Prepublication issue for EPA libraries and State Solid Waste Management Agencies PHYSICAL, CHEMICAL, AND BIOLOGICAL TREATMENT TECHNIQUES FOR INDUSTRIAL WASTES Executive Summary This is the executive summary from the final report (SW-148c) which describes work performed for the Federal solid waste management program under contract No. 68-01-3554 and is reproduced as received from the contractor Volumes I and II examine 47 unit engineering processes for- their applicability to the task of treating hazardous industrial wastes. Copies of both volumes will be available from the National Technical Information Service U.S. Department of Commerce Springfield, Virginia 22161 U.S. ENVIRONMENTAL PROTECTION AGENCY 1977 ------- This report was prepared by Arthur D. Little, Inc., Cambridge, Massachusetts, under Contract No. 68-01-3554. Publication does not signify that the contents necessarily reflect the views and policies of the U.S. Environmental Protection Agency, nor does mention of commercial products constitute endorsement by the U.S. Government. An environmental protection publication (SW-148c) in the solid waste management series. ------- FOREWORD There is a strong need for treatment processes which can detoxify, destroy, or apply resource recovery principles to industrial wastes. This study examined 47 unit engineering processes for their applicability to the task of treating hazardous industrial wastes. Of these unit processes, 10 can be applied for phase separation, 3 are basically for pre-processing of bulk solids or tars, 12\react chemically to destroy or detoxify the hazardous components, while 25 can be used to separate specific components within the waste stream. Some of these unit processes are commonly used for industrial waste treatment while others require further R&D efforts before they will become commercially attractive. Four (dialysis, electrophoresis, freeze drying and zone refining) were found not to be applicable to waste treatment. Part Two of this report presents comprehensive descriptions of each of the unit processes, including information on the basic principles, areas of application, economics, energy and environmental considerations, and an outlook for future use on industrial wastes. Thus, Part Two is in essence an up-to-date reference textbook on potential treat- ment processes. A major problem is how to make all of the information in Part Two readily available and useful. Section IV of Part One focuses on that problem, and is organized as a series of reference tables to be used when screening processes for application to an individual waste stream. These tables will provide a method of screening out processes that do not have any potential for the waste in question. in ------- PREFACE BASES FOR COST ESTIMATES All capital cost estimates were prepared .on the basis of equipment and construction costs for a time period of early 1976. The bases used were either the Chemical Engineering Plant Cost Index of 188 or a Marshall and Swift Equipment Cost Index of 450, (Refer- ence - Chemical Engineering March 29,1976) for all of the processes except those based on biological activity. For the biological processes, the cost basis was the Engineering News Record Construction Cost Index (ENR March 18, 1976) of 2300. Operating labor costs were taken as $12.00/hour which was assumed to include supervision and overhead charges. Annual maintenance (labor and material) was taken as a fraction of investment and was varied according to the estimated severity of the operations. Chemicals were charged at unit prices derived from Chemical Market Reporter. Electricity was charged at $0.02/kwh. The annualized costs of capital were established on the basis of a 10-year capital recovery factor with money borrowed at 10 percent interest. This method of annualizing capital costs has been widely used in pollution control cost estimating and is equivalent to off-the-books financing that might be obtained through the use of industrial pollution control bonds. The capital recovery factor for these cost estimates is 0.16274, i.e., the annual cost of capital is 16.274 percent of the total capital investment. If cost estimates are to be prepared for different capacities, the following exponential scaling factors based on capacities are suggested. Capital Investment All processes except biological 0.7 Biological processes 0.5 Operating Labor 0.3 Utilities and chemicals 1.0 IV ------- TABLE OF CONTENTS Volume I Page PART ONE - SUMMARY List of Tables I. BACKGROUND 1 II. . SCOPE OF THE STUDY 3 A. OBJECTIVES 3 B. APPROACH 4 III. TREATMENT PROCESSES INVESTIGATED 7 A. PHASE SEPARATION • 8 B. COMPONENT SEPARATION 10 C. CHEMICAL TRANSFORMATION 10 D. BIOLOGICAL TREATMENT 10 IV. SELECTION OF TREATMENT PROCESSES FOR GIVEN WASTE STREAMS ' 15 A. PHILOSOPHY OF APPROACH 15 B. BACKGROUND QUESTIONS FOR TREATMENT PROCESS SELECTION 15 C. EXAMPLES OF PROCESS SELECTION PROCEDURES 19 V. WASTE TREATMENT PROCESS SUMMARIES 35 PART TWO - TREATMENT TECHNIQUES 1 ADSORPTION, CARBON 1-1 2 ADSORPTION, RESIN 2-1 3 BIOLOGICAL TREATMENT: OVERVIEW 3-1 4 BIOLOGICAL TREATMENT: ACTIVATED SLUDGE 4-1 5 BIOLOGICAL TREATMENT: AERATED LAGOON 5-1 6 BIOLOGICAL TREATMENT: ANAEROBIC DIGESTION 6-1 7 BIOLOGICAL TREATMENT: COMPOSTING 7-1 8 BIOLOGICAL TREATMENT: ENZYME TREATMENT 8-1 9 BIOLOGICAL TREATMENT: TRICKLING FILTER 9-1 10 BIOLOGICAL TREATMENT: WASTE STABILIZATION 10-1 11 CALCINATION 11-1 12 CATALYSIS 12-1 13 CENTRIFUGATION 13-1 14 CHLORINOLYSIS 14-1 15 DIALYSIS 15-1 ------- TABLE OF CONTENTS (Continued) PART TWO - Continued 16 DISSOLUTION 16-1 17 DISTILLATION 17-1 18 ELECTRODIALYSIS 18-1 19 ELECTROLYSIS 19-1 20 ELECTROPHORESIS , 20-1 Volume II 21 EVAPORATION 21-1 22 FILTRATION 22-1 23 FLOCCULATION, PRECIPITATION, AND SEDIMENTATION 23-1 24 FLOTATION 24-1 25 FREEZE-CRYSTALLIZATION 25-1 26 FREEZE-DRYING 26-1 27 FREEZING, SUSPENSION 27-1 28 HIGH-GRADIENT MAGNETIC SEPARATION (HGMS) 28-1 29 HYDROLYSIS 29-1 30 ION EXCHANGE 30-1 31 LIQUID ION EXCHANGE 31-1 32 LIQUID-LIQUID EXTRACTION OF ORGANICS 32-1 33 MICROWAVE DISCHARGE 33-1 34 NEUTRALIZATION 34-1 35 QXIDAJJON. CHEMICAL 35-1 36 OZONATION 36-1 37 PHOTOLYSIS 37-1 38 REDUCTION, CHEMICAL 38-1 39 REVERSE OSMOSIS 39-1 40 STEAM DISTILLATION 40-1 41 STRIPPING, AIR 41-1 42 STRIPPING, STEAM 42-1 43 ULTRAFILTRATION 43-1 44 ZONE REFINING 44-1 vi ------- LIST OF TABLES Table No. Page 1 Treatment Processes Identified ( 5 2 Categorization of Processes by Effort Needed 5 3 Phase Separation Processes 9 4 Component Separation Processes 11 * 5 Chemical Transformation Processes 12 6 Biological Treatment Methods 13 7 Treatment Processes for Hazardous Components in Waste Streams of Various Physical Forms 21 8 Applicability of Treatment Processes to Physical Form of Waste 22 9 General Characteristics of the End-Products of Treatment Processes 24 10 Comparison of Processes that Separate Heavy Metals from Liquid Waste Streams 27 11 Comparison of Treatment Processes that Separate Organics from Liquid Waste Streams 28 12 Processes that Destroy Organics 29 13 Comparison of Processes that Separate Toxic Anions from Liquid Waste Streams 30 14 Comparison of Processes that Can Accept Slurries or Sludges 31 15 Comparison of Processes that Can Accept Tars or Solids 32 16 Approximate Treatment Costs 34 vii ------- PART ONE SUMMARY ------- I. BACKGROUND A typical manufacturing establishment takes in raw materials, adds value through one or more processing steps, and produces one'or more products for sale. It is seldom possible to convert 100% of the raw materials into salable products, so there almost always is some waste or residual. In addition, there are usually gaseous and aqueous emissions, but recent air and water pollution control regulations limit the release of potentially hazardous materials in effluent water and gas streams. Water treatment and air pollution control systems usually act to remove rather than to detoxify hazardous materials. Potentially toxic or hazardous materials removed from air and water streams, or generated as waste in the course of normal industrial production, are 'not currently subject to Federal regulation; and most frequently these residual waste materials are dumped on land. Indiscriminate dumping of industrial processing wastes can lead to groundwater con- tamination, or other adverse effects, often 40 or 50 years after the initial waste disposal. Although methods have been explored to reduce leaching to groundwater, by, for example, encapsulating wastes prior to burial, and/or securing sanitary landfills, the amount of land available for dump sites still is decreasing, while the volume of residuals requiring disposal is increasing. As a normal course of events, large industrial plants are constantly seeking ways to convert process residuals into profitable by-products that can either be returned to the raw material stream within the plant, or marketed outside. The success of such resource recovery efforts is governed almost entirely by economics. The net costs of recovery (actual treatment costs minus credits for the recovered resource) must be less than the costs of alternative waste management methods. As long as the alternative of land dumping at $2-3/ton remains, the economically allowable investment in waste treatment is severely restrained. Clearly, however, continued release or re-release of contaminants into the environment via leaching to groundwater, surface water run-off, or airborne dusts from land burial sites cannot be permitted. As land disposal costs begin to increase in response to pressures for protecting the environment, other hazardous waste management alternatives can become more attractive. For the management of industrial processing wastes from the point of generation to the point of ultimate (and environmentally adequate) disposal, three technically desirable alternatives to immediate land burial are: • resource recovery (materials or energy), • detoxification, and • volume reduction, coupled with disposal. The resource recovery alternative is obviously attractive not only from the point of view of conserving materials supplies now beginning to be recognized as finite, but also as a potential means of reducing the quantity of hazardous material requiring disposal. The ------- detoxification alternative interposes a step prior to disposal that makes the waste stream innocuous, so that lowest-cost disposal methods become applicable. The volume-reduction alternative simply reduces the magnitude of trie waste disposal problem, permitting efficient utilization of available secured chemical landfill sites. ------- II. SCOPE OF THE STUDY A. OBJECTIVES The objectives of this study are to identify physical, chemical, and biological treatment methods with potential utility for the design and implementation of resource recovery, detoxification, and/or volume-reduction systems. This study is not meant to provide detailed designs of such systems for specific waste streams;rather, it aims to provide back- ground information that will aid subsequent systems designers in selecting relevant treat- ment processes. For each potentially applicable treatment method identified, Part Two of this study addresses, in depth, the: • Technical characteristics • Underlying physical, chemical, and/or biological principles, • Operating characteristics — Physical and chemical properties of suitable feed streams - Mode of operation — Physical and chemical properties of the output streams • Operating experience . — Principal current applications (including waste treatment) — Potential applications for treatment of hazardous wastes • Capital and operating costs (including credits for products recovered) • Environmental impacts — Waste streams or residues associated with the treatment process — Pollution control or further treatment requirements • Energy requirements — electricity — fossil fuels • Outlook for industrial waste treatment - current state-of-the-art — factors favoring and inhibiting widespread use — development needs ------- To increase the utility of the information provided on individual treatment processes, Part One of this report presents general guidelines for selecting those treatment processes which are potentially applicable to wastes of'particular characteristics. B. APPROACH 1. Literature Search An extensive literature search on potentially useful processes was initiated. The Hazardous Waste Management Division (HWMD) of the EPA made information available from its files, and conducted a computerized search of the SWIRS (Solid Waste Information Retrieval System) data bank for pertinent articles. Prior HWMD contractor reports(1>2'3) and the Division's Report to Congress^ ;were reviewed. An independent search of the general literature and patent literature was performed and trade and professional organiza- tions and government agencies, industries, and universities were contacted. By the time of this report, 47 treatment processes had been identified (Table 1). (Incineration and encapsulation processes are excluded, as they are the subjects of other U.S. EPA studies.) At least two processes were assigned to each of 12 ADL technical staff specialists for in-depth investigation, thus the study team was able to develop a high level of technical and professional expertise on all processes of real potential applicability to industrial wastes. 2. Interview Program The processes identified in the Literature Search were subdivided into the five cate- gories defined in Table 2. These categories were set up to guide the amount of effort required by the contractor for each process'. A site visit and personal interview program was planned to obtain first-hand information and expert opinion or advice on the processes in each category. In addition to hundreds of telephone .contacts, each expert made two to seven site visits for each identified Category II-V process. The visits covered commercial and industrial waste treatment facilities, equipment suppliers; industrial laboratories; government labora- tories; and/or experts. In all instances, each specialist gathered information for other team members as appropriate. 3. Analysis of Information a. Mini-Reports On the basis of the initial Literature Search, each technical specialist prepared a preliminary state-of-the-art report on his/her assigned processes. These reports, generally 5-10 pages in length, were used to help assign processes to categories (Table 2); to identify key information gaps for investigation in the Interview Program; and to report progress to date to EPA. 4 ------- TABLE 1 TREATMENT PROCESSES IDENTIFIED Physical Air Stripping Suspension Freezing Carbon Adsorption Centrifugation Dialysis Distillation Electrodialysis Electrophoresis Evaporation Filtration Flocculation Flotation Freeze Crystallization Freeze Drying High Gradient Magnetic Separation Ion Exchange Liquid Ion Exchange Steam Distillation Resin Adsorption Reverse Osmosis Sedimentation Liquid-Liquid Extracting of Organics Steam Stripping Ultrafiltration Zone Refining Chemical Calcination and Sintering Catalysis Chlorinolysis Electrolysis Hydrolysis Microwave Discharge Neutralization Oxidation Ozonolysis Photolysis Precipitation Reduction Biological Activated Sludge Aerated Lagoon Anaerobic Digestion Composting Enzyme Treatment Trickling Filter Waste Stabilization Pond Pretreatment of Bulk Solids of Tars Crushing and Grinding Cryogenics Dissolution TABLE 2 CATEGORIZATION OF PROCESSES BY EFFORT NEEDED No. Category Description I. Process is not applicable in a useful way to wastes of interest to this program II. Process might work in 5-10 years, but needs research effort first III. Process appears useful for hazardous wastes, but needs development work IV. Process is developed but not commonly used for hazardous wastes V. Process will be common to most industrial waste processors Work Effort for Each Process Enough to justify category assignment Same as Category I, plus description of what questions need to be answered by future effort Same as Category 11 plus description of current uses and projected applications to industrial wastes Same as Category III Description of how used, where, for what, including economics, environment, energy, etc. ------- b. Final Report After an extensive field Interview Program, each Mini-Report was revised and expanded into comprehensive final treatment process reports (Part Two). The results on individual processes are summarized and compared herein. ------- III. TREATMENT PROCESSES INVESTIGATED Most of the 47 processes identified in this study (Table 1) are unit processes or operations, several of which would normally have to be linked in series to form a complete treatment system for a particular waste stream. Four of the processes, however, were found to have little or no potential utility in a hazardous waste management system; that is: • Dialysis, while it does separate high-molecular-weight molecules from low- molecular-weight salts, results in; two output streams, both of which are more dilute than the original stream but not suitable for direct disposal. • Electrophoresis could in principle be used to remove suspended colloidal matter (1-20 /i particle size) from.any aqueous or organic medium, provided that the colloidal particles were charged relative to the liquid phase. How- ever, the process is not only underdeveloped, but also unpromising. There are no scientific or practical guides upon which to base a development program, so there is some question that high removal efficiencies could be achieved. Suitable equipment is not available. Furthermore, in any working unit, electrode reactions would have to be suppressed, the conductivity of the waste stream might have to be below 300 microhms/cm, turbulent mixing would have to be avoided, and potential problems of membrane plugging would have to be solved. i • Freeze drying is an operationally difficult, expensive and energy-intensive dewatering process whose use would not appear to be justified in the treatment of any real waste streams. • Zone refining is a slow, costly, energy-intensive process for purification of solids. It can only be operated in batch, on samples weighing less than 10 kg, which are relatively pure. It is impractical for the complex mixtures which are typical of waste streams. Thus, of the initial 47, this left 43 as1 potentially useful processes to be investigated. These processes fall naturally into four classes: (1) phase separation processes, potentially useful in volume reduction or resource recovery; (2) component separation processes, capable of physically segregating particular ionic or molecular species from multicom- ponent, single-phase waste streams; (3) chemical transformation processes, which promote chemical reactions to detoxify, recover, or reduce the volume of specific components in waste streams; and (4) biological treatment methods, which involve chemical transforma- tions brought about by the action of living organisms. ------- A. PHASE SEPARATION Waste streams, such as slurries, sludges, and emulsions, which are not single phase, will often require a phase-separation process (Table 3) before detoxification or recovery steps can be implemented. Frequently, phase separation permits a significant volume reduction, particularly if the hazardous component is present to a significant extent in only one of the phases. Furthermore, by concentrating the hazardous portion of the stream, sequential processing steps may be accomplished more readily. Phase-separation processes usually are mechanical, inexpensive and simple, and can be applied to a broad spectrum of wastes and waste components. Emulsions are generally very difficult to separate. Heating, cooling, change of pH, salting out, centrifugation, API separators, etc., may all be tried, but there is no accurate way to predict what might work. Appropriate methods can only be developed empirically, specific to any given situation. 1. Settlable Slurries Conceptually, the simplest separation process is sedimentation, or gravity settling. The output streams will consist of a sludge and a decantable supernatant liquid. If the com- ponents of the sludge are at all soluble, the supernatant liquid generally will be a solution. A closely related process and the phase separation process in most common use is filtration. Centrifugation is essentially a high gravity sedimentation process whereby centrifugal forces are used to increase the rate of particle settling, flotation is used extensively in ore separation, and in fact is the single most important process that has made it possible to recover value from lower and lower grades of metallic and non-metallic ores. It has not been extensively studied for hazardous waste applications. High-gradient magnetic separation is a relatively new process that appears to have potential for separating magnetic and paramag- netic particles from slurries. 