ORGANIC CHEMICALS MANUWACTURE R. W. MESS and C . J. CARII-EY, National Aniline Dieision, Allied Chemical & Due Corp., Buffalo, N. Y . T h e residuals from organic chemicals manufacture are comprised of not only reaction by-products but also unconsumed raw materials, many of which are process aids such as solvents. They are frequently produced in very complex mixtures in water solutions which painfully challenge the creative imagination in efforts to divert them from public waters. Pollution abatement programs have served in but a small measure to point out economic advantages of recovery and utiliea tion, because the industry
was founded on the utilization of residuals from the coking of coal, the spirit of which has permeated all subsequent developments. However, the monetary returns from recoveries are taken into account in deciding on whether the most economical solution of the pollution problem is in recovery, modification of the productive process, or waste treatment. Frequently, the last is found to be the most economical and is being developed heyond the frontiers of past practices.
A
LTHOUGH several attempts had been made during the decsiduals. Modifications giving increased yield usually reduce ade preceding the founding of the AMERICAX CHEMICAL operating costs but other modifications frequently increase them. the organic chemical industry did not gain a permanent 3. Treatment or disposal of residuals in harmless locations SOCIETY,
beachhead in this country until about the time when the ACS was founded. This victory was won by J. F. Schoellkopf, Sr. and Jr., when they founded the Schoellkopf Aniline and Chemcal Works a t Buffalo, N. Y . ,in 1879. For the next 35 years this beachhead was not greatly enlarged. I t s great expansion t o its present state of domination started with World War 1. Accordingly, the history of the organic chemical industry with its problems is essentially coincident with the history of the ACS One of t h e big problems of the organic chemical industry during the course of this history has been inherent in residuals from manufacturing operations. During the first 35 years the types of these were relatively few in number and simple in nature because of the relatively small number and simple nature of products manufactured. Most of the products were the simpler dyes, aniline and its elementary derivatives. Beginning with World War I they have steadily'become much larger in volume and much more diverse in character relative t o products manufactured because of the much greater complexity of the nature and of the necessarily more involved manufacturing operations. I n physical terms these liquid residuals are in the ngture of water solutions, liquids insoluble in water, suspensions, sludges and tars containing unreacted chemicals, by-products, process aids, and even the main product itself. Their volume is frequently much larger than t h a t of the main product, due in a large measure to the use of process aids. In chemical terms they are essentially hydrocarbons and their derivatives containing halo, hydroxy, nitro, nitroso, amino, carboxy, sulfo, keto, thio, cyano, and azo groups, in a multitude of combinations; mineral acids; alkalies; a large variety of inorganic salts; and water. In a single plant there are sometimes thousands of individual compounds, frequently in small amounts and in very complex mixtures, making utilization and disposal very difficult technically and economically. They are formed t o some extent by steps taken to avoid atmospheric pollution, such as condensation and absorption of vapors in water. I n common with other chemical industries the following activities of the organic chemical industry have been in the interest of pollution abatement. 1. Recovery and utilization of process residuals, which is profitable in some cases but which only partly pays related costs in other cases. 2. Modification of productive processes to minimize re494
with no monetary compensation.
