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Industrial Wastes from the Equipment Manufacturers' Selection of proper equipment for waste treatment is as important as devising the correct process and flow sheet. Not less than a billion dollars of equipment may be required to eliminate stream pollution. Fortunately the equipment is already in general use in chemical, metallurgical, and sanitary engineering, and requires only intelligent adaptation to meet the require ments of waste treatment. Each waste treatment problem must be regarded as separate and distinct, and usu ally will require extensive investigation in the field and in the laboratory. This means Viewpoint no incentive for the customer to order quickly, and accordingly this type of business has been costly to handle. Although the necessary units of equipment are doubtless available on the market today, they are scattered throughout the sanitary, chemical, and metallurgical fields, and the neces C. L. KNOWLES The Dorr Company, Inc., New York, N. Y. sary experience or ability to engineer each step in the treat ment process is likewise widely scattered. Plant wastes are usually a heterogeneous mixture, collected from various operations containing widely different materials in solution and suspension. Some accurate measurement of the hourly flows and some analysis of their make-up is neces HEN manufacturers consider waste treatment as a Wpart of the initial cost of any process operation and its daily cost a part of their operating cost, there will be sary before any flow sheet or equipment can be recom mended; and some such study is required before the problem can even be classified. no difficulty in finding suitable equipment to treat theseThis study costs money and the equipment manufacturer wastes. Most companies are taking a broad-minded atti should not be asked to do this work as a sales expense, par tude in the matter, and substantial progress has been made ticularly when many plants wish to delay any expenditure during the last decade; one survey shows 179 plants in the as long as possible, when they are tempted to use homemade United States in 1928 and 565 plants in 1938. units or the cheapest equipment possible, and when there is It has been difficult for a manufacturing executive to jus always a possibility that the waste and the problem may be tify substantial equipment when no financial returns are ex eliminated by closing the circuit and re-using the water with pected, and too many times makeshift or homemade units out the installation of new equipment. have been installed after only a cursory survey of the waste But few equipment manufacturers have the necessary staff treatment problem. This has made for high operating costs, with the varied experience required, and they obviously will frequent replacements, and expensive upkeep. Accordingly quote higher prices than companies with no research and this part of the plant was often a nightmare to everyone. development expense. However, each waste treatment prob Although it is true that many companies, after thoroughly lem must be regarded as separate and distinct, and usually will studying their waste problems, are able to increase their over-all recovery or yields by plugging leaks or minor changes in their processes, and although others may produce salable by-products from their wastes, it is perhaps wiser to consider waste treatment as man's duty to society and the cost as an require extensive investigation both in the field and in the laboratory. This means only that the problem must first be solved from an engineering standpoint by engineers compe tent to determine the treatment required before the question of suitable equipment can be considered. overhead on the manufacturing operation. This situation The handling of wastes within the equipment manu may change over the years, but such an attitude will prevent facturer's own organization is also difficult. Often the many disappointments. sanitary engineers, from their experience with municipal Estimates as to the probable expenditure required to elimi sewage, can best solve the problem technically, but the nate stream pollution only from industrial plants can be industrial or chemical engineers know the men in charge but little better than guesses, because the solution of many of of the plant polluting the stream and have more experi these problems is as yet unknown. Some figures indicate ence in working with this type of individual. It becomes an expenditure of a billion dollars for the United States and then a problem of "men vs. machines"; perhaps the best any sum of this magnitude is obviously of interest to equip compromise is to use the industrial engineer to