2. Colloidal Slurries The basic concept in all the above processes for settable slurries is to get the solid phases to drop out of the liquid phase,; through the use of gravitational, centrifugal magnetic, or hydrostatic forces. Such forces generally do not act on colloidal suspended particles. The simplest and most commonly used colloidal separation process is flocculation. Ultrafiltration has many industrial applications, including waste treatment, and is expected to have many more within the next five years. Further development effort is required, however, to demonstrate its full potential. ------- TABLE 3 PHASE SEPARATION PROCESSES Type of Waste to Which Process is Applicable Process Category1 V. Common in Waste Treatment IV.. Developed but not commonly used in Waste Treatment III. Need further development for Waste Treatment Settlable Slurries2 Sedimentation Filtration Centrifugation Colloidal , Slurries2 Flocculation Any Wastes With a Sludges3 Volatile Liquid Phase Filtration Solar Evaporation Distillation Flotation High-Gradient Magnetic Separation Ultrafiltration Freezing (with solvent recovery) Evaporation 1. Described in more detail in Table 2. 2. A slurry is defined as a pumpable solid-liquid mixture. It is settlable if the phases separates on standing, and colloidal if they do not. 3. A sludge is defined as a non-pumpable solid-liquid mixture. ------- 3. Sludges The major phase separation desired in the handling of sludges is dewatering. Vacuum filtration or press filtration are the processes in most common use. Some research has been done on simple freezing, but the process is not well developed and the work that has been done is not promising. 4. Volatiles Sludges and slurries (colloidal or separable) in which the liquid phase is volatile may be treated by either evaporation or distillation. Solar evaporation is very commonly used. Engineered evaporation or distillation systems would normally be operated if recovery of the liquid is desired. B. COMPONENT SEPARATION The many physical processes which act to segregate ionic or molecular species from multicomponent waste streams (Table 4) do not require chemical reactions to be effective. None are so commonly used as to be classified in Category V, but there has been a great deal of experience with most of them in the water treatment field. The majority of Category IV processes act only on aqueous solutions. C. CHEMICAL TRANSFORMATION The relatively few processes which involve chemical reactions (Table 5) are the only processes which we found are potentially capable of detoxifying hazardous components in waste streams (in addition to recovering resources or reducing volume for land disposal). By far the two most common processes are neutralization and precipitation. Since there is usually a pH range where the solubility of heavy metal precipitates is at a minimum, neutralization (interpreted broadly as pH adjustment) and precipitation are in fact often used together. D. BIOLOGICAL TREATMENT Biological Treatment methods (Table 6) are only effective in aqueous media, and are only capable of breaking down organic components. The four Category V processes are used essentially in polishing of soluble organics. The feed streams must be low in solids (<1%), free of oil and grease, and non-toxic to the active microorganisms (e.g., heavy metal content less than 10 ppm). The processes yield a bibmass sludge for disposal which contains heavy metals and refractory organics not decomposed by the biologically active species present. The Category IV processes, anaerobic digestion and composting, are useful for more concentrated waste streams and will tolerate solid contents of 5-7% and 50%, respectively. Composting will decompose oils, greases, and tars, yielding a concentrated metal sludge and a leachate containing partially decomposed organics. 10 ------- TABLE 4 COMPONENT SEPARATION PROCESSES IV. Process Category Developed, but not commonly used in Waste Treatment III. Needs further development for Waste Treatment Needs further research Function of Process Removal of heavy metal and toxic anions from aqueous solutions Removal of 'organics from aqueous solutions Removal of in- organics from liquids, slurries and sludges Solvent Recovery Liquid Ion Exchange Electrodia lysis Reverse Osmosis Ion Exchange Ion Flotation Ultrafiltration Solvent Extraction Carbon Adsorption Resin Adsorption Steam Stripping Air Stripping Distillation Steam Distillation Freeze crystallization • High-Gradient Magnetic Separation ------- TABLE 5 CHEMICAL TRANSFORMATION PROCESSES Treatable Components and Waste Streams IV. III. II. Process Category Common in Waste Treatment Developed but not commonly used in Waste Treatment Requires further development for Waste Treatment Needs further research Cyanides, phenolics, sulf ides, sulfites, and organics in aqueous solution Oxidation Ozonation UV/Ozonolysis UV/Chlorination Photolysis Catalysis Nitrates, carbonates, sulfates, hydroxides, in sludges, tars, and Heavy metals in solids aqueous solution Precipitation Calcination Reduction Electrolysis Precipitate Flotation Organic liquids, sludges, slurries Organic tars and solids Acids and Bases liquids Neutralization Hydrolysis Chlorinoly: Catalysis Microwave ------- TABLE 6 BIOLOGICAL TREATMENT METHODS Process Category V. Common in Waste Treatment IV. Developed but not commonly used in Waste Treatment II. Needs further research Functions of Process Decomposition of soluble organics in dilute aqueous streams Activated sludge Aerated Lagoon Trickling Filter Waste Stabilization Pond Enzyme Treatment Decomposition of hydrocarbons (non-chlorinated) Composting Anaerobic Digestion Enzyme treatment has been shown to be effective for phenols and some hydrocarbons, but the waste stream must be of constant composition and free of inorganic contamination. 13 ------- IV. SELECTION OF TREATMENT PROCESSES FOR GIVEN WASTE STREAMS A. PHILOSOPHY OF APPROACH There are a variety of ways to approach the problem of selecting the appropriate process(es) for treatment of a particular waste stream. Individual engineers, chemists, equipment manufacturers, salesmen, environmental managers, plant managers, regulatory authorities, etc., will each have slightly different perspectives on the problem, different data needs, and different ways of manipulating the data to reach a final conclusion. No one approach is "right" for everyone. The sequence of steps that to one individual seems necessary and immutable, may to another seem irrelevant or illogical. Within the scope of this report we cannot duplicate the thought processes of the many different kinds of individuals who might be involved in the selection of waste treatment alternatives. We also cannot impose our own thinking — no matter how logical it may seem to us - on individuals'who approach the problem differently. To resolve this dilemma, we have chosen first to pose some of the questions to which various people might require answers before even beginning to match wastes with treatment processes. Next, we have provided a number of examples of possible steps in process selection for some typical wastes. We leave it to the individual reader to decide what questions he must have answered, and in what sequence, in order to be able to develop a procedure that meets his needs for choosing the treatment processes applicable to particular waste streams. No matter how one approaches the problem of process selection,' there are two seemingly conflicting criteria to keep in mind. The first is to eliminate inappropriate processes from consideration at the earliest stage feasible. The second is to maintain an open mind for consideration of attractive processes as long as possible. B. BACKGROUND QUESTIONS FOR TREATMENT PROCESS SELECTION • Nature of the Waste — What are the characteristics of the waste stream? — Is it a liquid, an emulsion, a slurry, a sludge, a solid powder, or a bulk • solid? — What is its chemical composition? - Which components are potentially hazardous for land disposal; or more generally, what is the problem? — What are the physical properties of the waste stream — e.g., viscosity, melting point, boiling point, vapor pressure, Btu content, specific gravity, etc.? 15 ------- — Is the waste stream corrosive? - Over what range will the typical physical and chemical properties vary? — What is the volume or mass of waste that will require treatment from a typical plant and/or region? — Where does the waste stream originate and at what points could it be intercepted for treatment? Questions on the nature of the waste, stream are asked for several reasons. One is to determine whether the waste stream characteristics match the feed stream requirements for various treatment processes. In a positive sense, this may be of interest to select processes for further consideration; or in a negative sense, to rule out processes that are not and could not be made useful for the particular waste under any circumstances. Another is to determine whether the waste stream is compatible with typical treatment process equip- ment, materials of construction, pumps, throughput rates, temperature, size of pipes, etc. A third, reflected in the last question, is to determine whether air and water pollution controls, or the method of waste collection used, might in fact create a stream which is more difficult to treat than the waste originally generated in the manufacturing operation. • Objectives of Treatment — Desired Characteristics of the Output Stream — What is the present treatment/disposal method and why is this unac- ceptable? — What are the objectives or goals of treatment, in order of priority, i.e., purification, resource recovery, detoxification, volume reduction, safe disposal to land, safe disposal to water, compliance with regulations ? — What are the air, water and other environmental quality regulations which must be complied with? — What must be removed to make the waste stream amenable to disposal? What level of removal is necessary; i.e., what are the maximum allow- able concentrations in the output stream(s)? — What are the chemical and physical property requirements for recycle or reuse of the output streams? — What are the physical and chemical property requirements for disposal to land or water? 16 ------- Questions on the desired characteristics of the output streams are asked to: (1) clarify the objectives of a treatment process, (2) explicitly learn what regulatory standards must be met, (3) help establish criteria for judging the usefulness of various treatment alternatives in meeting the objectives; and (4) establish a bench mark for improvement by identifying current practice. • Technical Adequacy of Treatment Alternatives - What processes, alone or in combination, are capable of meeting the treatment objectives? — If a sequence of processes is needed, are the processes technically compatible? — Can the key process selected for meeting the objectives handle the waste stream in its existing form? If not, can the waste stream be put into a form amenable to the process? — What key processes are really attractive technically? — Are there any components of the waste stream that would inhibit application of an otherwise technically attractive key process? Can these potentially inhibiting effects be minimized or eliminated? — If no process, as presently conceived, can meet the objectives, can any process be modified to do the job? — What function can each process perform, and how can the processes be grouped to achieve the objectives? — Are there any processes that must be eliminated on technical grounds? Questions about technical adequacy are asked to help distinguish processes that are technically feasible for use on the waste from those that are totally infeasible treatment alternatives. • Economic Considerations — What are the capital investment requirements for process implementa- tion? - What are the operating costs? 17 ------- - To what extent will credit for recovered material help offset operating costs? — How do projected costs for alternative treatments compare with current costs of disposal and with each other? — If recovery was an objective,,is there enough value in the potentially recoverable material to be worthwhile? — Are the technically optimal operating parameters in the proper range for economic operation of apparently attractive processes? — If process modifications are required, what will they cost? — For technically and operationally acceptable processes with equal operating costs (including capital amortization), is there any economic reason to prefer the lowest capital cost alternative? — What is the cost impact of any necessary environmental controls? From the industry point of view, economic questions are paramount in selecting alternative treatment methods for in-plant use and in choosing a waste treatment contractor. • Environmental Considerations — Will air pollution control devices be required to clean up effluents? — Will output streams require clean-up prior to discharge into water bodies? i. i. t • — Will secured chemical landfill areas be necessary for solid residue(s) from process? ;', ' Waste treatment processes, like any manufacturing process, almost always result in some residue for disposal. Environmental questions are directed towards tracing the fate of the hazardous components present in the waste feed stream to the point of ultimate disposal. • Energy Considerations — What are the energy requirements for process operation? - What form(s) of energy will be used, i.e., electricity, natural gas, oil, coal, etc.? 18 ------- — Are estimated energy costs niore than 10% of operating costs? Questions of energy utilization are asked in order to assure that treatment processes satisfy current national objectives of both,.environmental protection and energy conserva- tion. Both the absolute quantity of energy required and the form of the energy required are important. Energy-intensive processes generally would be in disfavor, unless there are compensating benefits (e.g., materials recovery). Processes that use natural gas, which is in short supply, might be particularly unattractive. The economics of treatment processes for which energy costs represent a significant fraction of operating costs would, of course, be tied to the price of fuel, which has in the recent past been quite volatile. • Overall Evaluation —• What factors are most important in selecting a treatment process? - Are there any standard, state-of-the-art processes that can be used for baseline comparisons? ; — Are costs "reasonable"? - Does any process have clearly desirable (or undesirable) features that make it attractive (or unattractive) for treating a particular waste stream? The final choice of a treatment system, or treatment process sequence, for a given waste stream involves engineering judgment, which is always highly subjective. The indi- vidual faced with the choice must not only establish his/her own selection criteria, but also weight those criteria in accordance with personal priorities. Questions asked in an attempt to make an overall evaluation, therefore, are directed towards a determination of the degree to which the objective features of alternative treatment systems meet subjective needs. C. EXAMPLES OF PROCESS SELECTION PROCEDURES 1. Selection Based on the Nature of the Hazardous Wastes For the purposes of identifying possible treatment processes, and eliminating those that are not likely to prove useful, a given waste stream is conveniently characterized with respect to three broad dimensions: (a) Physical form - Is the waste stream as generated a: • liquid? • emulsion? • pumpable slurry? 19 ------- - colloidal or non-colloidal? • non-pumpable sludge? • tar? • bulk solid? • powdered solid? (b) Hazardous components - Does the waste stream contain: • heavy "metal" cations (Sb, As; Cd, Cr, Hg, Pb, Zn, Ni, Cu, V, P, Be, Se, Mn, Ti, Sn, Ba, etc.)? • heavy metal anions (chromates, chromites, arsenates, arsenites, etc.)? • non-metallic toxic anions (cyanides, sulfites, thiocyanates, etc.)? • organics (hydrocarbons, organic acids, organic peroxides, esters, alco- hols, aldehydes, phenols, chlorocarbons, amines, anilines, pyridines, organic sulfur compounds, organic phosphorus compounds, alkaloids, sterols, etc.)? (c) Other properties - For example, • Is the liquid phase primarily aqueous or non-aqueous? • What is the concentration of each of the hazardous components in each of the phases present? • What are the non-hazardous components in each phase? For a given waste stream, characterized by physical form and hazardous components, the matrix presented in Table 7 may be used to select potentially applicable treatment processes. For example, liquid ion exchange (LIE) might be capable of removing heavy metals from solid powders. The matrix in Table 8 focusses on processes that are inapplicable for given waste streams. It provides some 'guidance for ruling out processes that are not likely to be technically feasible for certain types of waste streams. 2. Process Selection Based on Desired Characteristics of the Output Streams The, output streams from any given treatment process may or may not be suitable for reuse or amenable to disposal without further treatment. In evaluating and analyzing treatment processes that might be applicable to particular waste streams, it is usually necessary at some stage to define the objectives of treatment and the desired characteristics of the output streams. 20 ------- TABLE 7 TREATMENT PROCESSES FOR HAZARDOUS COMPONENTS IN WASTE STREAMS OF VARIOUS PHYSICAL FORMS Treatment Processes* Physical Form Liquid Emulsion Slurry Sludge Tar Bulk Solid Solid Powder Heavy "metal" cations* and metal anions** (IE), (FC), (UF), (ED), (RO), (Red),(LIE),(Ppt),(E1) (UF) (FC). (UF), (Red), (HGMS) (LIE), (FC), (Red) (Cal) (Cal) (LIE) Non-metal anions*** (CA), (LIE),(FC),(UF), (ED), (Oz), (RO), (Ox),(E1) (FC), (UF), (Ox) (FC), (Ox) (Cal) . (Cal) (Cal) Legend: (AS) Air Stripping (CA) Carbon Adsorption (Cal) Calcination (CD Chlorinolysis (Dis) Distillation (ED) Electrodialysis (E1) Electrolysis (FC) Freeze Crystallization (HGMS) High-Gradient Magnetic Separation (Hy) Hydrolysis - (IE) Ion Exchange (LIE) Liquid Ion Exchange (MW) Microwave Discharge (Ox) Oxidation (Oz) Ozonation (Ph) Photolysis Organics (CA), (RA). (Dis). (IE), (AS), (SS), (UF), (SE), (RO), (Ox), (Oz).(Hy). (C1),(MW),(Pb),(UF) (Dis), (AS), (SS). (UF), (Oz), (Hy) (Dis), (Cal), (Oz), (Hy). (Ox) (Cal), (Hy) (Cal) (Cal), (Hy) (Ppt) Precipitation (RA) Resin Adsorption (Red) Reduction (RO) Reverse Osmosis (SE) Solvent Extraction (SS) Steam Stripping (UF) Ultrafiltration *e.g., Sb. As, Cd. Cr. Hg. Pb, Zn, Ni, Co, V, P,Be, Se, Mn, Ti, Sn, Ba **e.g., chromates, arsenates, arsenites, vanadates ***e.g., cyanides, sulfides, fluorides, hypochlorites, thiocyanates ------- TABLES APPLICABILITY OF TREATMENT PROCESSES TO PHYSICAL FORM OF WASTE 1. Phase Separation Processes Filtration Sedimentation Flocculation Centrifugation Distillation Evaporation Flotation Ultrafiltration HGMS Precipitation 2. Component Separation Processes Ion Exchange Liquid Ion Exchange Freeze Crystallization Reverse Osmosis Carbon Adsorption Resin Adsorption Electrodialysis Air Stripping Steam Stripping Ammonia Stripping Ultrafiltration Solvent Extraction Reverse Osmosis Distillation Evaporation 3. Chemical Transformation Processes Neutralization Precipitation Hydrolysis Oxidation Reduction Ozonolysis Calcination Chlorinolysis Electrolysis Microwave Biological Catalysis Photolysis Single Phase Liquid Solid n n n n n n n n P n s n V n n n n n n V y n P n n n W6S n n P n n n y n n n n n n Inorganic n n n n n n n n n n y y y y y. y y n n V y y v n y y Y n Y Y y Y n y n n Y n Organic Y Y Y y V y y y Y y y Y y y Y Y Y y y y Y n n n n n n n n n n n n n n n n n Mixed n n n n n n n n n n Y n n y. Y Y y Y y n Y Y y Y Y y y y y y y y y y y Y Y Y Two Phases Slurry y y Y y Y y y y y Y Y y Y y y y * n n n n n n n n n n n n n n n n n n n n n n Sludge n n n n y Y n n n n n Y Y n n n n n n n n n n Y Y y n y n n n y n n n Y n n "Slurry is defined here as a pumpable mixture of solids and liquids. y = yes, workable; n = no; p = possible. 22 . ------- For example, if the treatment objective is to convert the given waste stream to one or more streams which can legally be discharged to a water body, the Federal and local water pollution control regulations will govern the characteristics of the output streams. If the treatment objective is recovery, those processes must be sought which either lead directly to a reusable resource, or which convert the waste to a form from which resources may be more easily recovered. .; Table 9 provides some general characteristics of the output streams (end products) from various processes to aid in assessing their capability, alone or in combination, to meet defined objectives. Where processes are routinely or conveniently used in combination, follow-on steps are suggested, predicated, on the assumption that the only hazardous components in the waste stream are those that the process listed can act on. If, for example, a waste stream containing both low-molecular-weight organic and heavy metal contaminants were treated by reverse osmosis, only the heavy metals would be concentrated in one of the output streams (RO1), and the other output stream (R02) would have to be treated further to remove or detoxify the organics. 