1. Treatability and reaction kinetics of a reactive textile dye-bath effluent, RTDE
Thole1*, A.; Ikhu-Omoregbe1 D.I.O; Narsingh1, U and Thamae2, M.
1 Cape Peninsula University of Technology, Chemical Engineering Depart, Symphony Way, Bellville, 7535 CAPE TOWN.
2Durban university of Technology, school of Education, 15 JF Sithole Rd, Imbali, 3201, PETERMARITZBURG
3Corresponding author:
Tel: Fax
INTRODUCTION
There are concerns about the eminent collapse of textile dyeing and finishing (TDF) industry with dire negative consequences, resulting in the loss of thousands of skilled and semi-skilled jobs. A major contribution to the production costs is the fact that, most TDF fail to meet effluent discharge limits and are subsequently charged for colour, COD and conductivity levels violations by Water Services Authorities (WSA). TDF can become more economically viable by treating its effluent for reuse or at least for safe discharge. There has been intensive research on textile effluent treatments including electrocoagulation technology (ECT). However, textile effluents (TE) pollutants are complex, due to dyeing procedures and chemicals that are used. In most research, TE are created by mixing dyes with auxiliary chemicals, followed by several dilutions without actual dyeing.
In this work, textile dyeing was carried out by using sample dyeing machines so as to create all the dyeing steps resulting in a Simulated Textile Effluent (STE). STE was then treated with six iron electrodes electrocoagulation. ECT is becoming a preferred industrial effluent treatment technology for removal of colour, turbidity, COD and heavy metals. However, there is a lack of focus on reaction kinetics studies. The aim of this research was to study the treatability of RTDE by iron electrocoagulation (IEC) with an intention to evaluate its reaction kinetics.
Figure 1.0 Pre-bleaching and dyeing Block flow diagram
Table 1 BLEACHING
Stock %
Ratios (g/L)
Amount (g)
Antifoam (mL/L)
100
0.20
0.2
Wetting agent (mL/L)
1.00
1.0
Sequestering agent (g/L), EDTA
Caustic Flakes (NaOH) (pH = 12) g/L
4.00
4.0
50% Hydrogen Peroxide (mL/L) 50
5.00
10.0
Acetic Acid 99
1.01
RESULTS
Dye colour removal by absorbency and true colour measurements were about 97% and 90% respectively. Turbidity and TSS might have been affected by residual iron but 63% and 66% removal were achieved respectively immediately after treatment. 97%, 95% and 82% of chlorides, free chlorine and total chlorine respectively were removed from the textile effluents. Dye colour removal by absorbency and COD reaction kinetics follow pseudo first order models as shown in figure 2. Although reactions were carried over an hour, 60 to 80% removal of most pollutants were achieved in 30 minutes.
Table 2 REACTIVE DYEING
% Conc. Stock
Ratios
g/L
Amount
g or(ml)
Antiform (g/L)
100
0.2
0.0
Wetting agent, (g/L)
1.0
Lubricant (anti-crease) (x%)
2.0
Levelling agent (Rucotex T-Z)1.0 ml/L
NaCl(g/L) (5-80)
70.0
Combinations (NaOH and Na2CO3)
50% NaOH (ml/L) 50
Na2CO4 (g/L)
3.0
1% Brilliant Red 3BS (150%), Remazol
150
0.67
3% Brilliant Blue E-FFN,(150%) Levafix)
1.0% Yellow
METHODOLOGY
100 g of cotton material was pre-bleached and dyed at 20:1 liquor ratios. Chemical compositions are shown in tables 1 to 4 while the block flow diagram in figure 2 shows the full dyeing cycle. Triplicates of 3.5 L of simulated textile effluents were treated by six monopolar stainless steel electrodes electrolysis with 5A and 16 volts power supply at 25oC over one hour at pH Sampling was done every 5 minutes for turbidity, total dissolved solids (TDS), total suspended solids (TSS), conductivity (k), chlorine and iron analyses, COD, absorbency, true colour and chlorides. Most of these parameters were analysed by HACH DR2800 spectrophotometer; turbidity by HANNA HI and HACH 2100 and pH, conductivity, k and resistivity, W by HANNA HI 4522 pH multimeter.
Table 3. SOAPING OFF
Stock %
Ratios (g/L)
Amount
g or(ml)
Detergent (NP9) g/L
100 2
2.0
Antifoam (g/L) 1
1.0
Acetic Acid (g/L)
2.5
Sequestrate (EDTA) (g/L)
Figure 2.0 Pseudo first order reaction models
CONCLUSIONS
Reactive textile effluents are treatable with iron electrode electrocoagulation. Reaction kinetics studies with respect to COD and colour removal follow pseudo first order. The final effluent can be discharged within safe environmental limit or further treated for reuse.
ACKNOWLEDGMENTS
The authors acknowledge the financial support from the CPUT’s, University Research Fund and the Department of Chemical Engineering. CPUT,s Chemistry Department and Textile Station for their facilities Dystar SA for providing dye samples.
Table 4. SOFTENING
Conc. (%)
ratios
(g)
Softener
100
2.0