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.
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.
One of the alternatives that may be adopted here is the use of predetermined enzymes in breaking down the organic material instead of the microorganisms. This method is, unfortunately, inefficient as it is not possible to produce all the enzymes that would be required. Compared to using microorganisms, it is also 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.
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.
One of the alternatives that may be adopted here is the use of predetermined enzymes in breaking down the organic material instead of the microorganisms. This method is, unfortunately, inefficient as it is not possible to produce all the enzymes that would be required. Compared to using microorganisms, it is also 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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