Recovery amd Utilization of Process Residuals There are two types of process residuals-unconsumed raw materials and reaction by-productp. The spirit of utilization of residuals is inherent in the initial concept of this industry, which was founded on the utilization of residuals from the coking of coal. Development of the industry from these residuals involved the highest type of scientific endeavor which was extended to all manufacturing operations. The unvarying objective has been the highest possible yields and the utilization of all residuals, coincident with development of productive processes when profitable. During the past two decades, when utilization was not profitable, they have been utilized in some cases t o help defray the cost of diverting them from the atmosphere and public waters. I n many cases they are being treated or disposed of in ways to avoid pollution because of lack of economic value or lower cost than processing for utilization. It has been the constant practice t o carefully weigh the merits of these alternatives. Pollution abatement programs have served but little t o point out the economic advantages of utilizing the residuals of the organic chemical industry. In exemplification of this, one manufacturer of organic chemicals tried repeatedly but unsuccessfully for fifteen years, before being confronted with a pollution abatement program, to profitably recover a commercial component of one of its wastes as an addition to its own line of products Finally, during 1938 chemical destruction of the waste was established and has been practiced continually since t h a t time in the interest of pollution abatement. This company also had a waste liquor containing, as a by-product, a chemical which i t manufactured by another process from a different raw material. When confronted with a pollution abatement program i t undertook intensive research t o determine whethei it had overlooked an opportunity for profitable recovery in its earlier inrestigations. The outcome was that it was sent t o the municipal disposal plant with the approval of its management. I t was concluded t h a t this chemical could be manufactured a t a cost, including the sewer tax, lower than t h a t of recovery. Examples of utilization of these residuals are as follows. Unconsumed Raw Materials. There are two types of unconsumed raw materials which are recovered for re-use. One class consists of reactants, t h a t is, those which enter into reaction t o
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Liquid Industrial U'aetes give the desired product but are used in excess t o favor the reactions by serving as solvents, dehydrating agents, catalysts, or other kind of process aid. The second class is composed of those which are used simply t o favor the desired reactions without any part of them being consumed in the desired reactions. Sulfuric acid, one of the major volume residual raw materials of the organic chemical industry, belongs t o both types in some cases. It is used in many types of unit operations. Large quantities are used for solvent and dehydrating actions in sulfonations, nitrations, chlorinations, condensations, etc. A substantial proportion of this is discharged from processes at a strength and quality which makes recovery and re-use profitable. In one plant alone the amount of this acid recovered for re-use amounts to about 12,000,000 pounds annually. , Sulfonation of some hydrocarbons is a n example of the first type. Slightly diluted excess acid, containing some organic matter, is phase-separated and applied to certain special uses. I n the sulfonation of alkyl aryl compounds t o produce synthetic detergents the entire charge is neutralized with alkali t o form the necessary amount of sodium sulfate when t h e slurry is dried. Production of nitro compounds ie a n example of t h e second type. A large proportion of nitration reactions is effected by use of mixtures of nitric and sulfuric acids in which t h e latter serves as a n aid only. The residual is slightly diluted sulfuric acid in a separate phase containing a small amount of nitric acid, nitrous oxides resulting from reducing action of the organic materials, and varying kinds and amounts of organic matter, depending on the raw material used. It is separated and consumed without further processing to a limited extent in some processes, after aeration t o remove nitrous oxides and volatile organic substances in other processes, and after concentration and refortification in still other processes. A common procedure for recovering excess reactant is separation and rectification of the liquid phase from the water layer, and extraction of the latter with the raw material uRed for production of the reactant. Recovery and utilization of excess aniline, used as a reactant in many processes, is a n example of this. A common procedure for recovering this material is steam distillation, condensation of the vapor, and removal of the aniline oil by use of a continuous separator with continuous return of water t o the still. Aniline dissolved in the water of this and other types of processes is extracted with nitrobenzene which is used as a raw material for production of aniline, thereby recovering this residual in the finished product. A common procedure for diverting from the atmosphere the volatile raw materials carried away by by-product gases is t o pass t h e mixtures through scrubbers, which contain the raw materials! a n d condensers. This then gives a liquid residual in a form which may be re-used. A synthetic detergent process is a n example of this. By-product hydrogen chloride carries off some of the aliphatic hydrocarbon in the chlorination reaction and some of t h e aromatic hydrocarbon in the Friedel-Crafts condensation. In some cases the excess reactant is removed from the reaction charge by dry distillation and is then rectified or purified by other procedures for re-use. Recovery of excess alcohols used for alkylation of amines exemplifies this. Many processes for organic chemicals use such substances as benzene, nitrobenzene, chlorinated benzene, aniline, toluene, solvent naphtha, acetic acid, pyridine, and phenolic substances t o serve as solvents or as process aids in other respects. Usually these are recovered and purified for re-use by procedures indicated above for excess organic reactants Reaction By-products. The initial utilization of reaction byproducts started with the founding of the organic chemical indust r y in the manufacture of intermediates for coal tar dyestuffs. I n the production of these intermediates there were formed many isomers and other types of by-products which have been utilized in the production of new types of dyestuffs. Later, as productive processes were established, by-product
March 1952
ammonia and alkali from production of indigo; sulfur dioxide and sodium sulfite from production of phenol and 2-naphthol; sodium thiosulfate from production of sulfur dyes; hydrogen sulfide from sulfuration reactions; chromium, lead, and copper compounds from oxidation syntheses; iron and zinc oxides from reducing reactions; mixed nitrotoluenes from production of dinitrotoluene; polychlorobenzenes from production of chlorobenzene; and diphenylamine from the ammonolysis of chlorobenzene t o give aniline, were recovered and used.
