Status: Delivered · Region: East China · Ref. D-045
What We Delivered
Client: a municipal wastewater treatment plant in East China, originally running an A²/O process; its name is withheld under our client-confidentiality policy. As required by the competent authority, the plant's effluent was upgraded to Class 1A of GB 18918-2002 (Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant) and its capacity expanded; the project has been put into operation.
Together with the local design institute, our engineering team carried out the technical assessment and option comparison, and took part in process design, equipment supply (per contract scope) and commissioning for both the retrofit and the expansion. The scheme implemented was an MBR retrofit of the original 10,000 m³/day system plus a new 20,000 m³/day A/O-MBR system, with UV disinfection (see "Engineering Design" below). Total treatment capacity was expanded from 10,000 m³/day to 30,000 m³/day, and the effluent was upgraded from Class 1B to Class 1A of GB 18918-2002; treatment continued without a plant shutdown during the retrofit.
Delivery Record
The table lists what each delivery stage covered on this project and the record it produced.
| Stage | What it covered on this project | Record produced |
|---|---|---|
| 1. Design basis confirmation | Confirmed the existing plant's design capacity of 10,000 m³/day, its A²/O process, its Class 1B discharge standard and its overloaded operation at the time; confirmed the targets of upgrading to Class 1A and expanding to 30,000 m³/day. | Design basis sheet |
| 2. Process & mechanical design | Options compared and the scheme selected jointly with the local design institute (MBR retrofit of the existing system + new A/O-MBR + UV disinfection); our engineering team took part in the process design for both the retrofit and the expansion (anoxic zone HRT 3 h, aerobic zone HRT 8 h, MBR design flux 20 LMH, etc.). | Option comparison report, process flow diagram, P&ID, general-arrangement (GA) drawings, equipment list |
| 3. Manufacturing & quality control | Material inspection and in-process inspection, per contract scope, of equipment including the submerged PVDF membrane modules, permeate extraction and membrane cleaning systems, UV disinfection units (3 in parallel), rotary fine screen (3 mm bar spacing) and screw-stack sludge dewatering machines (3 units). | Material certificates, in-process inspection records |
| 4. Factory acceptance test (FAT) | Pre-dispatch inspection and trial run of in-scope equipment against the design parameters. | FAT record |
| 5. Packing & dispatch | In-scope equipment packed according to the list and dispatched to site. | Packing list, dispatch list |
| 6. Installation | Carried out in the no-shutdown retrofit sequence (new system built first, existing system retrofitted afterwards; see "Construction and Commissioning Notes" below); division of work per contract scope. | Installation record |
| 7. Commissioning | The new system was commissioned and brought on stream, and the existing system was returned to service after its MBR retrofit; for how commissioning issues were handled, see "Construction and Commissioning Notes" below. | Commissioning log |
| 8. Performance verification (against the design basis) | Operational verification against the Class 1A design effluent targets (COD ≤ 50 mg/L, BOD₅ ≤ 10 mg/L, SS ≤ 10 mg/L, ammonia nitrogen ≤ 5 mg/L, total phosphorus ≤ 0.5 mg/L). | Performance test record |
| 9. Training, handover & after-sales | Operating requirements handed over to the plant's operators, including membrane module operation and cleaning, aeration system maintenance, and operation of the UV disinfection units and screw-stack sludge dewatering machines. | O&M manual, training record, handover documents |
Delivery records for this project are on file and can be reviewed by qualified buyers under a confidentiality agreement.
Designed For
- An overloaded existing A²/O plant — effluent quality was unstable.
- Effluent standard upgrade — Class 1B → Class 1A (GB 18918-2002).
- Capacity expansion — 10,000 m³/day → 30,000 m³/day.
- No plant shutdown — treatment continued during the retrofit.
- Reuse of existing structures — membrane modules added to the original aerobic tank, and the original secondary clarifier converted to a sludge thickener.
Project Background
The plant originally used a conventional A²/O process with a design capacity of 10,000 m³/day, with effluent required to meet Class 1B of GB 18918-2002. As the urban area expanded and the population grew, actual inflow exceeded the design capacity for a sustained period, and overloaded operation made effluent quality unstable. The competent authority required the plant to upgrade its effluent to Class 1A and to expand to 30,000 m³/day.
