The primary goal of this research is to conduct a long-term field test of a prototype Surfactant-Modified Zeolite/Vapor-Phase Bioreactor (SMZ/VPB) treatment system for removing dissolved organics from produced water prior to demineralization to yield water that can be used by utilities or other industrial users.

Department of Civil, Architectural, & Environmental Engineering, University of Texas at Austin, Austin, TX 
Department of Earth & Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 
Los Alamos National Laboratory, Los Alamos, NM

Results 
The major achievement of this project has been the development of an integrated treatment system for produced water that can remove dissolved organics to levels that would make downstream reverse osmosis treatment cost-effective and allow for a range of water reuse applications. A treatment system consisting of a SMZ column coupled with a VPB can be used to remove the BTEX constituents from produced water. A field test of this coupled system performed well over repeated feed and regeneration cycles demonstrating the viability of the process for BTEX removal. Regeneration of the SMZ using air sparging was found to be sufficient in the field to maintain the SMZ adsorption capacity and to allow continuous operation of the system. As expected, the BTEX concentrations in the regeneration off gas streams were initially very high in a given regeneration cycle. However, a GAC-fixed bed adsorption column placed upstream of the VPB reduced the peak BTEX concentrations to acceptable levels for the VPB. Compared to the effective removal of BTEX in the SMZ/VPB system, the organic acids or carboxylates present in the produced water were not effectively removed; therefore, an additional biological treatment system was added to achieve additional organic acid removal. The need for this process would depend on the desired reuse application.

The combined process consists of three major components: surfactant modified zeolite (SMZ) adsorption, vapor phase bioreactor (VPB) off-gas treatment system, and a membrane bioreactor (MBR). The specific results for the performance of each of these components and the overall project include the following:

• Analysis of pilot data indicates that most of the TPHs (total petroleum hydrocarbons) in the influent produced water were removed in the SMZ column, as were most of the volatile organic compounds (VOCs) present in the produced water.
• The response of the SMZ/VPB system to varying water flow rates and air-stripping regeneration cycles was evaluated in laboratory and pilot-scale tests of the system.
• SMZ regeneration using air sparging was found to be sufficient to maintain the SMZ adsorption capacity and to allow continuous operation of the system.
• Repeated feed and regeneration cycles during the pilot test demonstrated the viability of the process for longer-term operation.
• VPBs packed with polyurethane foam can achieve high BTEX removal efficiencies when provided a steady VOC feed and an adequate nutrient supply. However, frequent nutrient additions are required to maintain performance – a fact that would be cumbersome at some field applications where minimal operating support is provided.
• VPBs packed with compost-based materials are also capable of achieving high BTEX removal efficiencies. In laboratory studies, mixing of a concentrated nutrient solution during biofilter start up ensured high removals of BTEX for extended periods without external nutrient addition.
• Both foam and compost-packed biofilters can recover rapidly from short-term shutdowns indicating that these systems are resilient to the short-term, discontinuous feed conditions that are common in field applications. Both biofilters show improved performance after repeated one-day shutdowns, suggesting that the biomass can acclimate to repeated short-term shutdowns. As the shutdown period increases to 2.8 days, however, the negative impact on VOC removal efficiencies following resumption of the VOC feed is more significant.
• Biofilters have a limited capacity to handle sudden variations in inlet VOC concentration as would be expected during the regeneration of a SMZ column treating produced water. For instance, the removal of BTEX in the compost-based biofilter decreased from 95% to 75% when the biofilter was subjected to repeated adsorption/air regenerations in inlet BTEX concentration. These results suggest that if a biofilter must handle sudden increases in inlet VOC concentration, a supplementary, load equalization system will be necessary to attenuate the VOC concentrations entering the VPB.
• A short, fixed bed adsorption column containing GAC can be used to attenuate and smooth the gas-phase VOC concentrations entering a downstream biofilter. The fixed bed adsorption system can be operated in a passive mode such that VOCs adsorb to the GAC during periods of high inlet concentration, and desorb VOCs during periods of low inlet concentration. At low-RH conditions (below 10%), inlet toluene concentrations as high as 1000 ppmv can be reduced by 97% in a GAC bed operated at a one second-EBCT. However, the buffering capacity of the GAC will diminish after repeated adsorption/air regeneration cycles if the sorbed VOCs are not regenerated completely in a given regeneration period.
• The regenerated gas stream from an SMZ column is saturated with water which can diminish the adsorption capacity of a fixed bed adsorption system containing GAC. Using single-adsorption equilibrium parameters and short bed adsorber (SBA)-determined kinetic parameters, the Homogeneous Surfaced Diffusion Model (HSDM) was used to predict the adsorption of VOC mixtures under high relative humidity conditions. The film diffusion coefficients determined in SBA experiments were more consistent with those predicted using a gas phase film transfer correlation whereas the experimentally determined surface diffusion coefficients were more consistent with aqueous surface diffusion estimates. Competitive adsorption of benzene and toluene was predicted very well by ideal adsorbed solution theory (IAST). The calibrated HSDM predicted bi-solute column data under continuous and variable loading conditions.
• A submerged MBR system simultaneously biodegraded the organic acid/carboxylates and BTEX constituents present in saline produced water. An aerobic, submerged MBR operated at a 9.6-hr residence time achieved 92% removal of acetate and malonate from synthetic produced water containing 10 g/L TDS. When BTEX was simultaneously supplied to the MBR in the gaseous phase, approximately 80% of the BTEX was biodegraded and when the BTEX was introduced in the aqueous phase, approximately 95% was biodegraded.
• Fouling of an MBR membrane by inorganic precipitates is a significant problem that leads to high trans-membrane pressure and ultimately reduced flux across the membrane. For the synthetic produced water investigated in this research, decreasing the pH of the solution crossing the membrane was effective at reducing the trans-membrane pressure.
• A coupled SMZ/MBR system can be used to simultaneously remove the carboxylate and BTEX constituents present in produced water under field conditions. Acetate (the predominant organic anion detected in the produced water at the field site in New Mexico) was not removed in the SMZ column; however it was removed to below detection limits in the MBR. The SMZ column removed most of the BTEX constituents in the produced water during the field trial; however, approximately 95% of the BTEX that penetrated the SMZ and entered the MBR was biodegraded in the MBR. Prediction of effluent benzene concentrations using lab-determined kinetic coefficients were reasonable, and suggest that the removal of benzene from produced water in the MBR is primarily controlled by biodegradation. Overall, the combined SMZ/MBR system achieved TOC removal efficiencies ranging from approximately 75 to 90%.
• An engineering cost study was performed to compare costs of current oil and gas water disposal practices versus the cost of treatment with the SMZ-VPB system along with reverse osmosis (installed and annualized costs). Treatment and disposal of co-produced water have a direct impact on the profitability of O&G production. The disposal cost for a barrel (40 gal) of water is between $1.76 and $4.91 (2006 prices). Treatment using the SMZ/VPB system with RO has a lower cost at higher flow rate. At 6 gpm, the total per barrel cost varies from $0.16 to $0.19, and at 40 gpm, from $0.13 to $0.14. Even when the cost of disposing of residual reject water from the RO system is included, this is competitive.

