PAC 31% Textile Dyeing Wastewater Treatment — Case Study at Nhơn Trạch IP Factory | Lộc Thiên Chemicals
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PAC 31% Textile Dyeing Wastewater Treatment — Case Study at Nhơn Trạch IP Factory
TL;DR: A textile dyeing factory at Nhơn Trạch Industrial Park (Đồng Nai) uses PAC 31% from Lộc Thiên at 150 mg/L to treat wastewater containing Reactive Blue dye, reducing Color from 450 to 36 Pt-Co (92% efficiency), COD 780→215 mg/L. Compared to alum, PAC 31% produces more stable flocs, a pH working window twice as wide, and 33% lower operating costs. ZDHC MRSL v3.1 compliant.
Factory Background
A textile dyeing factory at Nhơn Trạch Industrial Park (Đồng Nai) with 2,000 m³/day capacity, specializing in woven fabric dyeing using reactive dyes — primarily blue shades (Reactive Blue 19, 21) and dark colors. Reactive dyes are the most difficult group to treat with conventional coagulation because their anthraquinone backbone and sulfonate groups carry high negative charge, are fully water-soluble, with molecular weights of 600–1,400 Da.
The factory is a processing satellite for EU fashion brands — requiring stringent waste control and periodic ZDHC audits. The wastewater contains Reactive Blue 19 (an anthraquinone-based reactive blue dye with vinyl sulfone group) — one of the most difficult dyes to treat: stable ring structure, not biodegradable under conventional aerobic conditions, persistent color.
Before this case study, the factory used alum (Al₂(SO₄)₃·14H₂O) at 300 mg/L, achieving only 55–65% color removal efficiency, post-sedimentation color of 150–200 Pt-Co, unstable, frequently exceeding the 150 Pt-Co limit of QCVN 13-MT:2015/BTNMT column B. During dark blue dye batches, outlet color reached 200–250 Pt-Co — requiring dilution or retreatment.
Jar-test was conducted with PAC 31% from Lộc Thiên to replace alum, supervised by QC Technician Võ Thị Như Hòa.
Influent Wastewater Characteristics
| Parameter | Average Value | QCVN 13 Column B |
|---|---|---|
| pH | 9.0 ± 0.4 | 5.5–9 |
| COD (mg/L) | 780 ± 85 | 200 |
| Color (Pt-Co) | 450 ± 60 | 150 |
| TSS (mg/L) | 240 ± 45 | 100 |
| BOD₅ (mg/L) | 280 | 50 |
| Alkalinity (mg CaCO₃/L) | 520 | — |
| Cl⁻ (mg/L) | 680 | — |
| Conductivity (μS/cm) | 2,850 | — |
The wastewater exhibits a deep blue color characteristic of Reactive Blue 19 — spectral absorption at 596 nm, high color intensity even at low concentrations (450 Pt-Co equivalent to ~8–12 mg/L dye).
Jar-test: PAC 31% vs Alum
Jar-test was conducted at the Lộc Thiên laboratory under the supervision of QC Technician Võ Thị Như Hòa, with fixed parameters: rapid mix 200 rpm/2 min, slow mix 40 rpm/15 min, settling 30 min, room temperature 30°C. Each 500 mL sample of actual Nhơn Trạch wastewater, three replicates.
Detailed jar-test procedure:
- Measure pH and color of raw wastewater
- Adjust each beaker pH to target value using HCl 5%
- Dose coagulant according to test schedule (5% stock solution for PAC, 2% for alum)
- Rapid mix 200 rpm for 2 minutes
- Dose polymer PAM 0.1% concentration
- Slow mix 40 rpm for 15 minutes
- Settle 30 minutes — measure pH, COD, color of supernatant
Jar-test Results
| Coagulant Type | Dose (mg/L) | Optimal pH | Color After (Pt-Co) | Color Removal (%) | COD After (mg/L) | COD Removal (%) |
|---|---|---|---|---|---|---|
| Alum | 300 | 7.0 | 168 | 62.7 | 395 | 49.4 |
| Alum | 350 | 7.0 | 145 | 67.8 | 370 | 52.6 |
| Alum | 400 | 6.8 | 132 | 70.7 | 348 | 55.4 |
| PAC 31% | 100 | 6.5 | 95 | 78.9 | 310 | 60.3 |
| PAC 31% | 150 | 6.5 | 36 | 92.0 | 215 | 72.4 |
| PAC 31% | 200 | 6.5 | 42 | 90.7 | 225 | 71.2 |
| PAC 31% | 250 | 6.3 | 55 | 87.8 | 260 | 66.7 |
PAC 31% at 150 mg/L achieved 92% color removal and 72.4% COD removal — far superior to alum across all dose ranges. Critically: PAC at 150 mg/L gave post-treatment color of 36 Pt-Co, over 4 times lower than alum at 400 mg/L (132 Pt-Co). PAC flocs appeared after 3 minutes, fully settled after 20 minutes — while alum flocs took 6 minutes to appear.
