Cleaning up sites with on-site process plants Fourth in ajve-part series
Peter S. Daley Chemical Waste Management, Inc. Oak Brook, IL 60134 The Superfund law (the Comprehensive Environmental Response, Compensation, and Liability Act, or CERCLA) of 1980 began a broad national program to clean up chemically contaminated sites across the United States. Estimates number these sites in the tens of thousands. About 1200 have been identified as representing a sufficient threat to be placed on the National Priority List (NPL) for cleanup under Superfund (1). 1. Winston Porter, former head of the EPA cleanup program, and others believe that the prime impediments to cleanup actions are not technological (I). Arguments over who pays, standards, where residuals will go, and health and safety threats from cleanup activity tie up decisions for years. These are undeniable problems. However, with super technologies that could eradicate chemical wastes without cost, emissions, or residuals, the problem would have been cleaned up long ago. Better technological approaches will speed cleanup, save money, and improve environmental restoration. Cost is a controlling factor. MultimiS i 2 Enviran. Sci. Technol., Vol. 23, No. 8, 1989
lion-dollar cleanups are common. Ten Superfund cleanups recently evaluated by the Congressional Office of Technology Assessment averaged $12 million each. This translates to one-half to one million dollars per acre (2). Thomas Grumbly of Clean Sites, Inc., a nonprofit organization dedicated to mediating cleanup settlements, cites a $30 billion estimate to do the job (3).Because the Superfund sites represent only part of the problem, the total bill is much bigger. Further, future costs will be greater unless better methods become available. Every tick of the clock seems to bring additional concern about the emissions and residuals from cleanup activity. Seemingly minor changes in standards can have large impacts. For example, in October 1988, EPA issued a clarification concerning cleanup of PCB spills (4). Prior to that time, ambiguous standards led to cleanup levels of 1-50 ppm. Ambiguity still exists, but if the remedial choice returns decontaminated soil to the site, the l-ppm standard applies. Table 1 lists compounds that will probably be newly listed as “characteristic” hazardous wastes before the end of 1989. These wastes are found at many remedial sites where CERCLA standards apply in fad or de facto (5).These more demanding
standards will eliminate many low-cost methods from consideration. Technology improvement is pivotal in achieving our cleanup goals; it is the only choice available to reduce costs in the face of tighter standards. Without improving technology, cleanup will continue, but the cost will be unnecessarily great, the schedule slow, and the results less than satisfying. Given this situation, what chemical waste cleanup methods are being used today, and what does the future hold? I will review the subject in three parts: classification of the problem, present technologies, and future trends. Because in situ biotreahnent methods and aqueous treatment were covered in earlier articles in this series, the focus here is on traditional chemical process a p proaches to the problem (6, 7). Clearly, there are many cases for which this a p proach is not the optimum solution; these are ignored here only for brevity. Nonetheless, many of the observations apply to the entire range of cleanup problems.
Classification of the problem Attempts to classify chemical waste cleanup problems identify one reason for slow progress: the enormous range of problems encountered. This range forces costly site-specific solutions. Ta-
0013936W891W250912$01.5010
B 1989 American Chemical Society
ble 2 shows a matrix to help simplify matters (8). Although the matrix encompasses many combinations of technology and waste materials, it is not exhaustive. In addition, the matrix does not take into account troublesome antagonism (e.g., biotreatment is not effective on a biotoxic waste) or the many important subdivisions in each technological area. Decision makers must recognize both the technical and regulatory complexity of the problem or they will make costly mistakes. No single approach is likely to be successful for any large portion of the cleanup task. Costs of various approaches range widely. Figure 1 compares the costs of treatment technologies (9). Engineers must balance the cost, versatility, effectiveness, and risks of a host of approaches in recommending a cleanup plan. The problem can be classified by using tools such as Table 2 and Figure 1, but the ultimate plan must carefully consider the specificparameters of each site.
