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.
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.
For the primary stage, large tanks are required. These tanks hold the effluent for some time and allow for sedimentation to take place. A continuous slow flow in and out of these tanks takes place but the average residence time allows for most suspended solids to settle at the bottom. The solids that settle at the bottom are known as sludge. They may be digested to produce methane or disposed in landfills.
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.
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.
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.
For the primary stage, large tanks are required. These tanks hold the effluent for some time and allow for sedimentation to take place. A continuous slow flow in and out of these tanks takes place but the average residence time allows for most suspended solids to settle at the bottom. The solids that settle at the bottom are known as sludge. They may be digested to produce methane or disposed in landfills.
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.
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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