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COMPARISON OF METHODS OF SEWAGE PURIFICATION

BY THEODORE CLIFFORD PHILLIPS AND EDWARD JOHN SCHNEIDER

THESIS FOR DEGREE OF BACHELOR OF SCIENCE IN MUNICIPAL AND SANITARY ENGINEERING

COLLEGE OF ENGINEERING UNIVERSITY OF ILLINOIS

PRESENTED JUNE 1900

UNIVERSITY OF ILLINOIS

_May 31, 1900._

THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY _Theodore Clifford Phillips and Edward John Schneider_ ENTITLED _Comparison of Methods of Sewage Purification_ IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF _Bachelor of Science in Municipal and Sanitary Engineering_.

_Arthur M. Talbot_

HEAD OF DEPARTMENT OF _Municipal and Sanitary Engineering_.

_Contents_

Comparison of Methods of Sewage Purification Dilution Irrigation Intermittent Downward Filtration Chemical Precipitation Septic Tank Contact Bed Discussion Conclusion

_Comparison of Methods of Sewage Purification._

The disposal of sewage is one of the most important problems that confront the municipal and sanitary engineer to-day.

The study of this subject dates back to 1844 when the Healths of Towns Commission of London made the report which first showed the real course of the rapid increase in the death rate of the larger cities. In this country practically nothing was done until 1872 when the Massachusetts Legislature instructed the State Board of Health to investigate and report on the subjects of sewerage, sewage disposal, and the pollution of streams, and to-day Massachusetts leads in the investigation of the best methods of sewage disposal.

Six different methods for the treatment of sewage are now in use. These methods are used separately or in combination, the choice depending upon local conditions and the amount of purification required:—

These methods are:

1— Dilution.

2— Irrigation.

3— Intermittent Downward Filtration.

4— Chemical Precipitation.

5— Septic Tank.

6— Contact Bed.

The purpose of this thesis is to investigate each method and make a comparison along the following lines:

1— Purification.

2— Capacity.

3— Applicability.

4— Cost.

_Dilution_

Disposal of sewage by dilution is the most common method at the present time, and no doubt will continue to be for some time to come where the stream or body of water is not used for domestic purposes. Under certain conditions this affords a satisfactory solution of the problem. However, if the water into which the sewage is discharged is a source of water supply, two very important questions arise. They are: 1—How large must the dilution be? 2—How far must the polluted stream flow before the water way may be used with safety to public health?

In 1867 Dr. Letheby and others in England made the statement that if sewage is diluted at least twenty times its volume, it will not only be made inoffensive but be thoroughly destroyed after flowing a dozen miles or more.

The Rivers Pollution Commission of Great Britain in 1878 maintained that no river in England was long enough to allow of a complete disappearance of sewage matter discharged into it.

Mr. F. P. Stearns in an article on The Pollution and Self-Purification of Streams in the Massachusetts State Board of Health Report 1890 gives a table showing, “The calculated composition of sewage for different degrees of dilution in a running stream”. A comparison was made of the Blackstone and Merrimack rivers, and extended over three years. It was from this investigation that the Commissioner of the City of Chicago reported that the flow of the Chicago Drainage Canal should be four cubic feet per second per 1000 inhabitants.

The purification by dilution may be due to three things:

1— Oxidation of organic matter.

2— Subsidence.

3— Destruction of the organic matter by small animals and plants.

The oxidation is a very slow process and depends mainly upon bacterial life and conditions favorable to it. Subsidence depends upon the difference in the specific gravity of the suspended matter, and the clarification is increased as the velocity is diminished.

In regard to the destruction of the organic matter by small animals and plants Dr. Sorby says, (_Journal Royal Microscopic Society, 1884 p. 988_.) “It appears to me that the removal of impurities from rivers is more of a biolytic than a chemical question, and it is most important to consider the action of minute animals and plants, which may be looked upon as being indirectly most powerful agents.”

_Irrigation_

Although the method of broad irrigation has been carried on successfully in several of the largest cities of the old world, it has not been used to any great extent in the United States, except at a few state institutions in the east, and in the arid districts of the west.

