Status: Delivered · Region: East China · Ref. D-044
What We Delivered
The client is the central wastewater treatment plant of a chemical industrial park in East China; the park is made up mainly of fine-chemical, pesticide-intermediate and dyestuff manufacturers. The client's name is withheld under our client-confidentiality policy. Design capacity is about 1,000 m³/day, and the plant is in operation.
Working from detailed water-quality analysis and bench-scale tests, our engineering team completed the design and commissioning of a multi-stage combined process for the plant; equipment supply was per contract scope. The delivered process is Fenton pretreatment + UASB anaerobic reactor + A/O + activated carbon adsorption + ozone advanced oxidation (full flow sheet under "Process Design" below), with the effluent designed to the quasi-Class IV standard (COD ≤ 30 mg/L, referencing surface-water Class IV).
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 | Influent water-quality analysis and bench-scale tests (key parameters under "Designed For" and in the water-quality table below); confirmation of the quasi-Class IV effluent target. | Water-quality analysis data, bench-test records, design basis sheet |
| 2. Process & mechanical design | The multi-stage "Fenton pretreatment + UASB + A/O + activated carbon adsorption + ozone advanced oxidation" process and the design parameters for each stage were fixed (Fenton pH 2.5–3.5, 60 min reaction; UASB HRT 24 h, 35 °C; A/O MLSS 4,000 mg/L, HRT 24 h; O₃ dose 20 mg/L). | Process flow diagram, P&ID, general-arrangement (GA) drawings, equipment list |
| 3. Manufacturing & quality control | Material inspection and in-process inspection of the equipment within contract scope. | Material quality certificates, in-process inspection records |
| 4. Factory acceptance test (FAT) | Pre-dispatch inspection and trial run of the equipment within contract scope, checked against the design parameters. | FAT record |
| 5. Packing & dispatch | Equipment within contract scope packed against the packing list and dispatched to site. | Packing list, dispatch list |
| 6. Installation | Carried out per contract scope. | Installation record |
| 7. Commissioning | Start-up and commissioning of each treatment unit; for UASB granular-sludge cultivation, see "Commissioning Notes" below. | Commissioning log |
| 8. Performance verification (against the design basis) | Continuous-operation verification against the design effluent targets (COD ≤ 30 mg/L, ammonia nitrogen ≤ 1.5 mg/L, volatile phenols ≤ 0.1 mg/L, colour (dilution factor) ≤ 30, among others). | Performance test record |
| 9. Training, handover & after-sales | Operating requirements handed over to the operators: Fenton chemical dosing and pH control, UASB granular sludge and alkalinity management, activated carbon replacement and ozone system operation, among others. | 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
- High strength — COD about 15,000 mg/L, ammonia nitrogen 450 mg/L, total nitrogen 600 mg/L.
- Poor biodegradability — BOD/COD about 0.15.
- Toxic and hazardous constituents — a range of refractory organics and benzene homologues (BTEX-type aromatics); volatile phenols about 45 mg/L.
- Wide swings in water quality — pH 4.5–9.0.
- High colour — dilution factor about 2,000.
- Effluent standard — quasi-Class IV (COD ≤ 30 mg/L).
Project Background
The park's wastewater treatment plant collects and treats the park's wastewater centrally, with a design capacity of about 1,000 m³/day. The incoming flow is typical high-strength, refractory, toxic and hazardous industrial wastewater.
The original process (physico-chemical + aerobic biological treatment) could not produce effluent meeting the quasi-Class IV (COD ≤ 30 mg/L) requirement.