3. Selection Based on Technical and Operational Adequacy of Treatment Alternative Table 7 shows that there are a number of treatment alternatives for various types of hazardous components in waste streams of different physical form. Tables 4-6 show further that several of the alternatives function similarly; i.e., they remove or detoxify certain types of hazardous components. All processes which function similarly on similar types of waste streams are not necessarily technically equivalent, however. The allowable feed stream concentrations may differ. The treatment efficiencies and hence concentration of hazardous components in the output streams may differ. The degree of interference by other com- ponents in the waste stream may differ. Throughputs may differ and the available experi- ence with using the processes to treat hazardous wastes may also differ. Table 10 compares treatment processes capable'of separating heavy metals from liquid waste streams with respect to feed stream properties, output parameters and state-of-the-art. Tables 11-13 provide similar comparisons for processes that separate organics from liquids and toxic anions from liquids. Table 14 compares processes (other than phase separation processes) that can accept feed streams in the form of slurries or sludges. Table 15 compares processes that can accept feed streams in the form of tars, bulk solids or solid powders. It is clear that the vast majority of processes considered in this program operate mainly on liquids. Some have potential for handling slurries and sludges, but in most real cases, a liquid/solid separation would precede treatment and/or disposal. None of the processes can directly treat bulk solids contaminated by heavy metals, such as slags from the metallurgical industries (an enormously large waste stream in the aggregate). Few processes can work directly on tarry or even powdered solid feeds. Unfortunately, water treatment sludges, still bottom tars, powdered particulate from air pollution control devices and oil-contaminated solids account for a larger fraction of the wastes destined for land disposal than do liquids. 23 ------- TABLE 9 GENERAL CHARACTERISTICS OF THE END-PRODUCTS OF TREATMENT PROCESSES Treatment Type Process 1. Phase Filtration Separation Sedimentation Centrifugation Flotation HGMS Flocculation Distillation Evaporation 2. Component Separation a. Inorganics Ion Exchange Liquid Ion Exchange Carbon Adsorption Reverse Osmosis Output Streams Possible Follow-On Steps Landfill, Calcination Component Separation Decapitation Skimming Component Separation Recovery Component Separation Sedimentation, Filtration, Centrifugation " Calcination Sale Resource Recovery Recovery or Disposal Precipitation, Recycle, Electrolysis with hazardous components Discharge at ppm levels Code No. F 1 F2 S1 S2 FI1 FI2 H 1 H2 Fc Dis1 Dis2 E1 IE1 IE 2 Form Sludge Liquid Sludge Liquid Stabilized Liquid Slurry Liquid Sludge or Slurry Sludge Liquid Solid Liquid Liquid Liquid Characteristics 15-20% solids 500-5000 ppm total dissolved 2-1 5% solids 10-200 ppm suspended solids particle-bearing froth solution solids magnetic and paramagnetic particles solution flocculated participates still bottoms pure solvent condensate concentrated solution of hazardous components purified water with hazardous componer Similar to Ion Exchange CA1 Solid CA 2 Liquid RO 1 Liquid JRO 2 Liquid adsorbate on carbon purified water concentrated solution of hazardous components purified solution, TDS > 5 ppm Chemical Regeneration Discharge Precipitation, Electrolysis, Recycle To Water Treatment ------- TABLE 9 (Continued) to Treatment Type Process Electrodialysis Freeze Crystallization b. Organics Carbon Adsorption Resin Adsorption Steam Stripping Solvent Extraction Distillation 3. Chemical Transformation Neutralization Precipitation Oxidation Ozonation Reduction Output Streams Code No. ED1 ED 2 FC1 FC2 CA1 CA2 RA1 SSI SE 1 >••-•• SE2 Dis1 Dis2 N Ppt1 Ppt2 Form Liquid Liquid Sludge Liquid Solid Liquid Solid Liquid Liquid Liquid Liquid Liquid Sludge Liquid Unchanged Sludge Liquid Characteristics concentrated stream, 100-500 ppm dilute stream concentrated brine purified stream, ~ 100 TDS adsorbate on carbon purified water adsorbate on resin purified water, < 10 ppm organics salts aqueous steam concentrated in volatile organics dilute aqueous stream with 50-100 ppm organics concentrated solution of hazardous- - - • components in extraction solvent purified liquid; hazardous component concentration < 1.0 ppm still bottoms pure liquid stream of altered pH supernatant with concentrations o Liquid Slurry governed by solubility of precipitate CO2, H20 and other oxidation products heavy metals and residual reducing agent Possible Follow-On Steps Precipitation, Metal Recovery To Water Treatment Recovery To Water Treatment Thermal or Chemical Regeneration Discharge Solvent Regeneration To Water Treatment Recovery; Incineration To Water Treatment Recovery of Extraction Solvent •-- Recycle or Discharge Incineration Sale Component Separation Landfill, Calcination Depends on Product Stream Composition Depends on Product Stream Composition Filtration ------- TABLE 9 (Continued) Treatment Output Streams Possible Follow-On Stream Type Process Calcination Hydrolysis Electrolysis Photolysis Microwave Discharge Code No. Call Cal2 Hy EM El 2 P M Form Solid Gas Liquid .Slurry or Sludge — Liquid Gas Characteristics oxide and/or other residue volatiles (CO2 , NOX, SOX, hydrocarbons, fine particulates) mixture of products that may or may not be toxic ' cathode reaction products anode reaction products solution of photodecomposition products similar to incinerator emissions Landfill or Recovery Wet Scrubbing Resource Recovery Often a Recovered Metal Depends on Nature of Products Depends on Nature of Products Wet Scrubbing 4. Biological Treatment Catalysis Activated Sludge Aerated Lagoon Trickling Filter Waste Stabilization Pond Anaerobic Digestion Composting Depends on Reaction Catalyzed AC1 AC 2 W An1 An 2 Com 1 Com 2 Liquid Sludge Liquid Sludge Gas Sludge Liquid clean water heavy metals and refractory organics clear water CO2, methane concentrated in metals leachate solution of partially degraded organics Discharge • Calcination Discharge Incineration Fuel Recovery Calcination or Recovery Component Separation ------- TABLE 10 COMPARISON OF PROCESSES THAT SEPARATE HEAVY METALS FROM LIQUID WASTE STREAMS Process Physical Removal Ion Exchange Reverse Osmosis Electrodia lysis State-of-the-Art Used but not common (Cat. IV) Cat. IV Cat. IV Required Feed Stream Properties Characteristics of Output Stream(s) ^ Liquid Ion Exchange Cat. IV Freeze Crystallization Needs development (Cat. Ill) Chemical Removal Precipitation Reduction Electrolysis Common (Cat. V) Cat. IV Cat. Ill Con. < 4000 ppm; aqueous ' solutions, low SS Con. > 400 ppm; aqueous solutions; controlled pH; low SS; no strong oxidants Aqueous solutions; neutral or slightly acidic; Fe and Mn < 0.3 ppm; Cu < 400 ppm Aqueous solutions; no con- centration limits; no surfact- ants; SS< 0.1% Aqueous solutions; TDS < 10% Aqueous or low viscosity non- aqueous solutions; no con- centration limits Aqueous solutions; concen- trations of heavy metals < 1 %; controlled pH Aqueous solutions; heavy metal concentrations < 10% One concentrated in heavy metals; one purified One concentrated in heavy metals; one with heavy metal concentrations > 5 ppm One with 1000-5000 ppm heavy metals; one with 100-500 ppm heavy metals Extraction solvent concentrated in heavy metals; purified water or slurry Concentrated brine or sludge; purified water, TOS ~ 100 ppm Precipitated heavy metal sulfides, hydr- oxides, oxides, etc.; solvent with TDS governed by solubility product of precipitates Acidic solutions with reagent (oxidized NaBH4 or Zn); metallic precipitates Recovered metals; solution with 2-10 ppm heavy metals ------- TABLE 11 COMPARISON OF TREATMENT PROCESSES THAT SEPARATE ORGANICS FROM LIQUID WASTE STREAMS to oo Treatment Process Carbon Adsorption Resin Adsorption State-of-the-Art Used but not common (Cat. IV) Cat. IV Required Feed Stream Properties Characteristics of Output Stream(s) Ultrafiltration Air Stripping Steam Stripping Solvent Extraction Distillation Cat. IV Cat. IV Cat. IV Cat. IV Cat. IV Steam Distillation Cat. IV Aqueous solutions; concen- trations < 1 %; SS < 50 ppm Aqueous solutions; concen- trations < 8%; SS < 50 ppm; no oxidants I Solution or colloidal suspension of high molecular weight organics Solution continuing ammonia; highpH 'f Aqueous solutions of volatile organics f Aqueous or non-aqueous solutions; concentration < 10% Aqueous or non-aqueous solutions; high organic con- centrations Volatile organics, non-reactive with water or steam Adsorbate on carbon; usually regenerated thermally or chemically Adsorbate on resin; always chemically regenerated One concentrated in high molecular weight organics; one containing dissolved ions Ammonia vapor in air Concentrated aqueous streams with volatile organics and dilute stream with residuals . Concentrated solution of organics in extraction solvent Recovered solvent; still bottom liquids, sludges and tars Recovered volatiles plus condensed steam with traces of volatiles ------- K> Process Biodegradation Oxidation Ozonation Calcination Hydrolysis Photolysis Chlorinolysis Microwave Discharge State-of-the-Art Cat. V Cat. IV Cat. IV Cat. IV TABLE 12 PROCESSES THAT DESTROY ORGANICS Required Feed Stream Properties Characteristics of Output Stream(s) Dilute aqueous streams with soluble Pure water organics Dilute aqueous solutions of phenols. Oxidation products in aqueous solutions organic sulfur compounds, chlor- inated hydrocarbons, etc. Aqueous solutions; concentrations Oxidation products in aqueous solutions Needs development (Cat. Ill) Needs research (Cat. II) Cat. Ill Cat. Organics and inorganics that de- compose thermally Aqueous or non-aqueous streams; no concentration limits Aqueous streams; transparent to light; components that absorb radiation Chlorinated hydrocarbon waste streams; low sulfur; low oxygen; can contain benzene and other aromatics; no solids; no tars Organic liquids or vapors Solid oxides; volatile emissions Hydrolysis products Photolysis products Carbon tetrachloride; HCI and phosgene Discharge products; not accurately predictable ------- u> o TABLE 13 COMPARISON OF PROCESSES THAT SEPARATE TOXIC ANIONS FROM LIQUID WASTE STREAMS Process Physical Removal Ion Exchange Liquid Ion Exchange Electrodialysis Reverse Osmosis State-of-the-Art Cat. IV Cat. IV Cat. IV Cat. IV Freeze Crystallization Needs development (Cat. Ill) Chemical Removal Oxidation Ozonation Electrolysis Cat. III-IV Cat. IV Cat. Ill Required Feed Stream Properties Characteristics of Output Stream(s) Inorganic or organic anions in aqueous solution Inorganic or organic anions in aqueous solution Aqueous stream with 1000-5000 ppm inorganic salts; and pH; Fe and Mn < 0.3 ppm Aqueous solutions with up to 34,000 ppm total dissolved solids , Aqueous salt solutions Aqueous solutions of cyanides, sulf ides, sulf ites etc.; concen- trations <1% Aqueous solutions of cyanides; concentrations < 1 % Alkaline aqueous solutions of cyanides or concentrated HCI solutions (>20%) Concentrated aqueous solutions Concentrated'solutions in extraction solvent Concentrated aqueous stream (10,000 ppm salts); dilute stream (100-500 ppm salts) Dilute solution (~ 5 ppm TDS); concentrated solution of hazardous components ..•.-.. Purified water; concentrated brine Oxidation products Cyanate solutions Cyanides to ammonium and carbonate salt solutions; HCI to CI2 gas ------- TABLE 14 COMPARISON OF PROCESSES THAT CAN ACCEPT SLURRIES OR SLUDGES Process Calcination Freeze Crystallization HGMS Liquid Ion Exchange Flotation Hydrolysis Anaerobic Digestion Composting Steam Distillation Solvent Extraction State-of-the-Art Used but not common (Cat. IV) Needs development (Cat. Ill) Needs research (Cat. II) Cat. IV Cat. Ill Cat. II Cat. IV Cat. IV Cat. IV Cat. IV Required Feed Stream Properties Waste stream with components that decompose by volatilization (hydroxides, carbonates, nitrates, sulfites, sulfates) Low-viscosity aqueous slurry or sludge Magnetic or paramagnetic particles in slurry Solvent extractable inorganic component Flotable particles in slurry . Hydrolyzable component Aqueous slurry; < 7% solids; no oils or greases; no aromatics or long chain hydrocarbons Aqueous sludge; < 50% solids Sludge or slurry with volatile organics Solvent extractable organic Characteristics of Output Stream(s) Solid greatly reduced in volume; volatiles Brine sludge; purified water Particles adsorbed on magnetic filter Solution in extraction solvent Froth '.•-.'. Hydrolysis products Sludges; methane and CO2 Sludge; leachate Volatile, solid residue Solution of extracted components; residual sludge ------- TABLE 15 COMPARISON OF PROCESSES THAT CAN ACCEPT TARS OR SOLIDS Process State-of-the-Art Required Feed Stream Properties Characteristics of Output Stream(s) Calcination Used but not common (Cat. IV) Tars or solids that can be volatilized Volatiles; char and/or metal oxides Hydrolysis Needs development (Cat. 111) Tars or solid powders Hydrolysis products Steam Distillation Cat. IV Solids contaminated with volatile Purified solids; condensed organics organics Dissolution Cat. IV Tars, solids, or solid powders that Liquid solution for further treatment; will dissolve in some reagent solid residue Crushing and Grinding Cat. IV Bulk solid Powdered solid to Cryogenics Needs research (Cat. II) Tar, bulk solid Reduced particle size ------- Crushing and grinding, and dissolution are therefore likely to play important roles in subsequent design of alternative hazardous waste treatment systems. Tars, which are often neither easy to crush and grind nor to dissolve, might be reduced to smaller particle size by cryogenic cooling. The smaller particles thus formed should dissolve more rapidly than the bulk tar removed from the reactor. 4. Selection on the Basis of Economic Considerations Processes performing similar functions are compared with respect to capital and operating costs in Table 16. The bases for the cost estimates are summarized in the Preface to Part Two. For more detailed descriptions of the types of waste streams assumed in developing the costs in Table 15, refer to the individual process reports. In deriving costs of alternative treatment systems (generally a sequence of processes) for any given waste stream, operating parameters specific to the particular situation should be taken into account; the costs in Table 16 and the economic analyses given in Part Two only provide general guidelines. 33 ------- TABLE 16 APPROXIMATE TREATMENT COSTS Process Phase Separation Sedimentation Vacuum Filtration Cent rifugat ion Freeze Crystallization Evaporation Annual Volume or Mass of Waste Stream Treated (typical), gpd 5,000,000 36,000 36,000 50,000 20,000,000 Metal Removal From Liquids Precipitation . 400,000 Electrodialysis •' 9,000 Ion Exchange 80,000 Liquid Ion Exchange 80,000 Reduction 2,000 Reverse Osmosis 3,000 Electrolysis 20,000 Organic Removal From Liquids Carbon Adsorption 100,000 Resin Adsorption 67,000 Solvent Extraction Steam Stripping Steam Distillation Distillation Hydrolysis Oxidation Ozonation Other Neutralization 1,000,000 Calcination 156,000 Chlorinolysis 20,000 Capital Costs $ 200,000 $ 140,000 $ 280,000 $1,300,000 $ 300,000 $ 24,000 $ 40Q.OOO $ 300,000 $ 230,000 $ 12,000 $ 31,000 $1,200,000 $ 720,000 100,000 720,000 750 i;ooo 30,000 1,000 800,000 $ $ $ $ $ $ $ 400,000 500,000- 850,000 130,000 230,000 320,000 100,000 330,000 $1,050,000 $2,900,000 $5,500.000 Operating Costs $0.10-0.50/1000 gal $5-7/1000 gal $5-7/1000 gal $6-12/1000 gal $1-2/1000 gal $1-2/1000 gal $5-7/1000 gal $4-6/1000 ga) $3-5/1000 gal : $150-200/1000 gal $9-11/1000 gal $1-2/1000 gal $5-20/1000 gal (high figure with regeneration) $11-13/1000 gal $4-6/1000 gal ~$10 $0.25-0.90/1000 gal $264/1000 gal $20-30/1000 gal $229/1000 gal $0.40-1.00/1000 gal $2-3/1000 gal $15-20/1000 gal $3000/1000 gal Fraction of Operating Costs Attributable to: Labor Energy Materials Other* 45 35 52 3 47 62 36 24 32 29 24 11 53 14 57 44 26 15 10 1 4 5 16 92 2 3 2. "1 21 6 10-35 5-25 (high with thermal regeneration) 40 1 17 — — . . 5 7 46 12 ' 15 — — 15 Regenerating 50 43 32 5 46 28 - 16 63 32 65 — 36-56 Solvent recovered 72 6 12 17 4 20 1.5 26 4 15 59 88 21 41 74 26 37 54 24.5 64 7 •Capital amortization, water, maintenance, etc. ------- V. WASTE TREATMENT PROCESS SUMMARIES The following pages summarize briefly the salient features of each of the treatment process considered. More complete process descriptions are provided in Part Two. 35 ------- ADSORPTION, CARBON I. CONCLUSIONS AND RECOMMENDATIONS Carbon adsorption should be given serious consideration whenever it is desirable to remove mixed organics, or to recover select organic or inorganic species from aqueous waste streams with adsorbate concentrations less than 1%. II. PROCESS DESCRIPTION A large variety of organic solutes, and a more limited number of inorganic solutes can be removed from aqueous waste streams by adsorption onto activated carbons with a high absorptive surface area (500-1500 m2/g). Adsorption of organic solutes is commonly followed by thermal regeneration of the carbon and simultaneous destruction of the absor- bates. In a few cases, the carbon may be regenerated and the adsorbate recovered by treat1 ment with acid, base, steam, or solvent. III. APPLICATIONS TO DATE There are about 100 full-scale carbon adsorption systems currently in use for industrial/ municipal wastewater treatment. In general, the process works best with chemicals that have a low water solubility, high molecular weight, low polarity, and low degree of ionization. The concentration of adsorbates in the influent should be less than 1%, and suspended solids must be low (^50 ppm) for most systems. Recovery is possible if the adsorbate may be easily volatilized or dissolved off the carbon. Thermal regeneration (with organic adsorbates) is economical if the carbon usage is above about 1000 Ib/day. IV. ENERGY, ENVIRONMENT. ECONOMICS Energy requirements include electricity: for pumps and fuel for the regeneration furnace. Energy costs may be around 25% (or higher) of the total operating costs where concentrated waste streams are being treated and the carbon is thermally regenerated. Energy may constitute no more than 5% of total operating costs if regeneration is accom- plished by non-thermal means. Capital costs for a 100,000-gpd facility would be in the neighborhood of $1,000,000. Total operating costs would be in the range of $5-20/1000 gal. If spent carbon is not regenerated, it presents a problem for disposal. If it is thermally regenerated, the regeneration furnace will usually require an afterburner, a scrubber, and perhaps a dust filter. V. OUTLOOK FOR WASTES For aqueous waste streams containing up to 1% of refractory or toxic organics, carbon adsorption is an excellent, proven process. For more concentrated waste streams, solute removal would be even more efficient, but the more frequent regeneration required would significantly increase costs. Development of new methods of regeneration, particularly ones that allow recovery of the adsorbate, could greatly expand potential applications of the process. 37 ------- ADSORPTION, RESIN I. CONCLUSIONS AND RECOMMENDATIONS i1* • Resin adsorption, like carbon adsorption, is a useful process for extraction of organic solutes from aqueous waste streams. Resin adsorption will generally be preferred when it is desirable to recover the adsorbate. Carbons are usually thermally regenerated with de- struction of the adsorbate. Resins are always chemically regenerated (with caustic or organic solvents). II. PROCESS DESCRIPTION Resin adsorption uses synthetic resins (which can vary significantly in their chemical and physical nature) to extract and recover, if desired, dissolved organic solutes from aqueous waste streams. Resins with either (or mixed) hydrophobic or hydrophylic natures are available, and can be used to extract, respectively, hydrophobic or hydrophylic solutes. Resins are always chemically regenerated. When organic solvents are used as the regenerant, solute recovery is generally via distillation. III. APPLICATIONS TO DATE Current industrial waste treatment applications include: phenol recovery; color re- moval; and fat removal from aqueous waste streams. The phenol concentration can be as high as 8% by weight in the feed. Proposed waste treatment applications (near-term) include removal of toxic chemicals from munitions facilities' effluents; removal of pesticides from aqueous streams; carcinogen removal from laboratory waste waters; and removal of phenolics; and removal of chlorinated hydrocarbons. ' ; IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are small when the regenerant is not recycled. When both solvent and solute are recovered, the steam requirements for distillation (up to three stills required) will be significant. If the regenerant is not recycled, it must be disposed of. If the regenerant is recycled (e.g., by distillation), the still bottoms must be disposed. Capital costs are moderately large; while no furnace is needed for regeneration (an expensive item with carbon systems), resins costs are high. Operating costs may be below $1/1000 gal in some applications, but may reach $5-20/100 gal when concentrated waste streams are treated and the solute recovered. Credit for recovered solute can allow a system to operate at a profit in favorable cases. V. OUTLOOK FOR WASTES Resin adsorption is particularly attractive for removing organics from aqueous waste streams when material recovery is desirable, and when the waste stream contains high levels of dissolved inorganic salts: Applications appear to be expanding. 