Use of Alum to Hasten Sludge Drying at Stratford, Conn.Author(s): Walter ThompsonSource: Sewage Works Journal, Vol. 17, No. 2 (Mar., 1945), pp. 376-378Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25030022 .

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376 SEWAGE WORKS JOURNAL March, 1945

USE OF ALUM TO HASTEN SLUDGE DRYING AT STRATFORD, CONN.*

By Walter Thompson

Chief Operator, Sewage Treatment Plant, Stratford, Conn.

This brief report describes the successful use of alum in making pos sible the satisfactory operation of a small and greatly overloaded sew

age treatment plant. When the present plant was built at Stratford, Conn., in 1921, the

population was 12,000. Since January, 1944, the plant has served an

additional 14,000 employees of the Chance Vought plant of United Air craft and a new federal housing project, bringing the present estimated

population served to 32,000. The aircraft plant alone contributes ap

proximately 400,000 gallons per day of sewage. The treatment works comprises six Imhoff tanks and two sludge

drying beds. When it was realized that the sludge drying area was

overloaded, the problem was discussed with representatives of the Con

necticut State Department of Health and the use of alum suggested. Reference was made to the work of Sperry at Aurora, Illinois {This Journal 13, 855, September, 1941) for guidance in application of the alum.

A 10-inch pipe carries the sludge to the two sludge drying beds, each of which holds about 70,000 gallons. The alum must be added to the

sludge just as it is discharged into the drying beds and to accomplish this a large horizontal concrete T was built at the discharge end of the

pipe, so arranged that the sludge can be diverted into either of the beds

by plank gates. A 1-inch pipe was passed through the wooden gate and connected by

an elbow to a vertical pipe of convenient length for adding the alum so

lution. To the inner end of the pipe through the gate was secured a 15 inch length of flexible rubber hose. The object was to mix thoroughly the alum solution with the sludge as it passed through the box and the

movement of the flexible hose together with the turbulance in the box seems to accomplish this in a simple and thoroughly satisfactory man

ner. Previous to using the rubber hose, a rigid metal pipe was used

but the mixing was not satisfactory. The streaked appearance of the

sludge as deposited in the bed made it evident that the alum was not

being used efficiently. It is also important that the alum be entirely dissolved for good re

sults. In the earlier experiments, the alum in granulated form was

added in a dry state to the flowing sludge and this seemed to have very little beneficial effect, probably because the alum crystals settle to the bottom and were dissolved by the water draining out of the sludge.

The procedure at Stratford is to use 200 gallons of water to dissolve *

Presented at Fall Meeting, New England Sewage Works Association, Worcester, Mass., September 13, 1944.

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Vol. 17, No. 2 USE OF ALUM IN SLUDGE DRYING 377

400 pounds of alum. This amount of water is probably five times the volume actually required to effect complete solution but the excess is

desirable in that the solution is accomplished more quickly and is more

easily mixed with the sludge. It is believed that any more water would

only add to the amount which must be drained away and that the mix

ing operation would not be improved. It is well known that the time required for the dewatering of sludge

in open beds depends upon the season, the temperature, the amount of

rainfall, wind, humidity and other factors. The experience at Strat

ford proves definitely that there is a surprising advantage in the use of alum regardless of season or other conditions.

For the purpose of comparison between alum treated and untreated

sludge, the following data may be considered average for non-freezing weather. If a 12-inch depth of alum-treated sludge is drawn to the

drying bed, the depth will drop to about 7 inches in 24 hours, whereas the depth of untreated sludge will be 8% to 9 inches at the end of the same period. The first cracks in the drying residue will appear in 4

days in treated sludge, whereas 8 to 9 days are required for cracks to

appear in the untreated bed. In the treated bed the residue cracks more uniformly and with many more cracks and this, of course, speeds the drying and makes it possible to remove the dried residue sooner.

The treated sludge will dry out so that it can be removed in about 8

days while the untreated sludge under the same conditions requires about 20 days.

It is also noticeable that the dried residue from the treated sludge is of less thickness and lighter in weight. Also, because of the more

numerous cracks mentioned before, the residue is more easily broken

up and can be removed more easily from the bed.

Another interesting and important advantage to the use of alum is

the almost complete elimination of objectionable odor. As will be ap

preciated, this feature alone would make the use of alum desirable

where the sludge beds are located near a residential section.

To summarize briefly, the Stratford experience indicates the follow

ing points are of interest regarding the use of alum :

1. A good working concentration of alum solution is about two

pounds of alum to a gallon of water.

2. The alum must be completely dissolved.

3. The alum solution must be thoroughly mixed with the wet sludge just before it enters the drying bed.

4. The reduction in depth of sludge or, in other words, the reduction

of water content in 24 hours is nearly twice as great for treated

sludge as for untreated sludge. This is an important point in

freezing weather.

5. The treated sludge dries in less than one half the time required for untreated sludge. This means that the beds can be used more

efficiently and that a greater volume of sludge can be handled each month.

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378 SEWAGE WORKS JOURNAL March, 1945

6. The dried residue is thinner and lighter in weight and, therefore, more easily removed.

7. Because the residue cracks more uniformly and completely, it can

be easily broken up for removal.

8. Objectionable odor is almost entirely eliminated.

9. No elaborate equipment is required for the application of alum.

Any operator can improvise a setup for adding the solution at a

uniform rate and arrange for thorough mixing. 10. The cost of alum, about $8.00 per 70,000 gallons of sludge, is of

little consequence when compared with the results in an over

loaded plant.

TIPS AND QUIPS

Tidbits from Toronto, where the Canadian Institute on Sewage and Sanitation held its largest meeting in history on November 2-3, 1944 ... an attendance of 336, which was 66 per cent above the highest re

corded at any previous meeting ... an entertainment innovation in

the form of a "Club Room," sponsored by the Canadian Sanitation

Equipment Association, which contributed much to the social aspects of the annual banquet and luncheon . . . the "discussingest" gather

ing of individuals we have had the pleasure to meet, carrying overtime

two hours on the open forum which concluded the program . . . and

no wonder, since the Guided Discussions which are given so much em

phasis in the programs of this organization are carefully outlined and

distributed to all members before the meeting, permitting them to give advance thought, to their remarks ... a well founded and well pre sented paper on the industrial waste problem by G-. E. Symons of

Water Works and Sewerage . . . other commendable program con

tributions on postwar planning by J. F. MacLaren and Alderman Don

ald M. Fleming, both of Toronto ... an obvious surplus of film and

flashlight bulbs in Canada, the photographers laying down a continu ous barrage during every session ... a preview of the beautiful Hotel

Royal York, headquarters for the 1945 Annual Meeting * of the Federa

tion . . . and a Canadian hospitality that is determined to make the

next Federation conference an unforgettable occasion !

Walter Sperry, whose first "Daily Log" column appeared in the

November, 1944, Journal, is already receiving "fan mail." One of

these letters came from his old friend, C. T. Mudgett of Muskegon, Mich., who questioned the statement made that the Holbrook Avenue

pumping station at Aurora had been out of service for 108 days be

cause of the river elevation being above the elevation of the overflow

* Subject to issuance of permit by O.D.T.

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