The Utilization of Sewage Sludge in Birmingham, England Shallow Tanks and Thoro Digestion Furnish Sludge Without Odor and With Great Possibilities as an Organic Fertilizer thruout the world has greatly increased the expense of intensive farming, which is so important in the truck gardens surrounding all of the larger cities. One of the greatest wastes of nitrogenous matters is in sewage, and it has been claimed that millions await the man who will devise an economical method of reclaiming this material. A long step towards SQUEEGEEING SETTLED SLUDGE FROM TANKS AT SALTLEY, Sludge screen with mechanically-operated rakes for cleaning seen at the economical and satisfactory reclaiming of sewage sludge has been taken in Birmingham England, under the direction of John D. Watson, who has very successfully operated the stupendous sewage disposal work of Birmingham for many years. Settling the Sludge After the inflowing sewage from a population of about 750,000 persons passes thru the detritus tank, from which the heavy solids are dredged by an electrically operated dredger, it flows thru the five sedimentation tanks working in parallel, each with a capacity of slightly more than 1,000,000 gallons. The crude sludge retained in the sedimentation tanks alone amounted to 1,523,000 cubic yards during the past four years, or an average of 380,750 cubic yards per year, the whole of which was transferred to the 39 sludge digestion tanks or lagoons possessing a total capacity equal to 28,250,000 gallons. The density of the sludge removed depends chiefly upon the frequency of the cleaning operation. In 1915 the tanks were emptied once in two or three weeks, when the average water content of the sludge was 87 per cent, whereas the cleaning operation during the last four years yielded sludge with a water content of about 92.5 per cent. right Primary Sludge Digestion The sludge from settled sewage of the Saltley, Birmingham, plant is squeegeed to the sumps, is screened by bulb rails placed 8 to 10 inches apart which are cleaned by mechanically operated rakes, and then pumped to a great digestion tank, where for about two months it undergoes septic action, which reduces the volume by about 25 per cent. The digesting tanks used at first consisted of an existing installation of 20 tanks, 16 of them with an aggregate capacity of 4,500,000 gallons, and 4 having a total capacity of 2,700,000 gallons. For the first two years the digestion operations were conducted in two stages in this installation of 20 tanks. The 16 tanks were used for primary digestion, and the 4 larger ones for the secondary digestion. Two stages were adopted, as it was found in the very early days that vigorous fermentation was better maintained in this way, and tank space was saved to such an extent by pumping from one tank to another that the second pumping was economical when compared with the prospect of an increased capacity. It was soon discovered, also, that inoculating raw sludge with ripe sludge obtained from the secondary tanks had an excellent effect upon the "speeding-up" pro cess. Further, temperature was too obviously a beneficial factor in the success of the process to be ignored. In cold weather the sludge is transferred by the main set of pumps from the particular sedimentation tank whose turn it is to be cleaned out into the selected digestion tanks. Simultaneously, some of the ripest of the available sludge is forced by a small pump into the same delivery main in the proportion of 1 to 4, thus inoculating at the earliest possible moment the fresh sludge with fermentative organisms. In addition, steam from one of the boilers is injected into the delivery main to produce temperature conditions most favorable to fermentation. In moderately warm weather, steam injection is abandoned, and during the heat of summer neither inoculation nor steam injection is used. The biological factor governing the digestion process must necessarily be somewhat complicated, and it is only by the most careful observation of the conditions which bring about the right balance of living organisms that success can be attained. The sludge, which varies constantly in character, amounts to about 1,000 tons per day, and is drawn thru a locality literally surrounded with dwelling-houses, factories and shops. Formerly this gave rise to loud and serious complaints; but since the intake and discharge pipes of the sludge digestion lagoon have been placed beneath the heavy scum, there is little or no trouble from odors. Functions of Lagoons Five miles below the Saltley, Birmingham, plant are the Minworth works, which form part of the installation of 39 tanks. These were formed by surplus soil from the trickling filter site and dry sludge from the drying-bed area, and they perform three functions: first, they give time for the completion of the fermentation process; second, they permit, with almost no detriment to the installation, the admission of humus from the trickling filter, flushings from tanks, and flushings from distributing pipes; third, they act as decanters of supernatant water. The first function is, of course, the primary purpose of the lagoon. The average requirement for digestion for the past four years has been equal to a storage of about four months. It has been proved conclusively that sludge dries more rapidly when the digestive process has been carried to exhaustion, before it is pumped to the drying area; hence the economy of ample primary tankage. The second function is the most important. The "humus" or mineral residue from the trickling filter, like the sludge discharged from