Sewerage and Sewage System PDF

Sanitation health lecture four  Sewerage and sewage system Off-site sanitation: sewerage and sewage system. Off-site system are forms of sewerage which transport excreta through sewer pipes using water. Conventional sewerage systems usually transport excreta and wastewa...

Sanitation health lecture four  Sewerage and sewage system Off-site sanitation: sewerage and sewage system. Off-site system are forms of sewerage which transport excreta through sewer pipes using water. Conventional sewerage systems usually transport excreta and wastewater to centralized treatment plants. Sewerage is removal of excrete, flushing water from toilets and house holds, sullage through a pipe or sewer net work to a treatment works or disposal point, as shown in figure. They are the norm in urban areas of most developed countries and use large diameter pipes with significant hydraulic gradients to ensure continuous suspension of solids. usually require significant volumes of water to transport the waste and therefore require high levels of reliable water supply service. Sewerage systems need to be maintained regularly to prevent leakage. Sewerage systems need to be maintained regularly to prevent leakage. Leaking sewers are likely to represent a significant risk to groundwater where centralized wastewater collection is practiced. In many areas of the world, however, sewage is allowed to flow directly in to rivers untreated, representing a major public health risk. In some settings, sewerage systems include rainwater drainage from roads and other paved surfaces, and these overflow periodically when water volumes from precipitation are beyond their capacity, thus leading to an overflow of a mixture of excreta and surface runoff that is commonly discharged to surface or marine waters with no or mechanical treatment. The advantages of sewerage are that it can remove large amounts of waste water and it provides great user convenience. The main disadvantage are the high capital and operating costs, and the effluent still contains large numbers of germs. Conventional sewage treatment Sewage can be treated in a conventional sewage treatment plant to remove the solid material in the sewage and also to make the liquid part of the sewage less harmful to humans and fish when it is passed in to a river or the sea. Conventional sewage treatment employs:  physical treatment, such as screening, sedimentation, filtration, aeration and drying. Biological treatment using biofilters such as trickling filters and rotating biological contractors, activated sludge, oxidation ponds, and aerobic and anaerobic digestion. The sewage effluent may still contain a very large number of pathogenic organism after it has passed through the treatment plant. After treatment, the solid part of the sewage can be used as fertilizer for crops. The liquid part of the sewage can be used for The irrigation of crops. The advantages of a conventional sewage treatment plant are:  Can treat large amounts of sewage quickly.  Uses a relative small area of land. The disadvantage of a conventional sewage treatment include:  The treatment plant is expensive to build and maintain. Sewage effluent may still contain large numbers of pathogen when it leaves the treatment plant. Leaking sewers Leaking sewers have been shown to be a significant source of groundwater pollution in numerous urban settings of the world though information on the full extent of the potential hazard confronting groundwater is rather poor. Factors that influence leakage of sewers include:  type of subsoil  height of groundwater level above sewers  standard of workmanship in laying pipes  type of pipe joint, number of joints and pipe size  total length of sewer (including house connections)  number and size of manholes and inspection chambers  rainfall (daily and seasonal)  age of system.  Comparison of Wet and Dry Sanitation Feature Wet Sanitation Dry Sanitation Water usage High Low or none Complex (sewer systems, Simple (composting Infrastructure septic tanks) toilets,, pit latrines) Potential for water Generally more Environmental impact pollution sustainable Cost Higher Lower Urban and suburban Rural areas, remote Suitability areas locations Convenience High Lower Reduced with proper Increased if not managed Health risks treatment properly Requires regular Less maintenance Maintenance maintenance and required inspections