38 ------- BIOLOGICAL TREATMENT: ACTIVATED SLUDGE I. CONCLUSIONS AND RECOMMENDATIONS Activated sludge treatment is extensively used in industry, and is probably the most cost-effective method of destroying organics present in an aqueous waste stream. Neutraliza- tion and equalization of the waste stream,- as well as suspended solids removal, should precede the activated sludge system. It is a safe and reliable process which is relatively uncomplicated to operate and relatively inexpensive. Improved understanding of activated sludge microbiology and enzyme catalysis will improve process operating efficiencies in the future. II. PROCESS Aqueous organic waste streams having less than \% suspended solids have flocculated, biological growths continuously circulated arid contacted in the presence of oxygen. Since the process was introduced at the turn of the century it has been modified through improved methods of maintaining aerobic conditions under varying organic loadings. The process involves an aeration step, followed by solids-liquid separation, with recycle of a portion of the solids. The basic system has an open tank for the mixture of the active biomass with influent wastewater and air, followed by a clarifier. Bacteria in activated sludge systems serve to perform hydrolysis and oxidation reactions. III. APPLICATIONS TO DATE The activated sludge process has been applied extensively to treat wastewater from municipal sewage plants, canneries, paper and pulp mills, refineries, breweries, and steel, textile, petrochemical, pharmaceutical, and timber processing plants. It has also been applied to photo processing wastes and to the propylene glycol wastewater from polyvinyl chloride production. IV. ENERGY, ENVIRONMENT, ECONOMICS The activated sludge system is energy-intensive, with over 10% of total operating cost based on energy needed for pumping, aeration and clarification. The system is basically environmentally sound; no chemicals are added and natural degradation takes place. Capital costs are about 10^ per 1,000 gallons for a 10 mgd facility. These costs increase to over $1 for facilities handling less than 1 mgd. Processes handling dilute wastewaters are reported to have total costs of 10-40^ per 1,000 gallons. 39 ------- V. OUTLOOK FOR WASTES Activated sludge systems are employed in at least two facilities for treatment of hazardous wastes. The system is environmentally sound because it employs natural micro- bial metabolic processes; no chemicals are added. 40 ------- BIOLOGICAL TREATMENT: AERATED LAGOONS a I. CONCLUSIONS AND RECOMMENDATIONS The aerated lagoon biological treatment process decomposes organics in wastewater containing less than 1% solids, employing essentially the same microbial reactions as activated sludge. The aerated lagoon, however, does not have a sludge recycle system for continuous circulation of microorganisms, and microbial strains do not acclimatize to the same extent. BOD removal efficiencies range from 60 to 90%. The process is not as attractive for industrial waste treatment as the activated sludge process; removal efficiencies are not as high and the process is less flexible in maintaining effluent limitations under varied influent loading. II. PROCESS The aerated lagoon technique developed from adding artificial aeration to existing waste stabilization ponds. Usually the lagoon is an earthen basin with sloping sides and about 6-17 feet depth. For the treatment of industrial wastes, it may be necessary to line the basin with an impermeable material. Because wastewaters in aerated lagoons are generally not as well mixed as those in activated sludge basins, a low level of suspended solids is maintained. If mixing and aeration are not complete, a portion of the solids settles to the bottom and undergoes anaerobic microbial decomposition. Retention times are slightly longer than for activated sludge; and where anaerobic decomposition is encouraged, the time is even longer. III. APPLICATIONS TO DATE The process has been successfully used for petrochemical, textile, pulp and paper mill, cannery, and refinery wastewaters. IV. ENERGY, ENVIRONMENT, ECONOMICS For comparable treatment efficiency, energy requirements are comparable to those for activated sludge treatment; but generally the aerated lagoon employs less energy for aeration and longer retention periods. Chemical requirements are essentially limited to addition of nutrients. As in activated sludge treatment, the effluent is a clarified liquid and a biomass sludge residue; the biosolids are more difficult to flocculate and settle from the mixed liquor because of the longer retention time. Total costs range from 10 to 30(^/1000 gallons of dilute influent; if basin lining and high aeration is required, treatment costs may be nearly $2/1000 gallons. V. OUTLOOK FOR WASTES The process is not as attractive as activated sludge treatment for a wastewater influent with highly variable organic and metal concentrations. 41 ------- BIOLOGICAL TREATMENT: ANAEROBIC DIGESTION I. CONCLUSIONS AND RECOMMENDATIONS .;. Anaerobic digestion is a biological treatment process for the degradation of simple organics in an air-free environment. Part of the carbon substrate is used for cell growth and the other is converted to methane and carbon dioxide gas. The microbiology is complex and still not well understood. Two types of interdependent organisms are present, and steady- state environmental conditions must be maintained to keep them balanced. Because of this delicate balance, the process is not suitable for treatment of most industrial processing sludges. Oil, fat, and grease are also troublesome. II. PROCESS . ; The organic sludges and biomass sludges from primary clarification and biological treatment are processed to reduce their volume and improve their stability. In the conven- tional process, the waste stream is fed into: the middle zone of a closed tank with no agitating mechanism. The solids are digested by the organisms, gas rises, bringing scum to the surface, and the gas is collected from the;roof of the tank. Usually this gas is used to maintain the temperature of the installation arid sometimes to heat other parts of the plant. The digested sludge settles to the bottom of the tank after 30 to 60 days. There is only a small volume of digested sludge, which is stable and inert and can be disposed of for land reclamation or by ocean dumping. The bacteria are sensitive to pH, temperature, and the composition of the waste, but usually with time the system will achieve its own balance. Modifications have been made for some installations, usually involving agitation or heating, shortening the process to several days to two weeks. III. APPLICATIONS TO DATE Most installations have been for the digestion of sewage sludge, as the final step in a complete municipal waste treatment facility. Boston and Chicago both use anaerobic digesters: Boston disposes of the waste by.ocean dumping; Chicago, whose plant is the world's largest, treating a billion gallons of wastewater per day, uses the waste for land reclamation. In the past 20 years, the system, has been studied for meat packing wastes, and there are several plants operating commercially. It has also been studied for cotton kiering liquor, brewery wastes and alcohol distillery wastes. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy demands are relatively low; some electric power is needed to mix the reactor contents, recycle some of the effluent sludge to the reactor and heat the incoming sludge. Essentially all of the power for the heat exchanger is provided through production of methane gas. 42 ------- The presence of arsenate or mercury in anaerobic digestors could lead to formation of toxic compounds. In municipal wastewater treatment plants, costs for anaerobic digestion are difficult to segregate. Estimates for a facility treating 100,000 gal/day of sludge with 5% solids would be: capital investment, $1.25 million,annual fixed costs would be $219,000, and variable costs $171,000. The cost for treating 103 gallons would be $10.69. V. OUTLOOK FOR WASTES There seems to be a potential for disposal of feed lot wastes, culture material from pharmaceutical processing, and food processing wastes. For industrial processing sludges, the method may be suitable if there is a steady volume and flow, oil and grease are removed, and soluble metal content is low. 43 ------- BIOLOGICAL TREATMENT: COMPOSTING I. CONCLUSIONS AND RECOMMENDATIONS Composting provides a means of achieving aerobic digestion of organic wastes by microorganisms inthepresenceoftheirownreleasedheat.lt is the only biological treatment process relatively insensitive to toxicants and it encourages adsorption of metals. Costs are higher than for other biological processes, but lower than for incineration. II. PROCESS Composting basically involves piling ground waste in windrows and aerating the piles by periodic turning. All that need be done is scheduling of spreading and turning with earthmoving equipment, adding some nutrients and alkalis if necessary, and providing for collection of leachate and runoff water to protect groundwater. There are over 30 process modifications involving rotating drums, forced aeration, etc. Complete digestion of most organic wastes take place in three or four months, although refinery wastes or other difficult organics may take up to a year. III. APPLICATIONS TO DATE Systematic composting has been widely(used in Europe, where there is a ready market for composted waste as an organic soil conditioner. Most of the demonstration projects in the United States have closed for lack of a market for humus, but some cities use this cost-effective disposal technique for municipal refuse and give the compost away. Chicago uses the system to dispose of high-strength organic sludges, and several petroleum refineries use it for refinery wastes. It has also been used for cannery solids, pharmaceutical and meat packing sludges. IV. ENERGY, ENVIRONMENT, ECONOMICS i Energy demand is low, limited primarily to fuel costs to operate earthmoving equip- ment and pumps. The only emissions from composting are carbon dioxide, steam, a liquid effluent containing partially oxidized organics and a barnyard smell indicative of healthy microbial activity. Costs for composting are about $30/thousand gallons of influent, exclusive of land acquisition or further treatment of collected leachate. The capital expenditure to handle 100,000 gpd would be $1.5 million; fixed costs $275,000 annually and variable costs $802,500. 44 ------- V. OUTLOOK FOR WASTES Composting is applicable to high-organic wastes, including oils and tars and industrial processing sludges. 45 ------- BIOLOGICAL TREATMENT: ENZYME TREATMENT I. CONCLUSIONS AND RECOMMENDATIONS Enzyme treatment of industrial processing wastes is totally impractical. Enzymes catalyze specific reactions and cannot adapt.well to the varying composition of typical waste streams. Furthermore, enzyme production is very expensive. II. PROCESS DESCRIPTION Enzymes are highly selective chemical catalysts which act on specific molecules. The urease enzyme, for example, breaks down urea into carbon dioxide and ammonia. A hydrolase enzyme derived from yeast has been shown to oxidize phenol to carbon dioxide and water. The cellulose enzyme, produced by a stream of fungus, Trichodenna viridi. catalyzes the hydrolysis of cellulose to glucose^ III. APPLICATIONS TO DATE f'. There are no known full-scale applications of enzyme treatment processes in hazardous waste management. There are commercial applications in meat tenderizing, de-hairing of hides prior to tanning, cheese-making, pharmaceutical manufacture, and detergent production. ; The Army's Natick Research and Development Command is operating a 1000 Ib/mo. pilot plant to convert waste paper into glucose. A number of Government, university, and industrial laboratories are investigating the use of lactose for recovery of monosaccharides from cheese whey. Groups at Oak Ridge National Laboratories and the University of Pennsylvania have studied the enzyme decomposition of phenol. IV. ENERGY, ENVIRONMENT, ECONOMICS Due to the specificity of enzyme reactions and the fact that current waste treatment applications are limited in number and lab scale, no useful generalizations can be made about energy, economics, or potential environmental impacts. V. OUTLOOK FOR WASTES Enzyme treatment may be useful for specialized industrial applications, particularly in cases where salable reaction products result. Enzymes have little or no potential in general waste treatment. 46 ------- BIOLOGICAL TREATMENT: TRICKLING FILTERS I. CONCLUSIONS AND RECOMMENDATIONS The trickling filter process is a proven technology for the decomposition of organics in waste streams with less than 1% suspended solids. The process brings the wastewater in contact with aerobic microorganisms by trickling the water over media supporting the microorganisms. BOD removal efficiencies range from 50 to 85%. The process is used in industry to accept wastewater loading variations and provide a relatively uniform effluent for treatment by other biological processes, such as activated sludge. II. PROCESS Wastes are sprayed through the air to absorb oxygen, and then allowed to trickle through a bed of rock or synthetic media coated with a slime of microbial growth. Process modifications employ various media and depths to retain the microorganisms under varying hydraulic and effluent recycle conditions. The primarily metabolic processes are aerobic, and the microbial population is similar to the activated sludge population. However, because of the relatively short contact time, the percentage removal of organics is not as great. The process involves open tanks or towers to house the filter packing, followed by effluent clarifiers. Recycle pumps may be used to recirculate filter effluent. A rotating spray dosing system feeds influent wastewater to the filter surface. III. APPLICATIONS TO DATE Trickling filters have been extensively used in sewage treatment and in treatment of refinery wastewaters containing oil, phenol, and sulfide. They are applicable to the same industrial waste streams as the activated sludge process, including cannery, pharmaceutical, and petrochemical wastes. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy demands are low, as little as one-tenth that of activated sludge treatment. Dilute wastewater is treated at a total cost between 10 to 30tf per 1000 gallons; for concentrated waste requiring filter recycle the cost may be $2 per 1000 gallons. The process effluents are a liquid wastewater from which a major portion of the dissolved organics have been removed and a biomass sludge. V. OUTLOOK FOR WASTES The process could be used in sequence with other biological treatment, such as activated sludge, but it is not generally efficient enough to use as the sole method of biodegradation. 47 ------- BIOLOGICAL TREATMENT: WASTE STABILIZATION PONDS I. CONCLUSIONS AND RECOMMENDATIONS Waste stabilization ponds utilize natural bibdegradation reactions in wastewaters con- taining less than 0.1% solids with low concentrations of organics. The process is more sensitive to concentrations of inorganics and suspended solids than any of the other biological treatments discussed in this report. It is suitable for industrial wastes only where preliminary treatment has removed most contaminants and final effluent polishing is needed before discharge to a receiving water. ! II. PROCESS • : . . Waste stabilization ponds are large shallow basins where wind action provides aeration and a mixed autotrophic and heterotrophic microbial population provides decomposition of organics over a long retention time. Deep: ponds, more than 4 feet deep, may promote anaerobic decomposition of settled sludge. III. APPLICATIONS TO DATE Waste stabilization ponds have been widely used for sanitary sewage and dilute industrial wastes, mostly to provide final effluent polishing. Industries using the method include meat and poultry packing, canneries, dairies, iron and steel works, paper and pulp mills, textile mills, oil refineries and petrochemical plants. IV. ENERGY, ENVIRONMENT, ECONOMICS Large land acreage is the principal capital cost; energy and chemical requirements are insignificant. Total costs for treating dilute wastewaters in unlined basins range from 5 to 15^ per 1000 gallons; for more concentrated waste streams in clay-lined basins, the cost is about $1.70 per 1000 gallons. Energy is needed only for pumping. A polished liquid effluent and some biomass sludge are the end-products. V. OUTLOOK FOR WASTES The process can be employed only where substantial land acreage is available and where climate is suitable. Toxic inorganics must be removed before waste stabilization ponding because of the system's high sensitivity to inhibitors. The use of the method for final polishing provides extra insurance that final effluent guideline limitations will be met. 48 ------- CALCINATION I. CONCLUSIONS AND RECOMMENDATIONS f Calcination is a well established process, and one of the few that can satisfactorily handle sludges. Calcination is recommended as a one-step process for treatment of complex wastes containing organic and/or inorganic components. The organics are destroyed; the inorganics are generally reduced in volume and converted into a form of low leachability suitable for landfill. II. PROCESS DESCRIPTION Calcination is a thermal decomposition .process, generally operated around 1000°C at atmospheric pressure. It can be applied to aqueous solutions, slurries, sludges, and tars to drive off volatiles and to produce a dry powder or sintered solid. Typical calciners include the open hearth, rotary kiln, and fluidized bed. III. APPLICATIONS TO DATE Industrial applications include production of cement, lime, magnesia, titania, and wall plaster, and smelting of sulfide and carbonate ores. Waste treatment applications in- clude recalculation of lime sludges from water treatment plants; coking of heavy residues and tars from petroleum refining operations; concentration and volume reduction of liquid radioactive wastes; and treatment of mixed refinery sludges containing hydrocarbons, phosphates, and compounds of Ca, Mg, K, Na, S, Fe, and Al. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are generally high, but depend on the water and organic content of the waste stream. Calcination of dry material requires about 1-3x106 Btu/ton of solid product; calcination of a sludge or slurry with ^0% water requires about 20x106 Btu/ton of solid product. If this waste stream contains a combustible organic fraction, the energy re- quirements are reduced. ; In general, calcination systems will require fairly extensive air pollution control equip- ment, including particulate-removal devices, • wet scrubbers, and possibly final gas adsorp- tion systems. Capital investment costs for a calciner are in the range of $10,000-$30,000/ton of throughput daily. Operating costs are highly variable, depending on the water and organic content of the waste stream, and the possibilities for resource recovery credits. V. OUTLOOK FOR WASTES Calcination has been used widely in industrial and waste treatment applications. Its use is likely to expand, particularly in the treatment of tars, sludges, and other residues which present particularly difficult problems for disposal. 