activated-sludge plant, is a valuable fertilizer. At first it was decided that the humus might be pumped back to the detritus tank; but, inasmuch as this was five miles away, it would not be economical. Second, it was thought that a second lagoon might be set aside for the humus, but experiments showed that injection into the sludge lagoons and mixing with large proportions of well-digested sludge was far more satisfactory. Water rises to the surface of the lagoon when fermentation is exhausted, and may readily be decanted thru the frame shown in the illustration. When it is recalled that by reducing a sludge which is 90 per cent water to an 80 per cent sludge, one-half of the water is removed, the importance of decanting as much liquid as possible is evident. The Drying Beds The completely digested sludge is pumped direct to the drying beds, which are immediately adjacent. The drying beds con THE SECONDARY SLUDGE LAGOONS WHERE WATER IS DECANTED TO REDUCE WATER CONTENT OF SLUDGE to a sump, whence it is pumped to trickling filters. Each drying bed is formed by earth banks 2 feet high, and the area is provided with a system of small gage tracks for the removal of the dry sludge. The time for drying varies with the weather, and when the sludge has become sufficiently dry to be lifted in lumps, it is taken to the sludge dump, which is 15 feet high and several acres in extent. Utilization of Nitrogen about one-half of the Birmingham sludge with a view to recovering fats and fertilizers. Work on this was upset by the outbreak of the war. However, work is to be begun again shortly, and some very interesting and valuable results are expected. The success of this work is being watched with great interest by sewage engineers thruout the world. Other Work in England In Tadcaster, England, a centrifugal machine for the removal of suspended matters from crude sewage has been developed with considerable success. This eliminates the necessity of large sludge lagoons, and it is claimed that these machines are reducing suspended matters in a sewage to 10-20 parts per 100,000. The sludge produced will not contain more than 70 to 75 per cent moisture, while in the investigations at Tadcaster it has been found that the nitrogen content was 4 per cent, as against 2 per cent for the local precipitated tank sludge. A fifteen-year lease has been granted recently to a company that will take and dry Halifax works. This dried product will be treated for the recovery of grease and for a fertilizer base. With the object of recovering from the all the sewage sludge pressed cake at the dry sludge nitrogen and other products of distillation, boat-loads of it have been sent to the Saltley gas works each week for some time. Altho the results cannot be definitely stated until more producers are installed, still the engineer of the gas works states that he is willing to pay about 75 cents a ton for the sludge delivered at the Saltley works. With a view to securing all tilizer elements possible available fer from the sludge, the di rectors have recently entered into a contract with a fertilizing syndi cate under which the syndicate A 15-FOOT BANK OF DRIED SLUDGE, ACRES IN EXTENT, AWAIT- VERTING IT INTO FERTILIZER Private and Municipal Central Station Lighting and Power Plants in the U. S. Reprinted by permission from the McGraw Central Station Directory and Data Book, 1919. Profit in The Experience of Lansing, Mich., Shows That Proper Care Increases Revenues T Superintendent, Garbage Department and Hog Farm, Lansing HE question of garbage disposal has been a serious one for years, not only in Lansing, but in other cities as well. Various methods have been tried out. Burial of garbage was found too costly, and disposal by private concerns under contract has often failed. Not until the present system of disposal by feeding to hogs inaugurated under municipal control did the garbage question begin to be less troublesome. rental charge of $1 per can per year. Many cans will not last a year. Freezing weather causes the greatest depreciation. indiscreet in what they place in the garbage They put such articles as glass, can. broken On account of the increase of requests for service since the close of the war and the increased activity in building operations, the equipment is so limited that only weekly collection is being given to the residential sections of the city, while daily collections are given to the restaurants, hotels, cafés, and other eating-places. Crockery, floor sweepings and tin cans into the cans with the garbage. This be detected until the cans are cannot emptied at the disposal place. Handling the can so often causes a rapid depreciation. Lansing is buying the cans at present from funds derived by making a The Collection Equipment The collection is made entirely with inotor equipment. It includes one Duplex 4-wheel drive truck with a 32-ton capacity, with a trailer of like capacity. When the truck is used for collection purposes it carries from 150 to 200 cans, but when used for transporting the cans of garbage from the city to the farm it will haul from 350 to 500 cans by using the trailer. This mode of transporting the garbage is used in winter or when the roads are impassable for the smaller trucks. The equipment also includes two I-ton Ford trucks, each with a capacity of 55 cans; two 2-ton Reo trucks, each with a capacity of 115 cans; and one 1-ton Republic with a capacity of 60 cans. To this equipment there will be added one or two more trucks during the coming year. On the Duplex truck, three men are used for collection; on the other trucks only two |