Hydrogen Peroxide in Soil & Groundwater Remediation

Transcription

1 Hydrogen Peroxide in Soil & Groundwater Remediation

2 Site remediation using hydrogen peroxide Introduction. Hydrogen peroxide is often the oxidant of choice for soil and groundwater remediation, as it is a safe and effective remediation tool. Techniques utilizing hydrogen peroxide show significant benefits, including reduced cleanup time and relative ease of application at the remediation site. This brochure presents various technologies available for treating contaminated soil and groundwater, including traditional and innovative treatments. Additional information included covers technologies using hydrogen peroxide, specifically direct peroxidation of soils, landfarming, bioreactors and in-situ bioremediation. Information on alternative oxygen sources for in-situ bioremediation and peroxide stability is also included. Case studies highlight different contaminants and site hydrogeological characteristics. Hydrogen peroxide from Solvay Interox offers a treatment alternative Treatment methods A number of different treatment technologies apply for use on contaminated soil and groundwater. Table One lists the pros and cons of each. Among the various cleanup methods, peroxygens perform well in several technologies, including peroxidation and bioremediation. Uses of hydrogen peroxide in soil remediation Pump and treat. Pump and treat technology involves the removal of groundwater from the aquifer and treatment of the various pollutants. Treatment can consist of a variety of technologies, including bioreactors, filtration, and oxidation systems. The clean groundwater is then reinjected into the aquifer. This process allows for the mass transfer of the pollutant from the soil to the groundwater and treatment to nondetectable levels in the soil. Unfortunately, the clean-up rate is limited by the solubility of the pollutant in the groundwater and cleanups can take decades. Hydrogen peroxide is used in a number of pump and treat systems, including iron removal systems and Advanced Oxidation Processes (AOPs), such as UV/ H O, and 0 /H O as well as bioreactor systems. Peroxidation. Peroxidation technology is the direct oxidation of organic contaminants in the soil. This treatment occurs either in-situ or ex-situ, with peroxide alone or catalyzed with Fenton s Reagent. To be effective, the soil pollutants must be amenable to oxidation. Peroxidation allows for much shorter treatment times than traditional pump and treat or bioremediation. In-situ peroxidation partially oxidizes the contaminants to improve the biodegradability of the compounds in the unsaturated zone. Once this is accomplished, in-situ bioremediation occurs at a greatly enhanced rate and reduced cost. Revised , Soil & Groundwater Remediation, Page 2 of 13

3 Biological treatment. Biological treatment can take a number of different forms, including landfarming, pump and treat bioreactor systems and in-situ bioremediation. In order for bioremediation to be effective, the contaminant must be biodegradable and the levels of contaminants must not be high enough to be toxic to the microorganisms. If toxicity exists, peroxidation may be used to reduce toxicity prior to biological treatment. Landfarming. Landfarming consists of plowing the appropriate microorganisms, nutrients and sometimes additional wastes into the soil to form a compost. This mixture provides the appropriate environment for the microorganisms to degrade the contaminants. A number of factors impact the success of this type of treatment, including: type and extent of contamination, moisture level and ph of the soil, and nitrogen and phosphate content. Weekly tilling or disking is often necessary to introduce oxygen into the system. Operators estimate cost for this type of treatment at $20-30/ton. 1 Recent studies indicate that the use of peroxygen compounds, such as Ixper calcium peroxide, can replace the normal tilling used for aeration of the soil. Solvay lnterox can provide additional information on this product. Bioreactor systems. Bioreactor systems, used in pump and treat systems, represent an efficient and inexpensive approach for treating halogenated aliphatics. Limitations in oxygen transfer can slow the rate of degradation, as well as increase capital investment significantly. Hydrogen peroxide improves bioreactor efficiency when dealing with limited oxygen solubility. In-situ bioremediation. In nature, biodegradation occurs slowly because of the low population of microorganisms with degradation ability. Degradation is also hindered because of environmental conditions, such as nutrient levels. For bioremediation to be commercially viable, site managers must stimulate the natural biodegradation of hazardous compounds to achieve practical remediation rates. By assisting nature, the cleanup time can be drastically shortened. In-situ bioremediation offers the advantage of being used where other technologies will not work, such as at sites that cannot be excavated. In-situ treatment avoids the cost of excavation as well as freight for off-site treatment. An added advantage is that you can treat the soil and groundwater in a one-step process with minimal equipment. Additionally, the treatment can easily follow the contamination plume in the groundwater. All of these factors make in-situ bioremediation more cost-effective. For in-situ bioremediation to be effective, the components must also biodegrade readily. As discussed previously, peroxidation may be useful in reducing toxicity of various contaminants prior to biodegradation. Revised , Soil & Groundwater Remediation, Page 3 of 13

