Reducing water and energy consumption in sustainable cotton dyeing using a low liquor ratio process

The textile dyeing industry consumes vast amounts of freshwater and toxic chemicals annually, resulting in high energy usage, increased costs, and severe environmental pollution. Reducing water and energy consumption during dyeing is crucial for sustainable production. This study examines the dyeing quality, ecological impacts, and energy consumption of low-liquor-ratio (LLR) reactive dyeing on cotton fabrics, utilizing varying liquor ratios. Experiments were conducted using liquor ratios of 1:3, 1:4, 1:6, 1:8, and 1:10 for light, medium, and dark shades, which were lower than those typically used in previous studies. Dyeing quality was assessed using reflectance and the K/S curve, while energy consumption was measured from thermal changes. Also, effluent was analyzed for Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Dissolved Solids (TDS), and pH. Results showed that LLR dyeing has lower energy consumption, with the 1:3 liquor ratio using the minimal energy, from 2.5 to 3.7 KJ, across all shades, which is approximately 34–38% less energy compared to the 1:10 liquor ratio. So, energy consumption was found to be directly proportional to the liquor ratio. Although the LLR generated less effluent with higher effluent concentrations, especially in BOD and COD values in dark shades (3.58% weight of fabric), in medium shade (1.754% weight of fabric) dyeing exhibited a more consistent quality, with slight variations across liquor ratios. In LLR, BOD and COD values at a 1:3 liquor ratio were approximately 42–55% higher than the values of a 1:10 liquor ratio. However, LLR dyeing entails environmental trade-offs due to concentrated effluents, especially with darker shades. So, optimizing LLR dyeing at 1:3 ratios can be used for light to medium shades for achieving sustainable dyeing with acceptable effluent management. Also, for sustainable practices, careful management of dyeing darker shades is essential to mitigate their environmental impact.