Recovery of a synthetic dye through adsorption using malt bagasse, a by-product of brewing industry: Study in batch and continuous systems

Reactive dyes are widely used in the textile industry and are known for their toxic and recalcitrant characteristic due to the N=N group and the complex aromatic structure. Improper disposal of such compounds in water bodies were linked to respiratory impairments in aquatic animals, photosynthesis reduction in plants, and carcinogenic properties in humans. In addition to the environmental concern, reactive dyes are valuable resources that could be recovered from textile wastewater by means of adsorption. On the other hand, the brewing industry generates about 20 kg of malt bagasse for every 100 L of produced beer. Therefore, this manuscript reports the adsorption of yellow Reafix-B8G (YR-B8G), a synthetic reactive dye, using malt bagasse in batch and continuous systems, aligning the conversion of a by-product of brewing industry into a valuable resource and the resource recovery of synthetic dye, supporting the circular economy. Malt bagasse with minimal processing, i.e., biomass dried at 303 K upon delivery from brewery industry, was effective for adsorption of YR-B8G in acidic pH. The possible adsorption mechanism of YB-B8G on malt bagasse is adsorption in the binding sites of the hydroxyl groups of adsorbent with physisorption was the main interaction. The malt bagasse was characterized as a lignocellulosic material with fibrous structure and low specific area (60.35 m(2) g(-1)). Even though the malt bagasse has low surface area, it is a waste material used without minimal processing and does not require chemical activation or further costly treatments to achieve adsorption capacity of 164.34 mg g(-1) for YB-B8G. Dye recovery from malt bagasse was best achieved using 50 % (v/v) ethyl alcohol as desorption solution with similar to 94 % of dye recovery. Adsorption in continuous system presented removal capacity superior to the batch removal, with the breakthrough curves strongly affected by the operating conditions. Malt bagasse has potential to be applied as part of the removal and recovery efforts of reactive dyes, contributing to the application of waste materials as valuable resources in the mitigation of organic contaminants in wastewater.

Automated summary

Reactive dyes in the textile industry are toxic and difficult to degrade. This study demonstrates the use of malt bagasse, a by-product of the brewing industry, for the adsorption of a synthetic reactive dye, allowing for waste material utilization and resource recovery. The malt bagasse showed good adsorption capacity and dye recovery, making it a potential solution for the removal and recovery of reactive dyes in wastewater.