Sewage treatment plant is the plant that works on the top of water treatment process to remove pollutants from wastewater,. It includes physical, chemical, and biological processes to remove these pollutants and produce environmentally safe treated wastewater and reusable clean water.
Activated Sludge Process was developed in England in 1914 by Arden and Lockett and was so named because it involved the production of an activated mass of micro organisms capable of stabilizing a waste aerobically.
Process Description:
The aerobic environment in the reactor is achieved by the use of diffused or mechanical aeration, which also serves to maintain the mixed liquor in a completely mixed regime. After a special period of time, the mixture of new cells and odd cells is passed into a settling tank, where the cells are separated from the treated wastewater. A portion wasted corresponds to the new growth of cell tissue associated with a particular wastewater. The level at which the biological mass in the reactor should be kept depends on the desired treatment efficiency and other considerations related to growth kinetics.
A sequencing batch reactor (SBR) is a fill-and-draw activated-sludge treatment system.
Process Description
SBR system following these steps: 1. Fill 2. React 3. Settle 4. Draw (Decant) 5. Idle
Fill
The purpose of the filling processes to add (raw water or primary effluent) to the reactors. If controlled by time, filling process normally lasts approximately 25% of the full cycle times.
React
The purpose of react is to complete the reactions that were initiated during fill. Typically, react takes up 35% of the total cycle time.
Settle
The purpose of settle is to allow solids separation to occur, providing a clarified supernatant to be discharged as effluent.
Draw
The purpose of drawing is to remove clarified treated water from the reactors. The time dedicated to draw an range from 5 to 30% of the total cycle time, with 45 mins being a typical draw periods.
Idle
The purpose of idle in a multi tank system is to provide time for one reactor to complete it fill cycle before switching to another unit.
It involves Three steps:
Primary Settlement
Where larger solids settle into the bottom of the primary tank and are removed periodically as sludge, and where other buoyant materials float upwards to be removed usually by a scraping/screening method.
Secondary Treatment
Where the biodegradable organic matter is degraded by the biomass on the SAFF media.
Final settlement/ Clarification
Where degraded solids are settled out of the biological treated effluent.
A rotating biological contactor consists of a series of closely spaced circular disks of polystyrene or polyvinyl chloride. The disks are submerged in wastewater and rotated slowly through it.
Process Description
In operation, biological growths become attached to the surfaces of the disks and eventually form a slime layer over the entire wetted surface area of the disks. The rotation of the disks alternately contacts the biomass with the organic material in the wastewater and then with the atmosphere for adsorption of oxygen. The disk rotation affects oxygen transfer and maintains the biomass in an aerobic condition. The rotation is also the mechanism for removing excess solids from the disks by shearing forces it creates and maintaining the sloughed solids in suspension so they can be carried from the unit to a clarifier. Rotating Biological Contactors can be used for secondary treatment, and they can also be operated in the seasonal and continuous
The bacteria/activated sludge grow on the internal surface of the carriers. The bacteria break down the organic matter from the waste water. The aeration system keeps the carriers with activated sludge in motion. Only the extra amount of bacteria growth, the excess sludge will come separate from the carriers and will flow with the treated water towards the final separator.