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I
I
1
ELECTWE' I *5YMBLY WASTE W A R *,APPLY FOREBAY
I
4
R
Figure 1. Waste Acid Neutralization in Sewers and at Intakes for 25 Million Gallons per Day of Cooling Water A . To Plant A sewer AC. Automatic control of lime feed B . To Plant B sewer FS. From storage I A . Instrument air M C . Manual control of lime feed M T . Mixing tee R . River water R M . From river water main RO. Rotameter SG. Sight glass S M . Synchro motor diaphragm valve TS. .Tostorage tank T W . From tank wagon
Some of the other reaction by-products which are being recovered from newer prpducts and newer processes and utilized are: acetaldehyde from the oxidation of hydrocarbons to other chemicals, from the ethylidene diacetate process for acetic anhydride, and from the process for converting alcohol t o butadiene; acetic acid from acetylation processes; acetone, methanol, methyl ethyl ketone, and propanol from oxidation of aliphatic hydrocarbons t o acetaldehyde; butanols from the process for production of butadiene from ethyl alcohol, from the oxidation of hydrocarbons t o acetaldehyde and formaldehyde, and from the synthetic process for methanol: carbon tetrachloride from the chlorination or chlorinolysis of higher hydrocarbons; diphenyl and diphenyl oxide from the production of phenol; propionaldehyde and mixture of dichloropropane and dichloropropylene from t h e process for allyl alcohol; ethyl acetate and ethylene from the ethyl alcohol process for butadiene; ethyl alcohol from the Fischer-Tropsch hydrocarbon synthesis; ethyl ether from t h e ethyl alcohol process for butadiene and from the ethylene process for ethyl alcohol; ethylene dichloride from the processes for allyl alcohol, ethylene chlorohydrin, and ethyl chloride; formaldehyde from the production of acetaldehyde by the oxidation of paraffins; maleic acid and 1,4-naphthoquinone from the catalytic process for phthalic anydride; methyl acetate from the methanol process for acetic acid; methylene dichloride from t h e process for producing methyl chloride by chlorination of methane; and tetrachloroethane from the process for ethyl chloride and ethylene dichloride. . Some condensation reactions-e.g., the Friedel-Crafts reaction
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LIquid Industrial Wastes -give considerable amounts of t a r which are processed and used for fuel oil. Another inorganic substance, by-product hydrochloric acid, has also come to be one of the major volume residuals from the manufacture of organic chemicals, LT hich produces a substantial proportion of this country's supply of hydrochloric acid. It is formed by absorption of hydrogen chloride gas in water. Purification a t some step is usually necessary for utilization. Sometimes this gas is contaminated with the original and chlorinated raw material, which is removed by passing through a scrubber containing the same material. Some sources of this by-product are the chlorination of benzene to chlorobenzene, of pentane to produce amyl alcohol, of cresol to produce tricresyl phosphate, and of various organic substances to produce insecticides. I t is also formed in the chlorination of aliphatic hydrocarbons and in the Friedel-Crafts reaction in production of synthetic detergents.
