, T. P. Clement, and Y. Sun. 1998. "Modeling

Natural Attenuation of Chlorinated Ethenes Using the RT3D Code." In: Proceedings

of the Water Environment Federation 71st

Annual Conference and Exposition,WEFTEC '98, Volume 3. Water Environment Federation, Alexandria, Virginia. pp.

225-247.Johnson, C.D., R.S. Skeen, M.G. Butcher, D.P. Leigh, L.A. Bienkowski, S. Granade, B.

Harre, and T. Margrave. 1999. "Accelerated In situ Bioremediation of Chlorinated

Ethenes in Groundwater with High Sulfate Concentrations." In: Engineered

Approches forIn situ Bioremediation of Chlorinated Solvent Contamination, A.

Leeson and B.C. Alleman (eds.). Battelle Press, Columbus, Ohio. pp. 165-170.

Leigh, D.P., C.D. Johnson, R.S. Skeen, M.G. Butcher, L.A. Bienkowski, and S. Granade.

2000. "Enhanced Anaerobic In situ Bioremediation of Chloroethenes at NAS PointMugu." In: Bioremediation and Phytoremediation of Chlorinated and Recalcitrant

Compounds, G.B. Wickramanayake, A.R. Gavaskar, B.C.Alleman, and V.S. Magar

(eds.). Battelle Press, Columbus, OH. pp. 229-235.Truex, M.J., C.D. Johnson, D.P. Leigh, and S. Granade. 2002. "Pulsed Injection Flow

Strategy for Aerobic Co-Metabolism of Vinyl Chloride." In: Remediation ofChlorinated and Recalcitrant Compounds2002, A.R. Gavaskar and A.S.C. Chen(eds.). Battelle Press, Columbus, OH. Paper number 2B-33.

Documents

A-01 Desclorinacion de Tricloroetano Tpc