anaerobic digestion of packing plant wastes

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  • Anaerobic Digestion of Packing Plant WastesAuthor(s): W. J. FullenSource: Sewage and Industrial Wastes, Vol. 25, No. 5 (May, 1953), pp. 576-585Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25032176 .Accessed: 17/06/2014 05:46

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  • Industrial Wastes

    ANAEROBIC DIGESTION OF PACKING PLANT WASTES

    By W. J. F?llen

    Chemist, Service Division, George A. Hormel and Co., Austin, Minn.

    Anaerobic treatment of packing house wastes has been under investiga tion by Geo. A. Hormel & Co. for the

    past Sy2 years. The initial laboratory work was done in 55-gal oil drums. After working a year with this labora

    tory unit, the results looked promising enough to warrant larger-scale investi

    gation.

    The work on the pilot-plant unit was

    started in July, 1950. Basically, the

    process consists of mixing in a digester the incoming raw waste with an ac

    tivated anaerobic sludge at a tempera ture of 92? to 94? F., and then effecting a separation of sludge from the mixture

    and returning it to the digester. Many

    changes were made in the different

    units during this investigation.

    Pilot-Plant Units

    The following is a description of the

    different units of the pilot plant as it

    is operating successfully at the present time :

    1. The holding tank, of 412-cu. ft.

    capacity, is 8 ft. square with 6-ft. side

    wall depth and hopper bottom of 45?

    slope. The tank is insulated and

    equipped with a constant-level supply

    box, from which the raw waste is fed to the digester.

    2. The digester is contiguous with the

    supply or holding tank. It is 16 ft. by 8 ft. in plan, with sidewall depth of 6 ft.

    and a double hopper bottom. The con

    tents are heated by passing the digester reeirculation flow through a heat ex

    changer utilizing live steam to heat a

    water bath around the 3-in. digester recirculation line. The temperature of the digester contents is controlled by a

    temperature recorder and controller in strument. The digester is completely insulated and gas is discharged to the

    atmosphere, A circulating pump draws the liquid from the two bottom

    hoppers and discharges on splash plates in the tank.

    3. A degassing chamber, operated under a 25- to 26-in. vacuum, is

    equipped with a series of plates over

    which the effiuent from the digester cascades. The vacuum chamber is situated on the top of a barometric leg (36-ft. height). The vacuum is pro

    duced by means of a Duriron water

    ejector, with raw sewage being pumped as the water supply for the ejector. The effluent from the digester flows

    continuously into the vacuum chamber, where it is held for 5 to 10 min. and then discharged to the clarifier. The difference in height of the water in the feed and discharge legs of the vacuum

    system causes the flow, and this in turn

    is caused by the discharge from the

    digester. The detention time in the vacuum chamber is regulated by rais

    ing or lowering the clarifier feed box, located on the discharge leg of the

    barometric leg. 4. The rectangular clarifier (8 ft. by

    4 ft. by 3 ft. high) has an effective

    capacity of 93.4 cu. ft. The influent enters through a perforated pipe lo

    cated about 1 ft. below the surface. A

    slotted baffle in front of the perforated

    576

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  • Vol. 25, No. 5 PACKING PLANT WASTES DIGESTION 577

    feed pipe seems to give good distribu tion.

    Sludge is removed hydraulically at a continuous rate through two slotted

    pipes that scavenge the bottom by mov

    ing at a rate of % ft. per minute. A

    reversing mechanism causes the back and forth movement of the scavenger

    pipes. Removed sludge is discharged back to the digester. The present rate of feed to the clarifier gives about 1-hr. detention in this unit.

    The discharge from the clarifier is taken off through a notched effluent

    weir. A manually-operated scum

    trough is provided for use when neces

    sary.

    Prior to installation of the vacuum

    system (Figure 1) and clarifier, sepa ration of the sludge from the effluent

    was effected by allowing it to discharge into a separation tank of one-half the size of the digester. The sludge would both rise and settle and a fairly clear effluent could be drawn off from be tween the two layers. This was fur ther clarified by flocculation and sedi

    mentation. Sludge was removed from

    both the top and the bottom of this

    unit.

