EPA United States Environmental Protection Agency Office of EPA #540/R-00/501 a Research and Development May 2000 Cincinnati, OH 45268 SITE Technology Capsule Pintail Systems Inc.'s Aqueous Biocyanide Process Introduction In 1980 the Congress passed the Comprehensive Environ- mental Response, Compensation, and Liability Act (CERCLA), also known as Superfund, committed to pro- tecting human health and the environment from uncontrolled hazardous waste sites. CERCLA was amended by the Superfund Amendments and Reauthorization Act (SARA) in 1986. These amendments emphasize the long term ef- fectiveness and permanence of remedies at Superfund sites. SARA mandates implementing permanent solutions and using alternate treatment technologies or resource recov- ery technologies, to the maximum extent possible, to clean up hazardous waste sites. State and Federal agencies, as well as private parties, are now exploring a growing number of innovative technolo- gies fortreating hazardous waste. The sites on the National Priorities List total more than 1,200 and comprise a broad spectrum of physical, chemical, and environmental condi- tions requiring varying types of remediation. The U.S Envi- ronmental Protection Agency (EPA) has focused on policy, technical, and informational issues related to exploring and applying new remediation technologies applicable to Superfund sites. One such initiative is EPA's Superfund In- novative Technology Evaluation (SITE) Program, which was established to accelerate development, demonstration, and use of innovative technologies for site cleanups. EPA SITE Technology Capsules summarize the latest information available on selected innovative treatment and site remediation technologies and related issues. These cap- sules are designed to help EPA remedial project managers, EPA on-scene coordinators, contractors, and other site cleanup managers understand the type of data and site char- acteristics needed to effectively evaluate a technology's ap- plicability for cleaning up Superfund sites. This capsule provides information on Pintail Systems, Inc.'s Aqueous Biocyanide Process, a bioremediation technology designed to treat aqueous process and waste solutions con- taminated with cyanide and heavy metals. Applicable ma- trices include mine process solutions, mine drainage, tail- ings effluent, groundwater, and industrial process effluents. The technology consists of a proprietary biological culture of microorganisms, immobilized on a porous ceramic filtra- tion media as an attached growth biofilm for aqueous treat- ment. Pintail Systems, Inc. has developed a companion technology for the in situ treatment of cyanide and heavy metals in ores, tailings, soils and sediments. A field treatability study was performed on a cyanide and metal contaminated "pregnant solution" from a gold mine heap leach at the Echo Bay/McCoy Cove Mine Site, in Ne- vada. Information in this capsule emphasizes specific site characteristics and results of the treatability test. The cap- sule presents the following information: Abstract Technology description Technology applicability Technology limitations Process Residuals Site requirements Performance data Technology status Sources of additional information ------- Abstract A two and one-half month field treatability study of an inno- vative biological treatment technology for the destruction of cyanide and immobilization of metals from an aqueous mine process stream was held at the Echo Bay/McCoy Cove mine site near Battle Mountain, Nevada. The Aqueous Biocyanide Process, developed and operated by Pintail Systems, Inc. of Aurora, Colorado, biologically detoxifies cyanide and removes heavy metals from contami- nated waste streams. The field treatability study was jointly sponsored by the Mine Waste Technology Program (MWTP), Activity III, Project 5, Biocyanide, and the Superfund Inno- vative Technology Evaluation (SITE) Demonstration Pro- gram. The primary objective for the field treatability study was to determine the effectiveness of the bioremediation process in degrading Weak Acid Dissociable (WAD) cyanide from a metal laden, high cyanide "pregnant solution." The preg- nant solution is the effluent form the heap leach process containing the extracted metals. The secondary objective of the study was to determine the ability of Pintail's process to remove and immobilize heavy metals from the pregnant solution. Pintail Systems, Inc.'s Aqueous Biocyanide Process uti- lizes a specially selected and augmented consortium of mi- croorganisms immobilized on a fixed media isolite. The isolite is loaded into bioreactors which can be controlled to provide specific environments for microbial degradation and