Sewage contains about 90% water. This means that there is a lot that can be obtained from recycling. The source of waste water comprises both commercial and residential premises with residential sources bringing in the larger proportion of solid waste. Before being recycled and reused, the waste water has to be taken through a thorough treatment process. A number of stages are involved in this sewage treatment process.
The first stage is known as the pre-treatment stage. In this stage the effluent is passed through a series of meshes with varying sizes. Foreign objects such as rocks, wood and cloth are trapped under these meshes and removed from the effluent as it heads onto the next stage. The smallest grate size is 1.5 millimeters and the largest is 5 cm. Large plants such as those serving municipalities may have mechanical rakes in place of meshes to perform the same function.
Another important use of the pre-treatment stage is to facilitate the removal of sand and grit. The grit found in sewage is in most cases caused from runoff from streets after a downpour. The act of separating grit from the rest of the effluent is greatly dependent on gravity. The plant is usually modified in such a way that the effluent flows through a V-shaped channel created out of gentle slope.
At the primary stage, the effluent is held in large tanks where it is held for a few days to allow for sedimentation to occur. A continuous outflow occurs simultaneously but there is enough time for all the effluent to undergo sedimentation. The solid that settles at the bottom is also termed sludge. Sludge is often subjected to anaerobic digestion to yield methane gas for domestic or commercial use. The remnant of the digestive process is buried in appropriate landfills.
The secondary stage is used for the digestion of biologic materials. For this to happen, the water is filled with anaerobic and aerobic microorganism (both bacteria and protozoa). The breakdown of this material produces energy and carbon dioxide and subsequently reduces that nutritional content available for bacterial survival. Additional sedimentation is also done at this stage to get rid of suspended solids carried over from the primary stage.
There may be some variations in the approaches that are used at this stage. One of the commonly used alternatives involves addition of enzymes to the effluent as opposed to using microorganisms. The blend contains most of the common enzymes required for the breakdown of organic matter. One disadvantage of this approach is the fact that it may not be possible to have all the enzymes needed for this process hence a lot of matter remains undigested.
At the tertiary stage, a number of things are done. Among them is the removal of elements such as phosphorus and nitrogen. If the levels of these elements remain high, they have the potential to lead to an effect termed eutrophication. Other important steps that are undertaken here include chlorination, improvement of odor and the reduction of residual organic matter by use of biologic filters.
The management of waste water has traditionally been conducted by local governments. The difficulty in setting up the required infrastructure has been the main barrier for potential investors. This is changing with time as better technologies to carry out the process are developed. Individuals who create their own treatment plants usually adopt two stages instead of four.
The first stage is known as the pre-treatment stage. In this stage the effluent is passed through a series of meshes with varying sizes. Foreign objects such as rocks, wood and cloth are trapped under these meshes and removed from the effluent as it heads onto the next stage. The smallest grate size is 1.5 millimeters and the largest is 5 cm. Large plants such as those serving municipalities may have mechanical rakes in place of meshes to perform the same function.
Another important use of the pre-treatment stage is to facilitate the removal of sand and grit. The grit found in sewage is in most cases caused from runoff from streets after a downpour. The act of separating grit from the rest of the effluent is greatly dependent on gravity. The plant is usually modified in such a way that the effluent flows through a V-shaped channel created out of gentle slope.
At the primary stage, the effluent is held in large tanks where it is held for a few days to allow for sedimentation to occur. A continuous outflow occurs simultaneously but there is enough time for all the effluent to undergo sedimentation. The solid that settles at the bottom is also termed sludge. Sludge is often subjected to anaerobic digestion to yield methane gas for domestic or commercial use. The remnant of the digestive process is buried in appropriate landfills.
The secondary stage is used for the digestion of biologic materials. For this to happen, the water is filled with anaerobic and aerobic microorganism (both bacteria and protozoa). The breakdown of this material produces energy and carbon dioxide and subsequently reduces that nutritional content available for bacterial survival. Additional sedimentation is also done at this stage to get rid of suspended solids carried over from the primary stage.
There may be some variations in the approaches that are used at this stage. One of the commonly used alternatives involves addition of enzymes to the effluent as opposed to using microorganisms. The blend contains most of the common enzymes required for the breakdown of organic matter. One disadvantage of this approach is the fact that it may not be possible to have all the enzymes needed for this process hence a lot of matter remains undigested.
At the tertiary stage, a number of things are done. Among them is the removal of elements such as phosphorus and nitrogen. If the levels of these elements remain high, they have the potential to lead to an effect termed eutrophication. Other important steps that are undertaken here include chlorination, improvement of odor and the reduction of residual organic matter by use of biologic filters.
The management of waste water has traditionally been conducted by local governments. The difficulty in setting up the required infrastructure has been the main barrier for potential investors. This is changing with time as better technologies to carry out the process are developed. Individuals who create their own treatment plants usually adopt two stages instead of four.
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