Benefits 
The increasing need for broader areas of beneficial reuse of produced water and other lower-quality waters has become apparent, given water supply and cost issues. As water becomes scarce in many regions of the country, particularly the arid western states, the valuation of water resources is expected to increase. Beneficial reuse of water normally not considered to be usable, such as produced water, is expected to increase proportionally. The results of this laboratory and pilot-scale program suggest that the SMZ/VPB system may contribute significantly to this trend. The most recent results from the prototype organic acid treatment system suggest that the effluent water quality is suitable for downstream treatment using reverse osmosis. This would allow for a greater range of reuse options for the produced water.

Coproduced water from the oil and gas industry is, by some estimates, one of the largest single waste streams in the United States. Over the past 5 years researchers involved with this project have been working under previous DOE contracts to develop a technology for treating produced water.

The process consists of an SMZ system developed under DOE Contract No. DE-AC26-99BC15221, Treatment of Produced Oil and Gas Waters with a Surfactant-Modified Zeolite, combined with a VPB developed under DOE Contract No. DE-FC26-02NT15461, Treatment of Produced Waters using a Surfactant Modified Zeolite/Vapor Phase Bioreactor.

Summary 
The process involves use of SMZ and biodegradation to remove BTEX and other organic contaminants. SMZ is an innovative filtration/sorption medium that can be produced cost-effectively using naturally occurring zeolites and commercially available surfactant. Researchers have demonstrated the potential of SMZ for BTEX removal at laboratory and pilot scale. They also have demonstrated the potential for VPB treatment of off-gas from the SMZ regeneration process. In addition, the researchers have demonstrated the potential for biodegradation of BTEX and organic acids in produced water via a membrane bioreactor system.

Researchers determined that SMZ could remove BTEX from produced water and be regenerated over numerous cycles without loss of BTEX capacity. They developed a VPB system that can treat the vapor-phase BTEX released during regeneration of the SMZ. The VPB system was tested for its ability to withstand spikes in influent concentration and periodic shutdowns. The system was found to be resilient to spikes; however, a small passive GAC column was found to be beneficial for attenuating spikes if necessary. The recovery time after periodic shutdowns was dependent on the length and frequency of the shutdown. The VPB acclimated to the frequent shutdowns, and the performance of the system was maintained. Laboratory studies also verified that a membrane bioreactor could be used to remove both BTEX and organic acid/carboxylates from a synthetic produced water under conditions representative of field conditions.