Influent Quality and Design Effluent Targets
| Parameter | Influent (mean, design basis) | Design effluent target |
|---|---|---|
| COD | 15,000 mg/L | ≤ 30 mg/L |
| BOD₅ | 2,200 mg/L | ≤ 6 mg/L |
| BOD/COD | 0.15 (poorly biodegradable) | — |
| Ammonia nitrogen | 450 mg/L | ≤ 1.5 mg/L |
| Total nitrogen | 600 mg/L | ≤ 15 mg/L |
| Colour (dilution factor) | 2,000 | ≤ 30 |
| pH | 4.5–9.0 (wide fluctuation) | 6–9 |
| Volatile phenols | 45 mg/L | ≤ 0.1 mg/L |
Process Design
After detailed water-quality analysis and bench-scale tests, our engineering team designed a multi-stage combined process:
Screening → equalisation tank (pH adjustment) → Fenton pretreatment → coagulation and sedimentation → UASB anaerobic reactor → A/O tank → secondary clarifier → activated carbon adsorption → ozone advanced oxidation → filtration → disinfection → discharge (to the design effluent limits)
Unit Design Notes (Design Values)
- Fenton pretreatment — pH 2.5–3.5, reaction time 60 min. Fenton pretreatment followed by coagulation and sedimentation is designed to bring COD down from 15,000 mg/L to 3,000–4,000 mg/L and raise BOD/COD to 0.35 or above, improving biodegradability and preparing the flow for the downstream biological treatment.
- UASB anaerobic reactor — HRT 24 h, mesophilic operation (35 °C), design COD removal 60–70%; the biogas produced is recovered for its calorific value. Design anaerobic effluent COD is about 1,000–1,200 mg/L.
- A/O tank — MLSS 4,000 mg/L, HRT 24 h, providing aerobic degradation, nitrification and nitrogen removal; design effluent COD ≤ 150 mg/L.
- Activated carbon adsorption — adsorbs the remaining refractory organics; design effluent COD ≤ 60 mg/L.
- Ozone advanced oxidation — O₃ dose 20 mg/L, removing colour and further degrading organics; design effluent COD ≤ 30 mg/L, colour (dilution factor) ≤ 30.
Commissioning Notes
The main difficulty during commissioning was cultivating anaerobic granular sludge in the UASB. Because of the wastewater's relatively high toxicity, granular-sludge cultivation took 3 months (typically about 2 months), and start-up was completed by dosing a glucose feed for sludge acclimation and supplementing alkalinity.
For Similar Projects
- For mixed chemical-park wastewater with poor biodegradability (BOD/COD about 0.15 on this project), carry out detailed water-quality analysis and bench-scale tests first, then set the operating conditions for Fenton or other pretreatment.
- The Fenton stage runs under acidic (pH 2.5–3.5), strongly oxidising conditions; select materials for equipment and pipework with this duty in mind.
- In toxic wastewater, UASB granular-sludge cultivation can take longer than usual; allow for this in the commissioning programme and have alkalinity supplementation ready.
- Where the effluent must meet quasi-Class IV, advanced treatment is needed after the biological stage (on this project, activated carbon adsorption + ozone advanced oxidation); settle the route for colour removal and refractory COD removal at the design stage.
Frequently Asked Questions
Why does high-strength, refractory chemical wastewater need Fenton pretreatment first?
On this project the influent COD was about 15,000 mg/L with BOD/COD about 0.15, so the biological stage would struggle to run stably if fed directly. The design uses Fenton pretreatment (pH 2.5–3.5, 60 min reaction) plus coagulation and sedimentation to bring COD down to 3,000–4,000 mg/L and raise BOD/COD to 0.35 or above (design values), preparing the flow for the downstream UASB and A/O.
How long does UASB granular-sludge cultivation take on toxic chemical wastewater?
On this project, because of the wastewater's relatively high toxicity, granular-sludge cultivation took 3 months, longer than the typical figure of about 2 months (for the start-up method, see "Commissioning Notes" above).
What COD limit does quasi-Class IV effluent set, and how was this project designed to meet it?
The quasi-Class IV standard applied on this project requires COD ≤ 30 mg/L. The design places activated carbon adsorption (design effluent COD ≤ 60 mg/L) and ozone advanced oxidation (O₃ dose 20 mg/L, design effluent COD ≤ 30 mg/L, colour (dilution factor) ≤ 30) after the biological stage.
