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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.
During pre-treatment (screening), meshes are used to remove extraneous elements carried in the sewage. There are three sizes of meshes arranged in series. The largest grate is about 5 centimeters and helps to get rid of wood, rocks, pieces of cloth and other objects. In larger plants, this may be achieved by use of large mechanical bar rakes that apply a continuous motion. The medium size is between 0.5 and 0.3 cm while the smallest is 1.5 to 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.
Secondary treatment is designed to breakdown biologic materials. Both anaerobic an aerobic microorganisms are involved in the process. The net effect is a reduction in the organic material which makes it difficult for harmful microorganisms to continue multiplying. The systems that are involved here can be broadly divided into two categories: fixed-film techniques and suspended growth techniques. The former use trickling filters and biological contactors while the latter involve a mixture between the sewage and biomass.
Another alternative approach is to use enzymes instead microorganisms in the secondary stage. The enzymes are similar to those that are produced by the microorganisms. This method appears to be less preferred due to the inability to produce all the enzymes needed. This makes the process very inefficient. At the same time, 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.
Treating waste water may be done in private septic tanks on commercial or residential premises. The guidelines that govern the process of installing and operating these plants vary from one place to another. Ensure that you are conversant with those that apply in your case. The onsite plants typically operate in two stages instead of four.
During pre-treatment (screening), meshes are used to remove extraneous elements carried in the sewage. There are three sizes of meshes arranged in series. The largest grate is about 5 centimeters and helps to get rid of wood, rocks, pieces of cloth and other objects. In larger plants, this may be achieved by use of large mechanical bar rakes that apply a continuous motion. The medium size is between 0.5 and 0.3 cm while the smallest is 1.5 to 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.
Secondary treatment is designed to breakdown biologic materials. Both anaerobic an aerobic microorganisms are involved in the process. The net effect is a reduction in the organic material which makes it difficult for harmful microorganisms to continue multiplying. The systems that are involved here can be broadly divided into two categories: fixed-film techniques and suspended growth techniques. The former use trickling filters and biological contactors while the latter involve a mixture between the sewage and biomass.
Another alternative approach is to use enzymes instead microorganisms in the secondary stage. The enzymes are similar to those that are produced by the microorganisms. This method appears to be less preferred due to the inability to produce all the enzymes needed. This makes the process very inefficient. At the same time, 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.
Treating waste water may be done in private septic tanks on commercial or residential premises. The guidelines that govern the process of installing and operating these plants vary from one place to another. Ensure that you are conversant with those that apply in your case. The onsite plants typically operate in two stages instead of four.
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