Sewage Collection Stations

Sewage Collection Stations, sanitary-technical facilities for receiving and processing wastewater and liquid waste removed from non-sewered properties by tankers. Depending on the method of processing and further fate of the wastewater, the following types are distinguished: a) Sewage collection stations with discharge of wastewater into the sewer system, b) Sewage collection stations with discharge of wastewater into the sea, c) Sewage collection stations in combination with equipment for processing wastewater into fertilizer mass with the aid of peat. The most common and implemented type in Moscow, Kharkov, Dnepropetrovsk, Kiev, Saratov, Gorky, and Rostov-on-Don are sewage collection stations connected to the sewer system. Below we discuss stations of this type. An example of the second type was the now-eliminated fecal receiving station in Leningrad. As for the peat-fecal sewage collection stations of the third type, only design specifications were prepared for them (in Moscow). Sewage collection stations cannot replace sewer systems, and their installation is usually permitted only as a temporary measure. The construction of such stations in cities with partial sewerage to serve non-sewered areas often makes it possible to solve two important tasks: a) rational disinfection of wastewater at city-wide treatment facilities together with sewerage wastewater, and b) reduction in the cost of wastewater removal, since the location of sewage collection stations can be permitted at closer distances from residential quarters than primitive dumping grounds. Despite the significant development of sewerage in cities of the USSR in recent times, sewage collection stations are gradually gaining considerable prevalence. The reason for this is that in cities with partial sewerage, sewage collection stations make it possible to satisfactorily solve the problem of wastewater removal from non-sewered areas both from an economic and sanitary standpoint. The design of sewage collection stations and the technological processes at them are determined by the composition and properties of the wastewater. From a technical standpoint, the purpose of sewage collection stations is to, before discharge into the sewer system, bring the wastewater to a state in which it cannot have a harmful effect on the sewer system. By physical composition, the wastewater delivered by tankers from non-sewered properties may contain: a) large solid impurities, b) small heavy impurities, mainly sand, c) light suspended substances, d) wastewater liquid. Large solid impurities in wastewater include rags, tow, chips, broken glass, kitchen scraps, feces, etc. The amount of these impurities retained on screens with 10 mm slots is on average determined at 2-2.5% of the volume of the total amount of wastewater arriving at the station, with fluctuations from 1% to 4% depending on local conditions. Small heavy impurities mainly consist of sand and earthy substances. Their amount for the warm season is determined at 1-1.5% of the total volume of the wastewater mass. Light suspended substances are all substances that, after the removal of large solid and small heavy impurities from the wastewater, settle out of the wastewater liquid only after more or less prolonged settling in a stationary state or with very slow movement. Observations have established that during natural settling of wastewater, the process of settling of suspended substances is completed in approximately 3 hours. The resulting sediment, or sludge, constitutes up to 25% of the volume of the entire wastewater liquid. The composition of the wastewater liquid and the settled sediment varies greatly; the content of suspended substances can reach up to 25 g per 1 liter. The details of sewage collection station design are determined depending on whether the wastewater liquid can be discharged into the sewer system together with the suspended substances or whether the latter must be separated from it at the station. In the first case, the main components of the stations are: a) a facility for unloading tankers, b) a facility with equipment for removing large solid impurities from the wastewater, c) sand traps for removing small heavy particles and mainly sand from the wastewater liquid, d) equipment for collecting and temporarily storing solid wastewater residues and sediments separated from the wastewater at the facilities specified in items 'b' and 'c'. In the second case, to the above-mentioned parts of the station are additionally added: d) sedimentation basins for removing suspended substances from the wastewater liquid, and e) equipment for drying the sludge from the sedimentation basins. In both cases, sewage collection stations must be provided with adequate water supply, ventilation devices, and have internal sewerage. The facility for unloading tankers must be equipped with wastewater receivers and appropriate access roads for horse-drawn vehicles with sewage barrels. When designing and constructing the receiving facility, it must be equipped with devices for unloading wastewater without spilling on the floor and for thoroughly washing the tankers, access roads, and receivers. The access road for tankers should preferably be made of cobblestone on cement mortar, and if cobblestone is not possible, of asphalt on a concrete base, asphalt-concrete, etc. It is recommended: a) to locate the main receiving channel in a specially insulated and heated corridor in winter, and b) to connect a water supply with a rubber hose and fire hydrant to each receiving point. Water at sewage collection stations is the main production material for processing wastewater. Its abundant consumption is an essential condition for the normal operation of sewage collection stations. Water is used for washing access roads and receiving facilities, for washing tankers, and for washing all other station equipment. Dilution of wastewater is necessary both for sanitary reasons and to prevent clogging of the pipelines into which the wastewater liquid is discharged. When determining the dilution coefficient, one must be guided by the composition of the wastewater liquid, the diameter, and the degree of filling of the receiving collector. When discharging wastewater with suspended substances at night, when the sewer pipeline operates with low filling, the dilution coefficient should be at least two. When choosing a location for a sewage collection station, one must first be guided by sanitary considerations, namely: 1) the station should be located in an isolated area from dwellings, at a distance of no less than 500 m from residential quarters; 2) with respect to prevailing winds, the station should be located so that noxious gases from it are not carried into the city. At the same time, when choosing a location for a sewage collection station, one must also be guided by economic considerations and locate the station as close as possible to the non-sewered area being served, near the sewer collector intended for discharge of wastewater, and with consideration for the need to have well-paved access roads to the station. The required area should be of sufficient size to allow for the free placement of all station structures and service buildings and for the construction of internal access roads of such length that all waiting tankers can be accommodated in the station yard. The plot of land for the sewage collection station should be enclosed by a fence at least 2 m high and surrounded along the perimeter by a strip of trees at least 10 m wide.