Modification of Productive Processes Company records are replete with this type of improvement but not many of these are available to outsiders because of competitive considerations. Int'ense application on improved yields and process simplification to minimize the loss of raw materials and the formation of by-products has been made continuously ever since the industry was founded. The process for making phenol from chlorobenzene is an example of this. Addition of diphenyl oxide, a by-product of the process, increases the yield of phenol. Modification of processes for the specific purpose of minimizing residuals related t o pollution is largely a development as the result of considerable research during the last two decades. In some processes in which phenolic taste-producing substances were used as a solvent or process aid, substitutions were made when recovery or destruction was less practicable. In processes using phenolics as a reactant, attention is being directed to being certain t h a t no unnecessary excesses are used. Mineral acids, which are neutralized before discharging into public waters, are being substituted for organic acids and their salts, which are used as process aids, to reduce the biochemical oxygen demand of the effluent. One example is in the preparation of azo dyes and another i s in the reduction of nitro compounds by use of iron. In the sulfonation step for some synthetic detergentas, the spent sulfuric acid layer containing orgahc matter was initially separated and discharged t o the stream. The sulfonic acid layer was then diluted with water and neutralized to form sodium salt. Sodium sulfate was added and the solution was dried. The entire sulfonation charge was then neutralized, thereby forming the required sodium sulfate. In the production of some arylaminosulfonic acids the raw niaterial is first sulfonated with strong sulfuric acid, then converted to the nitrosulfonic acid by addition of nitric acid. In some cases the nitro group is reduced by adding iron to the diluted solution giving a waste liquor containing a dilute solution of sulfuric acid and ferrous sulfate, the recovery of which is very difficult and costly. I n other cases stream pollution by the iron waste is avoided by neutralizing the diluted solution and applying the neutral reduction process; this gives a suspension of the granular form of iron oxide which can be easily recovered by filtration. One method which is being applied to reducing the amount of waste sulfuric acid is the substitution of liquid sulfur trioxide (Sulfan) for sulfuric acid in the sulfonation of organic compounds. No excess is required as is the case when sulfuric acid is used. Sometimes this also reduces the amount of organic residual by giving higher yields of desired products. Sometimes liquid wastes which result from absorption of gaseous wastes in water are eliminated or avoided by eliminating the gaseous waste. An interesting development recently in this connection is the catalytic oxidation of gaseous wastes. 496
Treatment or Disposal with No Monetary Returns A continuous history of recovering residuals and of improving processes to minimize the formation of residuals by the organic chemical industry still leaves a cross section of the residuals listed above which incur costs for treatment in the interest of abating present and preventing new pollution with no monetary return.
Discharge to Municipal Sewage Systems One of the earliest methods of treating liquid wastes was the discharge of some of them into municipal systems, although this was not very effective during the first fifty years of this industry because of the existence of only a few treatment plants. This was effective where there were treatment plants when these residuals were similar to sewage, a s was frequently the case. However, a s time passed, trouble was encountered because of increasing complexities of these wastes, overloading and refinements of municipal treatment systems. Considerable resistance by municipalities was encountered. ilt present this resistance seems to be decreasing because of better cooperation by both industry and the municipalities. Industry is being more careful in the selection and pretreat,ment of wastes for this method of disposal with the advice of treatment plant personnel. Municipalities are now tending to design plants and operations for handling the larger loads. Chemical wastes which are easily oxidized biochemically after neutralization, such as alcohols and carboxylic acids, are being discharged t o municipal treatment plants in considerable quantities. Bactericidal and taste-producing substances, such as phenols, are included in smaller quantities if secondary treatment is provided. They are excluded if primary treatment only i s provided to avoid release into public waters. Oxidizable inorganic substances, such as sulfides, sulfites, and thiosulfates, are limited in amounts t o avoid release of obnoxious gas from and damage to sewers. Mineral acids are excluded to avoid damage to sewer structures. Toxic substances, such as salts of heavy metals and cyanides, are rigidly limited t o avoid injury to biological processes. Large amounts of inert suspended matter, such as calcium sulfate, are excluded to avoid an objectionable increase in the volume of the dried or incinerated sludge. Flammable liquids and tars are excluded t o avoid fires and other troubles in the system. Industry is paying for the cost of municipal treatment, in a t least one location, in terms of chlorine consumed and quantity of suspended solids above domestic sewage, and of volume as related to pumping costs. Many organic chemicals such a s alcohols and the saturated carboxylic acids have low chlorine demand but, the costs of chlorine for sulfites, thiosulfates, and especiallysulfides, are relatively very high. Sccordingly, it is sometimes found to be less costly t o destroy thein chemically or biologicall>-,. or to recover them a t the manufacturing plant. Exclusion of objectionable components from r a s t e s discharged to municipal systems is effected by either pretreatment or careful selection of waste liquors. Wastes selected for this method of' disposal without treatment as well as after pretreatment are car'c-fully tested by the manufacturing plant in relationship t o operations in the municipal system and are checked by personnel a,t the municipal plant. In general, installations and operations for this pretreatment are similar to treatment for discharge to. public waters, except for completeness of treatment and certain special operations. For example, it may be necessary t o remove the suspension of calcium sulfate, formed by t,he neutralization of sulfuric acid with lime, which niay sometimes be discharged to the stream with the effluent. The investigation of pretreatnient was intensified during the 1930 decade \Then the installation of municipal plants was greatly expanded under the stimulus of federal funds. Application of
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. KtquU Industr2al Was&these and new investigations has been gradually extended since t h a t time. Avoidance of pollution by using inert solid wastes for land fill and by burning of solid and liquid organic wastes has been practiced since t h e early days of this industry. Recent developments in this connection are installations of costly incinerators, in which all types of organic wastes are burned by several companies, and the dumping of residuals in the ocean.
