Sewage treatment plantवाहित मल उपचार संयंत्र

NCERT Fig 8.6 · Class 12 Biology · Chapter 8 · interactive diagram

Parts and their functions

• Raw sewage (कच्चा वाहित मल) — Municipal waste-water, mainly human excreta + organic matter + huge numbers of microbes (many pathogenic). Cannot go straight into rivers.
• Screens — sequential filtration (छन्नियाँ — क्रमिक निस्यंदन) — Primary treatment step 1: floating debris is removed by filtering through screens one after another. Purely physical.
• Primary settling tank (प्राथमिक अवसादन टैंक) — Grit (soil, small pebbles) and solids settle down — sedimentation. Primary treatment = physical removal of particles.
• Primary sludge (प्राथमिक आपंक) — All the solids that settle at the bottom of the primary tank.
• Primary effluent (प्राथमिक बहिःस्राव) — The liquid on top (supernatant) after settling. It goes on to secondary (biological) treatment.
• Aeration tank (वायवीय टैंक) — Secondary treatment: primary effluent is constantly stirred and air is pumped in, so useful aerobic microbes grow fast into flocs.
• Flocs (ऊर्णक (फ्लॉक्स)) — Masses of bacteria held together with fungal filaments in a mesh-like structure. They eat up most of the organic matter, so the BOD of the effluent falls a lot.
• Air pumped in (हवा पंप करना) — Oxygen supply for the aerobic microbes. Aeration continues until the BOD is reduced significantly.
• Settling tank (अवसादन टैंक) — Effluent from the aeration tank is passed here so that the bacterial flocs can settle (sediment).
• Activated sludge (सक्रियित आपंक) — The sediment of flocs. A small part is pumped back into the aeration tank as inoculum; the major part goes to the anaerobic sludge digesters.
• Return sludge (inoculum) (वापस भेजा आपंक (निवेश द्रव्य)) — A small part of the activated sludge is pumped back into the aeration tank to seed it with flocs.
• Secondary effluent (द्वितीयक बहिःस्राव) — The treated water left after secondary treatment; generally released into natural water bodies like rivers and streams.
• River / stream (नदी / नाला) — Natural water body that receives the treated (secondary) effluent.
• Anaerobic sludge digester (अवायवीय आपंक संपाचित्र) — Big tank where other kinds of bacteria grow anaerobically and digest the bacteria and fungi in the sludge.
• Anaerobic bacteria (अवायवीय जीवाणु) — Work without oxygen; while digesting the sludge they release a mixture of gases (methane, hydrogen sulphide, CO₂).
• Biogas (बायोगैस) — Methane + hydrogen sulphide + carbon dioxide. It is inflammable, so it can be used as a source of energy.

Steps

1. 1. Primary treatment: screens remove floating debris, grit settles — primary sludge at the bottom, primary effluent on top.
2. 2. Aeration tank: air is pumped in; aerobic bacteria grow into flocs and eat the organic matter, so BOD falls.
3. 3. Settling tank: flocs settle as activated sludge; a little goes back as inoculum, the clean secondary effluent goes to the river.
4. 4. Anaerobic sludge digester: anaerobic bacteria digest the sludge and release biogas (methane, H₂S, CO₂).

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 8.6. Report a mistake