Several years ago this method of disposal was given much attention as it was thought the sewage if used would yield large profits, but more recent information shows conclusively that such is not the case.

Perhaps the most noticeable examples of this system that are now in operation in the United States are the plants at the State Hospital of the Insane, Worcester, Mass., at the Rhode Island State Institute, and at the Reformatory at Concord, Mass. In all cases the labor was done by the inmates so that it is not possible to get a fair statement of the cost. General information regarding the use of sewage for irrigation in the west may be obtained from Baker and Rafters’ “Sewage Disposal in the United States”.

Undoubtedly the best example of sewage farming is at Berlin. The following summary is given by James H. Fuentes, M. Am. Soc. C. E., in No. 2. Vol. 40 of the Engineering Record. The average quantity of sewage pumped to the farms and distributed amounts to from 6,000,000 to 7,000,000 gallons per acre per year, or in other words each acre serves for 750 people. The area farmed is divided into small beds about 150 by 200 feet separated from each other by slight embankments and ditches for distributing the sewage over the surface. The sewage is admitted into the carriers from the force mains through checking chambers made of woven willow and posts driven into the sand.

The farms are said to yield small profits over the expenses of working them, consequently contribute scarcely anything toward the cost of pumping the sewage.

The great reason why this method of disposal has been possible and profitable in a degree at Berlin is that this large and beautiful city lies in the midst of an extensive sandy area, the greater part of which in the immediate neighborhood is quite sterile and therefore comparatively thinly populated. Better conditions for such sewage farms could not exist.

Statistics compiled by Chas. S. Swan, M. Am. Soc. C. E. in his paper, Notes on European Practice in Sewage Disposal, in Jour. Assn. of Eng. Soc. Vol. 7 No. 7 shows the volume of sewage per acre per day (yearly average) to vary from 2155 to 29450 gallons, and the average depth per annum varies from 2.4 to 32.8 feet.

The nineteenth annual report of the Massachusetts State Board of Health 1888 states that on an ordinary farm in Massachusetts 2500 gallons per acre per day are as much as could be applied to any valuable grass crop. This would require such a large area for large cities that irrigation could not be depended upon for preventing the pollution of streams.

It is evident from the above report that the irrigation system can be used to advantage only where large tracts of low land can be obtained at a low cost, and where help and plenty of cheap labor can be obtained.

_Intermittent Downward Filtration_

Filtration means the concentration of sewage on an area of especially chosen porous ground, or on an especially prepared bed as small as will absorb and purify it. The intermittency of application is a necessary requirement even in suitably constituted soils wherever complete success is arrived at. The reason for this is that free oxygen is indispensable to nitrification and the nitrifying organism.

This method has been in operation only during the last thirty years, and the correct theory of its action has been found out within the last ten years.

Dr. Frankland, in the first report of Rivers Pollution Commission of England, shows that not only a chemical action but also a biolytic action takes place with the assistance of minerals and the oxygen of the air. This biolytic action is known as nitrification, and consists in the oxidation of the nitrogen of ammonia and its ultimate conversion into nitric acid. This change takes place in two stages, each characterized by a distinct organism. The office of one of these organisms is to convert ammonia into nitrite, while the other converts nitrites into nitrate.

The bacteria are present or quickly develop in the sewage which may be considered a nutrient medium for them by reason of containing a large amount of their natural nitrogenous food.

These organisms, according to Warrington, may be separated by successive cultivations in favorable media; from a potassium nitrate solution with no ammonia we may obtain nitric organism alone; from an ammonium carbonate solution we may obtain nitrous organisms in a pure state.

It is a noticeable fact that frost checks nitrification, but several satisfactory methods have been used so that no serious objection can be raised to intermittent filtration on this ground.

“The purification of sewage by this method depends upon the oxygen and the time of action” (Hazen). To obtain the highest efficiency the sewage must be applied intermittently and there must be a large percentage of voids in the sand.

Experiments made on especially prepared beds at Lawrence, Mass. show that by treating 85000 gallons per acre per day, 94 percent of the organic matter and 98 percent of the bacteria are removed, and by treating 60,000 gallons per acre per day, 97 to 99 percent of the organic matter may be removed. The above data shows that 100,000 may be successfully treated with a five foot bed of sand.

