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.
Sand and grit are the other important solids that are removed at the pre-treatment stage. The grit enters the sewage as part of street runoff created after rainfall. Gravity is used to separate the water and the grit by redirecting the effluent through a V-shaped channel on a gentle slope. The grit and sand will settle at the bottom and the water will be at the top making separation a lot easier.
One of the main features of the second stage, the primary stage, is the presence of large tanks. These tanks are used for sedimentation. One channel brings in effluent rich in solid waste and another leaves the tanks after most of the solids have undergone sedimentation. This is a process that occurs continuously. The solid that forms at the bottom is also called sludge. It is an important source of methane gas.
The next is the secondary stage. Aerobic and anaerobic organisms added to the sewage at this stage to facilitate biologic digestion of materials still in the water. These organisms are both protozoa and bacteria so as to ensure as much of the material as possible is digested. The exercise yields both energy and carbon dioxide. The consequence of continued digestion is a reduction of the amount of nutrients. The organisms eventually die off.
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.
The last step is the tertiary stage. The steps undertaken here are meant to optimize on the effects of the other three stages. Some of these stages include the removal of elements such as nitrogen and phosphorous. Both of these elements have the potential to cause an effect known as eutrophication. Other treatments carried out include improvement of odor, chlorination and the use of biologic filters to get rid of residual organic matter.
Waste water treatment has traditionally been carried out by local government authorities. This has been mainly due to the large scale of the exercise. Owners of commercial and residential properties are increasingly creating their own systems thanks to the better technologies that now exist. Private plants have only two stages instead of the four conventional stages.
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.
Sand and grit are the other important solids that are removed at the pre-treatment stage. The grit enters the sewage as part of street runoff created after rainfall. Gravity is used to separate the water and the grit by redirecting the effluent through a V-shaped channel on a gentle slope. The grit and sand will settle at the bottom and the water will be at the top making separation a lot easier.
One of the main features of the second stage, the primary stage, is the presence of large tanks. These tanks are used for sedimentation. One channel brings in effluent rich in solid waste and another leaves the tanks after most of the solids have undergone sedimentation. This is a process that occurs continuously. The solid that forms at the bottom is also called sludge. It is an important source of methane gas.
The next is the secondary stage. Aerobic and anaerobic organisms added to the sewage at this stage to facilitate biologic digestion of materials still in the water. These organisms are both protozoa and bacteria so as to ensure as much of the material as possible is digested. The exercise yields both energy and carbon dioxide. The consequence of continued digestion is a reduction of the amount of nutrients. The organisms eventually die off.
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.
The last step is the tertiary stage. The steps undertaken here are meant to optimize on the effects of the other three stages. Some of these stages include the removal of elements such as nitrogen and phosphorous. Both of these elements have the potential to cause an effect known as eutrophication. Other treatments carried out include improvement of odor, chlorination and the use of biologic filters to get rid of residual organic matter.
Waste water treatment has traditionally been carried out by local government authorities. This has been mainly due to the large scale of the exercise. Owners of commercial and residential properties are increasingly creating their own systems thanks to the better technologies that now exist. Private plants have only two stages instead of the four conventional stages.
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