experiments on anaerobic digestion of wool scouring wastes

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  • Experiments on Anaerobic Digestion of Wool Scouring WastesAuthor(s): M. T. SingletonSource: Sewage Works Journal, Vol. 21, No. 2 (Mar., 1949), pp. 286-293Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25031055 .Accessed: 14/06/2014 23:31

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    By M. T. Singleton

    Wiedeman and Singleton, Consulting Engineers, Atlanta, Ga.

    In the summer of 1947 the city of

    Lebanon, Tenn. made certain investi

    gations for the purpose of determining the feasibility of treating the indus

    trial wastes from the Lebanon Woolen

    Mills at the existing city sewage treat

    ment plant and to determine what ad

    ditions or alterations at the plant might be necessary for this purpose.

    The city sewage treatment plant is

    of the separate sludge digestion, trick

    ling filter type with provisions for

    applying chemical coagulants and

    flocculation ahead of the primary clari

    fier. The plant was designed for a

    capacity of 800,000 g.p.d. and is now

    treating a dry weather flow of between

    500,000 and 600,000 g.p.d.

    Volume and Character of Wastes

    The Lebanon Woolen Mills manufac

    ture woolen blankets. The wastes from

    this plant at the time of the investiga tions made under the direction of the

    author consisted of the usual dyeing,

    washing and finishing wastes, together with the waste from the wool scouring process. The total volume of waste

    from the mill is about 300,000 g.p.d. This included about 2,500 g.p.d. of

    wool scour waste at the time of the in

    vestigation. The volume of wool scour

    waste varies from 2,500 to 10,000 g.p.d.

    depending upon the amount of grease wool being scoured.

    Color did not seem to be a problem as it was well dissipated when equal

    * Presented at Second Annual Meeting, Ken

    tucky-Tennessee Industrial Wastes and Sew

    age Works Association; Chattanooga, Tenn.;

    August 23-25, 1948.

    ized and mixed with the cloth washing waste. The studies indicated that with certain modifications and additions to the plant, the equalized combined

    wastes other than the wool scour wastes could probably be successfully treated in combination with the city sewage. It is anticipated that plant scale ex

    periments with this in view will be con ducted at an early date.

    Wool scour waste has always been considered a difficult waste to treat by ordinary processes, due primarily to its high grease content. It will be pos sible to determine its effect on the

    trickling filter in this particular case after the mill waste is connected, but it was anticipated from the start that' some pretreatment of the wool scour

    waste for degreasing would be neces

    sary before discharge into the city sewer.

    When scouring the maximum volume of grease wool the volume of waste from the scouring process at this mill is about 10,000 g.p.d. The wool is scoured in the usual train of scouring bowls in a scouring solution of alkali and soap. The waste is a brown thick turbid liquor, in the nature of an emul sion in which the grease and organic

    matter removed from the wool is highly dispersed and remains in suspension. It contains some settleable mineral sol

    ids, but the greater portion of such solids is removed by a dusting opera tion before scouring.

    The strength of the waste varies de

    pending upon the pounds of wool scoured in the bowls before the scour

    ing solution is dumped. The range of


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    data from a number of analyses at this mill is as follows :

    Total Grease (p.p.m.). 8,000 to 14,000

    pH. 8 to 9.6

    5-day B.O.D. (p.p.m.). 5,000 to 14,000 Total Solids (p.p.m.). 25,000 to 65,900 Volatile Solids (p.p.m.). 18,000 to 41,000

    Treatment Methods Considered

    Most of the published literature on

    the subject states that biological proces ses of treatment are not applicable to the treatment of wool scour waste, due

    primarily to the high grease content. It is generally stated that the grease

    must be removed from this waste be fore any type of treatment is applied.

    Faber (1) has recently described a new process, known as the Hypochlo rite Process, involving the use of calci um hypochlorite as a coagulant fol lowed by acid treatment of the resultant sludge and scum for grease recovery.

    It might also be of interest to men

    tion here that Smith-Drum and Com

    pany of Philadelphia have been de

    veloping, over a period of years, a

    process and a machine for the degreas

    ing of wool by means of a synthetic solvent. This process is not being de

    veloped as a process of waste treatment

    but rather as a process of scouring wool, but it would seem that the waste

    treatment problem from such a process would be simplified. The wool would be degreased prior to washing in plain water in the standard scouring bowls to remove the remaining water-solubles

    and solids. The process involves de

    greasing the wool by the use of a syn thetic solvent, the solvent being re

    claimed for re-use by distillation and

    the solids, including the grease, which are removed by the solvent are recov

    ered in a dry form. One large ma

    chine is now being installed for trial

    on a production basis and a second

    machine is under construction.

    Where treatment has been required in the past the usual method recom

    mended for treating this waste has been to remove the grease by "acid

    cracking." By this method relatively large volumes of sulfuric acid are used to acidify the waste, after which the

    grease is removed as sludge or scum

    and may be processed for grease re


    Experiments carried out under the direction of the author with "acid

    cracking ' '

    of this particular waste gave inconsistent results, and at best it seemed it would be an odorous, messy process requiring careful control to obtain a satisfactory percentage of

    grease removal. The volume of the waste involved was small and variable, and neither the owners nor the city officials desired to undertake the re

    covery and sale of grease as a part of the process of treatment due to the op

    erating problems involved.

    Despite the fact that investigators have definitely stated that wool scour

    wastes could not be treated by biologi cal methods, the success reported in re

    cent years in the rapid digestion of other types of strong trade wastes by "Controlled Digestion" procedures, de

    veloped by Buswell and Boruff (2) and

    reported upon by Buswell and Schlenz

    (3), gave rise to the decision to experi ment with the destruction of wool scour

    greases by such controlled digestion methods.

    It appeared logical that if the diges tion of the waste could be controlled

    by following the procedures estab

    lished for the successful handling of

    other wastes as outlined hereinafter, the high content of grease in the wool scour waste could be greatly reduced.

    That grease and soaps could be com

    pletely digested to form methane and

    carbon dioxide was shown in 1927 by Neave and Buswell (4). They demon

    strated that gas yield was practically

    proportional to grease content of

    sludges studied. These results have

    later been confirmed by Rudolfs (5) and other investigators.

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  • 288 SEWAGE WORKS JOURNAL March, 1949

    Laboratory Digestion Studies

    The digestibility of this particular waste was first established by setting up a 5-gal. bottle sample at room tem

    perature. The sample was seeded with

    digested sludge. Gas formed almost

    immediately and at the end of a 30

    day period the volatile solid content was reduced about 60 per cent. The

    bottles were allowed to stand 7 weeks. At this time analyses indicated a vola tile solid reduction of about 75 per cent and the 5-day B.O.D. dropped from 8,600 p.p.m. to 1,010 p.p.m. There was no separation of the grease from

    the liquid to form a serious scum prob lem and the settled sludge by observa tion was but little more than the seed

    sludge added. The o


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