49 ------- CATALYSIS I. CONCLUSIONS AND RECOMMENDATIONS Whenever a waste stream can usefully be treated by a chemical transformation process, the possibility of catalyzing the reaction should be considered. In general, if a transforma- tion can be successfully catalyzed, operating .costs and energy requirements will be reduced. II. PROCESS DESCRIPTION Catalysis is not a process in itself, but rather a modification of the rate or mechanism of chemical reaction processes through the use of catalysts, which are themselves unchanged at the end of a reaction. III. APPLICATIONS TO DATE The industrial applications of catalysts in the petroleum refining, chemical, phar- maceutical, and textile industries are legion. In the field of waste treatment, catalytic oxidation is used quite widely as an alternative to incineration in the decomposition of waste organics. A number of catalytic processes have been investigated in the laboratory for destruction or detoxification of chlorinated pesticides, oxidation of cyanides, sulfides, and phenols, decomposition of sodium hypo- chlorite solutions, and conversion of mixed carboxylic acid waste streams to fumaric acids for recovery. IV. ENERGY, ENVIRONMENT, ECONOMICS In general, a catalytic process operates at a much lower temperature than the equiva- lent non-catalytic process and hence consumes less energy. Environmental impacts are generally the' same as those of the non-catalytic process. Catalytic processes may be higher in capital costs than non-catalytic processes in some cases. However, the less severe operating conditions (lower temperatures and/or pressures) almost always result in lower overall operating costs. V. OUTLOOK FOR WASTES As the use of chemical processing in waste treatment increases, the effort to develop catalytic processes should be increased as well. A great deal of work is needed to demon- strate the commercial practicality of catalytic reactions tested in the laboratory, and ex- ploralory work could be useful on catalytic hydrogcnation and low-temperature air oxidation. 50 ------- CENTRIFUGATION I. CONCLUSIONS AND RECOMMENDATIONS l ' . Centrifugation is a well-developed liquid/solid separation process being used in a variety of full-scale applications for material processing and waste treatment. In treating hazardous wastes, centrifugation can be used., to greatest advantage to increase the solids concentration, and thereby reduce the volume, of a high concentration liquid/solid mixture (sludge) by partially separating the liquid and solid phases ("sludge dewatering")- Centrifugation is generally technically and economically competitive with other sludge dewatering processes (e.g., vacuum filtration or the use of filter presses) and should be considered as a potential process for concentrating hazardous waste sludges and slurries. Equipment is commercially available in a large variety of sizes and configurations. II. PROCESS ' Centrifugation is a physical process whereby the components of a fluid mixture are separated mechanically by the application of centrifugal force, applied by rapidly rotating the mass of fluid within the confines of a; rigid vessel. Centrifugal forces acting on the revolving mass of fluid cause the solids suspended in the fluid to migrate to the periphery of the vessel where they can be separated. The particles are removed as a liquid/solid mixture significantly more concentrated than the original liquid. III. APPLICATIONS TO DATE : Some common applications of centrifugation are in separating oil and water mixtures; clarification of viscous gums and resins; classification and removal of oversize particles and unground pigment from lacquers, enamel and dye paste; clarification of essential oils, extracts, and food products, such as homogenized milk and fruit juices; separation of micro-organisms from fermentation broths, .recovery of finely divided metal such as silver from film scrap and platinum from spent catalyst; separation of acid sludges from the acid treatment of petroleum; recovery of crystalline solids from brine; dewatering of fibrous solids such as paper pulp and chemical fibers; dewatering and removal of starch from potato fibers, etc. Probably the main application for centrifuges at present is the dewatering of waste sludges. • IV. ENERGY, ENVIRONMENT, ECONOMICS Power requirements for centrifugation are typically 0.3-1.2 horsepower per gallon per minute of inlet waste feed. Power consumption is equal to or slightly greater than for other sludge dewatering processes. 51 ------- For most sludge dewatering purposes, centrifugation is generally cost-competitive with other dewatering processes such as vacuum filtration or press filtration. A conveyor bowl type centrifugation system capable of dewatering 6 tons per day of sludge (dry basis) will have an installed capital cost of approximately $140,000 and a total operating cost (including amortization) of $34.50 per ton of solids dewatered. In most applications, costs range from $20-$45/ton. V. OUTLOOK FOR WASTES The major application of centrifugation to waste treatment is the dewatering of waste sludges generated by water pollution control systems. Centrifuges have for many years been used on biological sludges from municipal treatment plants and from pulp and paper mills. Some expect the technique to replace vacuum filtration as the most common dewatering technique, especially for sticky or gelatinous sludges. It will also find further application in removing soluble metals from wastewater, as from the wet scrubbers used in the steel industry, to dewater sludges generated from sulfur dioxide air pollution control systems, etc. Because it is capable of totally closed operation, centrifugation is particularly well suited to treating liquids that are volatile, flammable, or otherwise pose health and/or safety hazards to operating personnel. 52 ------- CHLORINOLYSIS I. CONCLUSIONS AND RECOMMENDATIONS Chlorinolysis is capable of converting most liquid chlorinated hydrocarbons completely to carbon tetrachloride. It is not really a rwaste treatment process, but a manufacturing process that uses chlorocarbon waste streams and residuals as feedstocks. The process has excellent resource recovery potential (sufficient wastes are generated in the Gulf Coast region to support at least one 25,000 ton/yr chlorinolysis plant) if there is a market for the carbon tetrachloride. There may be, however, legal and institutional problems that might hinder transfer of wastes from generators to an operating chlorinolysis unit. II. PROCESS At temperatures around 500°C and pressures of about 200 atm in the presence of excess chlorine, the carbon-carbon bonds of hydrocarbons can be broken, and the molecules recombined to react with chlorine to form carbon tetrachloride. Because liquid chlorine is highly reactive, reactors and piping must be high-purity nickel, surrounded by a stainless steel jacket. The organic feedstock and preheated chlorine are introduced to the reactor, which is heated to initiate chlorinolysis; subsequently the process provides its own heat. At the end of the process, the pressure is released and the products are cooled and drawn off. Subsequent processing by distillation yields carbon tetrachloride, the principal product for sale. III. APPLICATIONS TO DATE j . This is not a waste treatment process, but a production process that can utilize waste streams. A semicommercial plant to produce 6000-8000 tons/year has been operating in Germany and a 50,000 ton/year plant is planned for the same site. IV. ENERGY, ENVIRONMENT, ECONOMICS Electricity and fuel requirements per ton of carbon tetrachloride are relatively small — 135kWh and 794 Btu, respectively. Chlorinolysis offers the opportunity of resource re- covery, but the process involves hydrochloric acid and phosgene gas effluents. Neutraliza- tion of the effluent streams will produce spdium hypochlorite, which is toxic to aquatic life. Capital and operating costs for a plant processing 25,000 metric tons/year of mixed chlorinated hydrocarbon wastes are estimated at $19,700,000/year; the process could produce carbon tetrachloride at 10.24 per Ib, and the selling price is now 19^. V. OUTLOOK FOR WASTES Chlorinolysis is an efficient, cost-effective process for recovering carbon tetrachloride from chlorinated hydrocarbon waste streams. The outlook for the process depends on the future demand for carbon tetrachloride, and the availability of a continuing supply of suitable wastes. ------- DIALYSIS I. CONCLUSIONS AND RECOMMENDATIONS Dialysis is one of the earliest membrane processes. It can separate salts and low mole- cular weight organics from colloids and high molecular weight solutes in aqueous waste streams. However, both of the output streams are more dilute than the feed stream, and neither is likely to be more suitable for disposal or recovery than the feed stream. Hence, dialysis has little or no potential for general waste treatment applications. II. PROCESS DESCRIPTION A solute-containing feed stream is passed across one free of a semi-permeable mem- brane and a higher volume wash stream is passed across the opposite face. Small solute molecules are transferred to the wash stream by diffusion across the membrane. Larger molecules and colloids are retained in the feed stream. III. APPLICATIONS TO DATE The best known current application of dialysis is hemodialysis, which removes salts, urea, and other wastes from the blood of people suffering from chronic kidney failure. Since the 1920's, dialysis has been used in the rayon industry to separate caustic soda from hemicellulose wastes. There are also other smaller scale applications in pharmaceutical and biochemical laboratories for special production and purification. Dialysis equipment is available commercially. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are low, being limited to the pumping of feed and wash streams. y- The two diluted product streams could' prevent difficult disposal problems if not reusable. : Capital costs depend more on the amount of material to be separated than on the waste stream throughput. A commercial dialyzer separating 1000 Ib/day of solute would cost about $3000. ' ' *• V. OUTLOOK FOR WASTES Dialysis is a mature technology; no major new developments are expected which would make the process at all useful for hazardous waste treatment. 54 ------- DISSOLUTION I. CONCLUSIONS AND RECOMMENDATIONS Dissolution is a first step that removes major or minor constituents from solids. The process is applicable to any solids that can be wetted by a suitable liquid. We recommend that more emphasis be placed on more complete characterization of solids to aid in specification and testing of possible dissolution processes. Efforts should also be made to utilize lower quality or waste reagents where possible. II. PROCESS Dissolution may be defined as the complete or partial transfer of one or more components from a solid to a liquid phase in contact with the solid. The reaction involves some degree of chemical transformation, such as solvation, ionization, or oxidation. The solids are contacted by the reagent in a mixer, following which the slurry is separated. Heat may be applied to speed the process and provide increased solubility. Solids can be treated sequentially with different reagents to remove components selectively. The products are a wastewater stream that requires further treatment, and residual solids that may be suitable for disposal, reuse, or further treatment. III. APPLICATIONS TO DATE Dissolution has been widely used in metallurgy since the early 1800's and in the synthetic chemical industry since its beginning. Many of these applications (e.g., separation of metals from ores) are closely related to treatment of inorganic wastes, but there appears to be little large-scale application to waste treatment. One installation involves production of chemicals for agriculture and other use from galvanizing wastes and flue dust. Another is used for recovery of metallic copper from.scrap, and a semi-commercial plant is being considered for recovery of metal from plating slimes. Several pilot and laboratories studies are now going on. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are limited to electricity for mixing and pumping, and heat, if required. Emissions to water are not harmful if the liquors used and produced are conveyed to the next process step without inadvertent losses. No land disposal problems are antici- pated if leached solids are adequately washed to remove leach liquor. Emissions to air will be significant only when gas is evolved in the process, or where an unintended reaction takes place (e.g., reaction of traces of sulfides in water to give off hydrogen sulfide). The diversity of materials potentially suitable for dissolution and the circumstances of reaction vary considerably. The process is especially sensitive to chemical and labor costs. 55 ------- An approximate cost for dissolving a hypothetical metal finishing sludge waste using fresh sulfuric acid reagent would be: $61 per ton of input solids or $300 per ton of desired metal removed; the cost of sulfuric acid is $24 per input ton. V. OUTLOOK FOR WASTES Further applications for waste treatment depend on cost-sensitive factors, such as utilization of waste reagents, and on better understanding of composition of sludges and mixed metal compounds. 56 ------- DISTILLATION I. CONCLUSIONS AND RECOMMENDATIONS Distillation is a unit operational process that is fully developed commercially and is often employed to separate or purify liquid.organic product streams. It is a non-destructive process, and practical limitations are primarily economic. With more stringent limitations on air, liquid effluents, and land site disposal, and with the rising cost of organic chemicals, distillation could become more competitive with other methods for recovery of useful materials from waste streams. II. PROCESS The basic principle of distillation is as simple as it is old: when a mixture of liquids is boiled, the vapor usually differs in composition from the liquid that remains. Only since the 19th century, however, has distillation been conducted on a large scale as a steady-state operation. In general, a feedstock is charged to a large vessel (still) which is heated, and vapors are removed as they are formed, and then condensed. There are a number of variations on this basic process. III. APPLICATIONS TO DATE Distillation has wide industrial application in petroleum fractionation, organic chemical purification, organic chemical intermediate manufacture, solvent recovery, and cryogenic air separation to produce oxygen, nitrogen, and argon. IV. ENERGY, ENVIRONMENT, ECONOMICS Because of the variables involved, there is no such thing as a typical cost on a unit product or unit feed basis. ; Distillation creates no air or liquid effluent problems. An economic analysis of a system that might be used for different types of organic liquid waste streams was made, based on a capacity of 8000 Ib 20% acetone in water waste/day. The solvent recovery cost in this system would be 4.2^/lb acetone. V. OUTLOOK FOR WASTES Hazardous wastes that can be economically treated by distillation (for organic chemical or solvent recovery) include liquid organic mixtures, such as solvent mixtures recovered from curbon air adsorption units, paint wastes, organic-containing plating wastes, and lube 57 ------- oil. The process is not suitable for treatment of thick, polymeric materials, slurries, sludges, or tars that can cause operational problems. The types and quantities of organic solvent and chemical wastes that are treated by distillation will increase as effluent regulations become more stringent. 58 ------- ELECTRODIALYSIS I. CONCLUSIONS AND RECOMMENDATIONS Electrodialysis has not been employed on a full-scale basis for any hazardous waste problem, per se. Nevertheless, it may have applicability where it can be tied into further concentration or reuse schemes. It will profit by the fact that it is a mature technology with well-known performance characteristics and price, and therefore can be easily evaluated as a potential component of any multi-process treatment being considered. II. PROCESS The general principle of electrodialysis is the separation of an aqueous stream under the action of an electric field into two streams, one enriched and one depleted. Success depends on synthetic membranes, usually based on ion-exchange resins, which are permea- ble only to a single-charge type of ion. Cation exchange membranes permit passage of only positive ions, while anion membranes permit only negatively charged ions to pass through. The feed water passes through compartments formed by the spaces between alternating cation-permeable and anion-permeable membranes held in a stack. At each end of the stack is an electrode having the same area as the membranes. A d-c potential applied across the stack causes the positive and negative ions to migrate in opposite directions. Feed material is first filtered to remove suspended particles that could clog the system. An operating plant usually contains many recirculation, feedback and control loops and pumps to optimize the concentrations and pH at different points for most efficient operation. III. APPLICATIONS TO DATE Electrodialysis has been used for desalination since the 1950's. The largest number of installations is in the production of potable water from brackish well or river water. Hundreds of such units, some of which can;handle more than one million gallons per day, are in use throughout the world. In the food industry, electrodialysis is used for desalting whey and de-ashing sugar. The chemical industry uses the technique for enriching or depleting solutions, and for removing mineral constituents from product streams. .IV. ENERGY, ENVIRONMENT, ECONOMICS Electrical requirements vary, but conventional systems take about 5 kWh of energy for each 1000-ppm reduction of salt in each 1000 gal. purified product water and up to 3 kWh to pump each 1000 gal. products. ------- The product streams must be recycled, sold, or otherwise disposed of. Electrodialysis may generate low levels of toxic or flammable gases that might present a hazard in an en- closed space. The capital costs for electrodialysis are .modest, about 20-25% of the total cost of water treatment. Both capital and direct operating costs are dependent on the volume of_ water treated and on the salts removed. Total water production costs of less than $.50/10 3 gal are reported for salt reduction from 2000 ppm to 500 ppm in plants treating 10* gal/day or more. Other plants may have higher costs or may receive significant credits for reclaimed material. A typical electrodialysis system to treat rinse tanks from an acid nickel plating line mighTcost about $6.00/163 gal. t V. OUTLOOK FOR WASTES Pilot operations have been carried out in the desalting of sewage plant effluent, sulfite-liquor recovery, and acid mine drainage treatment. Treatment of plating wastes and rinses, particularly to salvage chromium, may have some potential. 60 ------- ELECTROLYSIS * I. CONCLUSIONS AND RECOMMENDATIONS Electrolytic processes may be considered for reclaiming heavy metals, including toxic metals from concentrated aqueous solution and for polishing dilute metallic wastewaters. They are not generally useful for dissolved- organics, organic waste streams or viscous and tarry liquids. II. PROCESS Electrolysis refers to the reactions of .oxidation or reduction that take place at the surface of conductive electrodes immersed in an electrolyte, under the influence of an applied potential. III. APPLICATIONS TO DATE ! Electrolysis, including electroplating and anodizing, has been an important process of industrial chemistry for many years. Chlorine production, for example, depends on elec- trolysis, and many commercial metals are refined by electrolytic processes. Metals may be obtained from primary ores, and magnesium and aluminum are processed by electrolysis in molten salt baths. Electrolysis for waste treatment has been employed to a limited extent depending largely on costs. The most frequent application is the partial removal of concentrated metals such as copper from waste streams for recycle or reuse. Other applica- tions which have been successfully piloted include oxidation of cyanide wastes and separ- ation of oil-water mixtures. IV. ENERGY, ENVIRONMENT, ECONOMICS Electrical energy costs range from 10 to 35% of total operating costs, with treatment of concentrated metals at the low end, and dilute streams or cyanide treatment at the high end. ; Gaseous emissions may exist; some may be vented to the atmosphere, others may have to be scrubbed or otherwise treated. The process wastewater may be reusable or disposable, or may have to undergo further processing. Costs are highly dependent on the concentration and nature of the undesirable material. Electrolysis may offer significant trade-offs between capital and operating costs, depending on chemical and economic variables. 