Sewage Treatment Flocs
கழிவுநீர் சுத்திகரிப்பு மந்தைகள்
Do not confuse Flocs with simple bacterial colonies. Flocs are complex, symbiotic mesh-like structures essential for secondary sewage treatment. If you miss the role of fungal filaments, you lose the mark.
The idea
Flocs are masses of aerobic bacteria associated with fungal filaments to form mesh-like structures. During secondary treatment, these microbes consume the major part of the organic matter in the effluent. This process significantly reduces the Biochemical Oxygen Demand (BOD) of the sewage. The effluent is passed into a settling tank where the bacterial flocs are allowed to sediment.
Why it matters
Flocs provide a large surface area for aerobic bacteria to efficiently decompose organic pollutants in sewage water.
NEET lens
NEET focuses on the relationship between BOD and organic matter. Remember: High BOD equals high pollution. Questions often test the distinction between primary (physical) and secondary (biological) treatment. Memorize that Flocs are used in the biological stage, not the physical stage.
Clinical significance
Flocs maintain the ecological balance of water bodies by preventing eutrophication. If sewage treatment fails, untreated organic waste enters water bodies, causing rapid microbial growth and oxygen depletion. This leads to the death of aquatic life and the spread of water-borne pathogens like Vibrio cholerae.
Introduction
Flocs are masses of bacteria associated with fungal filaments that form mesh-like structures in the aeration tanks of secondary sewage treatment.
Core concept
Sewage treatment (NCERT): Primary treatment — physical removal of particles: floating debris removed by sequential filtration; grit (soil and small pebbles) removed by sedimentation; all solids that settle form the primary sludge; the supernatant forms the effluent. Secondary (biological) treatment — primary effluent passed into large aeration tanks with constant mechanical agitation and air pumping; vigorous growth of useful aerobic microbes into flocs; while growing, these microbes consume the major part of the organic matter in the effluent, significantly reducing BOD. The effluent then goes to a settling tank, where bacterial flocs sediment — the sediment is called activated sludge. A small part of activated sludge is pumped back into the aeration tank as inoculum; the major part goes into anaerobic sludge digesters.
Go deeper
Sewage treatment plants (STPs) are run with the help of heterotrophic microbes naturally present in sewage. Under the Ganga Action Plan and Yamuna Action Plan, the Ministry of Environment and Forests planned many STPs so that only treated sewage is discharged into rivers.
From Class 10
Before dirty city water is released into rivers, it is cleaned in treatment plants, where bacteria eat up most of the waste.