 |
NASA/California Institute of Technology Jet Propulsion Laboratory, Packed Bed ReactorPasadena, CASource: Information provided by Naval Facilities Engineering Command (NAVFAC) personnel, November 2000 Project Summary: The following text was excerpted from information provided by Naval Facilities Engineering Command (NAVFAC) personnel, November 2000: An effective, economical treatment technique is needed for groundwater impacted with low levels of ClO4-. Of the available treatment technologies currently considered feasible for groundwater treatment (IE, RO and biotreatment via bioreactors), the PBR may be preferred for the following reasons: It destroys ClO4- rather than concentrating it, as do IE and RO; It is easier to operate than other current biological techniques, and potentially better suited to the lower concentration groundwater application; Conventional equipment can be easily retrofitted for use as PBRs, thereby increasing its implementability. The PBR potentially is an effective and economical method for treating lower concentrations of ClO4- in groundwater. To our knowledge, the PBR has not been tested yet for the ClO4- application in the field. Objectives The primary objective of the proposed study is to demonstrate proof-of-concept for the PBR to treat low concentrations of ClO4- (<1 mg/L) in groundwater at a field scale. In addition, the study will evaluate three different inoculum/electron donor combinations in an effort to identify an efficient, cost-effective technique for obtaining a stable, effective ClO4- reducing system for future applications. This will involve evaluation of PBR performance using three separate PBR columns in parallel, each with a specific inoculum/electron donor combination, which will reflect the inoculum sources discussed above. The columns will be operated simultaneously at flow rates up to approximately 2 gallons per minute (gpm). Specific objectives of the proposed project are as follows: 1. Assess the time needed for each inoculum/electron donor combination to achieve effective colonization. 2. Evaluate achievable effluent ClO4- levels for each inoculum/electron donor combination. 3. Evaluate the residence time for each system versus treatment efficiency. 4. Evaluate population dynamics for each system using polymerase chain reaction (PCR) analysis. 5. Generate preliminary estimate of the footprint required for larger, full-scale systems. 6. Generate preliminary estimate of costs/kgallon of water treated for larger, full-scale systems. It should be emphasized that this field test is primarily to demonstrate proof-of-concept and to evaluate various approaches to biofilm development; the success of the bench-scale may not be achieved at the field-scale. Furthermore, optimal levels of nutrients will not be evaluated in this experiment. Inoculum/Electron Donor Combinations and Reactor Design To address these objectives, three PBR columns will be constructed and operated. A general overview of the reactor design and experimental procedures that will be used to address the objectives is provided in this section. Inocula/electron donor combinations will include: 1. Perc1ase/acetate 2. Food processing waste/ethanol (upon further consultation with US Filter) 3. JPL enrichment cultures/acetate (upon further consultation with Dr. Paul Hatzinger) Extracted groundwater (from MW-7) will be pumped into a holding tank. The water will be pumped out of the holding tank and split into three streams, to which the electron donors (acetate or ethanol) and nutrients (N and P) will be added. Nutrients (approx. 10 mg/L nitrate and 2 mg/L phosphate) will be dosed into flash mixing tanks. From the flash mixing tanks, the groundwater will be pumped into the bioreactor tanks containing Celite, a pelletized diatomaceous earth product, which will serve as a medium for the microorganisms to attach to. The bioreactor tanks will also contain heating elements to heat the groundwater to approximately 25o C. Bioreactor effluents will be combined and will undergo additional treatment to address residual carbon, VOCs, and ClO4- (if any), consisting of aerobic biological treatment, LPGAC treatment, and ion exchange. Final effluent will be held in a 21,000-gallon tank (frac tank) prior to final discharge, pending receipt of analytical results. Test Strategy The major objectives of the proposed study are to demonstrate proof-of-concept for the PBR to treat low concentrations of ClO4- (<1 mg/L) in groundwater at a field scale, and to evaluate three different inoculum/electron donor combinations to identify a cost-effective technique for future applications. Influent and effluent ClO4- concentrations, as well as respective electron donor (as total organic carbon) and NO3- levels will be measured periodically (see Section 4.3.2). As mentioned, electron donors will be maintained at concentrations in excess of what is required (present in effluent), and will not be optimized for this study. Ammonium and phosphate will be added at low concentrations to ensure that they will not be limiting in the reactor, but will not be tracked analytically. Influent and effluent pH and temperature will also be monitored using field instruments. Analytical results will be reported within 2 days following sample submission during the early portion of the test, thus allowing for changes to be made in reactor operating parameters in response to system performance. Laboratory turnaround time may be increased later in the test if deemed appropriate. Testing strategies are summarized below: 1. The time required to achieve effective colonization will be conducted during startup procedures (described below, Section 4.3.1). As noted, ClO4- concentrations in each system will be monitored during startup using a ClO4--specific probe while the reactors are operated in a re-circulation mode. Effective colonization time will be defined as the time required for ClO4- concentrations to drop from 100 mg/L (initially added to the medium) to below 1 mg/L. 2. Achievable effluent ClO4- concentrations, and residence time versus column efficiency, will be established for each column as follows: Determine an initial residence times such that non-detectable effluent ClO4- levels are achieved. This is expected to be approximately 1.5 to 1.0 hours. Incrementally decrease residence times until ClO4- breakthrough is achieved. Increase residence time to prior increment where non-detectable ClO4- levels were observed, to verify results. With respect to this experiment, this will be defined as the optimal residence time for each reactor, and the systems will be operated at this rate for the duration of the experiment. This will provide evidence needed to comparatively evaluate the performance of the systems. 3. Population dynamics will be evaluated using polymerase chain reaction (PCR) analysis. Initial inocula, along with weekly bacterial samples from each column will be analyzed to determine gross shifts in populations over the course of the experiment. It is noted that this analysis does not identify the bacteria present, rather it will provide an indication of whether the populations are changing over time. These analyses will be carried out at the University of California, Riverside. This pilot project is scheduled to begin in January 2001. Additional Info Source: Information provided by Naval Facilities Engineering Command (NAVFAC) personnel, November 2000 |
|
||||
      
|
||||||