61 ------- ELECTROPHORESIS I. CONCLUSIONS AND RECOMMENDATIONS r • • No suitable equipment for electrophoretic treatment of hazardous wastes is available. Many critical problems would have to be solved before such equipment could be developed, and even if the design problems were solved, there is no assurance that the process would be operationally practical. Further consideration of electrophoresis cannot therefore be justified. II. PROCESS DESCRIPTION Electrophoresis is the transport of electrically charged particles under the influence of a DC electric field. The charged particles (generally colloids in the l-20/i size range) migrate to a collecting membrane for subsequent removal. III. APPLICATIONS TO DATE Electrophoresis is used extensively as a laboratory tool in the analysis and separation of proteins, polysaccharides, and nucleic acids. It .has also been used commercially for creaming of rubber latex, and for fractionation of animal sera for veterinary vaccines. Numerous proposed applications have been researched and shown to be technically feasible. These in- clude deposition of paints, polymers, ceramics, and metals. The process has also been con- sidered for water purification (e.g., for separation of emulsions, and for color, virus, and algae removal). : IV. ENERGY, ENVIRONMENT, ECONOMICS In aqueous systems, the electrical energy requirements are of the order of 7 kWh/ 1000 gal. The process may evolve gases from electrode reactions. Both the concentrated sludge and the "treated" liquid may require subsequent disposal. Capital costs would be lower than the costs for electrodialysis. Operating costs might be in the range of $0.50-2.00/1000 gal, depending on the application. V. OUTLOOK FOR WASTES At least 5-10 years of effort would be required to develop electrophoresis equipment for waste treatment. In view of the lack of scientific and practical guides available, and the very significant problems of controlling electrode reactions, pH, conductivity, flow, tem- peratures, and membrane plugging, there is even some question whether an R&D effort would be successful. 62 ------- EVAPORATION I. CONCLUSIONS AND RECOMMENDATIONS Evaporation is a well-defined well-established process, used throughout industry. It is capable of handling liquids, slurries, sludges, both organic and inorganic, containing sus- pended or dissolved solids or dissolved liquids where one of the components is nonvolatile. It is energy-intensive, and specialized equipment can be expensive. II. PROCESS The process and equipment for applying heat to the solution are similar to that for distillation, except that the vapor is not separated. Open, direct-fired pans or solar evapora- tion from ponds are still used in some applications, but most evaporators are heated by steam condensing on metal tubes, through which the solution flows. Usually the steam is at low pressure and the boiling liquid is under a moderate vacuum. There are numerous variations on equipment and processes, depending on the application. III. APPLICATIONS TO DATE . In the chlor-alkali industry, evaporation is used to concentrate caustic soda and to produce calcium chloride. Evaporation of saline water to provide fresh water is well established; U.S. plants have a capacity of about 67 million gpd. Concentration of sulfuric and hydrochloric acids, citrus fruit juice, phosphates, and milk whey; crystallization of salts, sugar; dehydration of Glaubers salt, sulfur sludges are all well established. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements vary considerably within a range of 100 to 1100 Btu/lb liquid evaporated, with the average closer to the lower figure. There are generally no pollution problems with evaporation vapors. Where the vapors contain organics, the liquid is condensed and either disposed of or recovered by another process, such as distillation. Economic analysis of an operation to concentrate 100,000 gallons per hour of kraft black liquor shows capital investment of $1.3 million. Yearly operating costs would be $1.06 per 1000 Ibs of water. V. OUTLOOK FOR WASTES i Evaporation is already used in the treatment of radioactive wastes, and is very effective where suspended solids content is high and other methods are difficult. A combination of evaporation and simultaneous combustion is used to dispose of TNT wastes. Other 63 ------- applications include photographic chemicals, papermill wastes, molasses distillery wastes, and pickling liquors. Evaporation is not suitable for tars, solids, dry powders, or gases. 64 ------- FILTRATION I. CONCLUSIONS AND RECOMMENDATIONS Filtration is a well-developed liquid/solid separation process currently applied to the full-scale treatment of many industrial wastewaters and waste sludges. For the treatment of hazardous wastes, filtration can be used to perform two distinctly different functions: 1) Removal of suspended solids from a liquid (usually aqueous) waste stream with the objective of producing a purified liquid. 2) Increasing the solids concentration, and thereby reducing the volume, of a high concentration liquid/solid mixture (sludge) by removing liquid from the mixture ("sludge dewatering"). ; As a wastewater treatment process, filtration is usually most applicable when following some form of flocculation and/or sedimentation. As a sludge dewatering process filtration is usually technically and economically competitive with other dewatering processes. We recommend that filtration be considered as a potentially applicable process for hazardous waste treatment applications requiring the separation of liquid and solid phases. II. PROCESS Filtration is a physical process whereby particles suspended in a fluid are separated by forcing the fluid through a porous medium. As the fluid passes through the medium, the suspended particles are trapped on the surface of the medium and/or within the body of the medium. Filter media can be a thick barrier of a granular material, such as sand, coke, coal, or porous ceramic; a thin barrier, such as a filter cloth or screen; a thick barrier composed of a disposable material such as powdered diatomaceous earth or waste ash. The pressure differential to move the fluid through the medium can be induced by gravity, positive pressure, or vacuum. The intended application has a great influence on both the type of filter and its physical features. III. APPLICATIONS TO DATE The inorganic chemicals industry employs various forms of filtration to separate precipitated product from waste material. They are commonly used in the manufacture of titanium dioxide, sodium dichromate, aluminum sulfate, and magnesium. The organic chemicals industry also employs filter techniques, e.g., removal of acetylene carbon particles from aqueous quench streams, and removal of dye particles from the reaction bath. Rotary vacuum filters are used to remove impurities in the processing of sugar. Vacuum filtration is often used to remove impurities from lube oils. Boiler feed water and many types of industrial process water have stringent specifications on suspended solids. Filtration is often 65 ------- used in conjunction with precipitation, flocculation, and sedimentation to remove these solids. Filtration is also used as the final step in many industrial wastewater treatment plants. ; IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements for filtration are .relatively low. A vacuum filtration system capable of dewatering 36,000 gal/day of sludge containing 6 tons of solids will have a power requirement of only 25 horsepower. The cost of treatment for both vacuum filtration and press filtration is usually within the range of $20-$45/ton of solids treated (dry basis). For liquid purification the cost of filtration by granular media filters usually varies from $0.10-$0.50 per 1000 gallons of wastewater treated. V. OUTLOOK FOR WASTES Major applications are and will be in the removal of suspended solids from wastewater streams and in the volume reduction (dewatering) of waste sludges and slurries. As more and tighter restrictions are placed on wastewater discharge, filtration will often be used after precipitation, flocculation, and sedimentation. Decreased availability of solid waste disposal sites will further encourage the de- watering of sludges prior to disposal. Non-aqueous liquids can be subjected to filtration for removal of suspended solids, but highly viscous semi-liquids such as tars are generally not amenable to filtration. 66 ------- FLOCCULATIOIM, PRECIPITATION, AND SEDIMENTATION I. CONCLUSIONS AND RECOMMENDATIONS Flocculation, precipitation, and sedimentation are fully-developed processes currently used in a wide variety of industrial, processing and waste treatment applications. While flocculation, precipitation, and sedimentation are individual process steps, they are inter- related, and are often combined into a single overall treatment process. They can be quite readily applied to a variety of aqueous hazardous wastes for the removal of precipitable substances, such as soluble heavy metals and for the removal of solid particles suspended in the liquid. We recommend that these processes be given serious consideration for removal of heavy metals and/or suspended solids from an-aqueous waste stream. Although the process theoretically can be used to treat non-aqueous liquids, such applications are very rare. Precipitation, flocculation, and sedimentation are generally unsuitable for treating heavy slurries, sludges, and tars. II. PROCESS Flocculation is the process whereby small, unsettleable particles suspended in a liquid are made to agglomerate into larger more settleable particles. Precipitation is a physico- chemical process where some or all of a substance in solution is removed from the solution and transformed into a second (usually solid) phase. Sedimentation is a purely physical process whereby particles suspended in a liquid are made to settle by means of gravitational and inertial forces acting on both the particles suspended in the liquid and the liquid itself. III. APPLICATIONS TO DATE The processes have long been widely used for a variety of industrial applications, such as in the manufacture of many organic chemicals, the preparation of metal ores, and the preparation of sugar. ^ Practically every industry that discharges a process wastewater stream contaminated with suspended and/or precipitable pollutants employs some form of precipitation, floccula- tion and/or sedimentation. Examples are: removal of heavy metals from iron and steel industry wastewater; removal of fluoride from aluminum production wastewater; removal of heavy metals, from wastewaters from copper smelting and refining, and from the metal finishing industry. IV. ENERGY, ENVIRONMENT, ECONOMICS linergy consumption is very low compared to other processes. The processes produce a waste sludge, which can often present a serious disposal problem. A large (over 5 million gallons per day) system employing only sedimentation with no flocculating chemicals will typically treat wastewater at a cost of $0.10-$0.50 per 1000 gallons treated. 67 ------- A moderate size (0.5-5 million gallons per day) system employing precipitation, flocculation, and sedimentation and using moderate dosages of precipitating/flocculating agents will usually treat wastewater at a cost of $0.50-$3.00 per 1000 gallons. Small, especially designed systems (less than 0.5 million gallons per day) using high dosages of precipitating/flocculating agents can have costs that are higher, but these will rarely exceed $6.00 per 1000 gallons. V. OUTLOOK FOR WASTES Precipitation, flocculation, and sedimentation are generally practical, effective, and relatively low-cost processes for the removal of precipitable soluble substances and sus- pended particles from aqueous waste streams.The processes are particularly suitable for the treatment of high volume/low concentration waste streams. In determining the applicability of precipitation, flocculation, and sedimentation to specific waste streams, true research and development is usually unnecessary. Past experi- ence and simple laboratory treatability tests are usually all that is necessary in determining applicability. 68 ------- FLOTATION I. CONCLUSIONS AND RECOMMENDATIONS Flotation is a physical-chemical method of separating solid particles suspended in a liquid, when the valuable products to be separated constitute less than 10% of the total solids. Although flotation has found only limited application outside the mineral industry, it is our belief that, with further research and development, the technique could be used to separate many types of components from mixtures of solids. II. PROCESS DESCRIPTION The material is crushed or ground, mixed with water and reagents into a slurry or pulp, and agitated. Air bubbles carry the selected materials to the surface to form a stabilized froth, which is then skimmed off, while the waste materials remain. By using the correct reagents, it is possible to separate similar materials from each other. Some installations separate only one valuable component from waste; others separate two, three, or even four products. III. APPLICATIONS TO DATE : 5 Although flotation has been applied principally to mineral processing to separate valuable ore from tailings, a few other applications seem to have potential. When cellulose is recycled from paper, flotation can be used to remove ink, pigments, and coatings. A few years ago three plants in the United States treated about 25,000 tons of paper per year in this manner. Other possible applications outside the mineral industry, though there are no commer- cial plants, are as a means of removing cyanide from solutions or mixed suspensions. In one test, about 95% of the cyanide could be removed. Research also shows that microorganisms can be floated, concentrated, and removed from a suspension. IV. ENERGY, ENVIRONMENT, ECONOMICS The typical conventional flotation plant is a relatively large consumer of energy, averaging about 15 kWh/ton milled. Only about 15% of the total is consumed in the flotation step, with most of the energy used for crushing and grinding. Air emissions are not significant, since flotation is a wet process. Dust emissions occur at the ore crusher and at conveyor transfer points but are controlled with collecting hoods and water sprays. The waste effluent goes to a tailings dam from which water may be recycled, especially in arid areas. Costs depend on the size and nature of the process. Operating costs for sulfide ore flotations vary from $4/ton ore processed for a 500T/day plant to $1.50/ton fora 10,000 T/day plant. 69 ------- V. OUTLOOK FOR WASTES The best application for the flotation process would be for separating a hazardous solid from one that is not. Another application would be to separate all solid materials in a slurry; however, it is difficult to see any reason for doing it this way, when the simpler process of thickening and filtration would accomplish :the same purpose. Heavy metal ions (copper, nickel, cadmium) and cyanides might be amenable to removal by this process, as well as such inorganics as carbonyls and fluorides. As far as we know, however, no work has been done to utilize the process. On the other hand, some of the reagents commonly used for mineral and ore processing are themselves hazardous and, if used carelessly, may appear in the tailings. Care must be exercised in their use and control. 70 ------- FREEZE-CRYSTALLIZATION I. CONCLUSIONS AND RECOMMENDATIONS Freeze-crystallization has been successfully tested for desalination of brackish waters in pilot plants. It has been demonstrated in the laboratory for hazardous waste treatment, and is expected to find commercial applications in the near future. II. PROCESS DESCRIPTION Freeze-crystallization involves formation of "pure" ice crystals from a solution, and concentration of dissolved solutes in a residual brine. The ice crystals may be separated mechanically from the brine, washed, and melted to yield fresh water (or solvent). The brine must be treated further, or otherwise disposed of. III. APPLICATIONS TO DATE A number of freeze-crystallization processes were developed for desalination, but none have become commercial. Waste treatment applications tested in the laboratory include: sulfite liquors; plating liquors; paper mill bleach solutions; arsenal redwater; solutions con- taining acetic acid, methanol and aromatic acids; ammonium nitrate wastes; and cooling tower blowdown. IV. ENERGY, ENVIRONMENT, ECONOMICS Electrical energy requirements are in the range of about 60-75 kWh/1000 gal of pro- duct water. The major environmental problem is associated with further treatment, or disposal of the brine. Some emissions of refrigerant (e.g., butane or freon) are possible. Capital costs are estimated to be in the range of $600,000-5800,000. Operating costs might be in the range of $6-12/1000 gal of product water. V. OUTLOOK FOR WASTES Freeze-crystallization appears to be a very promising process for treatment of aqueous waste streams containing 1-10% TDS. Commercial applications are certainly anticipated within the next five years. Applications to some non-aqueous waste streams could probably be developed. 71 ------- FREEZE-DRYING I. CONCLUSIONS AND RECOMMENDATIONS Freeze-drying (lyophilization) has no apparent potential for treating hazardous indus- trial wastes. Although freeze-drying is used; commercially for desiccating biological and sensitive materials, it does not appear adaptable to economical waste processing on a large scale. The process is slow, costly, and energy-dritensive, with limited use for removing water. II. PROCESS DESCRIPTION [ Freeze-drying is a process for subliming frozen water from a material under high vacuum. Basic equipment consists of a vacuum chamber, a vacuum source, and appropriate refrigeration and heating equipment. Suitable feeds include wet solids, sludges, and slurries. III. APPLICATIONS TO DATE The largest current use of this process is,in the preparation of freeze-dried coffee which commands a premium price in the marketplace. It is also used in the manufacture of phar- maceutical and biological preparations. I.1" There are no known applications to waste treatment, and none is under development. IV. ENERGY, ENVIRONMENT, ECONOMICS Freeze-drying is energy-intensive and costly to operate. Capital equipment costs range from $300,000-500,000. Its pollution potential is low, except for secondary effects of energy generation. V. OUTLOOK FOR WASTES Freeze-drying development aimed at waste treatment is unknown and will probably remain so due to the serious limitations of the process. 72 ------- FREEZING, SUSPENSION I. CONCLUSIONS AND RECOMMENDATIONS Freezing of sludges can aid in the agglomeration of suspended particles, which then tend to separate rapidly on thawing, leaving a clean supernatant. There are no practical applications at this time. II. PROCESS DESCRIPTION Suspension or simple freezing (dewatering) of sludge causes the suspended solids to agglomerate and form relatively large floe particles which are more easily removed. Freezing is accomplished naturally outdoors or through use of a refrigerant. Flocculants may be used to accelerate coalescence of suspended solids during freezing. Separated solids are screened or filtered off, and the water is further treated if necessary. III. APPLICATIONS TO DATE No commercial suspension freezing or freeze dewatering applications exist. Freezing alum sludges typical of waste water treatment plants has been the center of interest in the laboratory. Development of freezing for other materials is not being advanced. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements for natural freezing outdoors are small. Mechanical refrigeration requires large energy expenditures. Suspension freezing is essentially a phase separation process, and both the separated solids and the supernatant liquid would generally require further treatment prior to disposal. Reliable cost data are not available, but are expected to be relatively high. V. OUTLOOK FOR WASTES Unless energy considerations are proven to be acceptable and a broader usage of sus- pension freezing can be found, it will remain limited in application to sludge dewatering. Its value as a viable waste treatment process remains to be demonstrated on a commercial scale. 73 ------- HIGH-GRADIENT MAGNETIC SEPARATION (HGMS) I. CONCLUSIONS AND RECOMMENDATIONS High-gradient magnetic separation (HGMS) should be considered for removal of magnetic materials, or recovery of certain high-value, nonmagnetic materials, from waste streams. The process is particularly attractive for high-volume applications. Aqueous or non-aqueous liquids, slurries, solids, and dry powders may be treated. II. PROCESS DESCRIPTION HGMS is a technique for separating magnet or weakly paramagnetic particles and other nonmagnetic materials (down to colloidal p'article size) from slurries, sludges, and (after chemical treatment) from solutions. The feed stream is passed through a fine ferromagnetic filter which, when magnetized, collects the magnetic material. The filter is periodically cleaned, with the magnetic material then recovered by a simple wash procedure. The re- moval of nonmagnetic material requires the feed to be treated with a magnetic seed (e.g., magnetite). III. APPLICATIONS TO DATE Current applications include clay whitening (removal of a small colored magnetic fraction), and upgrading of low-grade iron ore. Applications currently being investigated,: but not yet commercial, include: beneficia- tion of other ores, coal desulfurization, removal of flue dusts in air streams from blast furnaces, and wastewater treatment (including municipal wastes and steel mill wastewaters). IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements may be relatively large, especially if high magnetic fields are required. Electromagnets, used to generate fields of up to 20 kOe, have power ratings of around 400 kW for the larger machines. Disposal of the filter wash solution, if the material is not recovered, and additional treatment of .treated stream may also be required. Capital costs may be as high as $800,000, if high magnetic fields are required; they may be as low as $5,000, if the material being removed is ferromagnetic. Operating costs for high-volume applications are expected to be around 10-50^/1000 gal for removal of ferromagnetic materials, and of the order of $1-5/1000 gal for removal of weakly para- magnetic materials. V. OUTLOOK FOR WASTES HGMS has attractive possibilities for the removal of ferromagnetic and paramagnetic particulates from liquids or slurries (where seeding is not required). When other non- magnetic particles are present, the magnetic material should constitute only a small fraction of the total solids; total solids, however, may be as high as 10-15% by volume of the waste stream. Economics are probably favorable only for large-volume streams. The time frame for development is of the order of 5-10 years. 