Solution: Switch to PAC 31%
After jar-test, the factory switched from alum to PAC 31% Lộc Thiên (lot code PAC-2426-NT, COA certified by QC Technician Phan Cẩm Thủy). Official operating parameters:
- Coagulant: PAC 31% (Al₂O₃ basis ≥ 31%, basicity 72%), clear liquid form
- Dose rate: 150 mg/L commercial product
- Coagulation pH: 6.0–6.8 (adjust from pH 9.0 using HCl 32% in equalization tank before coagulation)
- Settling aid polymer: Anionic PAM 1.2 mg/L
- Settling time: 40 minutes
- Plant capacity: 2,000 m³/day
- Equipment: Existing dosing pumps retained, flow rate recalibrated only
60-Day Operating Results
Color
- Before (alum 300 mg/L): 450 → 180 Pt-Co (60% efficiency)
- After (PAC 31% 150 mg/L): 450 → 36 Pt-Co (92% efficiency)
- QCVN 13 Column B limit: 150 Pt-Co → met from day one of conversion
Color variation over 60 days:
| Week | Inlet Color | Color After PAC | Efficiency |
|---|---|---|---|
| 1 | 420–480 | 30–45 | 90–93% |
| 2 | 390–460 | 28–40 | 91–93% |
| 3 | 410–500 | 32–48 | 90–92% |
| 4 | 440–490 | 35–42 | 91–92% |
| 5–8 | 380–510 | 30–50 | 90–94% |
Outlet color remained consistently below 50 Pt-Co throughout the 60 days, with no abnormalities when switching between Reactive Blue 19 and 21 dye lots. PAC flocs remained stable across inlet color amplitude from 380 to 510 Pt-Co — no dose adjustment needed, unlike alum which required 25% dose increase when color exceeded 450.
COD
- Inlet COD: 780 mg/L
- COD after PAC 31%: 215 mg/L (72.4% efficiency)
- COD after biological treatment: 88–110 mg/L (meeting QCVN 13 Column A)
Compared to alum which achieved only 370–395 mg/L COD after coagulation, biological effluent COD of 150–180 mg/L — frequently exceeding Column A (100 mg/L) and occasionally Column B (200 mg/L) during peak production.
Sludge
- Chemical sludge volume: 8.2 m³/day (22% reduction from 10.5 m³/day with alum)
- PAC flocs are denser, solids content 3.2% vs 2.1% with alum → reduced sludge pressing costs
- Sludge pH 6.0–6.8 — easier to handle compared to alum sludge pH 5.5–6.0 (corrosive to press equipment)
- Reduced sludge volume extended sludge removal cycle from 3 days to 4 days
Operating Costs
| Item | Alum (300 mg/L) | PAC 31% (150 mg/L) | Difference |
|---|---|---|---|
| Unit price (VND/kg) | 4,800 | 6,200 | +29% (higher price) |
| Dose (mg/L) | 300 | 150 | –50% |
| Coagulation cost (VND/m³) | 1,440 | 930 | –35% |
| Polymer PAM (VND/m³) | 180 | 120 | –33% |
| HCl 32% (VND/m³) | 220 | 180 | –18% |
| Sludge treatment (VND/m³) | 520 | 350 | –33% |
| Total (VND/m³) | 2,360 | 1,580 | –33% |
Average savings of 780 VND/m³ × 2,000 m³/day × 300 days/year ≈ 468 million VND/year, together with effluent color exceeding standards — eliminating discharge violation penalties.
Detailed Comparison: PAC 31% vs Alum for Textile Dyeing Color
Reactive Dye Color Removal Capability
PAC 31% contains pre-hydrolyzed aluminum polymers (Al₁₃O₄(OH)₂₄⁷⁺) with an inherent high +7 positive charge, immediately neutralizing the sulfonate groups (–SO₃⁻) of reactive dyes. Alum requires time for hydrolysis to form Al(OH)₂⁺ and Al(OH)²⁺ — a pH- and temperature-dependent process taking 5–10 minutes to reach equilibrium.
Result: PAC achieves 90–95% color removal efficiency vs 55–70% for alum on the same reactive dye wastewater. Particularly effective with Reactive Blue 19 — the anthraquinone group with vinyl sulfone that is difficult to coagulate.
Working pH Window
- Alum: optimal pH 6.5–7.5 — narrow, easily disrupted if inlet pH fluctuates
- PAC 31%: optimal pH 6.0–8.5 — twice as wide, less sensitive to production pH variations
The Nhơn Trạch IP factory recorded wastewater pH varying from 8.2–9.6 per dyeing batch. With alum, more HCl was needed to bring pH to 7.0 ± 0.3 — inconsistent, with a 0.5 pH deviation causing 10% color removal reduction. With PAC, only adjustment to 6.5 ± 0.5 was needed for stable operation.