Choosing the Upgrade Option
Our engineering team carried out a technical assessment jointly with the local design institute, comparing two options:
- Option A: new A²/O biological tanks (adding 20,000 m³/day of capacity) + sand filtration and disinfection as tertiary treatment (for the full 30,000 m³/day).
- Option B: MBR retrofit of the existing 10,000 m³/day system (membrane modules installed in the original aerobic tank) + a new 20,000 m³/day A/O-MBR system + UV disinfection.
Following a techno-economic comparison, Option B was preferable to Option A in effluent stability, footprint and long-term operating cost, so Option B was adopted.
Engineering Design
Retrofit (existing 10,000 m³/day)
- Original aerobic tank retrofitted with submerged MBR membrane modules (PVDF membrane).
- Original secondary clarifier converted for use as a sludge thickener.
- New permeate pump station and membrane cleaning system.
- New associated UV disinfection units (3 in parallel).
Expansion (new 20,000 m³/day)
- New coarse screen + fine screen (rotary, 3 mm bar spacing) + vortex grit chamber.
- New A/O biological tank (anoxic zone HRT 3 h + aerobic zone HRT 8 h).
- New MBR membrane tank (PVDF membrane, design flux 20 LMH).
- New sludge thickener + screw-stack sludge dewatering machines (3 units).
Design Effluent Targets (Class 1A)
| Parameter | Design effluent target (Class 1A) |
|---|---|
| COD (mg/L) | ≤ 50 |
| BOD₅ (mg/L) | ≤ 10 |
| SS (mg/L) | ≤ 10 |
| Ammonia nitrogen (mg/L) | ≤ 5 |
| Total phosphorus (mg/L) | ≤ 0.5 |
Construction and Commissioning Notes
The project followed a no-shutdown retrofit strategy: the new 20,000 m³/day expansion system was completed and commissioned first; once it had taken over the entire inflow, the existing system was taken out of service for its MBR retrofit, and after the retrofit the plant went into full operation. The main issue during commissioning was that membrane flux in the new MBR system fell short of the design value. Investigation traced the cause to uneven air distribution in the aeration system, which raised the local transmembrane pressure (TMP) across the membrane fibres; replacing some of the diffusers and adjusting the aeration rate resolved the problem.
For Similar Projects
- For an expansion-and-upgrade project, compare both approaches — "new conventional biological treatment + tertiary treatment" and "MBR retrofit" — weighing effluent stability, footprint and long-term operating cost together.
- Where the retrofit must be carried out without a plant shutdown, build the new system first and let it take the entire inflow, then shut down and retrofit the existing system.
- Installing membrane modules in the original aerobic tank and converting the original secondary clarifier to a sludge thickener makes use of existing structures; verify the structural condition and dimensions of the existing tanks before implementation.
- If membrane flux falls short during MBR commissioning, first check whether aeration is evenly distributed and whether local transmembrane pressure (TMP) is high.
Frequently Asked Questions
Why choose an MBR retrofit for a municipal wastewater treatment plant expansion and upgrade?
This project compared two options: new A²/O biological tanks with sand filtration and disinfection (Option A), and an MBR retrofit of the existing system plus a new A/O-MBR system (Option B). Following a techno-economic comparison, Option B was preferable in effluent stability, footprint and long-term operating cost, and was therefore adopted.
How can a wastewater treatment plant stay in operation during a retrofit?
On this project, the new 20,000 m³/day expansion system was completed and commissioned first and took over the entire inflow; the existing system was then taken out of service for its MBR retrofit.
How do you troubleshoot MBR membrane flux that falls short of the design value?
First check whether the aeration system is distributing air evenly and whether local transmembrane pressure (TMP) across the membrane fibres is high. On this project, the shortfall in the new MBR system during commissioning was caused by uneven air distribution and was resolved by replacing some of the diffusers and adjusting the aeration rate (see "Construction and Commissioning Notes" above).