make the ment manufacturers, a challenge to the engineers, and a temp contact and the sanitary or metallurgical engineer as a tation to all others. consultant or technical expert on the job. The sanitary Handling of waste problem inquiries by equipment manu man is all important if the city sewer system can take facturers has been a difficult problem, quite different from part of the industrial waste, or if some cooperative arrange the engineering and sales work normally encountered. Here, ment can be worked out. probably, no return on the investment can be shown; there is To get any order out of these industrial waste problems, 1338 the problem must be solved by engineers competent to determine the treatment re quired before the question of suitable equipment can be considered. Industrial waste problems are complex on account of the diversity of their composi tion, the restrictions placed on offenders by the regulatory authorities, and the pos sible failure economically of a technically successful process. Waste treatment may be classified ac cording to the nature of the offense, the type of regulatory body, or the aim of the treatment. 1340 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 31, NO. n Figure 7 {upper left). Continuous Rotary Filter Figure 8 (lower left). Solid-Bowl Continu ous Centrifuge 3. The Health Department of city or state requires B. O. D correction, elimination of bac teria, etc., from a distillery, brewery, milk plant, or pulp or paper company. This begins to be a sanitary problem requiring aeration, digestion, etc., possibly combined with physical or chemical preliminary units. We might also classify as to type of treat ment--(1) physical (metallurgical), (2) chemical, (3) biological, or any combination of the three, or we might classify as to what is required or expected: (I) by-product re covery or (2) cheapest and most efficient elimination of the pollution with no credit. A pickling liquor layout perhaps illustrates the latter classification; shall it neutralize the waste economically or try to recover the iron and acid for re-use? Typical Flow Sheets A few typical flow sheets will indicate how these units are used and how the experience in the process industries is helping solve waste problems. Case 1. An anthracite coal mining company must discontinue discharging fine coal to the river since the settled some type of classification is necessary and obviously this may be done on several bases. Eldridge divided them into or ganic, toxic, and inert, but possibly the following discus sion will further clarify the situation, at least from an equipment point of view. We might classify as to pur pose--that is, what is the source of the difficulty, and what department is concerned with the problem?1 2 1. The War Department ob jects to the blocking of naviga ble streams. The offender would be a sand producer or a coal company and the wastes inert and granular and insoluble; per haps only physical treatment is required. 2. The city or state wants color or turbidity removed. The company may be an oil refinery, a dyer or cleaner, a paper or pulp mill, and almost any sort of physical or chemical treatment may be necessary. Figures. C-E Raymond Sludge-Drying and Incineration System NOVEMBER, 1939 INDUSTRIAL AND ENGINEERING CHEMISTRY 1341 10,FlGLtRE DeTRITOR, DEVELOPED FROM THE BOWL CLASSIFIER solids are building up behind a dam in the river. A pre liminary study indicates that the fine coal is marketable if the ash content can be reduced sufficiently. By hydraulic classification tests, it is demonstrated that the + 200-mesh material can be classified, tabled, or floated and burned as pulverized anthracite. The tails, ash, or float, together with the -200-mesh heads, must be dewatered even though no credit can be realized from them. The flow sheet finally evolved is then .classification, tabling, flotation, thickening, and filtering, obviously a straight metallurgical problem; each step is equipped with machines manufactured by com panies with long experience in handling metallurgical work of this type. This, then, is a physical operation made necessary by regu lations of the War Department because of obstructions to a navigable river below the dam and classifiers, sizers, tables, hydroseparators, flotation cells, thickeners, and filters are used--all metallurgical equipment. Case 2. A steel mill lias been advised by the state au thorities that it can no longer discharge its pickle liquor (sulfuric acid and ferrous sulfate) into the river adjoining the property. The problem obviously is one for the chemical engineer, regardless of whether sulfuric acid and iron oxide are to be recovered and re-used or whether the acids are