Chemical Treatment Next came chemical treatment of these wastes--this was being practiced to some extent shortly after World War I. An example of this is neutralization of waste acid. Even though large quantities are now recovered and utilized, this is one of the major volume wastes of the organic chemical industry. 3ulfuric acid is one of the main components of this waste; the reason for this is illustrated by one of the processes for l-amin0-3,6,8-naphthalenetrisulfonic acid (amino H acid), one of the important intermediates in the VENT dyestuff industry. I n this process I F RIC naphthalene is sulfonated by mixing with an excess of sulfuric acid, nitrated by adding nitric acid t o the same mixture in which the excess sulfuric acid serves as an assistant, diluted by adding the mix t o water, reduced t o the amino compound by the action of metallic iron on the diluted acid, precipitated by addition of sodium chloride, and separated by filtration. The filtrate contains a ]OW concentration of sulfuric acid Figure 2. Treatand ferrous sulfate, a high concen~ ~ tration of sodium chloride, some of Liquors the product, and some organic byproducts for which no use has been found and for which no practicable method of separation is known. Generally these weak and contaminated acid residuals from numerous and widely separated sources are colllscted by use of sewers in a compositing and equalizing basin from which they flow through a neutralizing installation and, in some cases, through a settling basin before being discharged into another unit for treatment of other components, or into municipal sewers or public waters. An example of this is a plant which uses byproduct lime supplied by a neighboring plant about one mile away. T h e impacted lime in collecting beds is converted to a slurry by a procedure similar t o hydraulic mining and pumped t o the point of use through a pipeline. An exception t o this method where sufficient land is not available for collecting and compositing basins is one in which the waste acid is neutralized in sewers. I n this case residual lime from the manufacture of acetylene at a plant ten miles away is used. A 25 to 30% slurry is prepared by the hydraulic mining procedure and hauled in tank wagons t o concrete storage and feed tanks with capacities of 15,000t o 45,000 gallons. , T h e amount of lime required t o keep the stream in acceptable condition is determined by the p H at nearby cooling water intakes and the rate of feed is regulated by a rotameter. At one cooling water intake, immediately between two sewer outlets, this lime slurry is fed into the pumping system by means of a p H recorder-controller to ensure maintenance of the required p H (Figure 1). During the past eight years the annual requirements for hydrated lime a t this plant varied, roughly, from 1000 t o 2400 tons. But little or no lime was required during the months of January, February, March, April, and December because of stream flow supplying adequate alkalinity. Generally, the heaviest require- . March 1952
ments were during August and September. Monthly and annual requirements over the entire period are shown in Table I. The cost of using this by-product is substantial, because of the preparation and hauling, but is somewhat less than t h a t for the commercial grade of calcium hydrate, which was used in this case for several years. Use of this by-product avoids skin irrita tions caused by the use of dry lime. Hydrated lime rather than calcium carbonate is used because greater activity is required for effecting neutralization in the sewers. Another method used for neutralizing waste acids, when sufficiently dilute, is passage through a limestone bed if the minimum p H requirement isn’t too high. If the sulfuric acid concentration is above 0.5% this method is ineffective because of coating the limestone with precipitated calcium sulfate. Another example of chemical treatment is the decomposition of sulfides and thiosulfate by action of acid. Apparently this was initiated during the third decade of this century. The principal reactions are:
+ Na2SO4 NazSzOs + HzS04+SO2 + S + Wad304 + HzO 2NagSz03 + SO2 -4 2Na~S04+ 35 2HzS + SO2 35 + 2Hz0 Na2S
+ H2S04--+
HzS
--.)
