PILOT TESTING OF A BIOREACTOR FOR PERCHLORATE- CONTAMINATED GROUNDWATER TREATMENT

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1 Paper 2H-03, in: A.R. Gavaskar and A.S.C. Chen (Eds.), Remediation of Chlorinated and Recalcitrant Compounds Proceedings of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2002). ISBN , published by Battelle Press, Columbus, OH, PILOT TESTING OF A BIOREACTOR FOR PERCHLORATE- CONTAMINATED GROUNDWATER TREATMENT Patrick Evans (evanspj@cdm.com), Allyson Chu, Stephen Liao, and Steven Price (CDM, Bellevue, Washington) Mieko Moody (University of California, Riverside) Doug Headrick City of Redlands, California Booki Min and Bruce Logan (The Pennsylvania State University, University Park, Pennsylvania) ABSTRACT: Groundwater at the Crafton-Redlands site in Redlands, California is contaminated with perchlorate in addition to chlorinated volatile organic compounds (VOCs). VOCs are removed from extracted groundwater using granular activated carbon, which is ineffective for perchlorate removal. Side-by-side pilot-scale bioreactors for perchlorate removal from extracted groundwater were tested at the site. Preliminary results showed that perchlorate was consistently removed from groundwater to concentrations less than 4 µg/l. Removal was dependent on consistent acetate feed, effective backwash strategy, and sufficient hydraulic residence time. INTRODUCTION Recent detection of perchlorate in several surface waters and groundwater wells used to supply drinking water has created an unforeseen water contamination crisis in the western states, and problems are likely to emerge at other sites where perchlorate has been used. It is estimated that as many as 12 million people could be affected by perchlorate contamination of drinking water. In March of 1997, the California Department of Health Services (CDHS) developed a method that reduced the detection limit of perchlorate from 400 µg/l to 4 µg/l. Based on EPA work, the CDHS established an action level of 18 µg/l for drinking water. Subsequent monitoring of 232 groundwater wells by the CDHS indicated perchlorate was present in 69 wells (30%) and at concentrations above the action level in 20 wells (9%) (AWWARF, 1997). In October of 2001, the Texas Natural Resource Conservation Commission (TNRCC) set an interim action level of 4 µg/l indicative of more stringent regulatory requirements for perchlorate treatment. New evidence of adverse health effects of perchlorate at low concentrations has prompted California to lower its action level to 4 g/l as well. Perchlorate contamination arises primarily from the manufacture and disposal of ammonium perchlorate, a highly reduced compound produced for use as the oxidizer in solid rocket propellant. It is highly soluble and not easily removed from water. Conventional water treatment technologies such as air stripping and advanced oxidation processes are ineffective for perchlorate removal or destruction. The costs associated with carbon adsorption and ion exchange processes are very high. While perchlorate may be difficult to chemically treat or physically remove from water, it is very biodegradable. It is known that some microorganisms are able to respire using chlorate (ClO 3 - ) and/or perchlorate (ClO 4 - ): that is, they can use either of these compounds as a terminal electron acceptor in the oxidation of many common substrates

2 such as acetate, simple sugars, and amino acids (Logan, 1998; Herman and Frankenberger, 1998). However, oxygen and nitrate are preferred over perchlorate as terminal electron acceptors and will be microbially reduced before perchlorate is removed (Logan, 2001). Previous work in laboratory columns has shown that perchlorate can be removed in packed columns containing the perchlorate-respiring bacterium KJ (Kim and Logan, 2001). This report describes pilot testing of this technology at the Texas Street Well Facility that formerly supplied drinking water in Redlands, California. Groundwater at this site (the Redlands-Crafton plume) is contaminated with perchlorate and chlorinated VOCs. While the VOCs were successfully removed from groundwater using granular activated carbon, removal of perchlorate was not observed. Detections of perchlorate resulted in the shutdown of the Texas Street Well Facility. METHODS A pilot-scale reactor containing side-by-side plastic- and sand-media modules was constructed at the Texas Street Facility as shown in Figure 1. Also shown in Figure 1 is a close-up of the plastic media in the reactor. The reactors were up-flow packed-bed reactors containing sand or plastic media. The plastic media floated in water and was held down with a perforated plate. The cross-sectional area for flow was 2 ft 2 (0.19 m 2 ) and the reactor height was 7 ft (2.1 m). Groundwater was pumped to an equalization tank and then acetic acid and ammonium phosphate were added to the reactor feed at concentrations of about 50 mg/l and about 4 mg-n/l, respectively. The initial groundwater flow was 1 gpm to each reactor. The reactors were started by bioaugmentation of the columns on May 9, 2001, with perchlorate-respiring strain KJ grown in batch on a mineral salts medium containing acetic acid. The media and microorganisms were recirculated in each reactor for 11 days and then groundwater flow was initiated at 1 gal/min (3.8 L/min) to each reactor on May 20, 2001 (Day 0). Backwashing with an air scour was conducted to remove excess microbial growth and to minimize short-circuiting or flow channeling. This procedure resulted in movement of the sand media but not complete fluidization. The plastic media were held down by the perforated plate and were not fluidized. Perchlorate, acetic acid, nitrate, dissolved oxygen, sulfate, oxidation-reduction potential (ORP), ph, specific conductivity, turbidity, phosphate, ammonia, and backpressure were measured in the reactor influent and effluent. Only perchlorate results are given here as part of this preliminary report. RESULTS AND DISCUSSION Table 1 shows the groundwater composition that was treated by the reactors. The groundwater was saturated with dissolved oxygen and contained 4.3 mg-n/l of nitrate on average. Reduction of dissolved oxygen and nitrate is required prior to use of perchlorate as a terminal electron acceptor. Perchlorate concentrations were about 75 µg/l in the influent, and the treatment goal was 4 µg/l in the reactor effluent.