4 Table One: Treatment methods for contaminated soil and groundwater Method Advantages Disadvantages Vitrification Non-leachable product High levels of clay necessary High electrical costs Low number of completed cleanups Fixation Low cost Contaminant is not destroyed Readily available raw material Long term effects not known Air Sparging/Soil Demolition and excavation Capital investment is high Vapor Extraction not needed Must have a volatile contaminant Steam Stripping Allows for removal of less Possible contaminant leaching volatile compounds problems High utility costs Incineration Able to treat a wide Soil excavation is necessary range of contaminants Soil must have a high BTU content Lengthy permitting requirements Negative public image High capital cost Pump and Treat Able to treat a wide Long cleanup time range of contaminants Peroxidation Reduced cleanup times Contaminants must be susceptible to Low capital investment to oxidation Bioremediation Can be done either Long cleanup time range of contaminants in-situ or ex-situ Able to treat a wide Microbial metabolic reactions cause slow natural biodegradation Application methods A typical bioremediation system includes ground water recovery and treatment, and the addition of nutrients, oxygen and acclimated microbes. Some sites discharge treated water offsite and supply fresh makeup water to the subsurface, in lieu of reinjecting treated water as makeup. 2 Groundwater treatment may consist of bioreactors, carbon adsorption and UV/H 2 O 2. Figure One illustrates a typical process diagram for in-situ bioremediation. Revised , Soil & Groundwater Remediation, Page 4 of 13

5 Figure One: In-situ bioremediation Oxygen source Nutrients Recovery Soil matrix Aquifer Optimum conditions and requirements Bioremediation relies on the ability of living organisms to utilize organic chemicals as sources of food and energy. Bacteria assimilate nutrient molecules, which are required for the maintenance of growth and metabolism of all organisms. Then enzymes act upon the nutrients. Although microorganisms normally utilize the same molecular food sources as humans (principally sugars and amino acids) almost any organic compound even a toxic pollutant theoretically can be used by microbes as a source of food or energy, if the bacteria can absorb the compound. Sequential pathways composed of one or more enzymatic reactions have evolved in all living organisms to allow cells to metabolize nutrients and convert them either into chemical building blocks for new cell growth or into energy. Since each living cell makes use of hundreds of different metabolic pathways to fulfill its myriad chemical needs, cells can metabolize a very broad range of carbon-based compounds. These metabolic reactions cause the slow, natural biodegradation of many chemicals in the environment. For difficult-to-degrade compounds, biodegradation may require co-metabolites. Along with a suitable food source and the presence of micronutrients, the site must also contain contaminant degrading microbes for bioremediation to occur. If indigenous microorganisms do not exist, then the addition of commercial microbes may be necessary. Additionally, soil ph and temperature can also impact bioremediation. Soils with a neutral ph and temperatures between 8 C and 30 C have proven most suitable. Table Two gives a simple screening mechanism for whether or not in-situ bioremediation is a good candidate. A treatability/feasibility study should still be done to confirm whether or not in-situ bioremediation could succeed. If conditions of the soil and water at the site do not provide optimum support for microbial growth, addition of nutrients, the addition of oxygen and microbes can improve the efficiency of the reaction. Normally added nutrients include ammonium phosphate, sodium chloride, magnesium sulfate and potassium phosphate. Revised , Soil & Groundwater Remediation, Page 5 of 13

6 Table Two: Test for determining the feasibility of in-situ bioremediation Parameter Score Contaminant characteristics Structure: Simple hydrocarbon C1 to C15 0 Hydrocarbon C12-C20-1 Hydrocarbon greater than C20-2 Alcohols, phenols, amines 0 Acids, esters, amides 0 Ethers, mono-chlorinated hydrocarbons -1 Multi-chlorinated hydrocarbons -2 Pesticides -2 Sources: Well-defined point sources +1 Undefined multiple sources -1 Hydrogeology Aquifer permeability (cm/sec): Greater than to to Aquifer thickness (feet): Less than 2-2 Homogeneity: Uniform, well-defined geology +1 Heterogeneous, poorly defined geology -1 Depth to aquifer (feet): Less than 2-2 Soil and groundwater chemistry Groundwater ph: Greater than Less than Groundwater chemistry: High Fe, S, Ca, Mg, Cu, Ni -0.5 High NH 4 + and Cl -0.5 Heavy metals (As, Cd, Hg) -0.5 Interpreting the total score 0 or greater Site appears to be suitable for bioreclamation -1 to -2 Possible areas of concern -2 to -4 Areas of significant concern Less than -4 Success is unlikely Source: Adapted from Remediation Technologies, Inc. 3 Revised , Soil & Groundwater Remediation, Page 6 of 13

