Industrial Wastes
drne 1880
The future of the sulfite wood pulp industry is doubtful unless waste control methods can be developed to reduce stream pollution by sulfite liquors bg Harold R. Murdoc&
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security of the sulfite wood pulp iiidustry is at stake and stream pollution is playing the major role in determining its destiny. Recently two state pollution control commissions have dealt the industry a staggering economic blow. The talking stage seems to be ended. Now definite action from individual mills is demanded through mandatory orders issued by the state authorities. In Wisconsin, six mills have been told what, when, and how they must meet the requirements of the commission. For instance, one large pulp mill is ordered to “reduce the average daily waste of sulfite liquor pollution of the Fox River by not less than 40% of the average daily contribution during the period July 1 to November 30, 1948, said reduction to be accomplished by not later than July 1, 1950.” The mandatory order in the State of Washington is also specific and drastic. Here the order requires “substantially complete” waste control facilities in the four leading sulfite mills by September 2, 1951. Similar action in other states where sulfite pulp mills are located is expected. Canada, Sweden, and other countries, who operate the sulfite pulping process, report similar experiences. The sulfite wood pulp industry has never doubted the seriousness of the pure stream sponsors in obtaining their objective. Tangible evidence to prove the diligence of the industry to find a practical answer can easily be found. For instance, in 1949 the Sulfite Pulp Manufacturers’ Research League, Inc., was organized by the sulfite pulp mills of Wisconsin and Michigan to make an extensive study of the waste sulfite liquor disposal problem. In cooperation with the Institute of Paper Chemistry at Appleton, Wis., they published in 1940 a comprehensive annotated bibliography on waste sulfite liquor, which in its 617 pages contained 2485 references to the literature. The Research League next made a thorough survey of the most promising existing methods and ideas. Today, these studies have resolved to either an evaporation and burning process or an animal feed yeast process as the most hopeful means for a practical answer. Pilot plants for these and other scheme8 for correction have been built in Wibconsin but to date no economical process has been found. However, the program has been pursued persistently and logically since the conception of the Research Leagut; In 1943 the forward-looking executives of the pulp and paper industry of the United States organized the National Council for Stream Improvement, Incorporated. The membership in this council represents over 80% of the total pulp, paper, and paperboard production in the United States. This organization has consistently carried out industry-wide technological studies in search for a practical method for abatement of stream pollution by waste sulfite liquors. The sulfite mills in the State of Washington, in 1944, showed appreciation of the need for correcting the method for disposal of sulfite liquors. An agreement was made with the University of Washington who have pursued the project actively in cooperation with the industry. Similar orgsnizaHE
tions have been studying the problem in both Canada and Sweden. These foreign laboratories and their pilot plants have been visited by many Americans in the past few years. Equipment and engineering companies have also given serious thought to the problem. Their efforts have been primarily to devise methods and suitable equipment for evaporating and incinerating waste sulfite liquor. These studies can be traced back to at least 1943. Of particular promise is the full scale plant at Weyerhaeuser Timber Company pulp mill, Longview, Wash., where magnesia base liquors are recovered in a specially designed incineration unit. This is an expensive installation still in the experimental stage of development. A recovery of 74% magnesium oxide and 53% sulfur and a steam production of 5770 I3.t.u. per pound of solids is reported. It is apparent that the industry has not been negligent to find a practical answer to this exigency. All reasonable efforts have been pursued. But the pure stream enthusiasts appear to have exhausted their patience and tolerance of these technological studies. What they are really proposing is curtailment of the industry in each locality to the ability of the receiving streams to correct pollution by natural means. Instaklation of methods so far available, ik practical, would require a major capital investment. A vital upheaval in the sulfite wood pulp industry appears inevitable. The object of the sulfite cooking process is to produce a fairly pure form of cellulose. To do this, trees such as spruce and