Sewage Disposal Systems PDF

Module 12 Sewage Disposal Systems Sewage Disposal System Public Sanitary Sewer A system of collection, transportation, treatment and A common sewer to which all abutters have equal rights disposal of sewage....

Module 12 Sewage Disposal Systems Sewage Disposal System Public Sanitary Sewer A system of collection, transportation, treatment and A common sewer to which all abutters have equal rights disposal of sewage. of connection. Drainage System The drainage pipes of a plumbing system taking the wastewater from the plumbing fixtures and delivering it to the sewer or some other outlet. Individual Sewage Disposal Systems An excreta disposal system serving a dwelling unit. Public Toilet A toilet facility located at public places like markets, bus stations, buildings, etc., intended for public use. Private Disposal Systems 1. Cesspool/Drywell/Absorbing Well/ Seepage Pit Communal Excreta Disposal System An excreta disposal system serving a group of dwelling units. Digestive Cesspool A pit for the reception or detention of sewage. A lined and covered excavation in the ground which receives the discharge of domestic sewage or other Distribution Line of a Leaching Tile System organic wastes from a drainage system, so designed The pipe from within the distribution box to the as to retain the organic matter and solids, but drainfield. permitting the liquids to seep through the bottom and sides; also called leaching cesspool or pervious Distribution Box cesspool. A small concrete receptacle between the septic tank and the drain field in which lines of drain tiles extends and which acts as a surge tank to distribute the flow of Distance of Cesspool in Proximity to the Following: 1. Should be located 45.7 meters away from any sewage equally to each line of drain tiles. water supply well; 2. 3 meters from public water main; 3. 2.4 meters from any building or structure; 4. 2.4 meters from lot line or adjoining private property; 5. 1.5 meters from a septic tank. 2. Privy Domestic Sewage Sewage containing human excrement and other liquid household waste; also called sanitary sewage.  Putrefaction Gases Produce in Septic Tanks Some gases are produced as a result of the decomposition process of sewage. These include the following: 1. Methane (CH4) 2. Carbon dioxide (CO2) - a combination of carbon and A structure which is not connected to a sewerage system oxygen and is used for the reception, deposition, and storage of feces or other excreta from the human body; also an 3. Ammonia outhouse used for the deposition of excrement. 4. Hydrogen Sulfide (H2S) 3. Septic Tank A watertight receptacle which receives the discharge of a 5. Carbon Monoxide (CO) plumbing system or part thereof, and is designed to accomplish the partial removal and digestion of the 6. Sulfur dioxide (SO2) suspended solid matter ion the sewage through a period of detention. 7. Nitrogen Oxides 8. Esters Basic Septic Tank Design Considerations: 1. Sewage flow 2. Detention period 3. Tank capacity 4. Tank dimensions 5. Sludge withdrawal and disposal Septic Tank Design The septic tank capacity may be determined using Definition of Terms sewage flow quantity value per given occupancy or type of building. For buildings with occupants, the number of Digestive chamber persons to be served shall be computed based on the number of rooms and considering each room occupied by two persons or on the basis of the actual number of persons served by the tank. Leaching chamber Inlet and Outlet Sludge 1. The invert level of the inlet shall not be less than Scum 50 mm above the liquid level of the tank. 2. A vented inlet baffle or sanitary tee shall be Influent provided to divert the incoming sewage downward. The baffles or tee shall penetrate at Effluent least 150 mm below the liquid level, but the penetration shall not be greater than that allowed Septage for the baffle or sanitary tee. 3. The outlet shall be fitted with a sanitary tee or Anaerobic bacteria baffle 4. The outlet baffle or sanitary tee shall extend Aerobic bacteria through the scum layer above the liquid level of the tank to approximately 25 mm from the inside Digestion top to the tank.  5. The invert of the invert pipe shall be at least not Septic Tank Maintenance less than 50 mm above the invert of the outlet 1. Septic tanks shall be cleaned before excessive pipe. sludge or scum is allowed to accumulate and 6. Inlet and outlet pipe fittings or baffles, through seriously reduce the settling efficiency. compartment partitions, shall have a free vent area 2. Septic tanks shall be inspected at least once a year, equal to the required cross-sectional area of the and be cleaned when the bottom of the scum mat house sewer discharging therein. is within 75 mm of the bottom of the outlet device or the sludge and scum has reduced the liquid Tank Proportions capacity by 50%. 