to be neu tralized as cheaply as possible at a minimum initial expense and the resulting gypsum stacked as a valueless product. The mill is small, and only 2 tons of sulfuric acid are used per day. An acid recovery plant eosts a quarter of a million dol lars and is economical only if operated at ten or twenty times this tonnage. It is therefore decided to spend thirty thousand dollars and thirty dollars a day to treat the waste pickle with limestone. Phosphoric acid experience indicates that the size of the gypsum crystals may be varied almost at will by recirculation. Chemical engineers know that ferric hydroxide will settle and filter but that ferrous hydroxide is slimy and difficult to handle. The flow sheet then becomes the following: Lime stone, the cheapest alkali available, is ground in a closed cir cuit (this operation comes from the mining or metallurgical engineer); the slurry is oxidized with air during precipitation; and recirculation is used to increase the settling and filtration rates. The resulting water is neutral and inert, and the filter cake can be stacked, not lagooned. This practice ob viously capitalizes on chemical engineering experience in many fields, . Case 3. A pulp and paper mill is in difficulty because alka line solutions discharge into a small river and because pulp in the white water decomposes and reduces the oxygen content of the stream. Here is a real problem. Possibly the paper mill circuit may be closed, and if so, putrescible solids are eliminated. Possibly an ADKA Save-all (a steal from the Kind of Plant Table I. Possible Treatment Required for Wastes from Various Plants TT* * 1 --..........Cited, by Acid- United City or Health ity, States state officer color, {physi- (cherni- (biologi- Segre- turbid- cal) cal) cal) gation ity B O, D. ,------------Treatment---- -- Metal- Sard- Cherni- lurgi- Anita- tary cal cal Screens tor Classifier or Floe- detri* culator tor Clariher or thickener Filter or centrifuge Blast furnace x1 ., X X XX X Brewery X XX XX X XX (_ annery X XX X X X Coal Coal-tar Dairy Distillery Dyehouse Gashouse x .. to. . X to to. . X to to, . X X XXX XXX X wX X X X XX {*) X X XX X XX X X XX XX X W to X XX XX Glue X XX X XX Laundry . . X to X to to X XX XX Packinghouse X XX X XX XX Paint .. X X X X X' X Paper . . X to X to to X XXX XX Pickling-liquor , - X X X X XX Pulp Refinery to X X . * (x) toX to X to XX XX X XX X Rubber X .,, X XX Sand X -. X XX XX X r'joap f'-ugar 1 annerv .. X XX X X to XX XX XX XX x XX X Textile .. X XX Wool XX XX XX Aera* tor X X X { X1 6c j X X (X) Digestor or Plotatrick- tion ling cell or filter ADKA X X X tXo (X) X X U) X X 1 x indicate!- equipment used; (x) indicates equipment which might be used on. secondary or alternative basis. 1342 INDUSTRIAL AND ENGINEERING CHEMISTRY (Reading from top to bottom) Figure II. Bowl Classifier for Finer Solids Figure 12, Type-F Straight Classifier Figure 13. ADKA Save-all for Applying Flotation to Paper Pulp and Filler YOL. 31, NO. 11 (Reading from top to bottom) Metallurgical Flotation Cell Metallurgical Table Classifiers in Closed Circuit with Tube Mills for Grinding NOVEMBER, 1939 INDUSTRIAL AND ENGINEERING CHEMISTRY metallurgical industry) will float the pulp from the white water down to 0,3 pound per thousand gallons of water; but what of the pulp mill waste? If the plant is produc ing kraft pulp, possibly continuous filters to replace diffusers will close the black liquor circuit or additional evaporator capacity will help. Mixing of the bleach and decker waters may neutralize them, and the mixture may be discharged without further treat ment. A trickling filter will reduce the B. 0. D, of any special liquors still carry ing the sodium salts of lignins in solution. This is a combination of the best in the chemical and sanitary engineers' experience. Case 4. Many articles have been written on packinghouse wastes, and several plants are in successful operation. Often the muni cipal sewer assists in taking some partially treated effluents. The flow sheet includes a fine screen flash mixer for dosing, flocculator, and two primary clarifiers, the clari fier underflows going to two-stage diges tion and finally filtration. Primary clarifier overflows are treated on trickling filters and the effluents are further clarified, the settled solids joining those from primary clarifica tion ahead of digestion. Incidentally this plant now includes a detritor and a gas holder for digester gas. This is a sanitary engineering operation throughout. If we assume that segregating solids offend the War Department, that acidity, color, and turbidity are forbidden by city or state, and that B. 0. D. and odors are obnoxious to the Health Department, we