Waste water management is an exercise that affects both residential and commercial buildings. The main reason for a sewage water treatment system is to produce an effluent that is safe to be discharged into the environment or reused for other purposes. The stages and the process that are involved vary slightly from place to place. In general, however, there are four main successive stages that are involved. These include pre-treatment, primary, secondary and tertiary treatment.
In pre-treatment, a series of meshes is placed in the path of the effluent to help trap foreign objects. The largest has a grate size of five centimeters and is most useful in the removal of objects such as wood, rocks and pieces of cloth among others. Larger plants may use mechanical rakes that move in a continuous motion making the process more efficient. The size of the medium mesh is between 0.5cm and 0.3 cm while the smallest ranges between 1.5 and 3.0 millimeters.
Another important step that is undertaken during the pre-treatment stage is the removal grit. Most of this grit joins the effluent together with street runoff when it rains. The separation technique is largely gravity dependent. The effluent is directed to a gently sloping V-shaped channel which allows the grit to sink at the bottom and the liquid component to remain at the top. The removal of all these solids helps reduce damage to the hardware used for subsequent stages.
Several large tanks are used to hold the effluent that is undergoing primary treatment. In this stage, the effluent is allowed to sediment so that solids settle at the bottom. This solid waste (also known as sludge) can be digested anaerobically to produce methane gas. The residual waste is usually disposed of in landfills. There is a continuous flow of sewage into and out of the tanks. The time for which water is held is enough for most of the suspended solids to be removed.
In the secondary stage, the main activity that is carried out is biological digestion. This is facilitated by anaerobic bacteria, aerobic bacteria and protozoa in some cases. These organisms break down the biologic substrate and reduce the survival of harmful bacteria. There are two main types of systems that are used. The first is the fixed film system that uses rotating biological contactors and trickling filters. The second is known as suspended growth technique in which sewage is mixed with biomass.
A different approach that may be adopted at this stage is the use of enzymes rather than organisms. This option is, however, less popular due to a number of the downsides that are associated with it. One of the major disadvantages is that it is not possible to have all the enzymes that are needed which makes it inefficient. The other disadvantage is that it is more expensive.
There are a number of processes that take place during the tertiary stage. One of them is the breakdown of organic matter that has been carried over from the secondary stage by use of biological filters. The amount of nitrogen and phosphorous is also markedly reduced at this stage. Disinfection is done by use of several methods such as chlorination, ozone and UV radiation.
It is possible to carry out the treatment using your own septic tank. All you need to do is to ensure that you are conversant with the public health guidelines that govern the installment and the operation of the tank. Most onsite plants comprise a two stage system rather than the standard four stages.
In pre-treatment, a series of meshes is placed in the path of the effluent to help trap foreign objects. The largest has a grate size of five centimeters and is most useful in the removal of objects such as wood, rocks and pieces of cloth among others. Larger plants may use mechanical rakes that move in a continuous motion making the process more efficient. The size of the medium mesh is between 0.5cm and 0.3 cm while the smallest ranges between 1.5 and 3.0 millimeters.
Another important step that is undertaken during the pre-treatment stage is the removal grit. Most of this grit joins the effluent together with street runoff when it rains. The separation technique is largely gravity dependent. The effluent is directed to a gently sloping V-shaped channel which allows the grit to sink at the bottom and the liquid component to remain at the top. The removal of all these solids helps reduce damage to the hardware used for subsequent stages.
Several large tanks are used to hold the effluent that is undergoing primary treatment. In this stage, the effluent is allowed to sediment so that solids settle at the bottom. This solid waste (also known as sludge) can be digested anaerobically to produce methane gas. The residual waste is usually disposed of in landfills. There is a continuous flow of sewage into and out of the tanks. The time for which water is held is enough for most of the suspended solids to be removed.
In the secondary stage, the main activity that is carried out is biological digestion. This is facilitated by anaerobic bacteria, aerobic bacteria and protozoa in some cases. These organisms break down the biologic substrate and reduce the survival of harmful bacteria. There are two main types of systems that are used. The first is the fixed film system that uses rotating biological contactors and trickling filters. The second is known as suspended growth technique in which sewage is mixed with biomass.
A different approach that may be adopted at this stage is the use of enzymes rather than organisms. This option is, however, less popular due to a number of the downsides that are associated with it. One of the major disadvantages is that it is not possible to have all the enzymes that are needed which makes it inefficient. The other disadvantage is that it is more expensive.
There are a number of processes that take place during the tertiary stage. One of them is the breakdown of organic matter that has been carried over from the secondary stage by use of biological filters. The amount of nitrogen and phosphorous is also markedly reduced at this stage. Disinfection is done by use of several methods such as chlorination, ozone and UV radiation.
It is possible to carry out the treatment using your own septic tank. All you need to do is to ensure that you are conversant with the public health guidelines that govern the installment and the operation of the tank. Most onsite plants comprise a two stage system rather than the standard four stages.
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