disposal of cheese whey by digestion

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  • Disposal of Cheese Whey by DigestionAuthor(s): David BackmeyerSource: Sewage Works Journal, Vol. 20, No. 6 (Nov., 1948), pp. 1115-1118Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25030997 .Accessed: 15/06/2014 03:44

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  • Vol. 20, No. 6 DISPOSAL OF CHEESE WHEY BY DIGESTION 1115

    This is not an entirely new prece dent since this division has made some

    tests in the past on special occasions,

    particularly for the Fire Prevention

    Bureau, but has never had the person nel to do such work regularly nor in the amount requested.

    It is recommended that a special assistant to the chemist be employed to do the. testing under the direct su

    pervision of the chemist and the

    undersigned. This assistant would also receive training in sewage labora

    tory work to the end that he would be available to take over the duties of the chemist whenever that may become nec

    essary. The cost of operating this bu reau would be negligible outside of the assistant's salary and the initial mod est expenditure for equipment.

    A summary of plant operation data is given in Table IV.

    TABLE IV.?Summary of Operation of the

    Item Average

    Rainfall (in.). 36.50

    Design flow (m.g.d.): Mean D.W.F. 80.0

    Max. D.W.F. 140.0

    Raw sewage flow (m.g.d.). 46.3

    Screenings (cu. yd. per month).... 204

    Grit removed (cu. yd. per month).. 73

    Suspended solids (p.p.m.) :

    Raw sewage. 199

    Plant eflluent.. 96

    Per cent removal. 51.4

    B.O.D. (p.p.m.): Raw sewage. 205

    Plant eflluent. 96

    Per cent removal. 34.4

    Per cent volatile solids:

    Raw sewage. 65.4

    Digested sludge. 44.4

    Digested sludge (cu. yd.) :

    To marsh. 30,525

    (Ohio) Sewage Treatment Plant for 1947

    Item Average

    To drying beds. 11,440 Tons dry sludge pulverized for

    fertilizer. 915 Tons fertilizer sold. 950

    Total sales ($). 9,525 Bay View pumping station costs

    ($ per m.g.) :

    Purchased power. 0.30

    Supplies. 0.33

    Supervision and labor. 3.38

    Total. 4.01

    Sewage works costs ($ per m.g.): Power. 0.008

    Supplies. 1.15

    Supervision and labor. 5.86

    Total. 7.02

    Gas engine economy ($) :

    Pumping cost if power purchased 23,638.49 Actual pumping cost. 6,058.91 Gas engine saving. 17,579.58

    DISPOSAL OF CHEESE WHEY BY DIGESTION By David Backmeyer

    Superintendent, Water and Sewage Treatment Utilities, Marion, Ind.

    The sewage treatment and garbage

    disposal plant at Marion, Indiana, was

    completed and placed in operation in

    July, 1940. This plant, which utilizes

    activated sludge for secondary treat

    ment, is equipped with complete fa

    cilities for separate sludge digestion of

    both sewage and garbage solids, to

    gether with gas engines for utilization

    of the digestion gas. The resident

    population of Marion in 1940 was

    26,676. The total gas production in

    1947 was 23.167 million cu. ft., which

    is the equivalent of 2.37 cu. ft. per capita per day.

    Whey Waste Problem

    During the past 3 years the sewage plant has been seriously overloaded

    during the spring months of each year from cheese whey discharged to the

    sanitary sewer by one of the local milk

    processing plants. As the treatment

    plant had been disposing of digested sludge in liquid form by hauling in tank trucks (Figure 1), the facilities of

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  • 1116 SEWAGE WORKS JOURNAL November, 1948

    ^v*' '

    >v

    FIGURE 1.?Liquid fertilizer tank trucks used for hauling whey to sewage plant.

    the sludge disposal plant were offered to the industry in an effort to com

    pletely eliminate the discharge of the

    whey to the sewer.

