The Process Involved In Sewage Water Treatment System
Waste water is an issue that affects virtually any settlement whether rural or urban. For obvious reasons, the problem is bigger in the urban setting where there are numerous sources that include both private residences as well as commercial premises. Sewage water treatment system is done for a number of reasons. Most importantly, it rids of the water of harmful organisms and makes it safe for disposal. There are four main stages that are involved in this process, screening (pre-treatment), primary, secondary and secondary stages.
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.
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.
Effluent leaving the pre-treatment stage enters large tanks that are used for the primary treatment. The tanks are used to hold the water for some time so as to allow for sedimentation. There is a slow continuous flow of effluent into and out of the tanks but the time that it remains within the tanks is enough to remove about three quarters of the suspended waste. The solids that settle at the bottom are also referred to as sludge.
The secondary treatment stage involves the breakdown of biological waste. This is achieved by use of microorganisms such as protozoa, anaerobic bacteria and aerobic bacteria. When the material is broken down, the concentration of harmful microorganisms is markedly reduced. There are two main types of systems that are involved: the fixed film system and the suspended growth system. In the former system, biological contactors and trickling filters are used while in the latter the sewage is directly 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.
The tertiary stage is the final stage in the process. It involves a number of process that are mainly used to optimize on the benefits that have been achieved with the other stages. Biological filters are often used here to break the organic materials further. Other important processes include disinfection, reduction in the levels of urea and the associated odor. Many plants tend to skip this stage if the water is not for reuse.
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.
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.
Effluent leaving the pre-treatment stage enters large tanks that are used for the primary treatment. The tanks are used to hold the water for some time so as to allow for sedimentation. There is a slow continuous flow of effluent into and out of the tanks but the time that it remains within the tanks is enough to remove about three quarters of the suspended waste. The solids that settle at the bottom are also referred to as sludge.
The secondary treatment stage involves the breakdown of biological waste. This is achieved by use of microorganisms such as protozoa, anaerobic bacteria and aerobic bacteria. When the material is broken down, the concentration of harmful microorganisms is markedly reduced. There are two main types of systems that are involved: the fixed film system and the suspended growth system. In the former system, biological contactors and trickling filters are used while in the latter the sewage is directly 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.
The tertiary stage is the final stage in the process. It involves a number of process that are mainly used to optimize on the benefits that have been achieved with the other stages. Biological filters are often used here to break the organic materials further. Other important processes include disinfection, reduction in the levels of urea and the associated odor. Many plants tend to skip this stage if the water is not for reuse.
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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