The Stages Undertaken In Sewage Treatment Process
The management of waste water is usually a local government responsibility but there are many people who have their own plants. Considering that at least 90% of sewage is made up of water, a proper sewage treatment process is necessary if this water is to be recovered and put to alternative uses. Apart from making it possible to recycle and reuse water, the exercise also makes it possible to produce safer solid waste.
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 final step is the tertiary treatment. This involves a process that is carried out beyond the other three stages. Commonly, it involves the removal of phosphorus and nitrogen both of which are known to contribute to a process known as eutrophication. The other important processes carried out here are chlorination, improvement of odor and further removal or 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.
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 final step is the tertiary treatment. This involves a process that is carried out beyond the other three stages. Commonly, it involves the removal of phosphorus and nitrogen both of which are known to contribute to a process known as eutrophication. The other important processes carried out here are chlorination, improvement of odor and further removal or 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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posted by Vittoria @ October 13, 2016
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