can prepare a table and at once make some sort of gen eral estimate as to the possible type of treat ment required and the equipment that might be used. This is inexact but at least gives an indication. It is surprising to note how much waste treatment is nonsanitary work. The following machines are representative: 1343 Sanitary Screen Flash miser Floeeuiator Detritor Clarifier Filter Centrifuge Aerator Digester Trickling filter Chemical Screen Agitator Thickener Filter Centrifuge ADKA Save-all Metallurgical Screen Agitator Classifier Thickener Filter Flotation cell As an example let us consider the first entry of Table I. This is flue gas from a blast furnace operation. The solids are inert and the liquid is practically neutral. The coarser solids would be removed from the furnace gases by dry dust catchers, some finer solids perhaps with electrical precipita tors, and the remainder by wet scrubbers. Thickeners would separate the wetted dust from the scrubber water, and filters might follow. This, then, is a metallurgical prob lem using equipment primarily from the metallurgical industry. Figure 17. Figure IS. Figure 19. Figure 20. Digester in a Sewage Plant Distributor Feeding a Trickling Filter Clarigester (Clarifier and Digester in a Single Tank) Claraetor (Aerators Surrounding a Round Clarifier) 1344 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 31, NO. 11 The next entry of Table I has to do with the removal of organic solids, both soluble and insoluble, from a brewery waste. These solids are putreseible and the health officer lias objected. Correction of B. 0. D. is re quired, and it is a sanitary problem probably making use of screens, aerators, digesters, trickling filters, and clarifiers. The third, a cannery waste, is funda mentally like the second; the fourth, a coal waste, is metallurgical again, probably using flotation, elosed-cireuit grinding, and tabling in addition to the units described under blast furnace, and so on. Figure 21. Figure 22. Figure -23. Turbo Flash Mixer Preceding Flocculator and Clarifier Turbo Oxidizer (Small Ones Induce Their Own Air) Agitators, Usually for Metallurgical Operations Equipment Although it might not be fair to say that no new equipment has been or need be de veloped for waste treatment, in general exist ing machines or modification of them will suffice. The illustrations demonstrate that we have an abundance of equipment units for mechanical handling of waste and that the principal remaining problem is to classify and segregate wastes and then develop a flow sheet using the equipment and process best suited. A discussion of equipment for waste dis posal should include machines and flow sheets for air pollution elimination. Tiiis is a large subject; and since my experience has been almost entirely with liquid wastes, I do not feel competent to discuss air pollution ex cept where it ties in closely with stream pollution. Blast furnace flue dust is ac tually air pollution, but with wet scrubbers the problem becomes a stream pollution problem. Other plants listed have air pollu tion problems and manufacturers have con tributed much to abate odor and dust nui sances by chlorination, activated carbon, and similar means. Monkhouse, of the Ministry of Health in Great Britain, made an address last March classifying air pollution problems into: Solid particles--grit dust and fume; calls for dry precipitation or scrubbing, followed by a physical or metallurgical plant. Liquid particles--mist; requires condensation, precipitation, or scrubbing. Gases--toxic, injurious, and offensive; be comes a chlorination or activated carbon prob lem. Liquid effluents emitting smell alone or when in contact with other liquids--uses chemical treatment, carbon, etc. Let us now consider some of the machines used, which are actually a combination of many operations known to the chemical, metallurgical, or sanitary engineer. Numer ous types of aerators, flocculators, clarifiers, filters, etc., are on the market, but the cuts shown were most readily a\railahle. Since tests indicate better clarity and more capacity for centrally fed clarifiers, this type is pre ferred. Rectangular clarifiers are illustrated because in some cases space limitations pre clude the use of the more efficient arrange ment. NOVEMBER, 1939 INDUSTRIAL AND ENGINEERING CHEMISTRY 1345 Since a sedimentation step appears in most waste treat ment flow sheets, let us consider first the thickener or clarifier. Many types are available. The unit-compartment centraldrive machine with torque arms (Figure 1) is used for coal, blast furnace flue dust, and the metallurgical type of plant; where floor space is at a premium, the tray may be preferable (Figure 