How to Use Textile Wastewater Decolorant in Water Treatment

Overview

Textile Wastewater Decolorant (dicyandiamide-formaldehyde polycondensate, CAS 55295-98-2) is a high-charge-density cationic polymer specifically engineered for the challenging color loads found in reactive dye and direct dye wastewater. Reactive dyes are the most common source of color in cotton dyeing and are notoriously difficult to remove by conventional coagulation alone because their sulfonate groups impart strong negative charges that resist inorganic coagulants at typical doses.

This decolorant works through a combined coagulation-decoloration mechanism: (1) its high cationic charge density rapidly neutralizes anionic dye molecules, and (2) the polycondensate backbone adsorbs and bridges dye fragments into settleable micro-flocs. The result is > 95% decolorization for reactive dyes at the correct dose and pH, along with 30–50% COD reduction. The liquid form (pH 3.0–6.0, density 1.15–1.25 g/mL, active content 45–55%) allows direct metered dosing without a dissolution step, reducing operational complexity.

This product is effective across a wide pH range of 4–10, giving operators flexibility when treating wastewater with variable pH from batch dyeing processes.

Preparation & Dissolution

This decolorant is a ready-to-use liquid. No dissolution or dilution is strictly required, but the following practice is recommended:

1. Pre-dilution: For small or manual-dosing systems, dilute to 10–20% concentration with clean water to achieve more precise volumetric control.
2. Temperature: Store and handle at 5–40 °C. Freezing causes precipitation and loss of activity. High temperatures (> 50 °C) accelerate decomposition.
3. Dosing equipment: Use HDPE or PVC metering pumps, pipes, and tanks. Stainless steel 316L is acceptable. Avoid carbon steel and aluminum.
4. Blending sequence: For combined treatment, add this decolorant before inorganic coagulant (PAC/FeCl₃). The pre-treatment decolorant step reduces coagulant demand significantly.

Dosing Guide

Application	Typical Dose (mg/L)	pH Range	Reaction Time	Notes
Reactive dye wastewater	150–350	4.0–9.0	5–10 min	>95% color removal achievable
Direct dye wastewater	100–250	4.0–10.0	5–10 min	Lower dose than reactive dyes
Disperse dye wastewater	200–400	5.0–8.0	10–15 min	Less effective; combine with PAC
Mixed textile effluent	150–300	5.0–9.0	10–15 min	Jar test needed to optimize
Printing wastewater	200–400	5.0–9.0	5–10 min	High color load; may require two-stage dosing
Paper mill colored water	100–200	5.0–8.0	5–8 min	Combine with PAC for turbidity removal

Jar test is mandatory before scale-up. Doses above are for liquid product at 45–55% active content.

Application Procedure

1. Sample the incoming wastewater and measure color (ADMI or Pt-Co), COD, TSS, and pH. Note the dominant dye class from the dyeing schedule.
2. Conduct a jar test at 5 dose levels spanning 100–400 mg/L. Test at both current wastewater pH and at optimized pH (adjusted with H₂SO₄ or NaOH to target range).
3. Select the optimal dose — the minimum dose achieving ≥90% color removal with well-formed, rapidly settling flocs.
4. pH adjustment (if needed): For very alkaline wastewater (pH > 10), pre-acidify with dilute H₂SO₄ to pH 7–9 before decolorant addition.
5. Dose the decolorant via metering pump into the flash mix chamber or the inlet of the equalization tank with vigorous mixing.
6. Rapid mix at 150–250 rpm for 2–5 minutes to ensure complete charge neutralization.
7. Add inorganic coagulant (PAC 30–60 mg/L) after the decolorant if a combined program is used. This removes colloidal turbidity that the organic decolorant does not address.
8. Slow mix at 30–50 rpm for 15–20 minutes to build larger, denser flocs.
9. Add low-dose anionic PAM (0.5–1.5 mg/L) in the final slow-mix stage to aid settling.
10. Clarify by sedimentation (30–60 min) or dissolved air flotation. Monitor supernatant color and COD.

Monitoring & Control

Parameter	Frequency	Target	Method
Effluent color (ADMI or Pt-Co)	Every 2 hours	≤ 50 ADMI or discharge limit	Colorimetry / spectrophotometer
Effluent COD	Daily	Discharge limit	Lab or online COD analyzer
Inlet pH	Continuous	4.0–9.0 (adjust if outside)	Online pH meter
Sludge blanket depth	Every 4 hours	< 50% of clarifier depth	Sludge blanket detector
Decolorant pump flow rate	Per shift	Set-point flow rate	Peristaltic pump counter
Effluent TSS	Daily	< 30 mg/L (typical)	Gravimetric

Common Mistakes

• Underdosing reactive dyes: Reactive dyes have a high charge density; insufficient decolorant leaves anionic dye molecules in solution, giving incomplete color removal even if flocs look acceptable. Always verify with spectrophotometer, not visual inspection alone.
• Adding decolorant after inorganic coagulant: The correct sequence is decolorant first, then PAC/FeCl₃. Reversing the order leads to competitive reaction between the coagulant and dye, requiring higher doses of both.
• Ignoring COD measurement: This product also removes COD by adsorption. Operators who only monitor color may not realize they are exceeding or under-optimizing COD removal, leading to non-compliance or over-use of chemical.
• Not accounting for batch variability: Textile plants often run multiple dye baths per day with different dye classes and concentrations. A fixed dose may work for one batch but over- or under-dose the next. Use flow-proportional dosing with periodic manual jar-test verification.
• Neglecting sludge dewatering: The sludge from dicyandiamide-type decolorants contains dye complexes and can have poor filterability. Pre-condition with cationic PAM before pressing to avoid blinding filter cloths.

Storage & Handling

• Store at 5–40 °C in a dry, shaded warehouse. Do not stack drums more than 3 high.
• Shelf life: 12 months from production date in sealed original drums.
• The product contains formaldehyde trace levels — handle in well-ventilated areas and wear appropriate PPE (gloves, safety glasses, respiratory protection in confined spaces).
• SDS (Safety Data Sheet) should be reviewed before first use.
• Spills should be diluted with water and collected into a holding tank for treatment. Do not discharge concentrated product to drains or water bodies.
• Keep away from strong alkalis (pH > 11) in storage, which can degrade the polycondensate.