Document pBJz2zeeRB2N4LaoeJxqzgvL6

AquaDetox Stripping System for Groundwater Remediation Gary Street Lanny Robbins James Clark Presented at Ground Water Protection Seminar Baton Rouge, LA -- May 12, 1988 ^01829 Introduction Enormous quantities of water are contained rela tively near the surface of the ground in the United States. It has been estimated that within one-half mile of the surface, there are between 33 and 100 quadrillion (1015) gallons of water. The volume of groundwater within this zone is estimated to be 4 times that of the volume of water in the Great Lakes. (1) Approximately 25% of all of the water used in the United States comes from this resource-and it is the source of 50% of the drinking water in the U.S. Groundwater supplies up to 90-95% of the needs of rural America. Approximately 35% of our cities depend-at least in part--on groundwater for their supply. (2) Our "thirst" for water is growing faster than our population. In 1950, 151 million Americans consumed 35 billion gallons per day of water; in 1980, our population had grown by 50% to 227 million, but our use of water had increased by nearly 160% to 90 billion gallons per day. (3) Incidents of groundwater contamination have oc curred in all 50 states. The industrial revolution, which began creating significant amounts of con tamination nearly 100 years ago, has multiplied manyfold since World War II. An important factor in this development has been the use of an ever growing number of chemicals--including some which can have a detrimental impact on the envi ronment. During the past 10-15 years, we have seen the emergence of ever more accurate and sensitive methods for detecting substances in water at ex ceedingly low levels-parts per billion, parts per trillion, and even lower. Fortunately, at the same time, there has been the development of a number of technologies that can be utilized to restore water to "drinking water" quality. Technologies that are in practice for the remediation of groundwater and contaminated soil include: Removal to hazardous landfill Incineration Wet air oxidation Solidification Soil air purging Carbon bed adsorption Membrane separation Ion exchange Stripping Each of these technologies have their advantages and disadvantages. The nature of the remediation, public aceptance of a given approach, experience of the responsible parties, and economics dictate the direction that is taken at any given site. AquaDetox Aqueous Purification Process-An Overview In this paper, stripping is defined as a process to remove dissolved, volatile compounds from water. A carrier gas, such as air or steam, is purged through the contaminated water with the volatile components being stripped from the water into the gas phase. While the physical principles involved are straightforward, the practice of the snipping has undergone very considerable development since the early 70's. The effort has focused on: 1. Development of the proper theoretical relation ships that allow a sound understanding of what is occurring. 2. Application of these relationships, along with the correct hardware, to attain extremely high levels of contaminant removal. 3. Development of the proper scale-up parameters to go from pilot units handling <1 gpm to production units handling over 3000 gpm. 4. Recognition that under the proper conditions, compounds with very high boiling points (e.g., 200 Q can be stripped from water. 5. Compilation of a vapor-liquid equilibrium data base with special emphasis on EPA priority pollutants. The effort necessary to address these criteria has been carried out by the Separations Section of the Applied Science and Technology Department of The Dow Chemical Company. The research and development has been under the direction of Dr. Lanny Robbins. By the early 80's, the result of this effort was the AquaDetox process, an integrated technology for the high efficiency stripping of organic contami nants from water. AquaDetox is capable of removing 92 of the 110 volatile compounds listed in CFR 40, July 1, 1986, by the EPA. Further, such systems have CTL018196 the demonstrated capability to remove these compounds to the very low ppb range. This represents remediation that goes several orders of magnitude beyond that of conventional stripping systems. The ability of AquaDetox to attain such low levels of contaminant in the effluent represents a major breakthrough. Since conventional strip pers will normally achieve only 80-95% removal of the contamination, their water effluent quality is unacceptable. Typically, carbon beds are added to attain final water effluent levels in the ppb range that are required by current environmental stan dards. With AquaDetox, carbon beds are not required. Another major concern raised regarding conven tional stripping systems is that they simply remove contaminants from the water, but discharge them into the air. The AquaDetox technology solves the air emission problem as well. A Case Study A typical groundwater remediation situation was selected to allow a comparison of the technical and economic merits of