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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 secondary stage follows the primary stage. The main activity here is the digestion of biologic materials in the waste water. This is facilitated by aerobic and anaerobic organisms (both protozoa and bacterial). When the materials are digested, energy and carbon dioxide gas are produced. Over time, the nutritional content of waste water is reduced markedly and the organisms die a natural death. Some sedimentation also takes place during this stage.
A different approach can be adopted at this stage to achieve results that are not very different from those obtained with the conventional method. Instead of using live microorganisms in the biological filtration process, enzymes may be used. The enzymes are combined in a manner that will target as much of the material as possible. The disadvantage is that a significant amount of the material goes 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.
Although the process of treating waste water is usually done on a large scale by municipalities, you can have your own treatment plant in an onsite septic tank. Just ensure that you fully understand the public health guidelines that apply with regard to the installation and use of such tanks. Generally, small treatment plants have two main stages rather than the standard four stages seen with the large plants.
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 secondary stage follows the primary stage. The main activity here is the digestion of biologic materials in the waste water. This is facilitated by aerobic and anaerobic organisms (both protozoa and bacterial). When the materials are digested, energy and carbon dioxide gas are produced. Over time, the nutritional content of waste water is reduced markedly and the organisms die a natural death. Some sedimentation also takes place during this stage.
A different approach can be adopted at this stage to achieve results that are not very different from those obtained with the conventional method. Instead of using live microorganisms in the biological filtration process, enzymes may be used. The enzymes are combined in a manner that will target as much of the material as possible. The disadvantage is that a significant amount of the material goes 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.
Although the process of treating waste water is usually done on a large scale by municipalities, you can have your own treatment plant in an onsite septic tank. Just ensure that you fully understand the public health guidelines that apply with regard to the installation and use of such tanks. Generally, small treatment plants have two main stages rather than the standard four stages seen with the large plants.
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