Wastewater Treatment Process: From Preliminary To Tertiary Stages
The wastewater treatment process runs in four tiers: preliminary (screen and grit), primary (settling), secondary (biological organics and nutrients), and tertiary (polishing and disinfection). Each tier removes a defined fraction of solids, carbon, nitrogen, phosphorus, and pathogens before the water is returned to the environment.
Preliminary And Primary Stages
Preliminary treatment removes rags, grit, and large solids that would damage equipment. Primary settling then lets heavier suspended solids drop out by gravity, cutting the load that the biological stage must handle. Together they protect the reactors and reduce aeration energy downstream.
Secondary Biological Treatment
Secondary treatment is where microbes consume dissolved and colloidal organics. Activated sludge, sequencing batch reactors (SBR), and biofilm systems such as UBF remove most of the carbon (COD and BOD). For nutrient limits, an anoxic and aerobic sequence strips nitrogen, while controlled sludge age or chemical addition captures phosphorus.
| Stage | Removes | Typical Equipment |
| Preliminary | Grit, rags, coarse solids | Screen, grit chamber |
| Primary | Settleable solids | Clarifier |
| Secondary | COD, BOD, nitrogen | Activated sludge, SBR, UBF |
| Tertiary | Remaining N, P, pathogens | Filter, disinfection |
Tertiary Polishing
When the permit is tight, tertiary steps polish the effluent: sand or membrane filtration, advanced oxidation, and disinfection bring nitrogen, phosphorus, and pathogens down to the final limit. Tertiary is sized only after the secondary train is defined, not as a generic add-on.
Where Tankage Fits
Every biological and settling stage needs a vessel. Bolted Glass-Fused-to-Steel tanks give corrosion-resistant, factory-coated reactors and clarifiers that assemble faster than concrete, which matters when a treatment train must be built on a fixed schedule.
Project Case Study: Indonesia Biogas Project In Dumai
Project / Application: Palm oil wastewater treatment plant, Dumai, Indonesia. Industry: Palm oil. Tank Type: Glass-Fused-to-Steel (GFS). Key Requirements: Rapid overseas tankage deployment for a WWTP.
| Field | Value | Source / Evidence |
| Application | Palm Oil Wastewater Treatment Plant | Company project reference |
| Tank Model | O19.86 x 8.4 m | Company project reference |
| Tanks Quantity | 3 Nos. of GFS Tanks | Company project reference |
| Installation Team | 7 engineers and technicians | Company project reference |
| Installation Duration | 40 days | Company project reference |
| Installation Date | November 2009 | Company project reference |
| Volume Per Tank | Not Provided In The Available Source | Dimensions only |
About The Supplier
Shijiazhuang Zhengzhong Technology Co., Ltd (Center Enamel) manufactures Glass-Fused-to-Steel tanks for every biological and settling stage, with enamel firing at 820-930 C and certifications including ISO 9001, NSF/ANSI 61, and CE-EN 1090. The bolted system supports fast, factory-controlled tank delivery worldwide.
Comparison: Secondary Technologies
| Technology | Best For | Note |
| Activated sludge | Steady municipal flows | Needs aeration energy |
| SBR | Variable loads, batch sites | Flexible cycle |
| UBF / biofilm | High-strength industrial | Compact footprint |
The wastewater treatment process is a chain of defined removals, not a single box. Design each stage to the load it receives, and choose tankage that lets the whole train be built and commissioned on schedule.
Frequently Asked Questions
Q1: What are the stages of wastewater treatment? A1: Preliminary, primary, secondary, and tertiary, each removing defined solids, organics, and nutrients.
Q2: What does secondary treatment remove? A2: Most dissolved organics (COD, BOD) and a large part of nitrogen.
Q3: What is tertiary treatment for? A3: Polishing nitrogen, phosphorus, and pathogens to meet tight discharge limits.
Q4: How are nutrients removed? A4: Anoxic-aerobic sequencing removes nitrogen; controlled sludge age or chemicals capture phosphorus.
Q5: Which tank suits each stage? A5: GFS reactors and clarifiers resist corrosion and assemble faster than concrete.
Q6: What is a UBF? A6: An upflow blanket filter, a compact biofilm reactor for high-strength industrial streams.
Q7: How fast can tankage be built? A7: One overseas WWTP installed three GFS tanks in 40 days with a 7-person crew.
Q8: Do all plants need tertiary? A8: Only when the permit requires it; many plants stop at secondary.
Describe your influent and permit to an engineer, or request a staged process and tankage plan for your plant.