the various types of AquaDetox processes to the more traditional remediation methods.. The basis of the studies was: Component Concentration (PPB) Inlet Outlet Toluene Benzene Trichloroethylene (TCE) Perchloroethylene (PCE) 20000 150 1000 5000 4 1 5 5 The cases selected for comparison were: Case 1: Removal of the entire contaminant load with carbon beds. The carbon would be recycled to supplier for regeneration. See Figure 1. Case 2: Removal of 95% of the contaminant load with a "conventional" stripping column. Since this would not attain the desired outlet requirements, carbon beds on both the liquid and vapor streams would also be needed. See Figure 2. Case 3: Removal of the contaminants to the required water outlet level using air AquaDetox technology. Carbon beds are needed only on the vapor outlet, to prevent air contamination. See Figure 3. Case 4: Removal of the contaminants to the required water outlet level using AquaDetox operating under moderate vacuum conditions. With this approach, the need for carbon beds, even on the vapor outlet, is eliminated. All of the organic contaminants are condensed in the overhead recovery system. See Figure 4. Case 5: Removal of the contaminants to the required water outlet level using AquaDetox operating under deep vacuum conditions. Again the need for carbon beds, on either the vapor or the liquid outlet, is eliminated. See Figure 5. The material balance data for each of the cases is summarized in Table 1. The economic data used to compare the cases is summarized in Table 2. A general schematic overview of each of the cases is shown in Figures 1-5. An Economic Model The data representing the operating costs and the capital costs for each of the alternatives was orga nized into an economic model on a Lotus 1-2-3* spreadsheet. As such, it was possible to consider a wide range of economic parameters, and to quickly assess their impact on the overall yearly cost for the remediation. The data selected for comparative purposes is summarized in Table 2. The model permits additional comparisons to be done very rapidly for different economic inputs. Results No such thing as the "normal" groundwater reme diation scenario exists. Each set of circumstances has their own unique characteristics. Certainly one of the most speculative parameters in a remediation is the length of time that will be required to satis factorily remove the contaminants. With this in CTL018197 mind we decided to look at the economics for two different time periods: o 3-year project life o 10-year project life The results, expressed as the TOTAL COST (S) TO REMEDIATE 1000 GALLONS OF GROUNDWATER, are summarized in Table 3 and Figure 6. For a project with a 3-year duration, a conventional air stripper (Case 2) would be expected to cost 55% of what it would cost to cany out the cleanup using only carbon beds (Case 1). On the other hand, using the AquaDetox technol ogy approach (Cases 3-5), again for a 3-year project life, would result in a cost that would be only 28-35% of the cost for relying on carbon beds (Case 1). The variation in total cost reflects the different types of AquaDetox processes that could be used. If the project were to have a 10-year life, the eco nomics are even more favorable toward the AquaDetox alternatives. In this instance, AquaDetox would cost between 16 and 26% of a carbon bed system, again depending on the exact method chosen. When the AquaDetox alternatives are compared only to the conventional stripper with carbon beds on both the liquid and vapor outlet streams, the economics continue to remain very favorable for AquaDetox. Table 3 reveals that for a 3-year life, AquaDetox will run approximately 50 to 60% of the cost of the conventional stripper with carbon beds. Over a 10-year life, AquaDetox is ap proximately 35 to 60% of the cost of the con ventional stripper with carbon beds. The range in cost for AquaDetox is due to the 3 different alter natives available. Figure 7 presents the initial capital that would be required for each of the alternatives. The carbon bed alternative clearly requires less initial capital. The other alternatives are roughly equivalent, with the air AquaDetox technology having a small advantage. However, as we have seen, when one considers operating costs as well as capital costs, it is clear that the most expensive alternative is Case 1 - car bon beds only, while the least expensive alterna tive is Case 5 - the deep vacuum AquaDetox. Summary Over the past several years, an effort has been un derway to gain a better understanding of how air stripping can be made more efficient for the re moval of contaminants from groundwater. This work has led to the development of AquaDetox technology for stripping, which far surpasses more conventional approaches to stripping. In most cases, AquaDetox can remove contaminants from groundwater down to near "drinking water quality," and thereby entirely eliminate the need for carbon beds on the liquid phase. Moderate vacuum and deep vacuum AquaDetox goes even further, allow ing the near total recovery of contaminants from the