74 ------- HYDROLYSIS I. CONCLUSIONS AND RECOMMENDATIONS Hydrolysis is potentially applicable to a wide range of waste forms and compositions. There are currently very few actual waste treatment applications, but the process does appear promising for detoxification and recovery of organics. Expanded R&D activity is recommended. II. PROCESS DESCRIPTION .: Hydrolysis generally refers to double decomposition reactions with water of the type: XY + H2 O >• HY + XOH. The reactions are usually carried out at elevated temperatures and pressures, often with acid, alkali, or enzyme catalysts. Suitable feed streams include aqueous or non-aqueous solutions, slurries, sludges, or tars. III. APPLICATIONS TO DATE The oldest application of hydrolysis is in the production of soap from heated fats in the presence of caustic (known as saponification). Hydrolysis is also used commercially for the manufacture of a variety of organics (e.g., production of phenol from chlorobenzene; production of ethylene oxide from ethylene glycol or ethylene chlorohydrin). Waste treatment applications are not widespread. However, in the petroleum industry, the sludge from acid treatment of light oils is often hydrolyzed to recover sulfuric acid for reuse; the other product, a tarry acid oil, may be concentrated and burned as fuel. Hydrolysis has also been used for detoxification of waste streams containing carbamates, organophosphorus compounds, and other pesticides. Hydrolytic waste treatment processes that have shown promise in the laboratory include acid hydrolysis of waste paper to sugar; conversion of organic sludge to animal feed; and decomposition of polyurethane foam to toluene diamine and a polyol. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements vary considerably with the application, but are generally high. Steam requirements for production of fatty acids approximate 120Btu/lb of product. Production of TiO2 from Ti(SO4)2 requires about 1500 Btu steam/lb of TiO2 produced. The products of hydrolysis of a complex waste stream are not readily predictable and may be toxic. The capital investment and operating costs are highly dependent on the specific process details. Capital investment figures for different processes range from about $2500-20,000/ ton of material handled daily. Operating costs might range from 0.3-1.5^/lb. 75 ------- V. OUTLOOK FOR WASTES Although not in widespread use as a waste treatment process, hydrolysis presents no fundamental problem. Handling of strong acids and alkalies requires care, and performing reactions at high temperatures and pressures necessitates close control and monitoring. i For hazardous wastes, hydrolysis can be adapted to handle liquids, gases, or solids. It does not appear promising for inorganic materials, but is suitable for a wide range of aliphatic and aromatic organics. 76 ------- ION EXCHANGE I. CONCLUSIONS AND RECOMMENDATIONS Ion exchange is well suited for general and selective removal of heavy metals and toxic anions from dilute aqueous waste streams. The upper concentration limit for efficient operation is about 4000 mg/1. Research on the use of polymer beads impregnated with liquid ion exchange materials has some promise for extending the concentration limits. II. PROCESS DESCRIPTION Ion exchange involves the interchange of ions between an aqueous solution and a solid material (the "ion exchanger")- After removal of the solution, the exchanger is then exposed to a second aqueous solution of different composition which removes the ions picked up by the exchanger. The process is most frequently carried out by pumping the solutions through one or more fixed beds of exchanger. III. APPLICATIONS TO DATE Full-scale operations include cleanup of dilute solutions from electroplating and other metal-finishing operations, recovery of effluents from fertilizer manufacturing, and indus- trial deionization. Promising applications include removal of cyanides from mixed streams and use of newer exchangers for selective removal of heavy metals. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are low, consisting primarily of electricity for pumping solutions. The dilute purified product stream is dischargeable to sewers. The regenerant stream requires further treatment for recovery or disposal. Minor amounts of exchange materials will require disposal occasionally. Capital costs are expected to be in the range of $200,000-$3 50,000, with a substantial investment in resin. Operating costs might be in the vicinity of $2-8/1000 gal. V. OUT LOOK FOR WASTES Ion exchange is a well developed process, which promises to be used more widely for recovery of heavy metals, and removal of both heavy metals and cyanides. 77 ------- LIQUID ION EXCHANGE ; I. CONCLUSIONS AND RECOMMENDATIONS Liquid ion exchange (LIE) is a process with demonstrated potential for removal of heavy metals and hazardous anions from aqueous waste streams. It covers a much wider concentration range than conventional ion exchange. Development of new applications and reagents for waste treatment may require special economic incentives, since historically such research has been stimulated principally by high-volume hydrometallurgical applications. II. PROCESS DESCRIPTION Liquid ion exchange involves, first, the extraction of inorganic species (principally ionic) from an aqueous stream into an immiscible organic stream containing special reagents to facilitate the extraction, and then subsequent transfer of the species to a second aqueous stream of different composition from the feed. Process equipment is that commonly used for liquid-liquid extraction: mixer-settlers, differential columns, or centrifugal contactors. III. APPLICATIONS TO DATE Full-scale commercial operations include removal of molybdenum and acids from metal pickling baths, zinc from textile production effluents, and copper from various streams. Promising applications include removal of cyanides and treatment of hydroxide slimes from electroplating. IV. ENERGY, ENVIRONMENT, ECONOMICS The LIE process has very low energy consumption, consisting principally of electricity for pumping and mixing. /. ; The cleaned feed stream will contain 10-50 mg/1 of the organic extraction solvent. The regenerative solution into which hazardous components are stripped from the extraction solvent will require further treatment. Capital costs depend upon the application. Values in the literature range from $10,000 (almost certainly too low) to $600,000. Total costs for treating dilute streams are estimated to be around $4/1000 gal. For concentrated stream, costs are highly variable, ranging from $0.20-$3.00/lb of metal removed. V. OUTLOOK FOR WASTES This method is well-developed, and particularly applicable to recovery of high-value metals from waste streams. 78 ------- LIQUID-LIQUID EXTRACTION OF ORGANICS I. CONCLUSIONS AND RECOMMENDATIONS Liquid-liquid extraction should be considered for the recovery of organic solutes from fairly concentrated aqueous and non-aqueous solutions. II. PROCESS DESCRIPTION Liquid-liquid extraction is the separation of the constituents of a liquid solution by contact with another (immiscible) liquid. If .the substances comprising the original solution distribute themselves differently between the two liquid phases, a certain degree of separa- tion will result. This may be enhanced by the use of multiple contacts. A total recovery process based on liquid-liquid extraction usually requires the use of other unit processes, such as stripping or distillation for solvent and solute recovery. III. APPLICATIONS TO DATE Current actual or proven areas of applicability include: 1. Extraction and recovery from aqueous solution of: • phenol; • acetic acid, and other aliphatic organic acids; » salicylic and other hydroxy aromatic acids; and • oils. 2. Extraction, (without recovery) of: • phenol from foul waters near a refinery. 3. Extraction and recovery from organic solvents of: • methylene chloride (from isopropyl alcohol); • freons (from oils and acetone, or alcohols); and • mixed chlorinated hydrocarbons (from acetone or alcohols). IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are usually quite small for just the extraction step. Where solute and solvent recovery require stripping or distillation, steam requirements will be significant. The only major environmental issues relate to (1) possible need for disposal of recovered solutes if such are not reusable, (2) the probable need for a polishing treatment on 79 ------- the raffinate, following extraction from water, and (3) the possible need for disposal of unwanted fractions following extraction of organic solutions. Costs cannot be generalized usefully. However, capital investment might be in the vicinity of $1 million. Total operating costs (without credit for resource recovery) might range from well under $1/1000 gal to more than $5/1000 gal. V. OUTLOOK FOR WASTES The process is most attractive for treatment of concentrated, selected, and segregated waste streams where material recovery is possible and desirable. Organic solutes, of almost any nature, may be economically removed if concentrations are in the range of a few hundred ppm to a few percent from aqueous waste streams. Organic solutions containing water-soluble and non-water-soluble components may be economically separated by extrac- tion with water. 80 ------- MICROWAVE DISCHARGE I. CONCLUSIONS AND RECOMMENDATIONS Microwave discharge treatment of hazardous wastes is currently in the research stage. Early results are very promising. II. PROCESS DESCRIPTION High-frequency microwave power is used to establish a plasma or gaseous discharge in which neutral molecules are partially decomposed into metastable, atomic, free radical and ionic species. The decomposition products typically recombine to form a variety of stable molecules, some of higher molecular weight and of higher toxicity than this feed. Plasmas may be initiated in low-pressure gases of all kinds, and solids and liquids exposed to the reactive species in plasmas generally undergo chemical change. Toxic vapors and liquids introduced into an oxygen plasma undergo reactions similar to those of incineration, but at much lower temperatures. III. APPLICATIONS TO DATE Commercial microwave discharge instruments are used in analytical chemistry, particu- larly for plasma or low-temperature ashing: The only large-scale applications are for photoresist removal and plasma etching in semiconductor device fabrication. Most research has been concentrated on polymer film deposition and organic synthesis. Lockheed is currently investigating the use of microwave plasmas, particularly oxygen plasmas for the treatment of organic vapors and liquids characteristic of waste streams. IV. ENERGY, ENVIRONMENT, ECONOMICS Line power requirements for microwave discharge treatment are estimated as roughly 14 kWh/lb of waste treated. In an oxygen plasma, organic waste components are converted to products similar to those of complete combustion. Capital costs for a 100 Ib/hr facility might be in the neighborhood of $100,000. Operating costs are estimated to be on the order of $1.00/lb. V. OUTLOOK FOR WASTES The process should be considered for small quantities of highly toxic materials that cannot be handled by any other means, or for recovery of high-value components. 81 ------- NEUTRALIZATION I. CONCLUSIONS AND RECOMMENDATIONS ' ' !- Neutralization (or more generally pH control) is a technically and economically proven process, currently in full-scale use in many ^industries. It has wide applicability to waste streams of diverse physical and chemical compositions, and would have to be available in almost any waste treatment facility. II. PROCESS DESCRIPTION Neutralization is a liquid-phase chemidal reaction between an acid and a base which produces a neutral solution. It may be carried out in batch or continuous flow. It requires reaction tanks, agitators, monitoring and control capability, pumps, and ancillary equipment for handling solids and/or liquids, and storage facilities. The treated stream undergoes no change in physical form, other than solids dissolution (or precipitation) or gas evolution. The process can be used on aqueous and non-aqueous, liquids, slurries, and sludges. III. APPLICATIONS TO DATE The process is in full-scale use throughout many industries, e.g., pulp and paper, petroleum refining, and inorganic chemicals. It is used to treat acid exhausts, pickle liquors, plating wastes, and acid mine drainage. It can be used on almost any stream requiring pH adjustment. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are primarily for -electricity used to run pumps and stirrers. Treated streams may contain precipitated solids which require additional handling. The solids must be recovered or sent for disposal as a solid waste. There is the possibility of toxic gas being evolved, particularly if sulfides or cyanides are present in the waste stream. Capital investment requirements are highly variable, depending upon the size of the stream to be treated. Operating costs range from $0.20/1000 gal to $4/1000 gal. V. OUTLOOK FOR WASTES Neutralization is and will continue to be a routine and accepted part of industrial processing waste management. 82 ------- OXIDATION; CHEMICAL I. CONCLUSIONS AND RECOMMENDATIONS Chemical oxidation and the technology for its large-scale application are well estab- lished. Oxidation-reduction, or "Redox" reactions are those in which the oxidation state of at least one reactant is raised while that of another is lowered. We recommend that chemical oxidation be considered for dilute aqueous streams containing hazardous substances or for removing residual traces of contaminants after treatment. Chemical oxidation should be considered as a first treatment step when trie waste contains cyanide, when it contains constituents not amenable to other treatment methods, or as a final step to remove traces of contaminants after other treatment. A more exhaustive study should be made of the potential for treatment of waste containing hazardous materials. Most of the literature deals only with very dilute waste streams, or with the preparation of materials.from basic raw materials via chemical oxidative techniques, and little has been published relative to treatment of concentrated hazardous wastes. II. PROCESS The first step of the chemical oxidation process is adjustment of the pH of the solution. The oxidizing agent is added gradually and mixed thoroughly. The agent may be in the form of a gas (e.g., chlorine), a liquid (e.g., hydrogen peroxide), or a solid (e.g., potassium permanganate). Because some heat is liberated, concentrated solutions may require cooling, or may require careful measurement and handling to avoid violent reactions. III. APPLICATIONS TO DATE Application to industrial wastes is well developed for cyanides and for phenols, organic sulfur compounds, etc., in dilute waste streams. The primary application has been in converting and destroying cyanides from plating and metal finishing operations. The chlor-alkali industry uses chemical oxidative techniques to remove mercury from ores, as well as from cell wastes. Mercury removal rates of over 99% are claimed for concentrated ores, and residual mercury levels of less than 0.1 ppm for chlor-alkali sludge. The technique is also used to remove organic residues from drinking water, or to remove residual chlorine after chlorine treatment. Gases have been treated by scrubbing with oxidizing solutions to destroy odorous substances. Chemical oxidation is also used for odor destruction in the manufacture of kraft paper and in the rendering industry. 83 ------- IV. ENERGY, ENVIRONMENT, ECONOMICS Total energy consumption is low; the only requirements are for pumping and mixing. A disadvantage of chemical oxidation for waste treatment is that it introduces new metal ions into the effluent that might require further treatment. The only waste that appears troublesome is the sludge that can develop in the oxidation treatment of cyanides when iron and some other ions are present. A facility for chemical oxidation of 103 gpd of highly concentrated cyanide waste from a plating operation, using batch alkaline chlorina- tion would require a capital investment of $100,000. Fixed costs would be $18,300 annually and variable costs $36,700, giving a unit cost of $229.20/103 gal. For a less highly concentrated waste (100 ppm copper cyanide and 100 ppm sodium cyanide), the operating cost would be about $170/103 gal. Costs coiild be lowered if the daily flow rate were to increase and the treatment operation could be continuous rather than batch. V. OUTLOOK FOR WASTES In addition to the already-established applications for removal of hazardous substances, chemical oxidation may be used to remove chlorinated hydrocarbons and pesticides from dilute streams. Laboratory and pilot studies have demonstrated the potential for this application. The extent to which the technique can be used to remove hazardous substances from industrial sludges may be limited because of inefficiency and incompleteness of the reaction. The use of chemical oxidation for concentrated wastes should have careful evaluation for reasons of economics, process safety, and the addition of chemicals that may add to the pollutant load. 84 ------- OZONATION I. CONCLUSIONS AND RECOMMENDATIONS Technology for large-scale ozone application is well developed. Feasibility has been demonstrated for treatment of cyanides and phenols, and laboratory and pilot studies indicate potential for chlorinated hydrocarbons, polynuclear aromatics, and pesticides. We recommend that ozonation be considered for treatment of aqueous or gaseous waste streams containing less than 1% oxidizable hazardous components and as a prelimi- nary treatment for more concentrated wastes not amenable to other techniques. We also recommend ozonation as a final treatment process where more complete removal of oxidizable substances is required. ':.. A more exhaustive study should be made of the literature on the susceptibility of various compounds to ozonation. Laboratory studies are needed to evaluate the effectiveness of treatment of pollutants of current concern. Additional research and development aimed at more efficient ozone generation and ozone/water mixing should be supported. II. PROCESS Since ozone is a powerful oxidizing agent and an extremely reactive gas that cannot be shipped or stored, it must be generated on site immediately prior to use. Ozone generated at a concentration of <2% and a pressure of <15 psi from a stream of air or oxygen previously dried to a dewpoint of -50°C or lower is introduced into a contact chamber designed to ensure good mixing with the waste stream. For aqueous wastes, a venturi injector, a porous diffuser, or an impeller is used to mix ozone and liquid at high velocity for 10 minutes or more. Liquid depth is at least 15 feet, and two or more reactors are frequently employed. For gaseous waste streams, a porous diffuser is used if ozonized air is generated at positive pressure; at atmospheric pressure, a wet scrubbing process is used, with a fine mist of ozone-saturated water sprayed into a contact chamber. Contact times for gaseous streams is 5-60 seconds. III. APPLICATIONS TO DATE Ozone, besides being a powerful reducing agent, has antibacterial and antiviral proper- ties. This disinfecting power has been responsible for most large-scale applications. The process is widely used in Europe to purify and improve drinking water, and there have been a number of installations in the United States for treatment of municipal sewage plant effluents. It has also been used to remove sulfide and other odors from rendering plant effluent; fermentation odors from a pharmaceutical plant; treatment of liquid effluent containing cyanides, siillides, sulfites and other hazardous components after biological treatment; reduce cyanide levels from effluent of a lire plant, a chemical plant, and an 85 ------- electroplating facility. In combination with activated carbon adsorption, ozonation has been used to remove color from waste dyeing water. Oxidation of phenols in coke oven wastes, wood products waste and biologically treated refinery waste. IV. ENERGY, ENVIRONMENT, ECONOMICS Ozonation can be expensive, but may be economically competitive for treatment of dilute waste streams. Generation of ozone1 is the dominant cost component in terms of capital and power. With air feed, energy requirements are from 7.2 to 9.0 kWh/lb of ozone generated. Power requirements are half this figure if oxygen is used for feed. Any improve- ment in ozone demand or efficiency would improve economics; the catalytic effect of UV light can extend the effect of ozonation dramatically and can reduce ozone demand by a factor of two. Labor and space requirements are low. Concentrations of ozone leaving the cohtact chamber are carefully monitored; some- times the ozonized air is cycled to provide pretreatment of incoming aqueous waste. The waste stream effluent is also monitored, and the dosage increased if necessary. Gaseous effluent is discharged directly to the atmosphere; aqueous effluent may be discharged to a sewer or natural body of water where the oxygen-rich water is beneficial. V. OUTLOOK FOR WASTES Complete oxidation to CO2 can sometimes be achieved; in other cases, oxidized intermediates may be formed that resist further ozonation. Whether a given degree of oxidation constitutes satisfactory treatment depends on the criteria for the particular waste stream or disposal site. Slurries, tars, sludges and solutions in oxidizable liquids are generally not suitable for ozonation. Although ozone itself is a toxic substance, the risk of exposure to toxic levels is small. 