Approaches to cleanup In fiscal year 1988 EPA issued 111 Records of Decision (RODS) requiring control of site contamination sources. Table 3 summarizes the technologies prescribed in these RODS (1). The fol-
lowing paragraphs review the specific approaches by technology group. Incineration and thermal destrnction. Rotary kiln incinerators dominate incineration applications. Approximately 80% of remedial actions involving on-site incineration employ nonslagging, rotary kilns. Other types of kilns include radiant-heat, moving-
hearth designs (IO),a circulating bed combustor, and fluid beds (11. 12). Compared to rotary kilns, the movinghearth design offers advantages in low gas volume and transportability but cannot handle materials that cannot be easily distributed over the moving hearth. The fluid and circulating beds likewise cannot handle as wide a range of feed materials as rotary kilns, but do have better thermal efficiency and cost less for the same capacity. The year 1989 marks an important change in chemical waste incineration technology. Early this year EPA accepted a proposal to incinerate residues at an NPL site using oxygen-enhanced, rotary-kiln incineration. This is significant because oxygen makes rotary kilns cheaper at a time when costs of traditionally cheap processes are rising in response to more stringent standards. Oxygen use increases the treatment capacity of rotary kilns for lowenergy wastes by 30-100% while lowering capital costs 5-15% (see Figure 1). Moreover, oxygen volume is much less than the air it replaces so that the kiln gas transport velocity is reduced. This reduces particulate emissions and solids buildup in the secondary combustor. An oxygen-enhand incinerator requires little increase in labor, instru-
I Proposed additions to the hazardous waste code list .categoriesdefined by the TCLP' leaching test
DO13 DO19
DO20
14 4 007 n n?
I
DO25 DO07 DO26 DO27 DO28
Chloroform Chromium o-Cresol m-Cre p-Cres
DO16 DO29 DO30 DO31 DO32
2.4-D 1.2-Dichlorobenzene 1.+Dichlorobenzene 1.BDichloroethane 1,I-Dichloroethylene
DO33 DO12 DO34 W35 DO36 DO37
2.4-Dinitrotoluene Endrin Heptachlor (and its hydroxide) Hexachlorobenzene Hexachlorobutadiene Hexachloroethane
Lindane Mercury Methoxychlor
DOO~ DO14
Benzene Bis(2-chloroethyl)ether
I
I lA;
Meihil ethyl k m n e Ndmbenzene
DO40 m 7 DO41
Pe"tlrhlom"bnnl
u'07 5.0 10.0 10.0 10.0
DO44 DO10 DO11 7045 )046
Pyridine Selenium Silver 1,I .1,2-Tetrachiomethane Tetrachloroethylene
0.40 0.1
DO47 DO48 DO49 DO15 DO50
1,1.2,2-Teirachloroethane 2,3,4,6Teirachlorophenol Toluene Toxaphene 1,l .l-Trichloroethane ~~~
0.13
0.003 0.001 0.13 0.72 4.3
DO51 DO52 DO53 DO54 DO17 DO55
10.0 1.3
~~~
~~~~
~~~
1,1,2;Trichloroethane Trichloroethylene 2,4,5Trichlorophenol 2,4,6Trichlorophenoi 2,4,5TP (Silvex) nyl chloride
I Source: Reference 5.
Environ. Sci. Technoi., MI. 23, No. 8, 1989 913
mentation, or other overhead. With these cost reductions, incineration is more competitive with stabilization and other approaches. In addition, incineration offers a permanent remedy for organic materials and makes stabilization of most inorganic residuals easier. There are questions about oxygen use concerning costs, safety, and high kiln temperatures (and attendant nitrogen oxide emissions). Oxygen has little effect on cost because one ton of oxygen replaces over five tons of air, which must be heated with purchased fuel and treated in the air pollution control system. However, oxygen requires careful control to ensure system safety. Innovative burner designs have overcome temperature and nitrogen oxide problem. The use of oxygen in rotary kilns has been studied by EPA and others (1315); its commercial use is a major accomplishment for EPA’s R&D program. Because of the cost and environmental benefits, it is unlikely that incineratorswithout oxygen will be cost-competitive for handling lowenergy wastes in the futnre. The Battelle Pacific Northwest Laboratory (Richland, WA) in situ electric vitrification process was selected in one ROD (2). Because this technology has never been used on a cleanup site, this application must be regarded as experimental. The uncertainty concerns wastes and waste by-products that may accumulate at the perimeter of the vitrified zone, but Battelle has reported good results from pilot demonstrations (16). Solidification, stabilization, and neutralization. Chemical stabilization technology has made progress in meeting demanding performance tests. Today’s stabilization criteria for several RCRA wastes are better than the RCRA criteria defining characteristic hazardous wastes (17). Lead, cadmium, chromium, and nickel are all commonly found in these RCRA wastes and on Superfund sites. Superfund wastes containing these elements can be stabilized in a way consistent with the RCRA criteria, although waste sites often present more difficult matrices than those encountered in RCRAregulated materials. EPA has evaluated stabilization extensively, including tests on a synthetic Superfund waste set (18, 19). This work has led to stabilization selection for a range of cleanups in recent RODS. However, the efficacy of some applications remains to be proven (2). Alternative treatment methods are available for some wastes. The best demonstrated available technology for mercury in chlor-alkali plant waste brines is acid leaching and sulfide precipitation (17). S14 Envimn. Sci.Teehnol..Vci. 23,No. 8, I989
TABLE 2
Predicted treatment effectiveness for contaminated soil
This method has not yet been used in a remedial action. Arsenic from biocides and pesticides is a common remediation problem, but stabilization performance is still difficult to predict and standards are unclear. EPA has proposed a 0.004ppm arsenic toxic concentration leachate potential (TCLP) standard for petroleum wastes (17). The 0 . W p p m
level is extremely difficult, if not impossible, to measure, much less achieve in a complex waste matrix. Stabilization is being pushed to and beyond its known performance l i i t s when tested against the TCLP standard. Better estimates of stabilization system performance, better stabilization methods, and alternative approaches (such
I
c
TABLE 3
Technologies prescrlbed by €PA in source-control records of decision (RODS) for waste site remediation Technology
Number of ROD8 (FVl 989L
lncinerationnhermal destruction Solidlstabilizatio neutralization Volatilizationlsoi aeralion Soil washinglflushing Biotreatment Vacuum extraction Other Subtotal Containment Totel'
22
18 7 7 0 10
9 79 32 111
I
'Total is not equal 10 number of RODSisued because some cleanups require more than one technology and some sites require no contaminant source con1roI. Source: Reference 9.
