Package treatment plant is a method of sewage treatment which uses physical, chemical and biological processes to remove physical, chemical and biological pollutants/contaminants. Package sewage treatment plant is beneficial for the areas like small town ships, hotels, villas, restaurants in their premise. Small sewage treatment plant used in minimal land area and for small/less population.
The major objective of mini sewage treatment plant is to produce an effluent (treated wastewater) and solid waste/sludge which is suitable for reuse or dispose back into the natural environment. The package plant includes fine screening, suspended growth biological treatment, and membrane filtration. Ultraviolet disinfection can easily be added to these systems for complete treatment.
Sewage treatment plants are available in a modular or package form. Small wastewater treatment plant involves three stages namely primary, secondary and tertiary treatment.
1. Primary Treatment : It is used prior to biological treatment. This treatment removes material that will either float or readily settle out by gravity. It involves grit chamber to slow down the flow so that sand, grit, eggshells, grease, small plastic material, will settle out of water and these are removed from a tank called sedimentation tank or primary clarifiers. The settled sludge is known as primary sludge and it is pumped out to sludge handler for removal. In this treatment about 60-70% suspended solids are removed but still the waste water is not fit for reuse hence further level of treatment is very much required. The partially treated wastewater from the primary tank then flows to the secondary treatment system.
2. Secondary Treatment : Treated wastewater from primary treatment is pumped to next stage of treatment called secondary treatment where it is aerated and biologically treated. It uses a process called activated sludge process. When the air is supplied to aeration tanks mixes with wastewater and the growth of microorganisms will be increased and break down of organic matter takes place. The aerated wastewater enters into a settling tank called secondary clarifier where heavy solids settle down and called as secondary sludge. Some part of it is again sent to aeration tank and the remaining is added with primary sludge for further processing called as sludge handler. Secondary treatment of small wastewater treatment plant removes up to 80-90% of BOD.
3. Tertiary Treatment : Package sewage treatment plants usually don’t involve pre-treatment or tertiary treatment. However, during reuse or disposing of wastewater into watercourses tertiary treatment is very much essential. This treatment is also known as advanced treatment which can use physical and/or chemical and/or biological processes to remove contaminants which cannot be removed by secondary and/or primary treatment. Since this treatment includes disinfection process, it is also called as disinfection treatment. It can be done with chlorine treatment or ultraviolet treatment.