Biofunctional hydrogel adsorbents for sustainable downstream dye purification and circular wastewater management

Introduction Although the use of clay–alginate composites and activated clays as adsorbents has been thoroughly examined for the removal of dyes, very few studies have addressed the effect of reactor hydrodynamics on the efficiency of the process. In this research, efforts were made to fill the knowledge gaps by adopting an approach combining batch adsorption tests, fixed-bed column studies, breakthrough modeling, and computational fluid dynamics (CFD) simulation in order to create connections between flow characteristics and mass transfer and adsorption kinetics involved in the removal of malachite green (MG) dye using mesoporous AC@SA hydrogel beads. Methods Mesoporous hydrogel beads possessed pore sizes in the range of 3–10 nm and exhibited a negative zeta potential of –8 mV (mean). Batch adsorption tests, fixedbed column studies, breakthrough modeling, and CFD simulations were conducted to evaluate adsorption performance and investigate the influence of reactor hydrodynamics on the adsorption process. Results Maximum MG dye removal efficiency was observed to be around 90% in batch adsorption tests at 50 g L −1 adsorbent dose, pH 7, and 150 rpm after about 120–150 min contact time. Column experiments showed an increase in bed height from 6 to 14 cm increased the breakthrough time from about 18 to 32 min, while increasing the influent dye concentration and flow rate reduced breakthrough times. The Thomas model showed excellent agreement with experimental data (R 2 ≈ 0.99), with adsorption capacities reaching 21.28 mg g −1 and rate constants ranging from 0.22 to 0.33 ml mg −1 min −1 . Further simulations by CFD revealed that a flow rate of 10 ml min −1 would ensure uniformity of velocity, lower turbulence, controlled eddy viscosity, and stable hydrodynamic conditions, hence maximized adsorption. Discussion Such an approach ensures not only knowledge from the material level but also at the reactor level concerning adsorption process optimization and scaling up. Additionally, the system has ensured achievement of SDGs 6, 9, and 12 due to the use of environmentally friendly materials and wastewater treatment approaches.