-
as oxygen-enhanced incineration) are needed. Neutralization is not the simple process it once was. When neutralizing strong waste acid or alkali, there are two significant environmental problems that previously have been rarely considered: evolution of toxic volatiles and increases in dissolved solids. Alternatives for managing n e u t r a l i i wastewaters with high levels of dissolved solids include evaporation, disposal in deep wells, discharge to the sea, and biological denitrification. The problems are manageable, but they are new to many engineers. Volatilization and soil aeration. Volatilization methods have increased in use over the past year. These methods were rarely selected in RODS before 1988. ' h o companies have commercially available units for low-temperature (100-500 "C) solid processing ofhazardous waste (16,20). EPA and others have performed extensive pilot tests (21, 22). Recent data indicate the methods are effective for
most volatile organics. Less volatile compounds, such as PCBs, may be treatable. FCBs were removed from some matrices to less than one ppm by volatilization in rotary dryers at temperatures of 350-550 "C (20,21). Soil washing and flushing. Soil washing has been a promising, lowcost technology since the beginning of the Superfund era. Heap leaching and other mining industry tecbnologies are some of the more recently proposed methods (see Figure 1) (27). Washing has not been widely used, however, because it often cannot reacb treatment quality goals; it may produce a great deal of wastewater or waste solvent, and the washing solution may carry away too much solid material. If an organic solvent is used, it may present fire, health, environmental, or safety problems. For these reasons,soil washing applications are l i i t e d . B i o b t m e n t . This subject was covered in another article in this series (7).
A new of the future k i n e r a t i o n and thermal deStNCtion. Beyond the use of oxygen, two major thermal process changes can be anticipated in the next five years: adap tion of many more slagging and vihifying technologies and expansion of pyrolytic technology use. The change to slagging and vitrifying is driven by leaching performance standards, a desire to adopt technologies that are indisputably p e m e n t e), and decreasing costs for these a p proaches. Tightening standards will raise the cost of chemical stabilization which, in combination with a dropping cost for slagging and vitrification, will make the latter the method of choice for an increasingly wide range of wastes. With increasing activity to clean up mixed (radiological and chemical) waste sites with associated tighter standards, slagging-vitrification will become more popular (23). Pyrolytic technologies are processes
that use little or no air. Increasing concern with air pollution favors these processes because they reduce the gross volume of air emissions by factors of 5 to 100. This decrease in emissions reduces air pollution control costs. Oxygen-enhanced incinerators and lowtemperature volatilization systems (some of which use inert, recycled carrier gases and emit almost no air pollutants) are part of this trend (20, 21). Pyrolyzer use will also be stimulated by programs to destroy chlorofluorocarbons. Low-air and no-air technologies will also be used in water treatment as operators encounter difficulty in meeting air emission standards for treatment plants. Solidification, stabilization, and n e n t m b t i o n . Expertise in this area is growing fast. The arsenic problem cited earlier will likely be solved this year, but not without some relief from the proposed 0.004-ppm TCLP standard. Given the breadth of the bans on land disposal of untreated waste, lab activity is high. We can expect a stabilization information explosion. The land disposal bans assure us that the use of chemical stabilization will grow over the next five years. At the same time slagging and vitrification will expand faster. Lead time for ,the development of significant numbers of slagging and/or vitriwig systems is four or five years. Wastewater treatment. Tighter standards here mean more elaborate treatment systems. New technologies will be adopted and others will mature, including: Supercritical oxidation. Modar, Inc., isready to build a full-scale unit. The system is expected to produce highquality water from feeds with up to 