The writers inspected the intermittent downward filtration plant at Mendota Illinois and the following data were obtained. The city has a population of about 6000 with 8 miles of sewers and 210 house connections. The average daily flow is about 350,000 gallons although during the rainy season there is a considerable amount of ground water present.

The disposal plant was constructed under the supervision of the Iowa Engineering Company of Clinton, Iowa, on a 15 acre tract of land, one and a half miles south of the city. Although original plans called for 18 beds with five feet of gravel, only four beds each 275 feet by 75 feet were finished, and instead of 5 feet of ground only 24 inches was used. The plant was complete in July 1899 and was operated until December, when it was discontinued on account of cold weather, it not being considered necessary to operate it during the winter. From December until April the sewage was discharged directly into a creek which runs along one side of the land.

The beds have no automatic device for distributing the sewage at definite intervals of time, but are connected with the main sewer by a number of gate valves which were regulated by the attendant. The sewage is distributed by means of a wooden sluice way which extended the entire length of the bed and has six inch openings on the side every 16 feet which gave a fairly even distribution.

Although no analysis of the sand and gravel was made, it was apparent that the uniformity coefficient was very large.

The material was shipped a distance of 90 miles and resembles ordinary ballast used for rail roads. The largest pieces were thrown along the sluice way to prevent excessive washing. The finest of the sand was of a size which would be considered too fine for good mortar sand. No attempt was made to screen the material. The gravel would not be considered first class for filtering beds.

Samples of the sewage and effluent were taken at two different times. The first was between 9:00 and 10:30 A. M., April 20, 1900. Until the day before no sewage had been applied to the beds since last fall. The second collection was made two weeks later, when samples of the sewage and effluent were collected at intervals of one hour during the day, and mixed into composite samples. The sewage was taken from a manhole just above the beds, and the effluent from the outlet of the underdrain about 900 feet below the beds.

The analysis is given in Table I. and the results show that the beds are not working as efficiently as might be expected from a first class plant. This may be accounted for from the fact that the filtration is too rapid and that the material which is less than two feet in depth is not suitable for such a purpose.

TABLE I.

Analyses of Sewage and of Effluent from Intermittent Downward Filtration Plant at Mendota, Ills.

Parts per 1,000,000 +----------------------------------------------------------------------------+ ¦ ¦ April 20, 1900 ¦ May 4, 1900 ¦ +----------------------+--------------------------+--------------------------¦ ¦ ¦Sewage¦Effluent¦Efficiency¦Sewage¦Effluent¦Efficiency¦ +----------------------+------+--------+----------+------+--------+----------¦ ¦Oxygen consumed: ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ Total ¦ 48.5 ¦ 6.50 ¦ 86% ¦ 27.7 ¦ 12.0 ¦ 55% ¦ ¦ In suspension¦ 33.4 ¦ ¦ ¦ 15.5 ¦ 4.6 ¦ 70% ¦ ¦ In solution ¦ 15.1 ¦ ¦ ¦ 12.2 ¦ 7.4 ¦ 40% ¦ ¦Nitrogen as albuminoid¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ammonia ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ Total ¦ 10.4 ¦ .32 ¦ 97% ¦ 3.68 ¦ .768 ¦ 79% ¦ ¦ In suspension¦ 9.28 ¦ ¦ ¦2.816 ¦ .416 ¦ 85% ¦ ¦ In solution ¦ 1.12 ¦ ¦ ¦ .864 ¦ .352 ¦ 59% ¦ ¦Total organic nitrogen¦17.960¦ .920 ¦ 95% ¦ 9.60 ¦ 1.860 ¦ 81% ¦ ¦ In suspension¦15.04 ¦ ¦ ¦7.500 ¦ 1.152 ¦ 85% ¦ ¦ In solution ¦ 2.92 ¦ ¦ ¦2.100 ¦ .708 ¦ 66% ¦ ¦Nitrogen as free ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ammonia ¦ 7.20 ¦ 2.40 ¦ 67% ¦ 3.84 ¦ 1.28 ¦ 67% ¦ ¦Nitrogen as nitrites ¦ .675 ¦ .375 ¦ ¦ 000 ¦ 000 ¦ ¦ ¦Nitrogen as nitrates ¦ 4.00 ¦ 18.00 ¦ ¦ .120 ¦ .120 ¦ ¦ ¦Chlorine as chlorides ¦ 53.0 ¦ 49.0 ¦ ¦ 47.0 ¦ 44.0 ¦ ¦ +----------------------------------------------------------------------------+

