used by industry in the treatment of waste waters are relatively quiet, shallow bodies of water. A depth of not over 5 feet is considered a practical limit to obtain the optimum advantage of sunlight on the biological life within the lagoon. Industry uses such lagoons t o dispose of the effluent from manufacturing processes, which is contaminated with relatively low percentages of soluble residual substances. Usually these shallow basins are constructed near the plant site. When properly designed, they offer possibilities of a complete treatment ahd, in many cases, at a relatively low cost of operation. New chemicals, combined with improved practice and design, will increase substantially the effectiveness of this method for disposing of dilute waste liquors. The disposal of vegetable and citrus fruit wash water from canning operations is often accomplished by the use of lagoons. Such operations have been hindered by the nuisance of flies and other insect pests which propagate in the waters. Odors have often prevented the use of lagoons at plants located close to residential properties. However, recent discoveries in the use of effective chemicals, such as DDT, for the control of insect pests herald a broader interest in lagoons. Sodium nitrate, sodium chlorite, and other chemicals have recently been found effective for the control of odors. Lagoons may be classified into three types. Retention lagoons are the simplest. They are merely storage basins for the untreated waters which are purged into streams at periods of high water freshets. Absorption lagoons are constructed to permit seepage of the residue waters into the ground. They are satisfactory only when porous soil is available, and great care must be taken in their design. Processing lagoons are the most adaptable type for chemical treatment; improved design and new processing methods assure a bright future for this type.
ing into the sandy soil s~tisfactorily. However, the knoll eventually reached a saturation point, and the raw waste material exuded from the foot of the knoll in many places. I n Iowa a canning plant which was packing peas and corn discharged its waste waters to an irrigation field of about 2 acres, The discharge amounted to about 176 gallons per minute during the hours of work and cleanup time. Furrows, approximately 24 inches wide at the top, 15 inches wide at the bottom, and 9-inches deep, were p e d to distribute the waste over the field. The ridges were 36 inches wide. This irrigation field has been in use since 1934 and is reported to be satisfactory. The soil of the field is shallow. There is evidence that the waste passing through the soil finds its way through crevices in the underlying limestone formation. The waste has been found to outcrop a fourth of a mile away at a low rate of 5 gallons per minute. No pollution of the stream near by has resulted, but this is another example of the hazards in adopting absorption-type lagoons. The sandy soil of the citrus belt of Florida is an admirable condition for absorption lagoon installations. At one location the citrus wastes are collected in a large pit which holds the sludge while the supernatant liquor is pumped into lagoons whose bottoms are 10 feet below the surface of the ground but still above the water table. Two lagoons, each about one acre in size, are treated alternately. While one is being treated, the other is allowed to stand for several days. When the lagoon shows signs of clogging, the ground is disked during the resting period t o break up the deposit which has formed on the bottom. This is an example of a highly favorable soil condition not available in many locations. Chemicals are sometimes added to waste waters in absorption lagoons. While lime frequentIy helps in the flocculation of suspended matter, it is undesirable because it tends to clog the pores in the soil. A dike built across the entrance to the lagoon provides an opportunity for the excess lime and precipitate to settle out. I n Wisconsin, a pea packing plant, which produces 3,400,000 gallons of waste water per season, treated its water with 3.4 pounds of sodium hydroxide per 1000 gallons of waste. The pH of the waste remained below 7.2 until the close of the pack. Laboratory studies showed that 5 and 11 pounds of sodium hydroxide per 1000 gallons were needed to keep the pH at 7.2 and 9, respectively.
