In most Indian cities, any residential project with more than 20,000 square meters of built-up area is mandated to treat 100% of its sewage on-site. When the STP fails, foul sewage odors invade ground-floor apartments and state pollution boards issue massive environmental violation notices.
State Pollution Control Board (SPCB) Discharge Standards
Treated wastewater must satisfy stringent statutory water quality parameters before it can be legally recycled for toilet flushing or landscape horticulture:
- Biochemical Oxygen Demand (BOD): Must remain below 10 mg/L.
- Chemical Oxygen Demand (COD): Must remain below 50 mg/L.
- Total Suspended Solids (TSS): Below 20 mg/L.
- Turbidity & Fecal Coliform: Less than 2 NTU and zero detectable coliforms after tertiary chlorination/UV treatment.
Maintaining Biological Health in Aeration Tanks
Most residential STPs use Moving Bed Biofilm Reactor (MBBR) or Membrane Bioreactor (MBR) technology, relying on live aerobic bacteria to consume organic sewage waste.
The number one reason apartment STPs produce rotten-egg odors is insufficient dissolved oxygen (DO). Blowers must run continuously to maintain a minimum 2.0 mg/L DO level. Heavy dumping of harsh cleaning acids by residents kills the microbial culture, requiring bio-augmentation re-seeding.
Common questions
Can treated STP water be used for washing cars in the society?
If the STP utilizes an advanced MBR system with tertiary ultrafiltration and chlorination that meets municipal clarity and bacterial standards, treated water is safe for external car washing and gardening.
Related DGate resources for society management
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