_Chemical Precipitation_

When certain chemicals are added to sewage a precipitate is formed which under favorable conditions may carry down with it all the suspended matter as well as a portion of the dissolved organic matter. The addition of the chemicals together with the working of the various appliances for grinding and mixing the same, the decanting of the effluent, and the caring for the sludge all constitute what is known as the chemical treatment of sewage, the complete process being in reality partly chemical and partly mechanical.

The following matter concerning the theory of precipitation is taken from Baker and Rafter’s Sewage Disposal.

The reagents chiefly used at the present time are lime, sulphate of alumina, and ferrous sulphate. In the case of lime, there is a combination of some of the lime and with free and partially combined carbon dioxide to form an insoluble carbonate of lime. There is probably a further combination of an additional part of the lime with a portion of the organic matter in solution. The insoluble substances so formed sink to the bottom, carrying with them the major portion of the suspended matter in the sewage in the form of sludge.

Sulphate of alumina exercises a precipitating effort by a combination of the sulphuric acid with lime while alumina hydrate forms a flocculent precipitate which entangles and carries down the suspended organic matters.

On November 11, 1899 the writers visited the chemical precipitation plant at Madison Wisconsin and through the kindness of Mr. McClellen Dodge, City Engineer, were shown the plant at that time in operation.

The sewage was screened as it came from the city and emptied into a well. Here it was dosed with lime and then pumped to one of the four settling tanks. These are 15 feet deep and 25 feet in diameter. The sewage enters near the bottom of the tanks. The sludge settles to the bottom and the effluent rises to the top, where it is carried away to three of the filter beds. These three beds are in continuous use. A fourth bed is out of use while it is washed and allowed to rest for one day.

The total area of the beds is 5550 square feet. The flow through the beds is about 8,000,000 gallons per acre per day.

The company that constructed and operated the plant agreed that the effluent on analysis should be found to be equal to the waters of Lake Mendota and the analyses of Lake Mendota water which was adapted as a standard of purity is reproduced in the Engineering News Vol. 42 No. 26 p. 414. Samples of the crude sewage tank effluent and filter effluent were taken and analyzed as shown in Table II. A comparison of this table with the standard shows that in no particulars does the effluent from the plant come up to the standard.

The company has since abandoned the contract and the city is considering other methods of disposal and purification “in order that there may be no more fiascos in civil engineering at the seat of this well known school.” (University of Wisconsin)

TABLE II.

Analyses of Sewage and Effluent from Chemical Precipitation Plant and Filter Beds at Madison, Wis.

