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.
The main activity that takes place in the pre-treatment stage is the removal of solid objects from the effluent. This is achieved by using a series of meshes of varying sizes. The largest has a size of about 5cm, the medium sized is between 0.3cm and 0.5cm and the smallest 1.5 and 3.0 millimeters. For larger plants, mechanical rakes may be used. These rakes move continuously to help separate the solids according to their sizes.
Apart from the foreign objects, grit is another important component that is removed at this stage. Most of the grit comes from street runoff that gets mixed up with sewage from residential and commercial buildings. Grit separation is a gravity dependent process. The effluent is allowed to flow gently through a V-shaped channel which causes the grit to settle at the bottom. The main benefit of the entire pre-treatment stage is to protect the hardware that is used in the 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.
Treatment of waste water may also be done on onsite septic tanks in residential or commercial compounds. You need to be aware of the guidelines that govern the process of installing and operating such plants before you embark on the process. Most of the onsite plants have a two stage process rather than the four stages found in the advanced plants.
The main activity that takes place in the pre-treatment stage is the removal of solid objects from the effluent. This is achieved by using a series of meshes of varying sizes. The largest has a size of about 5cm, the medium sized is between 0.3cm and 0.5cm and the smallest 1.5 and 3.0 millimeters. For larger plants, mechanical rakes may be used. These rakes move continuously to help separate the solids according to their sizes.
Apart from the foreign objects, grit is another important component that is removed at this stage. Most of the grit comes from street runoff that gets mixed up with sewage from residential and commercial buildings. Grit separation is a gravity dependent process. The effluent is allowed to flow gently through a V-shaped channel which causes the grit to settle at the bottom. The main benefit of the entire pre-treatment stage is to protect the hardware that is used in the 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.
Treatment of waste water may also be done on onsite septic tanks in residential or commercial compounds. You need to be aware of the guidelines that govern the process of installing and operating such plants before you embark on the process. Most of the onsite plants have a two stage process rather than the four stages found in the advanced plants.
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