immobilization pathways. For this study, an aerobic bioreactor was used in conjunction with an anaerobic bioreactorto provide the desired degradation and metal im- mobilization properties. The field treatability study was conducted between June 11, 1997 andAugust 26,1997. During this time, the period be- tween June 11 to July 22 was devoted to customizing and optimizing the system to the site-specific waste characteris- tics. Once optimized, continuous testing was performed from July 23 and August 26. Results from the study are summarized below: . The average % WAD CN reduction attributable to the Biocyanide process was 89.3 during the period from July 23 to August 26. The mean concentration of the feed over this period was 233 ppm, while the treated effluent from the bioreactors was 25 ppm. A control train, used to detect abiotic loss of cyanide, revealed no destruction of cyanide (average control effluent = 242 ppm). . Metals that were monitored as part of this study were As, Cd, Co, Cu, Fe, Mn, Hg, Ni, Se, Ag, and Zn. Sig- nificant reductions were noted for all metals except Fe and Mn. Average reduction in metals concentration after July 23 for all other metals were 92.7% for As, 91.6% for Cd, 61.6% for Co, 81.4% for Cu, 95.6% for Hg, 65.0% for Ni, 76.3% for Se, 94.6% for Ag, and 94.6% forZn. Reductions for As, Cd, Co, and Se are probably greaterthan calculated due to non-detect lev- els in some effluent samples. A biomineralization mechanism is proposed forthe removal of metals from solution. Biomineralization is a process in which mi- crobes mediate biochemical reactions forming novel mineral assemblages on solid matrices. . The Aqueous Biocyanide Process was operated for two and one-half months. During the first 42 days (June 11 to July 22) system performance was variable, and occasional downtimes were encountered. This was due to greatly higher cyanide and metals concentra- tion in the feed than was encountered during bench- scale and design phases of the project. Once opti- mized forthe more concentrated feed, the system per- formed well with continuous operation for 35 days (July 23 to August 26). The ability to "re-engineer" the sys- tem in the field to accommodate the new waste stream is a positive attribute of the system. Technology Description The Pintail Aqueous Biocyanide Process is a bioremediation technology forthe treatment of cyanide and metals in pro- cess and waste water streams. The technology utilizes a proprietary method for identifying, isolating, and growing a specialized consortium of microorganisms designed to treat the specific contaminants and characteristics of the aque- ous stream. Pintail uses microorganisms isolated from the environment of the aqueous stream and, if necessary, can augment the culture with microorganisms from their collec- tion of microorganisms. The microorganisms in Pintail's collection were recovered from a wide variety of extreme environments and were isolated and adapted to treat spe- cific contaminants. The optimized microbial consortium is then immobilized on a porous ceramic filtration media as an attached growth biofilm. Dependent on the application, one or more sets of microbial consortiums can be immobilized on separate media and used in tandem to achieve the treat- ment of complex waste streams. Forthe current application, both aerobic and anaerobic mi- crobial pathways were designed into a treatment train to degrade the cyanide and immobilize metals from the pro- cess stream. As part of this treatability design, a control train was used to determine abiotic losses of cyanide and metals. The system design is depicted in Figure 1 and de- scribed below. ------- Dual identical treatment trains are used in an alternating on- off mode. The reactors are operated as a plug-flow reactor system. The system is operated in 24 hour alternating cycles of treatment or reinoculationforthe two biotreatment trains. A typical complete 48 hour operation cycle for one of the biotreatment trains would include a 24 hour treatment pe- riod, followed by a four to five hour flush of inoculation bac- teria discharging to the drain, followed by a 20 hour bio- inoculation. Cyanide and metals contaminated solutions from the mine are fed to the reactor system which contains both an aero- bic treatment cycle and an anaerobic reactor. Optical level sensors on each aerobic tank turn a pump on and off to either transfer process solutions to the anaerobic reactors or to recycle aerobic bacteria/nutrient solutions back to the aerobic culture tank. The treatment bacteria are maintained as live cultures in a cess solutions from the anaerobic tanks before recycling inoculation solutions to the culture tank. After drawing down