Abstract
The presented study assesses the efficiency of selected adsorbents, zeolite 4A in two particle sizes and pelletized activated carbon (AC), for the potential removal of color, chemical oxygen demand (COD), total organic carbon (TOC) and metals from wastewaters after natural wool dyeing. Firstly, the natural coloring compounds were extracted from dried common walnut (Juglans regia) leaves and used further for exhaustion dyeing of wool fibers, together with three different metallic salts in two concentrations (meta-mordanting). Effluents with higher mordant concentration were additionally treated according to a shake-flask adsorption experiment. The obtained results revealed efficient removal of exceeded metallic ions by zeolite (up to 94.7%), on account of their superior ion exchange capability as compared to AC. The zeolites also reduced turbidity and electrical conductivity significantly. On the other hand, AC was more efficient for the reduction in organic pollution, COD up to 96% and TOC up to 95%, due to its higher specific surface area and total pore volume, and, thus, higher potential for adsorption of different compounds in comparison to 4A. All three proposed adsorbents lowered wastewaters’ coloration remarkably, up to 78% (AC) and up to 71% (4A), depending on the type of effluent/mordant and inspected wavelength; although, the spectral absorbance coefficient (SAC) values remained highly above the limit values for discharge of wastewaters into watercourses.
Highlights
Over the past decade, there has been a growing demand for eco-friendlier, non-toxic coloring compounds, with fewer negative effects on the organism, especially for healthsensitive applications such as the coloration of food, drugs and cosmetics, and dyeing of textiles for children [1]
The natural coloring compounds were extracted from dried common walnut (Juglans regia) leaves and used further for exhaustion dyeing of wool fibers, together with three different metallic salts in two concentrations
activated carbon (AC) was more efficient for the reduction in organic pollution, chemical oxygen demand (COD) up to 96% and total organic carbon (TOC) up to 95%, due to its higher specific surface area and total pore volume, and, higher potential for adsorption of different compounds in comparison to 4A
Summary
There has been a growing demand for eco-friendlier, non-toxic coloring compounds, with fewer negative effects on the organism, especially for healthsensitive applications such as the coloration of food, drugs and cosmetics, and dyeing of textiles for children [1]. With the aim to increase the color depth and fastness properties, different metal mordants are usually employed, such as copper, chromium, tin, zinc and aluminum salts, leading to the disposal of unfixed toxic metals into the environment after dyeing [7]. The addition of chemicals (acid or base) is inevitable during natural dyeing of protein- or cellulose-based textiles, influencing the pH of the effluent. Such kinds of wastewaters, when produced to a large extent, need to be handled properly before discharge into the environment
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