What Process Steps Treat Municipal Sewage?
Municipal sewage is treated in a fixed sequence of steps: preliminary screening and grit removal, primary sedimentation, secondary biological treatment (activated sludge or UBF), tertiary polishing for nutrients, and a sludge stabilization/dewatering line. Each step removes a defined fraction of pollutant; together they meet the discharge limit.
Step 1 — Preliminary (Screening and Grit)
Coarse and fine screens remove rags and debris that would foul pumps; grit chambers settle sand and grit that would abrade equipment. This protects every downstream unit.
Step 2 — Primary Sedimentation
In primary clarifiers, settleable solids drop out, removing roughly 50–60% of TSS and 25–40% of BOD. The settled primary sludge is sent to the sludge line. Equalization tanks upstream protect the train from diurnal flow swings.
Step 3 — Secondary Biological Treatment
The core step oxidizes dissolved organics. Activated sludge (aerated, suspended biomass) and UBF (Upflow Blanket Filter, attached biomass) both achieve high BOD/COD removal; UBF also recovers some biogas. Choice depends on footprint, energy, and sludge goals.
| Process step | Removes | Typical efficiency |
| Screening + grit | Debris, sand | protection |
| Primary sedimentation | Settleable TSS, BOD | TSS 50–60%, BOD 25–40% |
| Secondary (activated sludge) | Dissolved BOD/COD | BOD 90–95% |
| Secondary (UBF) | BOD/COD + some biogas | BOD 80–90% |
| Tertiary | N, P, fine SS | as permitted |
| Sludge line | Residual solids | stabilized |
Step 4 — Tertiary Polishing
Where limits require it, tertiary adds nutrient removal (anoxic/oxic for N and P), filtration, or disinfection. This step is what lets a plant discharge to sensitive receiving waters or enable reuse.
Step 5 — Sludge Stabilization and Dewatering
Sludge from primary and secondary is thickened, stabilized (anaerobic digestion or lime), and dewatered to manageable cake. Handling sludge correctly avoids odor and regulatory breach — it is a process step, not an afterthought.
Technical Considerations
Secondary tanks and clarifiers dominate volume; GFS bolted tanks (glass fused 820–930°C) resist H₂S and acidic liquors across the plant. Coatings, roofs, and mixers are specified per duty; quality control on linings prevents early corrosion failure.
Project Case Study
Domestic Sewage Treatment Project in Ghana. A 1,800 m³/day municipal plant using UBF + A²/O, achieving COD 1,000 → 100 mg/L, BOD₅ 500 → 25 mg/L, ammonia-N 30 → 10 mg/L, total P 10 → 2 mg/L — a documented end-to-end municipal sewage process result.
| Project | Domestic Sewage Treatment Project in Ghana |
| Location | Ghana |
| Industry | Municipal / Domestic Sewage |
| Application | Municipal sewage process (UBF + A²/O) |
| Capacity | 1,800 m³/day |
| Influent → Effluent | COD 1,000→100; BOD 500→25; NH₃-N 30→10; TP 10→2 mg/L |
| Status | Delivered 2021 |
About Center Enamel
Center Enamel supports municipal sewage quality through quality control in tank manufacturing: every GFS panel’s glass-to-steel enamel is fused at 820–930°C under controlled process control, inspected for holiday (pinhole) defects, and certified to ISO 28765 where applicable. That coating quality is what lets tanks survive decades in H₂S-rich sewage duty.
Advantages and Limitations
The staged process reliably meets municipal limits and enables reuse. Limits: tertiary nutrient removal and sludge handling add cost; and coating quality is non-negotiable in corrosive sewage liquors. GFS tankage with verified QC addresses the corrosion and service-life need.
Comparison: Activated Sludge vs UBF
| Attribute | Activated sludge | UBF |
| Biomass | suspended | attached blanket |
| Energy | aeration needed | low (some biogas) |
| Footprint | larger | compact |
| BOD removal | 90–95% | 80–90% |
Municipal sewage is treated in steps — screening, primary sedimentation, secondary biological (activated sludge or UBF), tertiary polish, and sludge stabilization — each removing a defined load. The Ghana plant shows COD 1,000 → 100 mg/L end-to-end. Send your limit and we will size the train and GFS tankage.
Frequently Asked Questions (FAQ)
Q1: What are the main municipal sewage steps?
A: Screening/grit, primary sedimentation, secondary biological, tertiary polish, and sludge stabilization/dewatering.
Q2: Activated sludge or UBF?
A: Activated sludge gives 90–95% BOD removal with aeration; UBF is compact and recovers some biogas at 80–90%.
Q3: What happens to sludge?
A: It is thickened, stabilized (digestion or lime), and dewatered to cake for disposal or land application.
Q4: What tank capacity is available?
A: GFS sewage tanks range 200 m³ to 60,000 m³.
Q5: What quality standards apply?
A: Tank coatings are controlled to ISO 28765; structure to AWWA D103 / EN 1090 as applicable.
Q6: What project result is documented?
A: Ghana municipal plant: COD 1,000→100, BOD 500→25, NH₃-N 30→10, TP 10→2 mg/L.
Send your municipal sewage flow and discharge limit. We will recommend the process steps, size the reactors and GFS tankage, and quote to your specification.