during the flush cycle every day, the tank is topped off with fresh water. Technology Applicability The Aqueous Biocyanide Process is applicable to process and waste streams containing cyanide alone, or in combi- nation with heavy metals. For the application tested in this study, the process was used to demonstrate its utility as a process to treat cyanide and metal contaminated process and waste streams derived from precious metal recovery. In these applications, cyanide is used as a lixiviant to ex- tract and recover precious metals such as gold and silver from heap and vat leach mining practices. The spent solu- tions typically contain high levels of cyanide and heavy met- als which must be treated prior to discharge. Cyanide is Pregnant Feed Aerobic Culture Tank Effluent Discharge Anaerobic Tank Anaerobic Tank Anaerobic Tank Anaerobic Tank Anaerobic Culture Tank Aerobic Inoculation Cycle Figure 1. Dual train Aqueous Biocyanide System design depicting on-off mode. Top train is treating while bottom train is being re-inoculated. continuous culture system. An aerobic culture and an anaerobic culture are maintained by scheduled nutrient and stock culture addition and are circulated through the aero- bic and anaerobic biomass during the twenty-four hour flush and inoculation cycle and are returned to the bioculture tanks in a continuous loop. Anaerobic cultures are applied to the anaerobic culture train during flush and inoculation cycles alternating between the biotreatment trains on a daily basis. A flush cycle of 4-5 hours is run between the treatment cycle and the full re- cycle inoculation. The flush cycle serves to discharge pro- typically complexed with a wide variety of metal species and sulfur causing the cyanide to be environmentally persistent and difficult to be destroyed by natural processes. In addi- tion, the effluents may contain high levels of metals and other constituents which may impact total water quality. According to Pintail, the process is capable of treating all forms of cyanide, as well as treating heavy metals in the effluent. Standard processes fortreating cyanide from heap and batch leach processes use peroxide to oxidize cyanide. The advantages of the Aqueous Biocyanide Process, as ------- compared to peroxide treatment, are: . The biocyanide process is a biological treatment tech- nology and does not utilize any hazardous or reactive chemicals. . The process is inexpensive to operate once the bioreactors are constructed. The only consumables used are nutrients and bacterial cultures. . The process treats heavy metals and may be engineered to treat other water quality impacting constituents. This eliminates the need to bring other technologies on-site. . The Biocyanide Process may be engineered to recover precious metals (gold and silver) from waste streams during operation. This feature can offset costs during waste treatment. In addition to mining wastes, the Aqueous Biocyanide Pro- cess may be used to treat cyanide contaminated wastewa- ter from other industrial processes as well as contaminated groundwater containing heavy metals. Applicable waste- water streams may include electroplating wastes and efflu- ents from spent aluminum pot liners. The biotreatment pro- cess can also be applied to the treatment of groundwater and surface water containing heavy metals and nitrates. Pintail Systems, Inc. has also developed and applied, at full-scale, a biocyanide process for the in situ treatment of cyanide and heavy metals in spent ore and mine tailings. In the Spent Ore Biocyanide Process, bacterial solutions and nutrients are injected into the subsurface where entrained cyanide is destroyed and heavy metals are immobilized. Pintail has shown at other sites that this process greatly reduces rinsing of heap leach pads, and can minimize the impact of acid mine drainage from tailings and spent ore. Technology Limitations According to Pintail, proprietary colonies of bacteria or iso- lated native bacteria can detoxify WAD cyanide as high as 500 ppm and effectively treat aqueous waste streams con- taining soluble metals as high as 400 ppm. The bacteria are able to accommodate fluctuations in contaminant concen- trations, however large variations in feed concentrations could be detrimental to the bacteria. A continuously mixed influent storage tankwould eliminate fluctuations in contami- nant concentration. In addition, cool water temperatures (35-45° F) could slow down biodetoxification and biomineralization. Water tem- peratures above 85° F could also be harmful to the bacteria. Process Residuals The primary residual generated from the Pintail process is the solid media containing primarily dead bacteria and im- mobilized metals. This waste material can be stored in 55 gallon drums before being shipped off-site for disposal. The developer believes that the precious metals which are fixed on the support media can be separated and recovered and sold as a commodity. Site Requirements The Pintail process, as tested, requires an enclosed level 20 foot by 80 foot area capable of supporting the bioreactor and all necessary support equipment. Once the piping and pumps are installed, the system can be operational within three weeks. According to Pintail, the bacteria can be grown and be inoculated onto the porous ceramic media and accli- mated to the waste stream in two weeks. The technology utility requirements are minimal and consist of the following: . 110 volt - single phase power . potable water Potable water should be available for field laboratory ana- lytical procedures and process make up water as well as personnel decontamination. Storage tanks should be avail- able for holding the treated water prior to discharge. A stor- age shed can be used to store nutrients such as ammonia and nitrogen. Performance Data Pintail Systems, Inc.'s Aqueous Biocyanide Process was used to treat a pregnant solution containing cyanide and heavy metal contaminants. The two and one-half month treatability test took place at the Echo Bay/McCoy Cove mine site near Battle Mountain, Nevada between June 11,1997 to August 26, 1997. The original system was designed and optimized based on the plan to treat a "barren solution" containing WAD cyanide concentrations in the tens of ppms and relatively devoid of heavy metal contaminants. However, upon mobilization of equipment to the site, the test feed was changed to a "preg- nant solution" containing WAD cyanide concentrations be- tween 250 to 350 ppm, and significant concentrations of heavy metals. Since the system was designed for the bar- ren solution, significant redesign of the system on-site was necessary to treat the pregnant solution. Therefore, the period between June 11 to July 22 was devoted to custom- izing and optimizing the system to the pregnant solution characteristics. Once optimized, continuous testing was performed between July 23 and August 26. Therefore, the period between July 23 and August 26 will be used for per- formance assessment purposes. The test system consisted of two identical treatment trains ------- (T-100 and T-200), and a control train (T-300). The control train was used to determine if any losses of cyanide or met- als occurred due to abiotic mechanisms. Four sample streams were evaluated as part of this treat- ability study. Streams included; (1) an influent stream des- ignated as the "process feed" or "pregnant feed," (2) a con- trol effluent from the control train, (3) an effluent from the aerobic treatment cycle, and (4) the effluent from the en- tire treatment process. Concentrations of cyanide from the influent stream were compared to the treated effluent to de- termine system efficiency. Results from the aerobic efflu- ent, as compared to the system effluent, were used to de- termine operating efficiencies of the individual aerobic and anaerobic segments. Analyses for weak and dissociable (WAD) cyanide were performed by two different methods. On-site field analyses were performed on a daily basis using a Perstorp analyzer: a ligand exchange/flow injection amperometric method of analysis. Several samples, but not all field samples, were also analyzed by a laboratory distillation procedure; Stan- dard Method 4500 CN.I. Total cyanide was also performed on samples submitted to the laboratory. Metals analysis of the process feed, treated effluent, and control effluent were performed on three composited samples taken each week. The samples were analyzed for the following metals: As, Cd, Co, Cu, Fe, Mn, Hg, Ni, Se, Ag, and Zn. Cyanide Destruction Table 1 summarizes WAD cyanide results from the study, and Figure 2 graphically depicts process efficiency during the performance assessment period as measured by WAD cyanide (field). Table 1. Average WAD CN (mg/L) from 7/23 to 8/26. Field Analysis Lab Analysis Influent 233 + 8 n=27 213 + 44 n=16 Control Effluent 242 + 22 n=27 231 + 24 n=16 Aerobic Effluent 160 + 30 n=27 Not Measured Effluent 25 + 18 n=27 23 + 17 n=16 Average % Red. 89.3 % 89.2 % Note: the value after+ is the standard deviation; n is the number of samples analyzed Results from the study demonstrate that, once optimized, the Aqueous Biocyanide Process was able to consistently reduce WAD cyanide by approximately 90%, based on an average influent value of 233 ppm and an average effluent 350 - 300 - 250 - 200 - S Q_ Q_ 150 - 100 - 50 - 0 - 7/1 £ Fi WAD Cyanide (Performance Assessment Period - 7/23 to 8/26) Control A Ğ- -v A AV- * ^\\'f\ / \ \ ^ Fee^ >? Y X'^^^^^^ ff ^ iET7\7^^3 .A V * V" "V Effluent .