1. The septic tank may take various shapes provided 3. Tanks shall not be washed or disinfected after the capacity, inlet, outlet, and depth requirements cleaning. A small residual amount of sludge shall are all met. Generally the septic tank is be left in the tank for seeding purposes. rectangular in shape. If two or more compartments 4. Sludge from septic tanks shall be disposed of by are used, the first compartment shall have the burial or any other method approved by capacity from one-half to two-thirds of the total authorities, and shall not be emptied into open volume of the tank. fields, ditches, or bodies of water. 2. The septic tank shall have a liquid drawing depth not less than 0.60 meters nor more than 1.80 m. Leaching Tile Field 3. The vertical distance for the liquid level to the inside top of the tank shall be at least 200 mm. Design 1. A leaching tile system utilizing trenches 450 mm Inspection Manholes – 900 mm wide is considered to be a leaching tile The septic tank shall be provided with an inspection field. manhole 508 mm in minimum dimension or by an 2. A leaching tiles system more than 900 mm is equivalent removable cover slab to the inlet and outlet considered to be a leaching bed. devices and to the compartment of the tank for inspection 3. Leaching tile fields/leaching beds/leaching and cleaning. One access manhole shall be located over wells/chambers shall not be installed in any of the each compartment. Septic tanks installed under concrete following: or block-top paving shall have the required manholes 3.1. In swampy areas or where ponding/flooding accessible by extending the manhole openings to grade. is likely to occur. 3.2. Where percolation rate exceeds 60 min. per Construction of Septic Tanks 25 mm of water fall. 1. Septic tanks shall be constructed of sound and 3.3. Where the depth normal to the groundwater durable materials, not subject to excessive or rock strata is less than 1200 mm below the corrosion or decay, and shall be watertight. Each bottom of the device. tank shall be structurally designed to withstand all anticipated earth or other loads and shall be House Sewers installed level on a solid bed. Structural and hydraulic design shall be in accordance with good Design engineering principle. The size of any house sewer shall be determined on the 2. Approved prefabrication septic tanks may be used. basis of the total number of fixture units drained by such After installation, the tank shall be filled with sewer. Minimum size shall not be less than 100 mm in sufficient amount of water to prevent floating. diameter. 3. Roof drains, foundation drains, area drains, or cistern overflows shall not be made to enter the Materials septic tank or any part of the treatment system. 1. Vitrified Clay Sewer Pipe 2. Asbestos Cement Pipe Septic Tank Locations 3. Cast Iron Pipe 1. The septic tank shall be located not less than 15.2 4. Bituminized Fiber Sewer Pipe meters from any water supply well; not less than 5. Glass Pipe 1.5 m from any water service line; and not less 6. Any other pipes approved by the Bureau of than 3.0 m from any water main. Standards (BS) or Department of Trade and 2. Septic tanks shall be located such that desludging Industry (DTI) equipment can have access to the opening manholes conveniently. Installation 3. Septic tanks shall not be located under the 1. The house sewer shall be laid in good alignment building. and at a uniform slope of not less than 0.02% toward the point of disposal; provided that, where  it is impracticable, due to the depth of sewer or to the structural features or to the arrangement of any building or structure, to obtain a slope of 0.02%, any pipe or piping 100 mm in diameter or larger may have a slope of not less than 0.01%. 2. Whenever the house sewer is located within 25 meters of a well or spring or any drinking water source, the house sewer shall meet the 10-foot head of water test for 15 minutes. When water is not available or when the danger of freezing is present, the air or smoke test may be used instead. 3. House or building sewer piping shall be laid on a firm bed throughout its entire length, and any such piping laid in ground on a bed of approved materials shall be adequately supported. Minimum Distances of Sewage Disposal Systems Min. Hor. Building Septic Disposal Seepage Clear Distance Sewer Tank Field pit or Required Cesspool Buildings or 0.6 m 1.5 m 2.4 m 2.4 m structures Property line Clear 1.5 m 1.5 m 2.4 m Water supply 15.2 m 15.2 m 30.5 m 45.7 m well Streams 15.2 m 15.2 m 15.2 m 30.5 m Trees --- 3.0 m --- 3.0 m Seepage pits or --- 1.5 m 1.5 m 3.7 m cesspools Disposal field --- 1.5 m 1.2 m 1.5 m Water service 0.3 m 1.5 m 1.5 m 1.5 m line Distribution box --- --- 1.5 m 1.5 m Public water 3.0 m 3.0 m 3.0 m 3.0 m main National Plumbing Code of the Philippines (NPCP)