hemlock are cut into logs and then into chips. The chips are fed into large digesters and covered with a solution of calcium bisulfite and free sulfur dioxide dissolved in water, The digester is closed and steam is introduced for several hours in order to facilitate the chemicals in dissolving the cementing ingredients of the wood, lignins, and hemicelluloses, and leave the cellulose fibers practically undamaged. The contents of the digester are released into a blow pit in which the waste liquor can be drained from the pulp through perforated plates in the bottom of the pit. This recovered solution is the waste sulfite liquor which has to be purged into a receiving stream. Why is the disposal of this material so difficult? The chief reason is that the industry and the waste volume are so large. During 1948, the sulfite pulp mills in the United States produced 421,921 tons of dissolving grade bleached sulfite, tons 1,487,478 of paper grade bleached sulfite, and 901,814 tons of unbleached sulfite pulp. This total of 2,811,216 short tons of sulfite pulp production in 1948 consumed 6,000,000 tons of dry pulp wood. Fifteen thousand square miles of forest area are necessary to grow the pulpwood needed by this industry in order that it may have a sustained supply in perpetuity. The waste liquor recovered from the blow pits of all sulfite mills in 1948 aggregated 8.5 billion gallons in which was dissolved 3,000,000 tons of wood (Continued un page 78 A ) 71 A
Industrial Wastes substances. The concentration of these solids was not over i l O % of wood substances and 32,000,000 tons of water must be evaporated if the solids are desired in dry form. But the huge water content of this waste is not. the only difficulty. This waste sulfite liquor has R pollution effect upon a stream equivalent to the sewage of 24,000,000 people. In other words, the mean value for each one of the 68 sulfite wood pulp mills in the United States is equivalent in pollution nuisance t o a city of 340,000 people. In 1949 there were only 27 cities in the United States which exceeded this population equivalent. I t is no wonder that the two states of Wisconsin and Washington are alarmed, for they have fifteen and thirteen sulfite mills, respectively, under their jurisdiction. Waste sulfite liquor is extremely corrosive and possesses a strong tendency to scale evaporator tubes. The recovery method of evaporation and incineration is faced with such formidable problems that it is not likely that an economic answer will be found by such a process. The capital investment will be a very expensive burden on the process, even with the new magnesium oxide process of Weyerhaeuser Timber Company. Biological disposal methods are not encouraging processes. The activated sludge process which can remove 95% of the B.O.D. value would require vast areas of stainless steel tanks. Only 1.5 to 1.7 pounds of B.O.D. can be removed per cubic yard of tank volume in 1 day. For similar reasons the trickling filter method is impractical. The production of alcohol from sulfite liquor fails economically to meet competitive methods and even then only 50% of the B.O.D. is removed. The animal feed yeast process is of greatest immediate interest t o the Wisconsin experimenters but its practicality appears doubtful. Recently, a rather simple waste control process has come to the writer’s attention. At first review it has excellent possibilities for a relatively cheap, effective solution of the problem, but scientific schemes cannot be turned into economically operated full scale plants in a few months. Extension of the mandatory orders of Wisconsin and Washington would avoid drastic moves from industry in abolishing the sulfite process until all possibilities have been exhausted. “Necessity is the mother of invention,” Rnd this may be the aim of the lawmakers. This writer hopes that such is the case. EEonomically the sulfite wood pulp industry appears to have its back against the wall. If it is to be forced to reduce production to the natural ability of the receiving streams to handle the waste sulfite liquor, it is doomed. If it must install ehpensive equipment to dispose of the waste it will fail economically in competition with the sulfate (kraft) process. The sulfite industry and each pulp mill must now appraise its future carefully. In doing so it will surely look toward the southern United States, where a virile kraft industry has grown up during the past decade. I t will learn that waste disposal is not such an imposing problem to the kraft wood pulp industry. Furthermore, it will learn that three times the United States sulfite tonnage is being produced as kraft pulp in the southern territory and that there is room for a kraft industry, well over ten times the present industry, where southern pine grows abundantly and permits a fully sustained and perpetual mill operation. 72 A