(1)
(2)
(3)
(4)
When it is not economical t o recover and utilize the hydrogen sulfide and sulfur dioxide they are caused t o react according to Equation 4, or the hydrogen sulfide is burned or released t o the atmosphere through a high stack and the sulfur dioxide is caused to react with thiosulfate according t o Equation 3. When the sulfur cannot be utilized it is discharged with the effluent or separated by filtration and hauled t o the dump (Figure 2).
Table I.
~
Tons of Hydrated Lime Used to Neutralize ? Acids ~ a t One~Plant Waste
$
January to April
May June July August September October November December Total
1950 1949 1948 1947 1946 1945 1944 1943 0 0 9 55 7 0 0 28 2 4 18 0 0 78 37 0 5 28 11 10 9 25 232 107 348 203 46 146 214 42 459 25 499 68 1002 228 575 350 546 260 474 570 388 460 216 796 322 341 2 465 137 107 476 350 366 741 0 30 0 227 0 310 298 405 0 48 0 __0 0 0 0 0 2147 1616 2417 1283 1478 942 2324 998 ~
Biochemical Treatment Great strides in the treatment of residuals from t h e manufacture of organic chemicals, without monetary compensation, are the biochemical treatment plant for phenolic substances erected by one company in 1937 a t a cost of $1,500,000, and another biochemical plant for mixed organic wastes erected in 1946 by the same company at a n initial cost of about $1,000,000,after years of costly research in which all the scientific and technological services of the organization were utilized. These are regarded as being outstanding world accomplishments in the field of waste treatment Further advances in the biological destruction of wastes from t h e manufacture of organic chemicals were made when one company reported in 1948 t h e installation and operation of a plant for treatment of sulfide residuals and another reported in 1950 the installation and operation 0f.a plant for formaldehyde residuals Each of these plants encountered their own particular problems, a s no one rigid method of biochemical treatment is applicable to all oxidizable residuals. Another significant development in the treatment of residuals from this industry, without monetary compensation, was the development of a program and installations in 1940 by another company. After extensive research, starting in 1937, it was de-
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Liquid Industrial Wustes cided t h a t most of the waste liquors could be improved by compositing, neutralizing, settling, aerating, and diffusing into receiving waters. The initial cost of the plant for these operations, including a 10,000,000-gallon compositing basin and a 60,000,000gallon settling lagoon, was reported t o be $325,000.
Carrent Developments Further extension of methods for treating liquid residuals from this industry is represented by a plant under construction, which projects a n expenditure of $1,600,000, for 1% aste disposal installations, including $460,000 for a deep disposal well. This installation also represents the grom-ing practice of management not to approve installations for productive operations until adequate provision for waste disposal has been incorporated in the design. The same company is pushing into new frontiers of m-aste disposal methods, as represented by the development of a catalytic method for destroying low concentrations of organic wastes in water vapors. It is reported t h a t this method also gives promise for dilute water solutions.
There are many individual or gioups of similar waste liquors which must be specially treated a t the process sources, because they cannot be treated satisfactorily in processes for general mixtures or because they are harmful to the processes for these mixtures, such as toxic substances in biochemical processes. Furthermore, manufacturing plants which are restricted as to available land for treatment of large volumes of process wastes place relatively more emphasis on elimination of existing and prevention of new pollution a t the process sources by recovery, process modifications, and treatment. That part of the problem in this industry remaining largely unsolved is comprised of a large number of waste liquors which do not present much of a problem individually but which are of considerable concern collectively. Individual treatment is not practicable and treatment of composites is made very difficult by exceedingly complex propelties of the mixtures. Treatment as a whole or as selected mixtures is further complicated by using process sewers for cooling n atel in many cases. RECEIVED for review September 6 , 1931.