AGOONS
R&Joond. Regardless of the method of disposal, efficient screening of the residual waters from industrial plants through a 20-40 mesh screen is essential. This removes the bulky suspended matter and reduces the load on the lagoon, particularly if the suspended substances have a biochemical oxygen demand. If the suspended material is of fine particle size, it can be settled out in a tank installed ahead of the retention lagoon. A single basin is used by some plants, and when there is high water in the receiving stream, the water in the lagoon is vigorously stirred by the activity of a motor boat before the contents of the lagoon are discharged to the swollen stream. Such crude attempts to solve the problem are to be condemned in the interest of riparian rights.
p-2Last month we discussed how the shallow flats of the Potomac River serve as remarkably efficient processing lagoons for the disposal of sewage and natural organic matter. Nature built this chemical plant; now man must simulate this splendid example. Processing lagoons in the hands of the chemist can be economical and satisfactory methods for the processing of industrial wastes. Chemists have the materials and the ingenuity required to meet the challenge of nature. The choice of a disposal method, whether it be one of the several types of lagoons, chemical or biological treatment, or disposal at a municipal treatment (Continued on page 98)
4 2 A certain large industrial plant located on tidewater was pressed by state authorities to abate the pollution of tidal waters with its high B.O.D. residual water. The plant produced over 15 million gallons of this raw waste each day. A knoll, adjacent to the plant and to a small community, was selected for the construction of a large absorption lagoon. The procedure worked well for about a year, and i t appeared that the waste was absorb97
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
plant, necessitates consideration of the degree of treatment esscntial in the interest of others, of relative coski, and of availability and topography of potential sites for the disposal plant. Chemical and biological treatments require little land space, but lagoons occupy considerable area. Complete biological treatment is often the most expensive process, but it is most effective when well supervised. Chemical treatments are sufficient in many cases but rarely accomplish a complete stabilization of the waste substances before they are discharged to the river. Lagoon treatments can be the most satisfactory, for they permit both biological and chemical treatments together with sufficient retention time for the waste waters during the processing period. Specifications for the addition of any material t o a stream without creating a nuisance can be stated simply. First, the substance must not be toxic t o animal and vegetable life. Second, it must be chemically stable t o the environment within the stream. Toxic substances can be removed by chemical treatment or by the use qf absorbent solids. Stability can be obtained by oxidation of the substances t o more stable materials. Stability has been obtained already in some industrial waste disposal operations. For instance, sodium nitrate has been added t o processing lagoons in the disposal of cannery wastes. The function of sodium nitrate is threefold. First, it makes available the oxygen needed for aerobic bacterial decomposition during the early stages of decomposition of the waste substances. Second, the nitrate stimulates the growth of chlorophyll-containing organisms within the lagoon so that these microscopic bodies can produce additional oxygen by photosynthesis with sunlight. Third, the sodium nitrate maintains a mild alkalinity in the lagoon. In other words, sodium nitrate augmenb the supply of oxygen
Vol. 37, No. 12
obtainable through natural aeration. In the case of cannery waate this chemical has removed odors so that the nuisanee is not noticeable 200 feet from the lagoon. The amount of sodium nitrate used is equivalent, in terms of oxygen, to about 20-25 % of the 5-day B.O.D. value of the cannery waste. Recently the Sulphite Pulp Manufacturers Committee on Waste Disposal of Wisconsin released some general information on abating the nuisance of disposing of waste sulfite liquors in the streams of that state. Studies in trickling filters and river reaeration are mentioned. Both of these methods depend upon oxygen stabilization of the waste. The latter is particularly interesting for it is a commendable attempt to supply the deficiency in available oxygen in the stream by diffusing large amounts of air into the river water. I n this case the entire river is used as a treating lagoon. Possibly there are good reasons why this waste cannot be treated in such a manner prior t o its addition to the stream. The use of treating lagoons should allow more control in such cases. The use of liquid oxygen for suah oxidation might be found efficient after an initial aeration in a lagoon. Producers of liquid oxygen as well as other chemical companies, may see opportunities in this experiment. Sodium chlorite has been used to the extent of 28% of the B.O.D. value of screened pea waste in a northern cannery with outstanding results. Economically the process fails, but with lower costs for this new chemical the process will find increasing use. The treatment of certain wastes with chlorine in lagoons has also passed the experimental stage in some industrial problems. The use of chemicals in solving difficult waste disposal problems is entering a new era. Lagoons will be found useful as reaction basins for this type of treatment.