7 Alternative oxygen sources One of the main reasons for decreased efficiency of bioremediation systems concerns lack of oxygen in the contaminated soil and aquifer. For this reason, oxygen is introduced into a system, so as not to be the limiting factor in biodegradation. Oxygen can be added through physical or chemical methods. Physical addition consists of air sparging, oxygen sparging, air venting and pumping oxygenenriched water into the contaminated aquifer. Problems exist with these forced air systems if biofouling of the sparging surface accurs, which is caused by the active biological population present at the interface of the biological and mechanical systems occurs. 4 This biofouling often causes problems with the phase transfer of oxygen into the aquifer. When using air for sparging, the highest concentration achievable within the aquifer is 8-10 mg/l. By using pure oxygen, the achievable oxygen concentration approaches 40 mg/l. Chemical addition consists of peroxide or nitrate (NO - - ) addition. Nitrate usage is problematic 3 because concentration is typically limited to 10 ppm in the groundwater due to its potential environmental impact. Nitrate addition only works in low oxygen or oxygen deprived systems. In determining oxygen requirements, both the biological oxygen demand and the non-biological oxygen demand must be considered. Non-biological demand results from the oxygen requirements of reduced, multivalent elements, such as iron, sulfur and manganese that may be present in the aquifer. 5 Hydrogen peroxide advantages Hydrogen peroxide is a clear liquid, slightly denser than water. Infinitely soluble in water, it efficiently delivers oxygen to groundwater. For example, 200 mg/l of 50% peroxide delivers 47 mg/l of oxygen. Bioremediation is normally started at low concentrations of peroxide (40-50 mg/l as 100% H ) or with pure oxygen. Once the bacterial population is established and acclimated to the hydrogen peroxide or oxygen, the concentration can be increased. Increments of approximately 50 to 250 mg/l in increasing time intervals from approximately one week to one month achieve an increased presence of oxygen. Such gradual increases of peroxide concentrations can continue up to a peroxide concentration of about 1000 mg/l. 6 Unlike mechanical means of aeration, biofouling has not been shown to be a problem with peroxide dosing systems. Therefore, the use of hydrogen peroxide can eliminate a major maintenance cost that exists with mechanical systems. 7 Revised , Soil & Groundwater Remediation, Page 7 of 13

8 Hydrogen peroxide-assisted bioremediation allows a shorter estimated cleanup time Hydrogen peroxide stability Stability of the hydrogen peroxide solution injected into the groundwater is extremely important. If peroxide decomposes too quickly into oxygen and water, the oxygen may not get far enough downgradient to serve as an oxygen source for the microorganisms. Also with poor stability, the amount of hydrogen peroxide necessary for a remediation project can increase dramatically, thus increasing the project cost. For this reason, the stability of hydrogen peroxide must be considered for each and every system. Many methods exist for determining this stability, including column tests which determine the half-life of a dilute (500 mg/kg) peroxide solution in soil. Peroxide decomposition can result from either homogeneous or heterogeneous catalysis. Iron and copper are the most common catalysts, but other metal species can also serve to decrease the stability of the peroxide. In addition to metal catalysis, enzymatic catalysts, such as catalase, also negatively affect peroxide stability. If peroxide stability is a problem, stabilizers can be added most easily by amending the nutrient formulation. For example, adding stannate or phosphate to hydrogen peroxide solutions decreases the catalytic action of iron. 8 Practical experience shows that excessive use of phosphate as a stabilizer, however, leads to aquifer plugging due to precipitation of the phosphates. This plugging problem can be avoided by using polyphosphates because of their higher solubilities. Sodium pyrophosphate reportedly stabilizes H by either precipitating or sequestering the ionic Fe species and acts as an effective stabilizer in the presence of up to 10 mg/l Fe. 9 To reduce decomposition from enzymatic catalysts, several options have been reported; however, the only stabilizer reportedly used under field conditions is citrate. 10 The addition of small amounts of sodium silicate increases peroxide stability. In addition, silicate can also improve soil permeability. Other peroxygen compounds, such as calcium peroxide and magnesium peroxide, demonstrate good stability during in-situ bioremediation. Case studies Montana, USA This creosote and pentachlorophenol contaminated site was the first site to have a Record of Decision (ROD) stipulating in-situ bioremediation for the contaminated upper aquifer. A preliminary feasibility study determined that dissolved oxygen (DO) was a primary limiting factor for biodegradation within the aquifer. Application of elevated levels of DO through the use of 100 mg/l H produced a high oxygen zone within the contaminant plume.11 Monitoring of the site nutrient and DO levels indicated sustained natural biological activity. Full scale cleanup of the site began in 1989 and will probably continue until after Although operators estimated bioremediation to cost more than a traditional pump and treat system, they realized savings from the shorter cleanup time, estimated at 50%. 12 Revised , Soil & Groundwater Remediation, Page 8 of 13