ACCEPTED
Jsnuary 15, 1952.
PACKING OUSES F. W. MOHLMAN, The S w a i t a r g District of Chicago, Chicago, Ill. W. V. HILL, GreeZeg und H # 6 n S @ n YClaicugo, Ill. Frequent investigations of treatment of packinghouse wastes have been made, but the processes in full-scale use are largely limited to use of activated sludge or trickling filters, provided there is sufficient dilution with human sewage to support biological processes. Prior to treatment, salvage processes such as screening, evaporation, or flotation reduce the concentration of the wastes to be treated. Surveys to determine unit losses are of value to show the degree of recovery and the remaining load that
must be handled by treatment processes. The largest treatment plant for packinghouse wastes is at Chicago, the Southwest Treatment Works of the Sanitary District of Chicago. This activated sludge plant is successful because of ample dilution and careful control of air and sludge flows. A recent process, anaerobic digestion, is being tested at Austin (Hormel C o . ) and in New Zealand. This promises to give satisfactory results at lower costs but so far has been tested onlv on an experimental basis.
P
dustry in research on processes and improvements, but until recently has ignored waste disposal. However, for the past two years papers on waste disposal (3, 7 ) have been included on the program of t h e annual conference. Also, the program of the Department of Packinghouse Practice of the institute included a paper (5) in 1950, and those a t the meeting evinced considerable interest in the subject. Thus, there n o v appears t o be an awakening interest in waste disposal, or a t least it has been publicly acknowledged t o exist.
ACKIKGHOUSE operations have been supervised for many years by scientific chemical control, and salvage of recoverable by-products has been associated wit.h this industry from its beginning. Innumerable by-products have been developed, many into quite profitable materials, and this salvage record is still progressing, stimulated by the discovery of cortisone, varieties of insulin, and various animal protein factors. It seems surprising, therefore, tmorealize that there is still a packinghouse waste problem, which has apparent,ly eluded the efforte of packinghouse chemists, but it is probable that management has the final decision concerning the money required for treatment facilities and perhaps t,he allocations for such facilities are not made until conditions become so bad that, something must be done. However, investigations of wast,e treatment are nunierous in the packinghouse industry, by employees of individual plants, municipal or state officials, or by the U.S.Public Health Service or similar agencies. Centers of t,hese investigations are the Sanitary District of Chicago ( 1 2 ) , the cities of Ft,. K o r t h ( 9 ) , Mason City, Ia. ( 6 ) , Sioux Falls, S. D. (a),South St.Paul and Fargo, N. D., Madison, Wis., Austin, XIinn. ( 4 ) , the Department of Health of Pennsylvania ( I d ) , and the City of huckland, N e x Zealand (13). Auckland has made a thorough, up-to-date survey of the entire subject of disposal of packinghouse ivastes, and some of the data from this survey will be quoted later. An aerial view of the Chicago stockyards is given in Figure 1. The investigations have not included such agencies as the American Meat Institute, which has long represented the in-
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The Waste Disposal Prsblem Degree of efficiency of salvage determines the magnitude of the waste treatment problem and therefore losses per unit of raxy material .(live weight) shovi the magnitude of the problem and the degree of success t h e packer has att’ained in preventing losses t o the sewer of recoverable materials. Unit, quantities have been reported frequently, even when losses were expressed per “hog unit,” since replaced by the unit “1000 pounds live weight.” When placed on this basis losses average 14 pounds of biochemical oxygen demand, 12 pounds of suspended solids, and 2 pounds of nitrogen per 1000 pounds of kill, and grease varies widely, possibly as low as 0.1 pound and up t o 6 pounds per 1000 pounds of kill (8). Mortenson (10) says t,he losses of floating fat can be kept as low as t h e minimum value-0.1 pound-with well-designed and operated grease-skimming basins. Note t,hat this does not mean total grease, but only the floating grease. Experience indicates t h a t most houses have much greater over-a,ll grease
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