5-Antigo Sludge Drying Bed. Concrete in Sludge Bed and Filter Bed was treated with asphalt. Note distribution chamber at center of Sludge Bed and underdrainage system connected to galaries in either side. 6-Heating coils in Antigo digester. These coils connect to a boiler in the pump room maintaining a temperature of 65° in the sludge. The temperature was maintained during the cold weather when the outside temperature was 15° below zero. tor is more likely to make the mistake of running the pump too much than not running it enough. Thirty minutes' operation a day is sufficient to remove the accumulated sludge from the clarifier. The night flow of sewage is permitted to pass through the clarifier without operating the pump at all, the sludge accumulating at the bottom, is immediately pumped in the morning when the operator starts the plant. The sludge digestion tank is a circular concrete tank, the bottom. of which is five feet below the surface and the top is elevated above the sludge bed in order to have a head of 10 ft. on the discharge of the sludge pipe. This digestion tank is 38 ft. in diameter with an effective depth of 15 ft. at the outside and 15′9 1/2′′ in the center. The digestor is equipped with a Dorr mechanism which revolves at the rate of 1 revolution in sixteen minutes. This mechanism keeps the sludge stirred up and the scum broken so that gases may escape from the digesting sludge. The capacity of the digestor is based on 3 cu. ft. per capita for ultimate population of 5,500, but with the present population of Hartford, it is in excess of this figure. The incoming sludge from the Dorrco pump is distributed over the surface by means of a channel which rides with the circulating mechanism. This affords a uniform distribution of the sludge and keeps the scum broken. The sludge bed is well underdrained and is enclosed by concrete walls and is subdivided into four sections to permit the withdrawal of sludge at four separate intervals. The total area of the bed provides a capacity of 0.6 sq. ft. per capita. The underdrainage system consists of vitrified tile supported by a concrete floor, the tile being shaped like a horseshoe and a 2" vitrified brick with a 1/4′′ slot covers the top opening of the tile and forms the floor of the sludge bed. There is a layer of 12" of coarse stone at the bottom, 6" of finer stone above it, and the surface of the bed is covered with 6" of sand. The sludge pipe leading to the bottom of the digestor is valved by an 8" gate valve. This outlet pipe discharges the sludge into a trough leaning to a central distribution chamber from which it may be directed to any one of the four beds. Several determinations of the removal of settleable solids by the clarifier were made during the first year's operation. In April, 1925 a Dorr Company engineer, using Imhoff tubes with 1 hour settlement, found 94% to 99% of settleable solids removed. The Sanitary Engineering Department of the Wisconsin State Board of Health, testing by weight, found a removal of 73% and their Official Report contains the following information: Total solids in raw sewage. 1,086 parts per million 302 parts per million. 82 parts per million .....73% The percentage of removal of the suspended solids varies with the time that the test is taken. The high removal may be attributed to the extremely strong domestic sewage, but a subsequent analysis practically confirms the test made by the Sanitary Engineering Department. These subsequent tests showed a removal of suspended. solids varying from 55% to 73% during a full week's test. Since this plant was put into operation sludge has been withdrawn four or five times. The fact that the sludge is not offensive permits 7-Sanitary improvements under construction in the industrial village of Kohler, Wis. Sanitary sewage will be treated in a Separate Sludge Digestion Plant. The storm water will discharge into the Sheboygan River. The main tunnel is excavated through hardpan and blue clay at a depth of 65' below surface. the city to withdraw the sludge in warm weather. At no time have complaints been registered by adjacent land owners on nearby residents. Under favorable weather conditions the sludge cracks in 36 hours and can be spaded and removed from the bed in from five to seven days. The Superintendent of Parks has experimented with the sludge as a fertilizer and has very conclusively demonstrated its value by using it around young trees in the Park, where a stimulated growth is already in evidence. Accurate cost records of the amount of current consumed by all of the motors at the plant during the fiscal year ending September 1925, showed that a total of 5179 k. w. hours were used, at a total cost of $279.00 or an average cost of $0.79 per day for the total power consumed in operating all the motors, and lighting the plant. In addition to this power cost there should be charged against the operation of the plant for that period approximately $350.00 for city labor and a portion of the Water Works Superintendent's time devoted to the Sewage Disposal Plant operation. This makes a total operating charge of $629.00 a year. This is less than the estimated cost of operating an Imhoff tank, for a greater sum would have to be expended in removing sludge, cleaning the tanks and keeping the plant in proper shape. A comparison of the total cost of plant and operation of the plant built by the city of Hartford with the Two-Story type considered by the officials of that city, is thus summarized. Two-Story Imhoff Tank, Requiring Deep Excavation. Ratio of total annual cost of Separate Sludge Digestion type to Two-Story type......72% The satisfactory service that the Hartford plant is rendering has caused other city officials and engineers to investigate the merits. of this method of treatment, and during 1925 and 1926 many engineers have visited the plant and studied its features. The fact that a very good alkaline sludge is so readily removed and disposed of, and that the plant is receiving continuous attention. which is made compulsory by its mechanical operation, are the principal features noticed by visitors. The city officials of Antigo, Wis., after studying the plant at Hartford and comparing its operation and performance with the results obtained in their disposal plant, accepted the recommendation of their engineer and approved plans for building a Separate Sludge Digestion type of plant in Antigo, the Clarifier and Digester being supplemented with some additional features. The digester has a tight cover made up of a reinforced concrete slab 4 inches thick which is carried by the same truss supporting the digester mechanism. The joint between the roof of the digester and the side walls is constructed for expansion and a copper seal inserted to permit free movement of the slab without opening a crack and allowing leakage. The groove on either side of this copper strip is filled with asphalt. In the center of the roof is a steel gas dome in which all the gases escaping from the digesting sludge will be 8-Kohler Tunnel Sewer at river portal. Note the separate pipes which provide for complete separation of storm and sanitary sewage. The 21" sanitary sewer will connect with a Separate Sludge Digestion Plant now being planned. Note the electric lights back in the tunnel, the farthest light being approximately 1500 feet from the camera. collected. From this dome the gas will be piped to a gas burner in the pump room and here used as fuel in heating the building and also used as a fuel in heating the sludge in the digester. The amount of gas that will be available for fuel will vary with the temperature of the digesting sludge, but one-third cubic foot per capita per day is a fair estimate of the amount. This will be equivalent to 200 pounds of coal per day in heat value. For three months |