86 ------- PHOTOLYSIS I. CONCLUSIONS AND RECOMMENDATIONS Technology for large-scale application of photolysis to wastes is not highly developed. Further laboratory studies of photolysis of selected candidate waste streams (for example, pesticide contaminated solvents) should be conducted. Pure photolysis is not likely to be a practical industrial waste treatment process', within the next 5-10 years, but UV-assisted ozonation and chlorination are promising in the near term. II. PROCESS DESCRIPTION : In photolysis, chemical bonds are broken under the influence of UV or visible light. Products of photodegradation vary according to the matrix in which the process occurs, but the complete conversion of an organic contaminant to CO2, H2 O, etc., is not probable. Equipment required includes a source of UV/visible radiation, such as a mercury arc. Re- actor geometry and materials of construction must allow adequate penetration of the light into the waste. III. APPLICATIONS TO DATE Pure photolysis has been investigated only in laboratory-scale studies. Combined UV/ ozonolysis and UV/chlorination have been used in pilot and full-scale applications in the hazardous waste area. IV. ENERGY, ENVIRONMENT, ECONOMICS Any photolysis process is relatively energy-intensive. There are not sufficient data to allow estimation of either process economics or environmental issues. In general, the process effluent is a stream with physical characteristics similar to those of the input stream, but with different chemical characteristics. Organic hazardous components are not completely degraded and the residues may still pose hazard. » V. OUTLOOK FOR WASTES Applications are probably highly specialized, detoxification of pesticide-contaminated solvents is one possibility. However, pure photolysis requires research and testing at labora- tory and pilot-scale to demonstrate applicability to hazardous waste. 87 ------- REDUCTION, CHEMICAL I. CONCLUSIONS AND RECOMMENDATIONS Reduction reactions are among the most common chemical processes; reduction- oxidation or "Redox" reactions are those!in which the oxidation state of at least one substance is raised while another is lowered/ The technology for large-scale reduction of some industrial wastes, sometimes allowing recovery of metals, is well developed. We believe that the process could well be adapted to remove hazardous substances from dilute wastes, to pretreat wastes that have constituents not amenable to other methods, and to remove traces of contaminants. II. PROCESS if The equipment for reduction processes is simple: only storage, metering, mixing, pumping and instrumentation, with the major cost for reducing chemicals. The economics vary with the substance being treated. Introduction of foreign ions into the stream is a real or potential disadvantage; otherwise it is straightforward. III. APPLICATIONS TO DATE The application to industrial wastes is already well established for dilute waste streams, especially those containing chromium (VI),". and other hazardous substances, such as lead and mercury. In addition to detoxifying hazardous substances, the process sometimes allows recovery of metals. The plating and tanning industries use the process to reduce highly toxic chromium (VI), to chromium (III), which is less hazardous and can be precipitated for removal. The process also finds application in the :chlor-alkali industry for removal of mercury from effluents. It appears to have potential for removing other hazardous substances, e.g., cadmium and antimony, in diluted streams. ;: • t ;: IV. ENERGY, ENVIRONMENT, ECONOMICS Total energy consumption is low; the only requirements are for pumping and mixing. A disadvantage of chemical reduction for waste treatment is that it may introduce new ions into the effluent that might necessitate further treatment. Air emissions are not significant. There may be problems with land disposal or residues, especially those sus- ceptible to acid leaking. A facility for chemical reduction of 2,000 gpd of chromium (VI) waste from a plating operating, using batch sulfur dioxide treatment would require a capital investment of $230,000. Variable operating costs would be $51,400 and fixed costs $41,600 annually. Unit costs would be $193.80/103 gal. Costs could be lowered if the daily flow rate were to increase and the treatment operation could be continuous rather than batch. 88 ------- V. OUTLOOK FOR WASTES We believe there should be a more exhaustive study of the potential for reduction processes for concentrated hazardous wastes. .It should certainly be considered as a treat- ment step whenever chromium VI is a constituent of the effluent. It may be a method for treating wastes that have constituents not amenable to other treatment, and as a final polishing step for removing traces of contaminants. 89 ------- REVERSE OSMOSIS I. CONCLUSIONS AND RECOMMENDATIONS Reverse osmosis (RO) should be considered for treatment of aqueous waste streams containing organic and inorganic species in solution. Total dissolved solids in the feed stream may be as high as 34,000 ppm. II. PROCESS DESCRIPTION The heart of the reverse osmosis processes a semipermeable membrane which is per- meable to solvent, but impermeable to most dissolved species, both organic and inorganic. Separation is brought about by means of an applied pressure gradient. To protect the mem- branes for chemical attack and plugging, oxidants, iron and manganese salts, and oils and greases are generally removed prior to application of RO. III. APPLICATIONS TO DATE •' i There are about 300 full-scale plants worldwide using reverse osmosis for desalination of sea or brackish water. Reverse osmosis has been used very successfully in the treatment of electroplating rinse waters, not only to meet.effluent discharge standards, but also to re- cover concentrated metal solutions for reuse. A limited number of other full-scale uses can be found in the treatment of sulfite streams from the paper industry and in food processing. IV. ENERGY, ENVIRONMENT, ECONOMICS Energy requirements are of the order of 10 kWh/1000 gal of product water. The concentrated brine or solute solution presents a problem for disposal, if not recoverable. Capital costs range from about $0.50-4/gpd of purified water output, depending on the volume of waste to be treated. Total operating costs are in the range of $1-5/1000 gal. V. OUTLOOK FOR WASTES Use of RO for industrial waste treatment is growing rapidly. The process is particularly useful for concentrating waste streams containing dissolved organics or inorganics, to facilitate recovery, or to reduce volume. 90 ------- STEAM DISTILLATION I. CONCLUSIONS AND RECOMMENDATIONS Steam distillation is a proven process for removing water-immiscible, volatile com- pounds from process or waste streams. It can be applied to any stream that can be contacted with steam or water without reaction or decomposition. It can be used with liquids, slurries, sludges, and solids. II. PROCESS Steam distillation takes advantage of the unique vapor pressure relationship of two immiscible liquids. The additive vapor pressures allow distillation at lower temperatures. It is usually conducted as a batch operation: the still is charged, the charge is heated to temperature, and the distillation conducted by bubbling steam through the liquid phase. In semi-batch operation, the charge containing a., high ratio of volatiles to non-volatiles is fed to the still continuously for a given period while the volatile component is steam-distilled from the mixture. III. APPLICATIONS TO DATE : ; The widest application is in the petroleum industry where steam and feedstock are introduced into a multi-tray distillation column to produce gasoline, lube oil, or naphtha. Without the use of steam or steam and vacuum together, the high distillation temperature would result in decomposition. The process is also used for removing low boiling compo- nents from a mixture. In the soap industry, glycerine is recovered from spent soap lye; in the naval stores industry turpentine and gum rosin are recovered from pine gum; fatty acids and tall oil rosin are obtained from crude tall oil, a by-product of sulfate wood pulp production. A solvent extraction process removes organics from paper before the wood fiber can be reused; through steam distillation the solvent is recovered. In the production of coke from .coal, quantities of aromatic hydrocarbons are also produced. The wash oils from the ovens are steam stripped to recover the aroma'tic hydrocarbons. IV. ENERGY, ENVIRONMENT, ECONOMICS The major energy requirement is for steam. In one application, the steam requirement would total 29,200 Ib per 3,000 gal of treated degreasing waste, or per 1,000 gal recovered perchlorethylene. Power requirements would be 30 kWh per 3,000 gal waste. The wastewater from condensed steam in the steam distillation process will contain traces of volatile organics, and may have to be steam-stripped before disposal. The fixed capital investment (new equipment) for a steam distillation unit with a capacity of 3,000 gal/week degreasing solvent would be about $130,000. Operating costs 91 ------- would be $1,424. Credits for perchlorethylene at $2/gal and $0.05/gal for the oil/grease mixture used for boiler fuel would more than offset treatment cost. V. OUTLOOK FOR WASTES ; ,' Numerous industrial wastes are treated, by contract disposal companies using steam distillation to recover valuable components or reduce waste volumes. With the increase in value of hydrocarbon solvents and increasingly strict regulations regarding landfill with sludges containing these solvents, the use of steam distillation is expected to increase. 92 ------- STRIPPING, AIR I. CONCLUSIONS AND RECOMMENDATIONS ' •! '! •< Air stripping of ammonia from biologically treated domestic wastewater is being 1* »- developed as a means of reducing nitrogen content before discharge. It is suitable only for dilute solutions, since the emission level of ammonia from a concentrated solution would be too high. Furthermore, steam stripping would permit recovery of the ammonia from more concentrated solutions. Application of air [stripping to other gaseous compounds would depend on the environmental impact of the resulting emissions. II. PROCESS ?• ; Holding ponds, with or without surface agitation, and spray ponds have been investi- gated, but the packed tower appears to be'the most compact and efficient means of air stripping. Removal efficiencies of over 90% have been obtained in pilot tests with wastewater containing 60 ppm nitrogen. The wastewater .containing ammonia and a lime slurry (lime added for phosphate removal) are fed to a rapid mix tank, and thence to a settling basin, where the calcium phosphate and calcium carbonate settle out. The clarified wastewater is pumped to the top of two towers packed wi.tli a series of horizontal pipes. Air is drawn up through the tower against the falling wastewater by large fans. After the ammonia is removed, the wastewater flows.into the recarbonation basin where compressed carbon dioxide-rich gas from the lime recalcining furnace is bubbled through to precipitate and recover calcium carbonate, for calcination and recycle of lime to .the system. III. APPLICATIONS TO DATE Full-scale packed towers have been used at two locations in California for treating domestic wastewater. I IV. ENERGY, ENVIRONMENT, ECONOMICS Electric power requirements for treating "15 million gpd are in the range from 1600 to 1800kWh/hr. The recalciner requires about 8 million Btu (8000ft3) natural gas/ton of feed, or 192 million Btu/day. When the ammonia concentration is .about 23 ppm and the air-to-water ratio is 500 ft3 /gal, the concentrated ammonia in the saturated air leaving the tower is about 6 mg/m3, well below the odor threshold. Disposal of about 25 tons/day of sludge requires a significant amount of land, but does not pose an environmental hazard. The capital investment would be about $7.8 million; fixed costs would be $1,420,000, and variable operating costs would be $940,000/year. 93 ------- V. OUTLOOK FOR WASTES It is unlikely that many other applications of air stripping will be found. 94 ------- STRIPPING, STEAM t I. CONCLUSIONS AND RECOMMENDATIONS Steam stripping should be considered whenever it is desirable to remove volatile components (e.g., organics, H2S, NH3) from aqueous waste streams. II. PROCESS DESCRIPTION ; Steam stripping may be considered a form of fractional distillation. Live steam is injected into the bottom of the distillation column, and carries dilute volatile components with it. There are two aqueous output streams, one a concentrated solution of the volatile organics and the other a dilute stream containing only residual traces of volatile organics. III. APPLICATIONS TO DATE !. ' c- Steam stripping has been used for many years to recover ammonia from coke oven gas. It is also used to recover sulfur as H2 S -from refinery raw waste. Other applications include phenol recovery, vinyl chloride monomer removal from PVC suspension resins, and removal of organics and sulfur from Kraft mill condensates. Research work is in pro- gress for steam stripping of light chlorinated hydrocarbons from industrial waste water. t IV. ENERGY, ENVIRONMENT, ECONOMICS The primary energy requirements are for steam. Between 0.5 and 2.5 pounds of steam are required per gallon of waste water. The concentrated stream containing the bulk of the volatile organic components is processed for recovery or incinerated. If the incin- erated stream contains sulfur, emission of SO2 must be considered. The impact of dis- charging the treated dilute stream depends'din the nature and residual concentration of the volatile organics of the waste water. ;' • Capital investment for a new 200-gpm, .single-stage (one column) "sour water" steam stripper would be between $500,000 for mild steel and $850,000 for stainless-steel con- struction. Treatment cost by this system would be about $10/1000 gal. A capital investment closer to $1,700,000, would be required for a two-stage, two-column, 200-gpm system that would recover NH3 and H2 S for credits. V. OUTLOOK FOR WASTES The use of steam stripping for industrial waste treatment is growing. The most attrac- tive applications are those that permit byproduct recovery, thus to offset fairly high operating costs. The process is energy-intensive, with steam costs amounting to close to 80% of operating costs. 95 ------- ULTRAFILTRATION I. CONCLUSIONS AND RECOMMENDATIONS Ultrafiltration is a membrane filtration; process that separates high molecular weight solutes or colloids from their surrounding media. The process has been successfully applied to both homogeneous solutions and to colloidal suspensions that are difficult to separate by other techniques. Commercial use has been focused on aqueous solutions. '• • • . J ;/ Retained solute or particle size is one characteristic distinguishing ultrafiltration from other filtration processes. It filters out particles as small as 10~3 to 10~2 microns. Where solutes are being separated from solution, .the process can'serve as a concentration or fractionation process for single-phase streams. .It competes with adsorptive and evaporative processes, and has the potential for broader applicability than conventional filtration. Usually the concentrate requires further processing if a pure solute is to be recovered. II. PROCESS Ultrafiltration membranes have an extremely thin selective layer supported on a thicker spongy substructure, and it is possible to tailor membranes with a wide range of selective properties. A solution containing molecules too small to be retained by the membrane and larger molecules that will be 100% retained is passed in a pressurized stream. The larger molecules are collected from the upstream side and the smaller molecules downstream. III. APPLICATIONS TO DATE ', Ultrafiltration is used for electrocoat paint rejuvenation and rinse water recovery, protein recovery from cheese whey, and metal machining oil emulsion treatment, with capacity to handle approximately 100 million; gallons per year for each application. There are also smaller (on the order of 10 million gpy) plants for treatment of textile sizing waste and wash water from electronics component manufacturing, and for production of sterile water for pharmaceutical manufacturing. IV. ENERGY, ENVIRONMENT, ECONOMICS Electrical energy for pumping to maintain flow at operating pressures may be as much as 30% of total direct operating costs. Ultrafiltration residues are typically a concentrate of the undesirable or hazardous components and usually require further processing unless valuable by-products can be re- covered. 96 ------- Capital and operating costs are dependent on the specific application and the capacity of the system. For large plants, capital costs may be $l-$4/gpd; operating costs may be $5-$ 10 per 103 gal. Coupled with the economies of reuse of salvaged materials, these costs are often acceptable. V. OUTLOOK FOR WASTES There are a number of other applications where ultrafiltration may become commercial within the next five years. These include: treatment of dye waste, pulp-mill waste, industrial laundry waste, and recovery of sugar from orange-juice pulp, protein from soy whey, products from pharmaceutical and fermentation industries, and purification of power-plant boiler feedwater and water for beverages. Application to hazardous wastes is already well advanced, since many of the aqueous solutions treated present severe sewage problems. 97 ------- ZONE REFINING I. CONCLUSIONS AND RECOMMENDATIONS Zone refining is unlikely to be useful for treatment of hazardous wastes. Although zone refining is an effective purification technique, it has inherent limitations which make its use for broad treatment of large quantities of waste unlikely in the near future. Zone refining is a slow and costly operation, energy-intensive, and, at present, suitable for opera- tion up to only about 10 kg batches. II. PROCESS DESCRIPTION Zone refining is a fractional crystallization technique in which a rod of impure material is purified by heating it so as to cause a molten zone to pass along its length. Basic equip- ment consists of a material support or ingot holder to contain the sample; a feed or travel mechanism; and a source of heat. The process may include a cooling step. It can be used on solids, liquids, and mixtures such as slurries. High viscosity and reactive materials are not suitable. III. APPLICATIONS TO DATE ' Zone refining is used to purify elements, metals, semiconductor materials, oxides, salts, and organic materials in the laboratory. Its primary commercial use is in purification of semiconductor materials. * It is used on relatively pure materials. It is not now used for hazardous wastes, and there are no known proposed applications for hazardous waste. IV. ENERGY, ENVIRONMENT, ECONOMICS Zone refining is an energy-intensive process and therefore expensive to operate. Its pollution potential is low. Equipment costs are not presently available, most equip- ment being engineered on a custom basis. V. OtiTLOOK FOR WASTES Zone refining, at present, is only useful for processing small quantities (up to 10 kg) of relatively pure material. Processing rates are under 10 cm/hr. The process is not practical for the complex mixtures that characterize most waste streams. Even for specialized applica- tions, the process is only operationally feasible if the distribution coefficients permit segre- gation of impurities. ------- |