    In March, 1947, arrangements were

    made with the industry to haul the

    whey from their storage tank directly to the sewage treatment plant in city tank trucks. The whey is unloaded at the plant directly into the garbage

    well from which it is pumped to the

    sludge digestion units. In this way the soluble B.O.D. load does not mix

    with the raw sewage flow and cannot, therefore, reach the activated sludge secondary treatment units.

    Whey Mixed With Garbage

    In the processing of the garbage at the treatment plant, the green gar bage is unloaded from the collection trucks onto an open platform at grade level, and is then shoveled into the

    hammermill grinder hopper. Sluicing water is added in the grinding process to bring the final slop to a solids eon tent of from 5.0 to 7.5 per cent, on dry solids basis.

    After some experimentation it was

    found that the liquid cheese whey made

    an ideal substitute for the sluicing water. The temperature of the whey

    was always from 100? to 140? F. when

    unloaded from the tank trucks. This warm liquid would serve as a temper

    ing agent when added to the garbage being ground, particularly in the cold

    months of November and December. Instead of pumping garbage slop to the digesters at 55? F., it was possible to maintain the temperature of this

    mixture of ground garbage and whey at 90? to 95? F. by unloading the whey tank truck as the garbage was fed to the grinder.

    Whey Increases Gas Production

    Cheese whey contains from 4.5 to 7.0 per cent total dry solids, and only about 8 or 9 per cent of the solids is

    inorganic ash. The other constituents,

    sugar, protein and fat, are readily di

    gestible and are easily converted into

    gas in the sludge digesters. By sub

    stituting whey for water in the gar

    bage grinding process it was further

    possible to recover valuable gas from the whey without overloading the plant digesters from the standpoint of liquid

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  • Vol. 20, No. 6 DISPOSAL OF CHEESE WHEY BY DIGESTION

    TABLE I.?Effect of Whey on Plant Operation

    1117

    Plant Operation Data Before and During Whey Discharge to Sewers

    Batch Discharge of Whey

    to Sewers, June 23 to

    July 7, 1946

    Continuous Discharge of Whey to Sewers

    Feb. 18 to Mar. 12, 1947

    May 18 to 30, 1948

    Average for

    1946

    Average for 76 Months

    Prior to Jan. 1, 1947

    B.O.D. (p.p.m.): Raw

    Settled Final

    % Reduction

    232 162

    7 96.8

    212 182 31 85.4

    219 149 29 86.7

    174 152

    13 92.8

    188 134

    13 93.4

    Sludge Index (Mohlman) 138 118 107 91 81

    D. 0. Aerator Effluent

    (p.p.m.) 1.8 0.9 0.8 3.1

    Activated Sludge Volatile Solids (%) 65 75.7 68.4 61.5 58.9

    Air Supplied, Cu. Ft./Gal.

    Sewage 1.04 1.06 1.32 0.90 0.89

    volume fed daily into the digestion system.

    A sharp rise in the gas production rate was evident within 30 minutes after the garbage-whey mixture was

    pumped to the digesters. On several

    days when peak loads of whey were

    handled it was necessary to pump the

    pure whey to the digesters without the addition of ground garbage. Gas pro duction volumes on these days soared to as much as 108,000 cu. ft. per 24 hour period.

    Although the addition of whey to the already heavily loaded digestion system made it extremely difficult to

    withdraw clear supernatant from the

    digesters, at no time was there any evi dence of foaming or excessive volatile acid accumulation in the digestion sys tem. The carbon dioxide content of the gas produced would increase from 33.0 per cent when small volumes of

    whey were being handled to about 36

    per cent when large volumes were taken and gas production was at its

    peak. No difficulty was encountered in using this fuel in the plant gas en

    gines.

    Effect of Whey on Plant Operation

    Two tables of plant operation data are presented. Table I shows the

    effect of the whey on the activated

    sludge units when it is dumped to the

    city sanitary sewers. When whey reaches the aerators a series of rapid changes takes place. The color of the

    activated sludge will change in a 12

    hour period from chocolate brown to

    slate gray. The volatile content of the

    sludge rises rapidly within a period of 6 to 10 days. It is almost physically

    impossible to supply eno

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