2). In the treatment of organic wastes and where flocculent light precipitates are to be removed, the sanitary type usually called a clarifier (Figure 3) is standard equipment. This may be round or square. The mechanism may rotate at a slower speed, and the feed should enter at the center--thus the siphonfeed principle. For rectangular tanks the Monorake illus trates a type (Figure 4). With these light materials floccula tion is often induced to aid settlement or clarification, either by mechanical flocculators or the building of a synthetic floe by chemical treatment or both. A conventional type of flocculator is shown in Figure 5. Since floes must be carefully handled to prevent breakage or dispersion, the combination flocculator-clarifier (Figure 6) has been developed and is in considerable demand. Clarifiers in general give a satisfactory effluent or over flow, but the settled solids or underflow still carry considerable water. These underflows are still a problem in many cases, but usually they may be filtered on a continuous filter (Figure 7) , and more recently the continuous centrifuge (Figure 8) seems to offer possibilities. Some of these filter cakes or recovered solids may be burned; Figure 9 illustrates an incineration system which is being used with good results. With organic wastes, bar and rotary screens often precede sedimentation for removal of the coarser suspended solids. Finer materials in suspension are classified ahead of sedimen tation ; the detritor (Figure 10) fills this gap in sanitary-type problems, and the bowl classifier (Figure 11) or straight classifier (Figure 12) is used in metallurgical-type operations. These units give a clean, well-washed sand and take care of this part of the problem. Light particles in suspension, such as pulp in white water from paper mills, are now recovered by flotation in the ADKA Save-all (Figure 13), metallurgical flotation reagents being commonly used. The effluents are abnormally clear, and the recovered stock is in admirable shape for return to the paper machine. Figure 14 shows a metallurgical type of flotation cell, as used in recovering coal from fines recovered from a river. The metallurgical table (Figure 15) recovers the coarse coal and separates it from the slate; flotation cells do the same for the finer suspended particles. In this operation closed-circuit grinding (Figure 16) may well be used. Clarifier effluents may be clean as far as suspended par ticles are concerned but unsatisfactory as to B. O. D., dis solved solids, etc. They may be aerated in many types of equipment. Underflows may be digested (Figure 17) or passed through trickling filters by means of distributors (Fig ure 18), and combinations of these units are available. Fig ure 19 shows a Clarigester, a clarifier and digester in one tank; Figure 20 is a Claraetor, clarifier and aerator together. Mag netite filters are used for further removal of turbidity or color from a clarifier effluent; this automatically washed sand filter may have a future of considerable interest. Agitators of many types are available. The flash mixer of the turbo type (Figure 21) appears in most plants; it requires addition of chemicals for flocculation and gives a few seconds or minutes of violent agitation to the total flow. The aerator type of turbo (Figure 22) will oxidize ferrous precipitates to the ferric to facilitate handling. Figure 23 illustrates the metal lurgical-type agitator for large tanks, and Figure 24 the slurry mixer for storing and blending suspensions to provide uniform flows. These may be used in tanks up to 40 feet in diameter and nearly as deep. These examples, together with the flow sheets, will bear out the statements that adequate equipment is available to handle any waste mechanically, and technical knowledge is also available, although it is possibly somewhat scattered. If any given waste is studied and classified, a solution may almost certainly be found. Feeders and Proportioners If waste treatment is to be a new overhead, it is obvious that the manufacturer should do all possible to make the plants self-operating and the daily cost a minimum. Equip ment is available to regulate the dosage with one or more chemicals and to vary it with the volume of feed and pH of the incoming waste. These units are dependable, accurate, and substantial, and are doing much toward solving waste prob lems. , It seems obvious that this is not just another operation or another unit process, but a subject far more complex. It calls for all the knowledge accumulated in the sanitary, chemical, and metallurgical fields, and each waste problem can doubtless be solved in a myriad of ways. Figure 24. Slurry Mixers in a Cement Plant