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http://www.perchlorateinfo.com/perchlorate-overview.html NASA/California Institute of Technology Jet Propulsion Laboratory, Anoxic FBR
Pasadena, CA
Source:
Executive Summary of report provided by Naval Facilities Engineering Command (NAVFAC) personnel, November 2000
Project Summary:
The following text was excerpted from Executive Summary of report provided by Naval Facilities Engineering Command (NAVFAC) personnel, November 2000:
The National Aeronautics and Space Administration (NASA), the Naval Facilities Engineering Command (NAVFAC), and the Naval Facilities Engineering Service Center (NFESC) are conducting a test of a Fluidized Bed Bioreactor to destroy perchlorate in groundwater at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The system is being tested for its ability to achieve non-detectable levels of perchlorate in the effluent assuming an influent concentration between 350 and 740 ug/l. Groundwater will be extracted at a flow rate of 5-6 gpm from JPL Monitoring Well #7 and fed through the FBR system described below.
Fluidized Bed Technology
The Fluidized Bed Reactor (FBR) is a fixed-film reactor column that fosters the growth of microorganisms on a hydraulically fluidized bed of media (activated carbon). The activated carbon media is selected for greatest assurance of producing a low-concentration effluent, i.e., part-per-billion (ppb) levels of contaminants of concern (COCs). The fluidized media provides an extremely large surface area on which a film of microorganisms can grow and produce a large inventory of biomass in a small reactor volume. The result of this biological growth is a system capable of high degradative performance for target contaminants in a relatively small and economical reactor volume. The activated carbon can also adsorb the organics in the groundwater. This leads to secondary removal of degradable organics. The FBR perchlorate destruction system is capable of reducing perchlorate concentrations to less than 4 ?g/L, the current analytical reporting detection limit. These levels are reached at ambient water temperatures.
The biological process inside the FBR completely destroys the perchlorate molecule. The products of the biochemical reaction are chloride ions and oxygen. Perchlorate is not transferred from one medium to another for subsequent treatment and/or disposal. The process also destroys nitrate, often necessary if considering reinjection of the groundwater. The only waste byproduct generated from the biodegradation of perchlorate and nitrate is a small volume of excess biosolids. These solids are removed from the system on a continuous basis. They are nonhazardous and can be disposed in a number of cost-effective manners.
The FBR is simple in design, containing a provision for distribution of the influent liquid flow and a component to control the expansion of the fluidized bed when necessary. When biological growth occurs on the fluid bed media particles, their diameter increases and their effective density is reduced, resulting in a bed expansion beyond that experienced with unseeded media. Under conditions resulting in extensive biofilm growth, it may be necessary to control the biofilm thickness to prevent the density of the biofilm-covered media from decreasing to the point where bed carryover occurs.
Treatment System Components
The basic components of an FBR system for treatment of nitrate and perchlorate include the bioreactor, granular activated carbon (GAC) bed media, a fluid distribution system in the bottom of the reactor, feed and influent pumps, a nutrient addition system, a pH control mechanism and a bed height control component when required. The complete treatment system at JPL also contains four GAC canisters for treating chlorinated volatile organic carbons (VOCs) and a supplemental Ion Exchange (IX) unit for removal of any perchlorate or nitrate not removed by the FBR.
Influent groundwater feed is combined with the effluent recycle from the FBR and pumped into the bottom of the FBR through the distribution system, fluidizing the media contained in the reactor. Nitrogen and Phosphorous (in the form of dibasic ammonium phosphate and urea) and ethanol are pumped continually into the reactor flow representing respectively a nutrient to support biomass growth and a carbon source to promote nitrate-N and perchlorate reduction in the FBR. Because biological nitrate-N reduction (denitrification) produces hydroxyl ions tending to raise the pH in the FBR if not neutralized, acid is metered into the reactor flow to maintain the pH in the FBR below 8 as necessary.
From the FBR, treated groundwater is passed through two sets of parallel configured GAC beds to remove any remaining chlorinated VOCs. The groundwater then passes through two ion exchange (IX) beds to remove any perchlorate not destroyed during the pilot test. This extra IX process would not be necessary on a full-scale FBR system, and is only added here to protect from discharge of perchlorate during system modifications and testing.
Process Microbiology
Biological treatment of perchlorate is a relatively new, but field-proven technology. Full-scale (4,000 gpm) and pilot-scale (5-20 gpm) systems are currently in service using biological means to reduce perchlorate. The process can be viewed as similar to nitrate reduction (denitrification) where in the absence of oxygen, the nitrate anion serves as the terminal electron acceptor for microbial metabolic activity. The microorganisms in these systems are facultative aerobes, meaning they require oxygen or a suitable substitute (i.e., nitrate or perchlorate) for normal activities. Aerobic operation without oxygen addition is termed anoxic. For perchlorate removal, the dissolved oxygen and nitrate anions have to be removed before perchlorate can be completely removed. There is evidence that perchlorate reduction can occur simultaneously with nitrate reduction, but to achieve high perchlorate removal efficiencies (i.e., effluent concentrations below 4 ppb), all the nitrate needs to be reduced before the perchlorate. The same carbon source (electron donor) can be used to remove dissolved oxygen, reduce nitrate, and reduce perchlorate. A sufficient quantity of these electron donors has to be provided to effect these biochemical reactions.
