Why is there is a need for sewage collection and treatment systems?
Wastewater from domestic and commercial sources contains both solid and dissolved pollutants including fecal matter, food residues and other contaminants. Wastewater cannot be directly discharged into streams and seas because it is contaminated and will generally result into hazards to health and life. Wastewater has to undergo the system of sewage collection and treatment for the removal of solids through physical screening and sedimentation. Soluble and finely suspended organic pollutants are removed through biological oxidation and absorption processes. After these forms of treatment, the byproduct is sludge that has to be treated and disposed of in the most economical and environmentally friendly way. Different of processes of treatment may be used according to the standard of effluent required and to comply with local regulations.
The sewage collection and treatment process
Primary treatment process
When wastewater finally reaches the treatment plant, it will encounter preliminary treatment where large solids are removed. Smaller solids will likely float to the surface or settle at the bottom. Wastewater then flows to the secondary treatment where it passes through the biological filters. Settling tans are designed with mechanisms that will remove both solids that float to the surface and those that settle at the bottom. After the preliminary treatment, finer solids will still remain but chemicals are added during this process to remove smaller inert solids.
Secondary treatment process
The secondary treatment in sewage collection and treatment is the biological process that makes use of aerobic bacteria to feed on the organic solids and convert them into a biological mass that can be removed. Fresh air is the key for the aerobic bacteria to work properly and efficiently. An essential part of the secondary treatment process is another set of settling tanks or clarifiers that will remove the biological mass that has resulted from biological treatment. The resulting sludge will combine with the sludge that has been generated through the primary treatment process and will be pumped to the solid treatment system for further processing.
Advanced treatment process
During the advanced treatment process, phosphorus has to be removed and ammonia has to be reduced so that there will be no negative impact on the receiving stream. Sludge that has been processed is dewatered and treated to reduce odors before it is injected into the ground and non-food crop fields as fertilizer. Sludge can also be incinerated to destroy its organic content and to reduce its mass to mineral ash that can be disposed off in the landfills.