I

N the rapidly developing industrial and residential area of north Jersey, there is no such thing as standing still. Plants are being outgrown daily. If there are no adequate records, operators are brought to a realization of the overgrowth by a notice from the State Board of Health to do something about the situation. Then a designing or consulting engineer is called in and told to design a new plant. In the absence of accurate records, he has only general information and rule-of-thumb methods upon which to base his new design. This is one of the causes of the large number of failures or partial failures in new plants designed. Another cause in the past has been that the consultant does not know what to do with the information if he has it. This is not a criticism of the consultant, but a statement of the general lack of information on the subject of sewage disposal.

Because of the excellent work of the New Jersey Sewage Experiment Station, fostered through the efforts of the New Jersey Sewage Works

over, the per person contribution of organic waste is reasonably constant. Data from Russia and Germany purporting to indicate a variation in this per capita distribution due to starvation diet during the stress of war conditions, really confirm the general rule by showing how comparatively slight this variation is under such extremes of conditions.

Various industrial wastes of an organic nature are being investigated in numerous places and by analysis and calculation, reduced to an equivalent per capita contribution. With such information at hand, the designer of the future will be able to determine accurately the pro

Association, the consultant, from now on, cannot get behind an alibi of general lack of information. The success of a plant will be squarely up to him, and pure laziness will be his only excuse for failure, provided the operator of the old plant can produce an accurate record of operation over a period of years.

What Records Should Be Kept? One of the most valuable records is that of the number and kinds of connections to the sewer system. Such a record should be demanded by state authorities for every sewer system, whether it has a disposal plant or not. This is necessary because the demand for a plant will inevitably develop in time.

The importance of data on number and kind of connections lies in the fact that, the world

spective plant loads from a study of the number and kind of sewer connections.

Of parallel importance is a record of the actual flow of liquid sewage. The number and kind of connections to the system will indicate the organic load on the plant or the amount of energy which will be required to purify the sewage. The record of the flow will indicate the size of pipes or flow channels neces

sary to carry the sewage at proper velocity, and also the dimensions of grit chambers, settling tanks, dosing siphons and oxidizing beds.

Flow records should show not only gross daily flow, but also hourly fluctuations or at least daily maximum and minimum rates and the amount of variation due to extremes of dry weather or local flood conditions and the duration of high flow after floods. These latter records the operator can make extremely interesting by connecting up the variations in flow with the habits of the community. For instance, in one town it develops that the community bath night is Friday instead of the time-honored Saturday night.

Meters should be installed where practicable in all sewer outfalls for determining the flow. Where meters are not available, weirs may be

used. Dosing devices or filling devices may be made to serve for measurement where other means are not at hand. Finally, if none of these conveniences are at hand, flow tests may be made between two manholes on a straight run of uniform size outfall line. In this case the depth of flow in the pipe line should also be recorded.

Though I do not for a moment wish to belittle the value of laboratory data, I would rather have a reliable record of flow and number of connections and character of connections to work on in designing a new plant than a complete record of analytical data with the flow and connection records missing.

Laboratory Records

The simplest and at the same time one of the most valuable laboratory tests is the determination of putrescibility, or the methylene blue test. This determination is so simple that there is no excuse for neglecting to make and record it very frequently. The results of this test inform the state board of health inspector or the consultant of the length of time during which the plant effluent may be left undiluted without causing a nuisance, and also of the quantity of stream water with which it must be diluted to prevent nuisance. A record of good tests of this kind is indispensable in defending damage action by persons farther downstream, for water pollution. The tests may be made very interesting to the operator by also keeping a record of the appearance of the growth on the outlet weirs or at the edges of the outflowing stream of sewage. It will be found that when the methylene blue color lasts for several days, the growths will be green, but that as soon as the blue samples go quickly, growths along the edge of the sewer outfall will be white. This is because the methylene blue requires oxygen to give it its color and because oxygen is required for the growth of the green organisms. It is interesting to try this and to observe how many hours or days the blue tests must give in order to produce a green growth at the outfall.

A somewhat more complicated test, yet one which anyone who can learn to weigh carefully can make, is the next in importance, namely, the weight of suspended solids in the sewage at different stages of purification and in the sludge. With this is of course coupled the determination of volatile matter and ash in the solids. The latter test is just a matter of burning off the volatile matter and reweighing the dish. In case the weighing of solids is entirely beyond the capacity of the laboratory equipment, the operator should not fail to make the very simple test for solids by volume in the

so-called cone glass or Imhoff glass test. There is considerable variation of opinion about even this simple test as to the time allowed for settling, before reading, and whether one should jar or disturb the cone before reading, to bring down the material collected along the sides. But if it is always done the same way and careful records are kept of the results, it is comparatively easy for the future investigator to transpose the records into the terms with which he is familiar by making a few representative tests by the operator's method and by his own.