Several microbial strains have been isolated with the ability to degrade perchlorate using the anion as a terminal electron acceptor. Many of these strains also reduce nitrate, and it is thought that the same enzyme system may be employed for either reduction. The enzymatic pathways involved in perchlorate reduction have yet to be fully elucidated. However, it has been suggested that a perchlorate reductase catalyses an initial two-step reduction of perchlorate (ClO4-) to chlorate (ClO3-) and then chlorite (ClO2-). The chlorite is further reduced by chlorite dismutase to chloride (Cl-) and oxygen (O2). Thus, microbial degradation of perchlorate yields two innocuous products, chloride and oxygen.
The reduction of perchlorate to chloride is a very favorable process from a thermodynamic perspective. In fact, based on its reduction potential (E0 = 1.287 V), perchlorate may yield more energy to a microorganism during reduction than even oxygen (E0 = 1.229 V). This means bacteria capable of using perchlorate are likely to have a distinct ecological advantage in contaminated environments. All of the energy from perchlorate reduction appears to come from the perchlorate to chlorite reaction. The reduction of chlorite while yielding little energy is necessary because it removes a toxicant for the microbes. Without microorganisms that can remove chlorite, the FBR system will have great difficulty in maintaining sustainable operation. For this reason, it is important to use the appropriate seed material when initiating FBR operation.
If necessary, treatment of perchlorate in the groundwater will also be performed using established ion exchange technology. The strong base anion resin to be used for this process is capable of removing perchlorate to below currently accepted detection limits of 4 ppb. Laboratory testing on a number of contaminated waters has demonstrated the versatility of ion exchange to remove both high and low levels of perchlorate from waters of varying dissolved mineral content. The perchlorate ion, having a high affinity for the selected resin, is preferentially exchanged over the other ions in solution. The resin will quickly equilibrate with the influent, such that the effluent from the ion exchange unit will be the same in composition as the influent, with the exception that the treated water is now free of perchlorate. Perchlorate loaded resin has been tested by an independent laboratory and has been found to not be a hazardous material in accordance with a specific DOT required test. This resin will be transported to an approved facility for final destruction.
Pilot Demonstration Objectives
Demonstrate the effectiveness of the fluidized bed reactor (FBR). Demonstrate that the FBR technology can reliably treat perchlorate-contaminated water to <4 ug/l. Develop full-scale design parameters. Demonstrate the robustness/reliability and operations simplicity of the design.
The pilot FBR is an actual commercial size unit currently in operation at many facilities. These units use fullscale control strategies, and are designed for around the clock operation. No scale up factor is required in moving to a full-scale treatment system. In contrast, the bench-scale FBR is used primarily to indicate if biological treatment of a waste stream is feasible. It is not equipped with the process controls of pilot/full-scale systems that preclude much of the operator attention that may create delays during a laboratory study. The laboratory bench-scale study results did indicate that the perchlorate could be successfully reduced biologically. However, the bench-scale system does not demonstrate the robust nature of an actual commercial system.
System Components
Cartridge Filter
The pilot system includes one in-line cartridge filter. The cartridge filter is a USFilter model FCROF4005 filter and is located downstream of the FBR and upstream of the FBR ion exchange polishers. The filter housing is 6" diameter x 40" high and is constructed of 304 stainless steel. The filter media is Rogard Type 2 media density polypropylene, 5 micron.
Fluidized Bed Reactor (FBR)
The pilot FBR is self-contained and includes a reactor 20" diameter by 15' tall, growth control system, media separation system, fluidization system (including fluidization pump), and granular activated carbon as the growth media.
Ion Exchange Unit (IX)
The pilot system includes one Anion Ion Exchange system. The system is located downstream of the GAC beds (below). The ion exchange system includes two vessels arranged in a lead-lag configuration. The vessels are USFilter model ZWDJOP-2598 vessels constructed of fiberglass reinforced plastic (FBR). Each vessel is designed to contain 2 cubic feet of resin. The resin used for this pilot program is anionic, Type II strong base resin. Each ion exchange vessel is 10" diameter and 58" high and weighs 165 lbs (vessel, water, & resin).
Chemical Feed Systems
Ethanol Feed System
Denatured ethanol is stored in 55 gallon drums with drum containment. The drum is vented to the atmosphere. The ethanol is fed to the FBR influent with an explosion proof diaphragm metering pump. A fire extinguisher will be included with the ethanol feed system.
Nutrient Feed System
Nutrients are made up of a mix of dibasic ammonium phosphate and urea. They are fed to the FBR influent via a 6 gpd diaphragm metering pump. Nutrients are mixed in a 25 gallon plastic tank.
pH adjustment system (if required)
In the event that pH adjustment is required, a 6 gpd diaphragm metering pump and a 25 gallon plastic tank are included.
Storage Tanks
One 300-gallon plastic tank is located downstream of the FBR for post aeration.
GAC Adsorption
The pilot system contains four USFilter/Westates ASC-200-2-CC-601 carbon adsorbers to remove chlorinated organics. These systems are located following the post-aeration tank after the FBR. The vessels contain a 12x30 virgin coconut shell carbon.
This pilot project is scheduled for completion in December 2000, and a report is to be issued on the project during the first quarter of 2001.
Additional Info Source:
Executive Summary of report provided by Naval Facilities Engineering Command (NAVFAC) personnel, November 2000
Guarini, B., 2000. "Biological Treatment of Groundwater Containing Perchlorate Using Fluidized Bed Reactors" in Perchlorate Treatment Technology Workshop, 5th Annual Joint Services Pollution Prevention & Hazardous Waste Management Conference & Exhibition, August 21-24, 2000, Henry B. Gonzalez Convention Center, San Antonio, Texas.