vapor phase - without the use of carbon. These results are attained without sacrificing costs. Indeed the total cost for a unit using AquaDetox technology will, in most cases, be substantially less than for either carbon beds alone, or a conven tional air stripper followed by carbon beds. AquaDetox technology can be used to remove a wide variety of volatile compounds, and can even be used to remove compounds that are normally considered "non-strippable," e.g., those with boil ing points in excess of 200 C. The application of AquaDetox for the removal of compounds greater than 200 C, as well as the use of vacuum, are technologies that are patented by The Dow Chemical Company. References 1. "Groundwater Examining a Resource at Risk," EPRI Journal, October, 1985, p. 7-8. 2. "Groundwater Saving the Unseen Resource," National Groundwater Policy Forum, Conservation Foundation in cooperation with the National Governors' Association, November, 1985, p. 5. 3. "Protecting the Nation's Groundwater from Contamination," U.S. Congress, Office of Technology Assessment, OTA-O-276, October, 1984, p. 5. A trademark of Lotus Development Corporation CTL018198 TABLE 1 REMEDIATION ALTERNATIVES - OVERALL MATERIAL BALANCES FLOW: 1000 gpm COMPONENT FEED ppb Toluoie Benzene TCE PCE 20000 150 1000 5000 OUTFALL ppb 4 1 5 5 AIR LESS THAN 10 LB/DA V TOTAL EMISSION OVERALL material BALANCES CASE 1 - CARBON BEDS ON WATER COMPONENT Stripper Inlet Outlet Toluene Benzene TCE PCE NONE REQUIRED T a/pitfj Carbon Bed Inlet Outlet 20000 150 1000 5000 4 1 5 5 Vapor Carbon Bed Inlet Outlet AIR EMISSIONS !b/day NONE REQUIRED NONE CASE 2 CONVENTIONAL STRIPPER WITH CARBON BEDS ON AIR AND WATER Stnppcr Removal: 0.9S Vapor Carbon Bed Removal: 0.97 COMPONENT Stripper Inlet Outlet T irpwH Carbon Bed Inlet Outlet Vapor Carbon Bed Inlet Outlet AIR EMISSIONS lb/day Toluene Benzene TCE PCE 20000 1000 1000 4 19000 570 6.8 150 7J 7.5 1000 50 50 1 5 142J 950 4.275 28.5 0.1 0J 5000 250 250 5 4750 1-42.5 1.7 Tout 8.9 CASE 3 - AQUADETOX AIR STRIPPER WITH CARBON BED ON AIR Stripper Removal: water outfall quality Vapor Carbon Bed Removal: 0.9S COMPONENT Stripper Inlet Outlet Liquid Carbon Bed Inlet Oitlet Toluene Beraene TCE PCE 20000 150 1000 5000 4 1 NONE REQUIRED 5 5 Vapor Carbon Bed Inlet Oitlet AIR EMISSIONS lb/day 19996 149 995 4995 599.88 4.47 29.85 149.85 71 0.1 0.4 1.1 Total: 9J CASE 4 - AQUADETOX AT MODERATE VACUUM Stripper Removal: water outfall quality COMPONENT Stripper Inlet Outlet liquid Carbon Bed Inlet Outlet Vapor Carbon Bed Inlet Outlet AIR EMISSIONS lb/day Toluene Ban TCE PCE 20000 150 1000 5000 4 1 NONE REQUIRED 5 5 NONE REQUIRED NONE CASE 5 AQUADETOX AT DEEP VACUUM Stnppcr Rsnoval: water outfall quality COMPONENT Stripper Inlet Outlet 1 i-y-vt Carbat Bed Inlet Outlet Toluene Benzene TCE PCE 20000 150 1000 5000 4 1 NONE REQUIRED 5 5 Vapor Carbon Bed Inlet Outlet AIR EMISSIONS lb/day NONE REQUIRED NONE CTL018199 TABLE 2 Economic Analysis Basis: Capital recovery costs are based on straight line depreciation. Project life: Power cost: Steam cost Taxes and insurance; Maintenace Miscellaneous Operational 10 years Dep. rate 10% per yr. 3 years Dep. rate 33% per yr. 0.08 $ per kwh 6.00 $ per 1000 lbs. 3.00 % of capital cost 4.00 % of capital cost 2.00 % of capital cost 8000 hours per year TABLE3 Cost Comparison for Remediation Alternatives CASE 1 CASE 2 CASE 3 CASE 4 CASE 5 S/Kgal % of Case 1 3-YEAR LIFE 4.951 2.735 1.735 1.589 1.381 100 55 35 32 28 % of Case 2 181 100 63 58 50 CASE 1 CASE 2 CASE 3 CASE 4 CASES 10-YEAR LIFE 4.723 2.152 1.249 0.957 0.749 100 46 26 20 16 219 100 58 44 35 CASE 1: Entire removal with carbon beds on liquid. CASE 2: Conventional air stripper. Carbon beds on liquid & vapor. CASE 3: Air AquaDetox with carbon bed on vapor. CASE 4: Moderate vacuum AquaDetox, no carbon beds. CASE 5: Deep vacuum AquaDetox, no carbon beds. CTL018200 GROUND WATER > 1,000 GPM CASE 1 Carbon Bed, removal from the liquid phase Figure 1 CTL018201 1.000 GPM WATER PHASE ORGANIC PHASE PRODUCT WATER CASE 2 Air Stripping with Carbon Bed clean-up of both liquid and vapor. Figure 2 CTL018202 10 PSIG STEAM ATMOSPHERIC AIR GROUND WATER > 1,000 GPM WATER PHASE ORGANIC PHASE CASE 3 PRODUCT WATER Air AquaDetox System with Carbon Bed clean-up on vapor Figure 3 CTL018203 f CASE 4 AquaDetox System with moderate vacuum Figure 4 CTI*028 204 CTL018205 FIGURE 6 Total Cost per 1000 Gallons Treated 3 Yr. Project Life l\\\1 10 Yr. Project Life Case 1: Entire removal with carbon beds on liquid. Case 2: Conventional air stripper, carbon on liquid & vapor. Case 3: Air AquaDetox system with carbon bed on vapor. Case 4: Moderate vacuum AquaDetox system, no carbon beds. Case 5: Deep vacuum AquaDetox system, no carbon beds. CTL018206 FIGURE 7 Capital Comparison 1600 1400 CASE 1 CASE 2 CASE 3 CASE 4 CASE 5 Case 1: Entire removal with carbon beds on liquid. Case 2: Conventional air stripper, carbon on liquid & vapor. Case 3: Air AquaDetox system with carbon bed on vapor. Case 4: Moderate vacuum AquaDetox system, no carbon beds. Case 5: Deep vacuum AquaDetox system, no carbon beds. CTL018207