    Operational Changes

    Inasmuch as changes in operation were made over the test periods re

    ported, appropriate designation for each test is given, as follows :

    Period No. 1?October 17, 1950, to

    March, 1951. The flow diagram during this period was as shown in Figure 2,

    except that the filter, Imhoff tank, and flocculator were not included.

    Period No. 2?August, 1951, to De

    cember, 1951. Tests during this period were run under the conditions shown in

    Figure 2. Period No. 3?January 1, 1952, to

    March 31, 1952. The plant during this

    period was run under the conditions shown in Figure 2, except that the

    separator underflow and top sludge were returned to the digester influent instead of to the holding tank. Sam

    pling points 1, 2, and 3 were on the raw waste line, Imhoff tank effluent, and filter effluent, respectively.

    Period No. 4?May 1-20, 1952. This

    EFFLUENT

    SLUDGE RETURN TO DIGESTER

    FIGURE 1.?Flow diagram of vacuum system on packinghouse waste treatment at Hormel pilot plant, Austin, Minn.

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  • 578 SEWAGE AND INDUSTRIAL WASTES May, 1953

    IMHOFF TANK

    _^^?0^torJ7b>jp_SJud^e _/7V_ f"

    **?TOP SLUDGE HOLDING TANK

    TRICKLING FILTER

    {y?-EFFLUENT

    Flow Dtwrston

    RAW

    (Pr? treat?*)

    FIGURE 2.?Flow diagram of anaerobic packinghouse waste treatment system prior to Jan. 1, 1952.

    run was made under the conditions of Period No. 3 after changing circulation

    discharge. Period No. 5?August 14, 1952, to

    September 23, 1952. The plant was run under the conditions shown in Fig ure 3.

    Analytical results for the several pe riods are given in Tables I, II, III, IV, and V, respectively. Loadings and effi ciencies of the various units for the several test periods are given in Table

    VI.

    Metering and Sampling

    The waste being treated is a com

    posite of what might be termed typical

    packinghouse wastes. Although the Hormel Co. purposely segregates con

    denser waters from the industrial wastes in order to reduce the problem volumetrically, tests have been run on

    wastes varying in strength from 900 to 2,000 p.p.m. B.O.D. There is every evidence that anaerobic digestion will

    work very well on weaker wastes and

    produce effluents of 20 to 35 p.p.m.

    B.O.D., but the economics are in ques tion and it is suspected that less work is done per unit of digester volume.

    Another important aspect of the proc ess is that the heat and mineral require

    ments are largely inherent in raw

    packinghouse waste.

    HOLDING TANK

    ^?Meter

    Sampling Point Not

    DIGESTER ?5TER VACUUM TANK CLARIFIER

    ?r-fi? ?*-Gas \ ! Water I

    _; *?Me*er ^ j Ejector t

    T

    j Meter

    l

    Recircu lotion Sampling

    Point No Z

    _ql _ J-J'iTifltC JiP-fJ1-?_? ^-Meter ~^~

    0

    SLUDGE HOLDING

    -^EFFLUENT

    Samplina Point No 3

    RAW WASTE (Pre treated)

    FIGURE 3.?Flow diagram of packinghouse waste treatment system from August 14, 1952, to September 23, 1952.

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  • Vol. 25, No. 5 PACKING PLANT WASTES DIGESTION 579

    TABLE L?Analytical Results, Period 1

    Item Sep. Em.

    Raw feed (cu. ft./day) SI. return (cu. ft./day) Gas (cu. ft./day) Total solids:

    P.p.m.

    Lb./day Total vol. sol.:

    P.p.m. Lb. /day

    Susp. solids:

    P.p.m.

    Lb./day B.O.D., 5-day:

    P.p.m.

    Lb./day

    5,160 183

    460 16.3

    226 8.0

    11

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