Towards zero waste discharge (ZWD) in agar production: Gracilaria dura byproduct-based activated carbon for sustainable environmental remediation.

Gracilaria dura; red seaweed used in agar production; generates substantial processing waste (PWs); including residual seaweed-mass (RSM) and aqueous alkaline waste (AAW). In this study; 1 kg G. dura processed for the production of 250 ± 5 g agar; 350 ± 25 g RSM and 12.5 ± 0.5 kg AAW. PWs, which are discarded in the environment; pose serious environmental risks to aquatic systems and carbon emission, etc. This study presents an innovative approach to mitigate these issues by converting PWs into activated carbon (AC) for environmental remediation and CO2 capture. However; AC was characterized using FTIR; NMR; SEM; TEM; XPS; XRD; and RAMAN spectroscopy. It demonstrated remarkable efficiency in removing ~100 % of dyes from the actual textile wastewater; validated through column-based separation. Furthermore; the AC exhibited impressive adsorption capacities; with methylene blue (MB, Qmax240 mg/g) and amoxicillin (AMX, Qmax588 mg/g). The adsorption behavior followed the Freundlich isotherm; with kinetic studies indicating pseudo-second-order and pseudo-first-order model. AC exhibited high surface area (1156 m2/g) and excellent CO2 uptake (~80 cm3/g); demonstrating selectivity for CO2 over nitrogen (N2) and methane (CH4). This study highlights the potential of transforming PWs into valuable materials; contributing to environmental remediation; carbon footprint reduction; and zero waste discharge "ZWD" agar process.