9 Fuel Pipeline Midwestern U.S. A 135,000 litre underground gasoline spill contaminated a 135 x 270 metre area of impermeable soil on top of a fractured lime stone bedrock. A collection system recovered 4,500 litres of petrol. The owner chose H assisted bioremediation because it allowed a shorter estimated cleanup time: months as opposed to a non-assisted time estimate of 20 years. They found that the existing microbial population in the groundwater could easily degrade the petrol. However, it would be necessary to expand the population by raising the oxygen level in the groundwater through H addition. Hydrogen peroxide addition began at 1,000 mg/l, based on a groundwater flow of 50 gpm. Lab work indicated an optimum feed rate of 300 mg/l, yet 700 mg/l proved most effective during the first 6 months of the full scale cleanup, due to the oxygen-depleted site conditions. After the initial treatment period, the peroxide dose level was reduced to the 300 mg/l level. Petrol Station Southeastern United States A spill of 4000 litres of leaded petrol contaminated a petrol station site. The soil was mainly a silty, sandy clay. They recovered a total of 675 litres of petrol via phase separation of the extracted water and from the excavated soil. The balance, 3400 litres, remained bound in the soil as the adsorbed phase, and dissolved in the groundwater. They augmented the recovered groundwater with nutrients and hydrogen peroxide after treatment through an air stripper. Then they reintroduced the groundwater to the contaminated subsurface through an infiltration gallery. Eighteen months of operation biodegraded over 3000 litres of hydrocarbon. 14 Petrol Station Velsen, Netherlands Work sponsored by Solvay Interox, in conjunction with DHV, a Dutch engineering and services firm, successfully remediated a contaminated petrol station site with hydrogen peroxide. 13 Contamination at the site existed in both the vadose and saturated zones. Along with the actual cleanup of the site, an additional objective was to determine whether or not catalase activity occurred in the hydrogen peroxide piping system. No measurable peroxide decomposition could be attributed to either the enzymatic activity of the catalase or the biofilm on the surface of the piping. In-situ bioremediation succeeded for several reasons: it met the cleanup objectives, no buildings were demolished, and the total cleanup cost reached only 85% of traditional treatment methods. Petrol Station Asten, Netherlands A petrol filling station in the Netherlands became contaminated with 36,000 litres of petrol and a small amount of diesel fuel. The site was mainly sand, allowing good permeability. Phase separation recovered a total of 24,000 litres of free product. The remainder of the cleanup used in-situ bioremediation with hydrogen peroxide. Total cleanup costs for the bioremediation portion approximated $125/ton, including the testing and monitoring program. Fuel Oil Spill Germany Approximately 112,500 litres of fuel oil polluted the vadose zone of a sandy soil in Germany. A nine month cleanup program reduced the concentration of hydrocarbons from an excess of 1000 mg/kg to less than 20 mg/kg. Hydrogen peroxide was added at 100 mg/l to the infiltration water source. Total cleanup costs approximated $45/yd3, with peroxide and nutrient addition accounting for 25% of the cost. 15 Revised , Soil & Groundwater Remediation, Page 9 of 13

10 References 1. Golden, Randy and Hopkins, Jeffrey, Fine Tune Landfarming, Soils, October, 1992, p Hicks, Brian and Caplan, Jason, Bioremediation: A Natural Solution, Pollution Eng., January 15, 1993, p Brubaker, Gaylen, Screening Criteria for In-Situ Bioreclamation of Contaminated Aquifers, RETEC, Wilson, S.B. and Brown, R.A., In-Situ Bioremediation: A Cost Effective Technology to Remediate Subsurface Organic Contamination, GWMR, Winter 1989, p Aggarwal, P. K. et al.; Methods to Select Chemicals for in-situ Biodegration of Fuel Hydrocarbons, Air Force Engineering and Services Center, July Staps, J.J.M., International Evaluation of In-Situ Biorestoration of Contaminated Soil & Groundwater, National Institute of Public Health and Environmental Protection, January Brown, Richard A., Oxygen Sources for Biotechnological Applications, Superfund 89, Hazardous Materials Control Research Institute, pp Schumb, W.C., Satterfield, C.N., and Wentworth, R.L., Hydrogen Peroxide, American Chemical Society Monograph Series Ibid. 10. Alyea, H.N. and Pace, J., Inhibitors in the Decomposition of Hydrogen Peroxide by Catalase, Journal American Chemical Society, Vol. 55, December 1933, pp Piotrowski, MR. and Carraway, J.W.; Full-Scale Bioremediation of Soil and Groundwater at a Superfund Site: A Progress Report, HazMat South 91, Tower Conference Management Company. 12. Piotrowski, MR., In-Situ Design For Aquifer Cleanup, Environmental Protection, p. 36, May DHV report to Interox on the Velsen site. 14. Wilson and Brown. 15. Staps, Revised , Soil & Groundwater Remediation, Page 10 of 13

11 Solvay Interox is dedicated to customer satisfaction We strive to make your experience with Solvay lnterox safe, efficient, and cost effective. Most of the important product and contact information is readily available at. You may also contact us by phoning , faxing or writing to Solvay Interox, Pty.Ltd. at McPherson Street, Banksmeadow, NSW Solvay Interox Quality Policy "Total Customer Satisfaction through Operational Excellence" This policy means that we pursue the highest standards of excellence in every facet of our business. We dedicate ourselves to this effort because we know that our success depends on satisfying you. Our Quality Management System demonstrates this commitment by meeting the requirements of the ISO 9002:1994 International Quality Standard. The manufacture and distribution of hydrogen peroxide at our plant in Banksmeadow, NSW, as well as the support activities at the Banksmeadow headquarters, are all registered to ISO 9002:1994. Safety Like all other powerful chemicals, hydrogen peroxide must be treated with respect and handled appropriately. For a full discussion of safe handling of this product, please see our publication "Hydrogen Peroxide Safety and Handling," available upon request, or as a download from our website at. Solvay Interox also conducts safety training sessions as part of it s PARTNERS program. Delivery Solvay Interox distributes product from the Banksmeadow site and a number of strategically located distribution warehouses. Hydrogen peroxide is packed in 25 kg carboys or 250 kg Mauser drums. Bulk hydrogen peroxide is shipped in 1,200 kg Intermediate Bulk Containers (IBCs), 2,500 kg Road Tanks and 20 or 24 tonne Isotanks. Responsible Care Recognising the importance of preserving the environment of the planet we share, and the health and safety of the employees who produce our products, Solvay Interox actively supports the Responsible Care program of PACIA. Revised , Soil & Groundwater Remediation, Page 11 of 13

12 PARTNERS PROGRAM PARTRNERS is a collaborative program of development between Solvay and it's customers. It aims to establish the appropriate levels of cooperation and services to be exchanged as part of the product provided by Solvay lnterox. Issues such as Safety Training, Audits, Engineering and Technical Support can be covered by the PARTNERS program. PARTNERS aims to more effectively focus resources from Solvay Interox on those issues of significance to our customers. This is achieved by an ongoing dialogue to develop programs and projects, which improves in total the on-site performance of peroxygens and the operations of both organisations. The nucleus of PARTNERS commences with safety and safety related topics such as operator training and safety audits. Other areas of potential development include engineering, design, HAZOP, production performance auditing and technical process investigations. The level of partnership development will evolve through time to include those areas of importance to both partners. Structured PARTNERS IN SAFETY training for your customers, staff, contract drivers etc. 24 hour emergency response hotline Safety audits of storage facilities. Technical service and advice. Staff training on efficient use of peroxygens and operational audits of processes. Access to our research and development findings. Participation in HAZOP studies. Engineering support for bulk installations and dosing systems. Revised , Soil & Groundwater Remediation, Page 12 of 13

13 Solvay Interox, Pty.Ltd McPherson Street Banksmeadow, NSW 2019 Tel: Fax: Disclaimer: " This Product Leaflet summarises our best knowledge of the health and sfety hazard information of the product and how to safely handle and use the product in the workplace. Each user should read this Product Leaflet and consider the information in the context of how the product will be handled and used in the workplace including in conjunction with other products. If clarification or further information is needed to ensure that an appropriate risk assessment can be made the user should contact this company. Our responsibility for products sold is subject to our standard terms and conditions, a copy of which is sent to our customers and is available on request." Revised , Soil & Groundwater remediation, Page 13 of 13