10% organic material and a range of inorganics. The cost is about 14 cents per gallon at the 20,ooO-gallon-perday level (24). High-pressure and critical h i d extraction. This technology, developed by CF Systems, Inc., will be installed at a waste treatment facility this year. It can remove nonpolar contaminants from wastewater very thoroughly for about 10-15 cents per gallon. It can also separate emulsions and dewater sludges (25). Evaporation with catalytic oxidation. This Chemical Waste Management, Inc., process W i l l be installed at a waste site in 1990. The process can treat a wide range of organic and inorganic wastewaters (up to 2% organics and 10% dissolved solids). Organic compounds are oxidized in the vapor phase over a solid catalyst. The treatment cost is about 10-15 cents per gallon. Membrane technologies. New chemEnviron. Sci. Technol., Vol. 23, No. 8. 1989 915
ically resistant and versatile membranes are becoming available for reverse osmosis, ultrafiltration, microfiltration, bipolar separations, pervaporation (permeate evaporation), and electrodialysis. Effective systems are being offered by Memtek, Inc., and others that will bring these technologies into wide application in the next five years (26). Evaporation with catalytic oxidation and supercritical oxidation are likely to be widely used in the waste industry because they can address both the organic and inorganic problems and can deal with the dissolved solids problem.
Rquatic Humic substances
Influence on Fate and T " n t
Df Pollutants
U
nnl now lrUe i n f o r " has been auai able on the m dy of humk sub stances. ms a " w new w~umeof. fena tohesrw compilabon of the lmeR re %arch in tnis arebbnngtng togerher lheorenca ana expenmenla. approaches. as ne as practical applcanons on this unque %pert of water pJnfitat on. Gffenng an in-aeptn .what a mde range of Imponant topics. inis b a able btle covers B
rhdnnamnmnand "l""l impM of aqualr n.m c w m n m m r reamons n mnl waten a d P d l W the I mtlmcn On m e r utamml
WIh 45 aestnpbve cnapters ma bookdetaik rowrage of naurdous u m e themlcak. waler wrIubi c) ennantement. wrrpaon. metal specia tion. ana phototnemimy In aadaon. spec& types of 1rea:ment protesses are examinedox dabon. enqmatic aetoufimon. adsorpnon. coag.lanon. .on extnange ana membrane P W M
m s uo ume draws togerher important re search and offers many tompelting. p r x t b l reawns for detai ea males.It WI I appeal m a van@ of readers interened tn ensunng e n 6 mnmental protenmn in a tethnolqual wiery I.H. Sum. Editor. Emrunmental Studler I n m t e . Drexel Unlventy Patrick MmrtM, EdROl, Colorado SChOOl of Mines h o p % hrm a q " u m rpaaaed tytheOm. LOP of EnnronmenulCnemam, d the dmerran Cnemo saptv ACS Advancis In ChmLmy Scrlw No.219 844 pages (19881Clothbound ISBN 0-8412.1428.X LC 88-38029 US 8 Canada $109.95 Emrt $131.95
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916 Environ. Sci. Technol.. Vol. 23.No. 8. 1989
Conclusion A changing regulatory climate, increasing environmental concerns, and maturing remedial action technologies will create a period of rapid change in the hazardous waste cleanup business. Unfortunately, the business will not become technologically simpler. Broad tightening of environmental standards will continue, but the resulting technical difficulties will be somewhat mitigated by better, more costeffective, more environmentally effective, and more popular processes. The most important current change is the switch to oxygen-enhanced combustion for low-energy waste incineration. This will lower costs and allow incineration to be used more widely. A number of emerging technologies will be more widely used: low-temperature volatilization of contaminants to remove them from solids, pyrolysis of organic contaminants. stabilization improvements, slagging and vitrification of solid residues, supercritical oxidation for wastewater, evaporation with catalytic oxidation for complex wastewaters, and membrane separations. The nation is entering an exciting period for waste site cleanups. With better tools our rate of progress will accelerate.
ment Printing Otlice: Washington. DC. 1988; EPA-6M)/9-88-021: pp. 558-70. Rarmusscn. G. F. et al. S r m d m l Handbook of Hazardour W m e Trmrmmt ond Di.vpmo1: Frecman. H. M.. Ed.: McCraw-Hill: New York. 1989. pp. 8.31* d"-" Rartholomew. C D Rcnedirt R W Pre\cntcd at the Air P