Sludge Volume
Alum produces porous, light flocs with 22% more sludge volume than PAC. PAC sludge is denser because Al₁₃ polymers are already in precipitated form, not requiring floc formation from free Al³⁺ ions. This is critical for factories with limited sludge holding capacity and pressing costs.
Operating Temperature
Textile dyeing wastewater from dyeing and washing processes ranges from 35–45°C. PAC 31% shows no reduction in coagulation efficiency in this range; alum begins to lose efficiency above 38°C because Al³⁺ hydrolysis to Al(OH)₃ is incomplete at high temperatures.
COA PAC 31% Lot PAC-2426-NT
| Parameter | Method | Result | Requirement |
|---|---|---|---|
| Al₂O₃, % by weight | TCVN 5886:2014 | 31.8 | ≥ 31 |
| Basicity, % | TCVN 5886:2014 | 72 | 65–85 |
| pH of 10% solution | TCVN 5886:2014 | 4.2 | 3.5–5.0 |
| Specific Gravity (20°C), g/mL | TCVN 2693:2012 | 1.38 | 1.35–1.42 |
| Insoluble residue, % | TCVN 5886:2014 | 0.02 | ≤ 0.1 |
| Cl⁻, % by weight | TCVN 5886:2014 | 8.5 | — |
COA for lot PAC-2426-NT issued from Đồng Nai warehouse, stamped by QC Technician Phan Cẩm Thủy. This lot has 72% basicity — ideal for textile dyeing wastewater treatment as it reduces the required HCl dose.
ZDHC MRSL v3.1 — PAC 31% Lộc Thiên
PAC 31% Lộc Thiên has been tested and meets ZDHC MRSL Version 3.1 — free of 14 banned chemical groups: APEO, chlorobenzenes, chlorophenols, CMR, organochlorine solvents, heavy metals (Cd, Pb, Hg, Cr(VI)), PFC, phthalates. Certification meets audit requirements of Nike, Adidas, Zara, H&M, Puma, Decathlon.
PAC 31% Storage Guidelines
PAC 31% liquid is stored in HDPE or composite tanks, protected from direct sunlight. Storage temperature 5–40°C — do not allow freezing. Shelf life 12 months. If white Al(OH)₃ precipitate appears at the tank bottom, circulate before use.
Summary
PAC 31% Lộc Thiên is the optimal coagulation solution for textile dyeing wastewater containing reactive dyes, particularly blue shades (Reactive Blue 19/21). At 150 mg/L dosage, it achieves 92% color removal and 72.4% COD removal — superior to alum across all metrics. The wide pH window of 6.0–8.5 ensures stable operation despite production variations, dense flocs reduce sludge by 22%, and total costs are 33% lower despite higher unit price. This is a strategic choice for FDI factories exporting to EU/USA requiring ZDHC certification.
Frequently Asked Questions
Why does PAC remove reactive dye color better than alum?
PAC exists as pre-hydrolyzed aluminum polymers (Al₁₃) — carrying an inherent high +7 positive charge, immediately neutralizing the sulfonate groups of reactive dyes. Alum must hydrolyze stepwise from Al³⁺ to Al(OH)₂⁺ then Al(OH)²⁺, slow and pH-dependent. With Reactive Blue 19, PAC achieves 92% efficiency vs only 62% for alum.
Does PAC 31% require settling aid polymer?
Anionic PAM at 1–2 mg/L is recommended to increase floc size and settling rate. In the Nhơn Trạch case, PAC 150 mg/L + PAM 1.2 mg/L gave optimal results. Without PAM, PAC flocs still settle but 15–20 minutes slower.
Does a factory currently using alum need to replace equipment?
No. Same injection point, same dosing pumps. Only pump recalibration and jar-test are needed — Lộc Thiên provides free jar-test support during conversion. Conversion time: 5–7 days including jar-test and trial operation.
Which dye colors can PAC 31% treat?
Most effective with reactive, direct, and vat dyes. Less effective with acid dyes on nylon and disperse dyes on polyester. For acid and disperse dyes, combination with FeCl2 or FeSO4 improves efficiency.
Does PAC 31% Lộc Thiên have COA meeting ZDHC?
Yes. PAC 31% meets ZDHC MRSL v3.1 (TÜV Rheinland). Request a copy of the certificate plus per-lot COA/MSDS.
Contact for PAC 31% Quote
🛒 Need PAC 31% for textile dyeing WWTP? Request a quote for PAC 31% — Lot-wise COA/MSDS, nationwide Industrial Park delivery, free jar-test support. Hotline 0979 891 929 — QC Technicians Phan Cẩm Thủy & Võ Thị Như Hòa provide technical consultation.