Domestic Sewage Treatment: From Preliminary To Nutrient Removal
Domestic sewage treatment moves through preliminary, primary, secondary, and tertiary stages. Preliminary and primary steps drop grit and settleable solids, the secondary biological stage removes most carbon, and the tertiary or polishing stage strips nitrogen and phosphorus, so the effluent is safe to discharge. The tankage is usually bolted Glass-Fused-to-Steel reactors and clarifiers chosen for corrosion resistance.
The Stage Sequence
Preliminary treatment removes grit and coarse screens. Primary settling drops the settleable solids. The secondary biological stage, often an anaerobic-anoxic-aerobic (A2/O) train or an upflow blanket filter (UBF), removes carbon and begins nutrient work. Tertiary polishing then meets the tight permit. Each stage hands a defined load to the next.
| Stage | Removes | Typical Equipment |
| Preliminary | Grit, screens | Screen, grit chamber |
| Primary | Settleable solids | Clarifier |
| Secondary | COD, BOD, some N | UBF / A2/O |
| Tertiary | Remaining N, P | Polishing train |
How Nutrients Are Removed
An anoxic-aerobic sequence removes nitrogen: nitrate is formed in the aerobic zone and returned to the anoxic zone where it is denitrified to nitrogen gas. Phosphorus is captured by controlled sludge age or chemical addition. The train is sized only after the upstream load is defined, not as a generic add-on.
A Boundary Condition
Domestic sewage is low-strength and variable compared with industrial effluent, so it is not a good feed for anaerobic digestion alone; the biological train should be sized to the actual daily flow and the seasonal peak, not to a nameplate that ignores wet-weather inflow.
Project Case Study: Domestic Sewage Treatment Project In Ghana
Project / Application: Municipal domestic sewage treatment, Ghana. Industry: Municipal. Tank Type: Glass-Fused-to-Steel (GFS). Key Requirements: Reliable nitrogen and phosphorus removal at community scale.
| Field | Value | Source / Evidence |
| Daily Treatment Volume | 1,800 m3/day | Company project reference |
| Reactor Types | UBF + A2/O + Sedimentation | Company project reference |
| UBF Tank | 1 set, O11.46 x 9.6 m | Company project reference |
| Secondary Sedimentation | 1 set, O14.52 x 4.8 m | Company project reference |
| A2/O Tanks | 2 sets, Outer O20.64 x 6.6 m | Company project reference |
| Installation Year | 2021 | Company project reference |
| Parameter | Influent | Effluent |
| COD Cr | 1,000 mg/L | 100 mg/L |
| BOD5 | 500 mg/L | 25 mg/L |
| Ammonia N | 30 mg/L | 10 mg/L |
| SS | 400 mg/L | 25 mg/L |
| Total P | 10 mg/L | 2 mg/L |
| pH | not stated | 6.5 to 9.0 |
About The Supplier
Shijiazhuang Zhengzhong Technology Co., Ltd (Center Enamel) manufactures Glass-Fused-to-Steel tanks rated for municipal and domestic sewage duty, with enamel firing at 820-930 C and certifications including ISO 9001, NSF/ANSI 61, and CE-EN 1090. The bolted system supports rapid overseas deployment and factory-controlled quality.
Comparison: Secondary Technologies
| Technology | Best For | Note |
| A2/O | Nitrogen and phosphorus | Compact, integrated |
| UBF | High-rate anaerobic | Low energy, low sludge |
| SBR | Variable loads | Flexible cycle |
Domestic sewage treatment is a staged removal problem: drop the solids, remove the carbon, then strip the nutrients. Choose tankage that lets the whole train be built and commissioned on schedule, and the permit becomes a measured result.
Frequently Asked Questions
Q1: What are the stages of domestic sewage treatment? A1: Preliminary, primary, secondary, and tertiary, each removing a different contaminant class.
Q2: What does each stage remove? A2: Grit and solids first, then carbon, then nitrogen and phosphorus.
Q3: How are nutrients removed? A3: An anoxic-aerobic sequence strips nitrogen; sludge age or chemicals capture phosphorus.
Q4: Which tankage suits STP? A4: GFS reactors and clarifiers resist corrosion and assemble faster than concrete.
Q5: What is an A2/O? A5: An anaerobic-anoxic-aerobic train that removes carbon, nitrogen, and phosphorus in one circuit.
Q6: Can domestic sewage make biogas? A6: Only the high-strength fraction; most domestic STP leans on aerobic biology.
Q7: How fast can tankage be built? A7: One overseas municipal plant installed several GFS tanks for a 1,800 m3/day train.
Q8: Do all plants need tertiary? A8: Only those with nutrient or tight reuse limits; many plants stop after secondary.
Suggested CTA
Describe your community flow and discharge permit to an engineer, or request a domestic sewage treatment and tankage plan.