The one other really valuable laboratory test to be made is that of pH, hydrogen-ion concentration. A practical and reliable method of making this test in sludges and sludge water is still to be developed.

There is at present little to be said in favor of the determination of various forms of ammonia, which has consumed many laboratory hours in the past and the results of which fill many volumes. In the light of modern information, it seems better to confine routine analysis to the determinations outlined above and to spend the rest of the operator's time and energy on intimate and practical problems which no operator needs to have pointed out to him. They stare him in the face constantly.

What Plant Records Really Show

The Plainfield and Dunellen Joint Sewage Disposal Plant was designed as of 1916 with the idea that it would carry on to 1931, when the probable population would be 40,000. This estimate was based on records of growth from other comparable communities, and the figures appear to be as satisfactory as could be expected. However, a shift of population to the suburban metropolitan district of which these communities are a part, upset all calculations, and the projected population was reached in 1923 instead of 1931.

A careful record of number of connections was available and has been repeatedly checked against other available population estimates. The flow of sewage as estimated in the basis of the design of the plant was 100 gallons per capita. This, too, seems reliable, as this rate has been maintained over a period of a number of years. However, a water-supply fight and alleged shortage of water resulted in the installation of meters in this district and, as the population increased, the per capita consumption of water or contribution to the sewer system decreased from 100 gallons to 80 gallons per capita.

Without available records, it would indeed have been a mystery how the population could have increased from 34,000 in 1919 to 47,000

in 1926 without any increase in flow of sewage, and why, with no increase in flow, the plant could not do as good work in 1926 as in 1919. Plainly, it would have been charged up to the operator.

But the records available did not stop there. Years of records on this sewage, previous to the building of the present plant, showed about 1.50 parts per million of suspended solids in the raw sewage. This ratio of 150 parts per million held until 1922, when the divergence between connected population and sewage flow began to show. The following is the record of population, flow and suspended solids in parts per million from 1920 to 1926, inclusive. Population is based on five persons per connection and checked by other information.

1920 flow high because of abnormal flow first six months. Industrial sewage of negligible character.

For purposes of distributing costs, there is a connection report sheet used at the Plainfield and Dunellen Joint Sewage Disposal Works. It is tabulated monthly from the sewer permit records.

In order to make the weight of suspended solids mean something more than a set of figures, ranging from 147 to 218, it is well to study a typical record of settling-tank influent and effluent.

In 1921, with a flow of 3.2 million gallons daily, there were 150 parts per million of suspended solids in the sewage entering and 59 parts per million in the tank effiuent. This is a difference of 91 parts per million, which represents the solids retained in the settling tanks. The flow was 3.2 million gallons, weighing 8.34 pounds per gallon, or 26.7 million pounds. From each million pounds of sewage there was retained 91 of dry solids, or a total of 26.7 times 91, which gives 2,429 pounds of dry solids.

In 1926, with the same flow of 3.2 million gallons daily, there were 218 parts per million solids in the sewage and 92 parts per million in the effluent. The difference is the quantity retained, equal to 126 parts per million. By the above calculation, 26.7 times 126 gives 3,364

pounds of dry solids. This-is almost exactly 33 per cent more material to handle, though the flow was the same.

The solids as they have to be handled are not dry, but constitute about 5 per cent of the weight of the, sludge which does have to be handled, the rest being water. Then the solids retained in 1921 represented 48,580 pounds, while those in 1926 represented 64,080 pounds of sludge daily. The former' represents a volume of 770 cubic feet, while the latter represents a volume of 1,017 cubic feet.

Calculation of Volume of Sludge

An example, of calculation of quantity of sludge is given below. Suppose exactly 100 parts per million of solids are retained in a settling tank from each million gallons of sewage. The operator knows whether he is handling 500,000, 333,000 or 2,000,000 gallons daily, and from his records and from the analyses returned by the state health department, he will know, whether he is retaining half a hundred parts, or three-quarters of a hundred parts, or may readily determine the quantity of green solids to be handled. It is very interesting to check this up by measuring the sludge in the tanks and on the beds. One million gallons of şewage, leaving 100 parts per million of solids in the settling tank, will yield in dry solids 8.34 times 100, or 834 pounds, and in wet solids (95 per cent moisture) twenty times this figure, or 16,680 pounds, equal to 266 cubic feet, or 1,995 gallons, or in round numbers 2,000 gallons.