^X A .-- - -. .' .---' \ -' S -V '"- ' -- A A. * - - * * 197 7/24/97 7/29/97 8/3/97 8/8/97 8/13/97 8/18/97 8/23/97 8/28/97 gure 2. WAD CN concentrations overtime. ------- value of 25 ppm. Furthermore, the WAD cyanide levels in the control effluent are statistically indistinguishable from influent concentrations, indicating that the biological system was responsible for the cyanide destruction. Analyses for WAD cyanide were also performed on samples taken after the Aerobic Treatment Cycle. The average WAD cyanide concentration during the period between July 23 and August 26 was 160 ppm. This represents an average reduction in WAD cyanide of approximately 31% attribut- able to aerobic respiration processes. Pintail offers the following explanation concerning the mecha- nisms of WAD Cyanide degradation in their treatment sys- tem: . In the Aerobic Treatment Cycle, the microorganisms directly metabolize cyanide. The aerobic microorgan- isms can metabolize the more easily degradable metal- cyanide complexes such as Zn-cyanide. Degradation rates are relatively rapid. This phase reduces the toxic- ity load to the anaerobic system. . In the Anaerobic Treatment Cycle, the microorganisms utilize cyanide as a co-metabolite. Degradation rates are relatively slow. Reduction of the more strongly complexed fraction of the WAD cyanide occurs. . The combination of the aerobic/anaerobic system al- lows forthe rapid destruction of easily degradable WAD cyanide in the aerobic phase as a pretreatment or con- ditioning step, in order to increase the efficiency of the slower anaerobic phase of the treatment. Metals Removal In addition to testing the cyanide destruction capabilities of the Aqueous Biocyanide Process, the system was sec- ondarily evaluated for its ability to remove metal species from the pregnant feed solution. Table 2 presents a re- view of the metals data during the performance assess- ment period of the project. Figures 3 to 6 illustrate the effectiveness of the removal process for several select metals. The results from the analyses indicate that the process was able to immobilize and remove significant quantities of heavy metals from the process feed. Specifi- cally, the metals arsenic, cadmium, mercury, and zinc ex- hibited reductions over 90%. Furthermore, the removal ef- ficiency of these metals were consistent overtime as de- picted in Figures 3 to 6. The metals iron and manganese exhibited apparent increases in the effluent as compared to the feed. The apparent increase is probably due to in- puts from process amendments in the form of humates. These metals are generally considered to be environmen- tally benign and do not add to the overall level of contami- nation. The process of metals removal during cyanide detoxifica- tion has been observed from other studies performed by Pintail. The mechanism involves the formation of biologi- cally mediated neo-mineral phases, termed biomineralization. Biomineralization is the process by which microorganisms catalyze and mediate inorganic re- actions. A biomineral is defined to include both biologi- cally formed authigenic minerals (pyrite, etc.) and com- plex bio-stabilized materials that are often clay- or gel-like (Fe,AI) silicates, sulfides and oxides of variable composi- tion that are presumed to be thermodynamically metastable phases. Formation of biominerals on the solid media within the reactors removes the soluble metal contaminants from the aqueous phase and immobilizes them into a more stable mineral phase. This is preferable to ion exchange reac- tions in which metals are not covalently bonded to the sub- strate and can desorb. Table 2. Average metals Gug/L) after 7/23. Analyte Arsenic Cadmium Cobalt Copper Iron Manganese Mercury Nickel Selenium Silver Zinc Influent 361 .3+ 5.8 23.3+ 4.4 121.2+ 49.0 133,016.7+ 30,286.7 1 ,409.7+ 848.59 12.2+ 9.0 164.0+ 13.3 1596.7+ 102.7 227.3+ 56.6 940.8+ 774.5 8,597.7+ 1,604.3 Control 339.2+ 12.9 21.5+ 2.5 139.2+ 75.6 136,250.0+ 30,626.4 803.7+ 319.8 3.7+ 2.2 139.2+ 24.6 1646.7+ 26.6 228.5+ 18.5 534.5+ 367.1 8,573.3+ 926.2 Effluent 26.3+ 13.7 <1.95 46.5+ 12.9 24,733.3+ 14,027.6 1 ,473.5+ 614.58 69.8+ 30.2 7.2+ 4.1 559.3+ 221.3 53.9+ 45.2 51.3+ 87.7 465.0+ 194.4 % Reduction 92.7 >91.6 61.6 81.4 -4.5 -470.9 95.6 65.0 76.3 94.6 94.6 ------- 450 -, 400 350 300 250 200 150 100 50 Arsenic Effluent 8/3/97 8/8/97 8/13/97 8/18/97 Figure 3 8/23/97 8/28/97 30 -, nc on a iĞs- S 1b m - Cadmium tnz^T^^^^ "\^* Effluent 8/3/97 8/8/97 8/13/97 8/18/97 8/23/97 8/2& Figure 4 200 -, 180 - \AT\ -ion .Q Q. mn - fin - on Mercury Feed __^ *,^ * XT * *^^_ A^ Control ^^^ ^^-4^^^ ^~~~-- A Effluent - " " * ~" 8/3/97 8/8/97 8/13/97 8/18/97 8/23/97 8/281'. Figure 5 Zinc 12000 n 10000 8000 g- 6000 4000 2000 0 Feed Control Effluent 8/3/97 8/8/97 8/13/97 8/18/97 Figure 6 8/23/97 8/28 System Operability The Aqueous Biocyanide Process was operated for two and one-half months. During the first 42 days (June 11 to July 22) system performance was variable, and occasional down-times were encountered. This was due to greatly higher cyanide and metals concentration in the feed than was encountered during bench-scale and design phases of the project. Once optimized for the more concentrated feed, the sys- tem performed well with continuous operation for 35 days (July 23 to August 26). Specific process modifications in- cluded: (1) Periodic flushing of the anaerobic culture tank with clean waterto remove built up levels of WAD cyanide; and (2) Adding additional tankage volume on the anaero- bic system to increase residence time. These processes significantly improved the levels and consistency of WAD cyanide degradation. The ability to "re-engineer" the sys- tem in the field to accommodate the new waste stream is a positive attribute of the system. One potential area of improvement would be to design a system that would minimize the channeling of fluids through the media. A common problem in many fixed media sys- tems is the development of channels through preferred pathways in the media. This greatly reduces the available surface reaction area and reduces the efficiency of the system. There is some evidence that channeling did oc- cur during the field tests. Technology Status Biotreatment processes for heap, tailings and process so- lution detox have been proven at other mine sites in a va- riety of environments. Biological processes are both site- specific and waste-specific and must be individually engi- neered and tested for each mine waste. Successfully adapt- ing treatment bacteria to the spent ore environment is a key to developing successful bioremediation potential. Working with a biotreatment population that has been spe- ------- specifically adapted to the ore and augmented to improve cyanide metabolism insures that biotreatment will be ef- fective. Pintail has developed biological detoxification processes for the decomposition of cyanide and has applied them at several gold mines. The following case studies have been provided by Pintail Systems, Inc. The information and data contained within these case studies are not associated or validated by the USEPA SITE program. Hecla Yellow Pine Mine The first full-scale demonstration of in situ biotreatment processes took place at the Yellow Pine Mine near Yellow Pine, Idaho. Approximately 1.3 million tons of agglomer- ated oxide ore were treated. The goals of the project were to reduce WAD cyanide to 0.2 mg/L in leachate solutions, treat the source of the cyanide in the ore, and enhance gold production during detoxification operations. Further- more, the site was a challenge to biotreatment processes due to low solution temperatures and extreme cold weather conditions throughout the operating season. Results demonstrated complete cyanide detoxification (< 0.1 mg/L WAD cyanide) after a 5-month treatment period. In comparison, treatment time estimates for conventional chemical treatments (peroxide and sulfur dioxide/air) sug- gested two to four operating seasons for complete detoxi- fication. Disclaimer While the technology conclusions presented in this report may not change, the data have not been reviewed by the EPA Quality Assurance/Quality Control office. Sources of Further Information: EPA Project Manager Patrick J. Clark U.S EPA National Risk Management Research Laboratory (NRMRL) 26 W Martin Luther King Jr. Dr. Cincinnati, OH 45268 (513)569-7561 Pintail Project Manager Leslie Thompson Pintail Systems, Inc. 11801 East 33rd Avenue, Suite C Aurora, Colorado 80010-1454 (303) 367-8443 A secondary benefit of the biotreatment process was an enhanced gold production above predicted recoveries for water rinse operations. Biological solutions catalyze sev- eral biooxidation and biomineralization reactions that con- tribute to enhanced gold recovery. Cyprus Copperstone Mine An in situ cyanide detoxification was completed at the Cyprus Copperstone Mine located near Parker, Arizona. At this mine, 1.2 million tons of ore were biologically treated over a 70 day period. The goal was to reduce WAD and total cyanide from 30 to less than 0.2 mg/L in heap leachate solutions. The rapid treatment (0.3 tons of solution per ton of ore) was attributable to high temperatures (80 to 90 degrees F) in the process solutions. Both WAD and total cyanides were reduced to less than 0.2 mg/L. ------- |