Two pilot-scale studies of the SMZ/VPB system have been completed at a facility in Farmington, NM, to assess the potential of this technology under field conditions. The facility is a produced-water disposal facility. The infrastructure was established for evaluation of the SMZ/VPB/MBR system: a building to house the system, onsite laboratory facilities, and an 8,800-gallon produced-water storage tank and associated piping. Data collected during the pilot-scale studies included influent and effluent water compositions, water and gas flow rates, SMZ adsorption and regeneration capacity, gas-phase VOC concentrations, BTEX removal in the VPB, as well as BTEX and organic acid/carboxyalte removal from a membrane bioreactor. Data from the pilot-scale study indicate that the combined SMZ/VPB/MBR system is capable of removing organic constituents from produced water and providing an effluent quality suitable for downstream reverse osmosis treatment.

(December 2008) 
All project activities have been completed. The final report is listed below under "Additional Information".

Critical evaluation of the pilot-scale data indicates that several design modifications to the field-scale improved performance of the system. These design changes included modifying the hydraulics of the SMZ columns and incorporating the MBR technology into the process scheme to optimize the system for subsequent reverse osmosis treatment. The results of the laboratory and field trials suggest that BTEX and organic acids can be removed from the process. Researchers are in the process of applying for a patent application for the combined process. We are currently completing the final report and have applied for a patent for the technology. The final report will include the following details:

• Phase 1: Detailed technical summary of the design phase and the preliminary testing results.
• Phase 2: A section summarizing the treatment process, problems, and system adjustments or changes. This report shall include all results of the field testing of the SMZ/Bio system. A detailed discussion of production facilities, operation, and produced water composition will be included.
• Phase 3: This section will contain details on the cost analysis and feasibility study for the SMZ/Bio system for produced water treatment. Regulatory hurdles to deploying the technology, and costs associated with obtaining regulatory approvals, shall be included in the feasibility analysis.

SMZ columns treating produced water at the McGrath salt water disposal facilities.

Funding
This project was selected in response to DOE Solicitation DE-PS26-04NT15460-02, Focused Research in Federal Lands Access and Produced-Water Management in Oil and Gas Exploration and Production.

$823,970

$243,536 (20% of total)

Other Government Organizations Involved: Los Alamos National Laboratory

NETL - Jesse Garcia (Jesse.Garcia@netl.doe.gov or 918-699-2036)
UT - Lynn Katz (lynnkatz@mail.utexas.edu or 512/ 471-4244)

Final Project Report [PDF]

Publications 
Altare, C., Bowman, R.S., Sullivan, E.J., Katz, L.E., and Kinney, K.A., “Removal of Organic Contaminants from Produced Water Using a Surfactant-Modified Zeolite System,” presentation (abstract only) at the Geological Society of America Annual Meeting & Exposition, Salt Lake City, UT, October 16-19, 2005.

Darby, E.B., Katz, L.E., Kinney, K.A., Bowman, R.S., and Sullivan, E.J., “New Opportunities for Re-use of Produced Water—Water Quality and Permitting Issues,” presentation (abstract only) at the Geological Society of America Annual Meeting & Exposition, Salt Lake City, UT, October 16-19, 2005.

Darby, E.B., “Engineering and Economic Assessment of a Surfactant Modified Zeolite/Vapor Phase Biofilter Process for Treatment of Produced Water,” Masters of Science & Engineering Report, Civil, Architectural & Environmental Engineering Department, University of Texas at Austin, TX, May 2006.

Noris, F. and Kinney, K.A., “Investigation of Bioaerosol Emissions of Bacteria and Fungi from Vapor Phase Biofilters,” Q-386, abstract only, Abstracts from the 106th General Meeting of the American Society for Microbiology, Florida, May 2006.

Altare, C., Bowman, R.S., Sullivan, E.J., Katz, L.E., and Kinney, K.A., “Application of Surfactant-Modified Zeolite for Oilfield Produced-Water Treatment: Examining Regeneration and Long-Term Stability,” poster presentation at the 7th International Conference on the Occurrence and Utilization of Natural Zeolites, Socorro, NM, July 6-9, 2006.

Sullivan, E.J. L. Katz, K. Kinney, S. Kwon, L.J. Chen, E. Darby, R. Bowman, and C. Altare, “Pilot-scale test of a produced-water treatment system for organic compounds,” 14th International Petroleum Environmental Conference, October 17-20, 2006, San Antonio, TX.

Darby, E.B., L. Katz, K. Kinney, R. Bowman, and E. Sullivan, “Assessment of a surfactant-modified zeolite/vapor phase biofilter process for treating produced water,” In Proc. Texas Section American Society of Civil Engineers, October 11-14, 2006, San Antonio, TX.

Bowman, R.S., E.J. Sullivan, L.E. Katz, and K.A. Kinney, “Treatment of oilfield wastewaters with surfactant-modified zeolite,” accepted for the 15th International Zeolite Conference, August 12-17, 2007, Beijing, China.

Altare, C., C., Bowman, R.S., Katz, L.E., Kinney, K.A. and Sullivan, E.J., “Regeneration and Long-Term Stability of Surfactant-Modified Zeolite for Removal of Volatile Organic Compound from Produced Water,” submitted to Microporous & Mesoporous Materials.