From such a calculation it is possible for any operator to determine the size of pumps needed to move the solids from the settling tanks, or, if there is trouble in getting the sludge digested, reference can be made to Dr. Rudolfs' 2 per 'cent rule or the writer's deposition and accumulation curve, Transactions, Am. Soc.. C. E., page 921, August, 1924.*. The operator may find that he has not sufficient sludge digestion capacity. If the deficiency is not too great, he may turn to the New Jersey Experiment Station data and, with a knowledge of the quantity of suspended solids and the percentage of these that are volatile or organic, he may determine the proper quantity of lime to be added to tide him over the difficulty.

By George H. Sandenburgh City Engineer, Ann Arbor, Mich. There are two problems involved in laying dust on unimproved city streets. The first is to keep dust from flying, and the second is to keep the surface of the streets smooth, that is, smooth enough for comfortable riding. There are two materials used for dust layingoil and calcium chloride. Both have been used with varying success.

There are many different kinds of oil used, but it is sufficient to consider two kinds, light and heavy, or they may be classed as hot and cold application oils. In order to get the best results, a heavy oil should be used, one that will form a mat or act as a binder to hold the road surface down. If a light oil is used that does not form a mat, dust will rise and will be more of a nuisance than if no oil had been applied. Although it is not so apparent to the eye, and one does not see so much dust, it is there just the same, and an oily dust is worse than plain dust.

Light Oil

Dirt and gravel street surfaces are bound to rut under traffic, and the only way to keep them in condition is by the use of graders and drags. If graders are used on a street treated with light oil, the effect of the oil is soon lost. We will therefore eliminate light oil as an economical material for dust laying on unimproved

streets.

Heavy Oil

If a heavy oil is to be used, especial attention must be paid to putting the street surface in a good, smooth condition before the oil is applied. The surface of the street should be graded smooth and all dust pockets removed before oil is applied. I have sprinkled a street before oiling and I believe that is better than to have a street too dry. The point I want to bring out is that there should be no thickness or layer of dust on the surface when the oil is applied. If there is, holes will soon develop and the street become almost impassable.

If a street is properly built with 6 to 8 inches of gravel and is curbed and guttered, a heavy oil will make it dustless. This gravel should be 80 to 85 per cent pebbles and be graded uni

formly from that passing a 34-inch screen to that retained on an 8-mesh sieve. With this form of material, a good, smooth, hard service can be obtained on which a heavy oil will give good results.

When we do this, however, we are getting away from an unimproved street and into the improved class. My experience has been that it is practically impossible to keep an unimproved street in good condition after it has been treated with a heavy oil. After the oil is applied, it is impossible to use graders or drags, and the only method of repair is to fill the holes that develop with a mixture of earth and oil. This is all hand work and is not economical, so we will eliminate heavy oil as an economical dust layer on unimproved roads.

Calcium Chloride

Three or, at the most, four applications of calcium chloride will keep the average unimproved street dustless during the dust season in Michigan. In my opinion, the great advantage in using calcium chloride is that the street can be maintained with graders and drags and kept in a good, smooth condition throughout the dust season. I would recommend 11⁄2 to 2 pounds per square yard for the first application and 1⁄2 to 3/4 of a pound for the succeeding applications.

The first application should be made as soon as the dust begins to fly in the spring, and succeeding applications should be made as needed. The last application is usually made in August. It must be remembered that the rainfall governs to a certain extent the number of applications of chloride and the time of application. Cloudy, humid weather is the best time to apply chloride. It then absorbs moisture from the air very rapidly and this moisture has a chance to penetrate into the surface of the street.

The flake calcium chloride should be used. It is now obtainable in 100-pound moistureproof bags. We have kept it over winter without having it cake. For spreading, we use lime spreaders and take the wheels off and attach the spreader to the rear of a 3-ton truck. The bags can then be emptied directly into the spreader from the truck. By using the flake chloride, an agitator in the spreader is not

dust laying should be raised by general tax. A petition method where the property owners collect the money is not good. The petitions straggle in all summer and applications of chloride cannot be made to advantage. The petition system keeps you running from one part of town to the other and you just get your spreading crew working nicely when you have to stop and wait for some more money to be paid in. Then the expense of making the distribution cost for the property owners is half as much as the cost of application. When the money is raised by general tax and all streets are treated, the chloride spreading can be done in a sys

ing the paved street clean, so I believe it is fair to raise money for dust laying by general

tax.

Permanent Improvement Preferred

I do not believe that any method of dust laying is really economical. The money spent for dust laying might better be spent for pavement. The cost of dust laying would pay the interest on paving bonds and enough would be left to retire the bonds. For example, we spent $21,975.76 for dust laying in Ann Arbor during the last season. This was all raised by general tax. Let us use $22,000 for easy figuring.