3 FIGURE 1. Pilot-Scale Reactor and Plastic Media Detail. TABLE 1. Redlands Groundwater Composition. Parameter Value Units Dissolved oxygen 8.9 mg/l Nitrate as nitrogen 4.3 mg-n/l Perchlorate 75 µg/l Sulfate 33 mg/l ph Trichloroethene 4 µg/l 1,1-Dichloroethene 1 µg/l Figure 2 shows influent and effluent perchlorate concentrations in the plastic media reactor during operation at 1 gal/min (3.8 L/min) through Day 32 and then at 2 gal/min (7.6 L/min) through Day 102. Effluent perchlorate concentrations exceeded 4 µg/l frequently through Day 102. Several reasons attributed to inconsistent removal. The first one to two months of poor performance was attributable in part to startup and the time required to develop an active biofilm on the plastic media. In addition, the backwash strategy needed to be developed to obtain consistent removal. Backpressures up to 200 in H 2 O (50 kpa) were routinely observed and led to channeling. Such high backpressures would also be uneconomical for a full-scale system. A weekly backwash strategy was instated to

4 120 Perchlorate Conc. (µg/l) Elapsed time (d) Influent Effluent FIGURE 2. Plastic Media Bioreactor Startup. eliminate this problem. Backpressures after Day 59 were maintained less at than 100 in H 2 O (25 kpa). The data from Days 65 to 95 demonstrated an average perchlorate effluent concentration of 4.8 µg/l. While close to the 4 µg/l goal, one effluent concentration was 12 µg/l. Thus, a flow rate of 2 gal/min (7.6 L/min) did not result in consistent attainment of the 4 µg/l goal. The sand media reactor was more severely affected by backpressure and channeling problems and demonstrated worse performance during this period. On Day 99 the flow rates to both reactors were reduced to 1 gal/min (3.8 L/min). Figure 3 shows that starting on Day 106 consistent removal to less than the 4-µg/L detection limit was observed in the plastic media reactor. Similar results were observed in the sand media reactor. The effluent concentration in both reactors exceeded 4 µg/l once on Day 128 due to cessation of acetic acid feed. Upon reinstatement of the feed, removal to less than 4 µg/l was reinstated in both reactors indicating the importance of dependable acetate feed and that reactor was capable of quick recovery following a process upset. CONCLUSIONS Pilot testing anaerobic biological perchlorate removal from groundwater demonstrated that packed bed reactors can successfully attain effluent concentrations less than 4 µg/l. Consistent operation is dependent on adequate hydraulic residence time, uninterrupted acetate feed, and effective backwash strategy to prevent channeling. Plastic media is preferred over sand media because it is less prone to channeling and development of high backpressure. Hydraulic residence time is dependent primarily on dissolved oxygen and nitrate concentrations because they are reduced prior to perchlorate being used as a terminal electron acceptor. Consideration of these factors has led to the conclusion that this technology is a cost-effective method of treating groundwater.

5 Perchlorate Conc. (µg/l) Elapsed time (d) Influent Effluent FIGURE 3. Plastic Media Bioreactor Perchlorate Removal. ACKNOWLEDGMENTS Funding from AWWARF through an EPA grant is gratefully acknowledged. REFERENCES American Water Works Association Research Foundation (AWWARF) Final report of the perchlorate research issue group workshop, September 30 to October 2. For more information, contact Frank Blaha, AWWA, Denver, CO. Herman D.C. and Frankenberger W.T Microbial-mediated reduction of perchlorate in groundwater. J. Environ. Qual. 27: Kim, K. and B.E. Logan Microbial reduction of perchlorate in pure and mixed culture packed-bed bioreactors. Wat. Res. 35(13): Logan, B.E A review of chlorate and perchlorate respiring microorganisms. Bioremediation J. 2(2): Logan, B.E Assessing the outlook for perchlorate remediation. Environ. Sci. Technol. 35(23):482A-487A.