Parts per 1,000,000. +----------------------------------------------------------------------------+ ¦ ¦ November 23, 1900 ¦ +----------------------+-----------------------------------------------------¦ ¦ ¦ Chemical Precipitation ¦ Filter-beds ¦ +----------------------+--------------------------+--------------------------¦ ¦ ¦Sewage¦Effluent¦Efficiency¦Sewage¦Effluent¦Efficiency¦ +----------------------+------+--------+----------+------+--------+----------¦ ¦Oxygen consumed: ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ Total ¦ 38.3 ¦ 23.2 ¦ 40% ¦ 23.2 ¦ 14.3 ¦ 38% ¦ ¦ In suspension¦ 27.2 ¦ 12.1 ¦ 55% ¦ 12.1 ¦ 3.5 ¦ 71% ¦ ¦ In solution ¦ 11.1 ¦ 11.1 ¦ 00% ¦ 11.1 ¦ 10.8 ¦ 3% ¦ ¦Nitrogen as albuminoid¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ammonia ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ Total ¦ 8.32 ¦ 4.00 ¦ 52% ¦ 4.00 ¦ 2.46 ¦ 38% ¦ ¦ In suspension¦ 7.12 ¦ 2.56 ¦ 64% ¦ 2.56 ¦ 1.60 ¦ 37% ¦ ¦ In solution ¦ 1.20 ¦ 1.44 ¦ –20% ¦ 1.44 ¦ .864 ¦ 40% ¦ ¦Total organic nitrogen¦15.30 ¦ 5.32 ¦ 67% ¦ 5.32 ¦ 3.56 ¦ 33% ¦ ¦ In suspension¦12.48 ¦ 1.86 ¦ 85% ¦ 1.86 ¦ 1.54 ¦ 17% ¦ ¦ In solution ¦ 2.82 ¦ 3.46 ¦ –23% ¦ 3.46 ¦ 2.02 ¦ 42% ¦ ¦Nitrogen as free ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ammonia ¦ 32.0 ¦ 32.0 ¦ 0% ¦ 32.0 ¦ 32.0 ¦ 0% ¦ ¦Nitrogen as nitrites ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦Nitrogen as nitrates ¦ .120 ¦ .240 ¦ ¦0.240 ¦ 0.60 ¦ ¦ ¦Chlorine as chlorides ¦ 134 ¦ 136 ¦ ¦ 136 ¦ 119 ¦ ¦ +----------------------------------------------------------------------------+

Another example of the use of chemical precipitation is at Alliance, Ohio. There are three tanks each with a capacity of 144000 gallons. The amount of sewage flowing into the tanks during the year 1897 averaged about 300,000 gallons per day. During the year 1897 each day 180 pounds of chemicals were added to the sewage and 650 pounds of sludge was precipitated and pressed daily.

The total cost of the disposal plant was $20755.00. The cost of operation and maintenance for the years 1897 and 1898 was $1290.00 and $1567.43 respectively. The average amount of lime used during this time was 95000 pounds yearly.

Two men perform all the labor necessary for the operation of the plant.

From the chemical analyses given in the Engineering Record Jan. 13, 1900 of the sewage and effluent, averages representing five months show the efficiency in albuminoid ammonia to be 40 percent and oxygen required 30 percent.

_Septic Tank_

We will now discuss a very different process of treating sewage, the septic method. The septic tank consists of a tank from which generally the air and light are excluded and through which the sewage flows with a slow velocity, thus allowing the matter in suspension to settle to the bottom or rise to the top by reason of its specific gravity, there to be further acted upon or decomposed by bacteria. The currents should be so guided that they are distributed over a considerable depth and not allowed to disturb the sediments at the bottom or the material at the top. The darkened ill ventilated and modestly heated conditions in the tank are all conducive to the propagation of a micro-organism known as bacteria. The activity of these organisms causes a chemical decomposition of the organic matter in the sewage a part passing off as gas and a part passing off in the effluent as inorganic matter, while another portion is deposited in the bottom of the tank as sludge.

So far only matter in suspension has been considered but it is also true that chemical action takes place to some extent in the organic matter in solution. This chemical action is a denitrifying action similar to that which takes place in intermittent downward filtration.

An important fact in the septic tank effluent is that its compounds have been broken down and it can now be more readily purified.

The septic tank process is self-regulating, self-acting, requires no attention except the occasional cleaning out of the sludge.

As an illustration of this process the septic tank at Champaign Illinois may be described.

This tank although designed in 1895, has only been in operation since 1897. The dimensions of this tank are 37 by 16 by 5 feet and it has a cubic capacity of 22,000 gallons. It has taken care of a dry weather flow of 300,000 gallons per day, about 13 times its cubic contents. The tank has operated with a range of from 11 to 27 times its cubic capacity with a high efficiency of purification though much of this was ground water.

The reduction of the organic matter in suspension, as shown by the reduction of oxygen consumed, nitrogen as albuminoid ammonia, and total organic nitrogen in three analyses averaged 94 percent. However it is not considered that an average of more than 80 to 90 percent may generally be expected. The reduction of organic matter in solution is considerable, averaging 17 percent.

This sludge at the bottom is a black muddy looking silt-like deposit containing about 60 percent of water and 5 percent of organic matter. Its value as a fertilizer is small.