SURVEY ON OCCUPATIONAL VAT DYEING IN KANO METROPOLIS, ITS ENVIRONMENTAL IMPACTS AND IMPROVEMENT ON THE DYEING PROCESSES USING DESIGN OF EXPERIMENT
SURVEY ON OCCUPATIONAL VAT DYEING IN KANO METROPOLIS, ITS ENVIRONMENTAL IMPACTS AND IMPROVEMENT ON THE DYEING PROCESSES USING DESIGN OF EXPERIMENT
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Date
2023-04
Authors
ABDULLAHI, Sani
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Abstract
Due to continuing decline of traditional indigo dyeing and availability of synthetic dyes, most occupational dyeing in Kano Metropolis today is done with vat dyes. The dyeing activities are scarcely documented to have an incline on who are the dyers and what they actually do. If dyeing/mercerizing wastewater is poorly managed, it may contaminate groundwater in the neighbourhood. If proper dyeing conditions are not employed, quality characteristics of the dyed material may be inferior. The aim of this study is to survey the occupational dyers, assess the environmental impacts of the dyeing activities, and improve on the dyeing processes. Baseline information was obtained using a structured questionnaire from 226 dyers selected by convenience sampling and the data was complimented with information from focus group discussions. It was found that majority of the dyers were male, of youthful age, natives, and educated. Their work experience ranged from 5 to 31 years (mean = 11.11± 5.01) where about one half of them earn more than the minimum wage of civil servants in the country. The dyers work as informal groups with synthetic vat dye, caustic soda, hydros, and woven fabrics (all imported from China). The dyers face numerous challenges which are rendering them jobless. Samples of caustic soda, hydros and dye powders were selected by purposive sampling from local markets and tested for heavy metals using Agilent 4210 MP-AES. Results show that the concentrations of heavy metals detected in caustic soda and hydros may not be of immediate environmental concern. Metal content of all the dyes investigated were found to be within ecological and toxicological association of dyers and organic pigment manufacturers (ETAD) heavy metal limits for dyes and are therefore safe to use. Effluent and groundwater samples were collected and characterized according to procedures described by American public health association (APHA). Based on the physico-chemical parameters and heavy metals investigated in dye effluent and groundwater samples, the former was found to be non-biodegradable while the latter was found to be unsuitable for drinking and irrigation. Occupational vat dyeing parameters were determined in selected dyehouses. Results showed that the dyers use an average of 21.43±3.46 g/l caustic soda and 18.99±2.05 g/l hydros which can be considered adequate based on previously reported vat dye formulations. An average temperature of 76±4 oC used by the dyers may aid in over-reduction of the dye. Mercerization experiment was carried out with different levels of input variables viz. temperature, time, caustic soda concentration, and fabric type and with shrinkage, tensile strength, and elongation as responses according to central composite design (CCD) by response surface methodology (RSM) using design expert® software version 7 (DX7) software. Multi response optimization of mercerization parameters were carried out using desirability function. The optimal conditions indicated mercerization using 250 g/l caustic soda at 85 oC for 3 min. Five sets of experiments conducted at the optimized conditions resulted in 6.9±0.4 and 9.7±3.6 % average shrinkage, respectively, for blend and cotton fabrics. The elongation of blend and cotton fabrics were 51.6 and 120.85 % higher than those of the original untreated samples. Dyeing experiment was carried out at 60 oC for 10 min. in a liquor ratio of 100:1 with different levels of input variables viz. caustic soda and hydros concentration, fabric type, and dyeing methods and with appearance rating (levelness) as the response. Optimization of dyeing parameters indicated that the use of 10g/l caustic soda and 20 g/l hydros is more desirable. Under the same dyeing conditions, the dry dyeing method was found to be the best for cotton fabric with an appearance rating of more than 98.8 %. It is suggested for the mercerized samples to be washed before wet-on-wet dyeing to avoid unlevelness. All finished fabrics (dyed and beaten locally) were found to have inferior strength compared to untreated and unmercerized samples. It is suggested for the finishing (beating) operation to be avoided. Fastness ratings of samples from the dyeing experiments are much better than those obtained from the occupational dyers. Soaping of dyed samples is suggested for improved fastness properties.
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A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN COLOUR CHEMISTRY AND TECHNOLOGY
DEPARTMENT OF POLYMER AND TEXTILE ENGINEERING,
FACULTY OF ENGINEERING,
AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA