How Wastewater Becomes Reusable Water: From Inlet to Reuse
A Sewage Treatment Plant is no longer optional — it is a necessity for environmental protection, water conservation, and sustainable development.
–By Rudmila Rahman, System Engineer (Muspana)
A Sewage Treatment Plant (STP) treats wastewater through multiple physical, chemical, and biological stages to protect the environment and public health. In this article, we briefly explain the main treatment stages, key processes, and modern technologies used in STPs.
STP installed by Muspana at NIB
Main Stages of an STP
Stage
Treatment Type
Purpose
Preliminary
Physical
Remove large solids
Primary
Physical + Chemical
Settle suspended solids
Secondary
Biological
Remove dissolved organic matter
Tertiary
Chemical + Physical
Disinfection & nutrient removal
Sludge Management
Biological + Mechanical
Safe disposal or reuse
STP Treatment Processes
Preliminary Treatment (Physical)
Purpose: Protect equipment and downstream processes.
Screening (bar screens, rotary screens)
Grit chambers (sand and gravel removal)
Oil & grease traps
Equalization tanks
Primary Treatment (Physical + Chemical)
Purpose: Remove suspended solids.
Primary sedimentation tanks
Coagulation and flocculation using alum, ferric chloride, or lime
Removes 30–50% BOD and 50–60% suspended solids.
Main stages of STP process
Secondary Treatment (Biological – Core of STP)
Aerobic Processes:
Activated Sludge Process (ASP)
Extended Aeration
Sequential Batch Reactor (SBR)
Moving Bed Biofilm Reactor (MBBR)
Membrane Bioreactor (MBR)
Trickling Filters
Anaerobic Processes:
Anaerobic Digesters
UASB (Upflow Anaerobic Sludge Blanket)
Imhoff tanks / Septic tanks
These processes biologically degrade organic matter into stable end products.
Tertiary / Advanced Treatment
Purpose: Final polishing and disinfection.
Sand and carbon filtration
Chlorination, UV, or ozone disinfection
Nutrient removal (nitrogen and phosphorus)
Reverse Osmosis (RO) for high-grade reuse
Final effluent typically achieves:
BOD < 10 mg/L
COD < 50 mg/L
Tertiary Treatment
Sludge Treatment & Disposal
Thickening
Digestion (aerobic/anaerobic)
Dewatering (centrifuge, filter press)
Reuse as compost or energy recovery via biogas
Advanced & Innovative STP Technologies Worldwide
Technology
Key Feature
Regions
MBR
Compact, high-quality output
Japan, Singapore, Europe
IFAS
Hybrid biofilm + sludge
USA, UK
SBR
Space-efficient batch system
India, SE Asia
UASB + Polishing
Anaerobic-aerobic hybrid
India, Brazil
Constructed Wetlands
Nature-based treatment
Europe, Bangladesh
Electrocoagulation + RO
Industrial reuse
Middle East
A Sewage Treatment Plant is no longer optional — it is a necessity for environmental protection, water conservation, and sustainable development. By integrating physical, chemical, and biological processes, STPs convert wastewater into a reusable resource while safeguarding ecosystems and public health.
