Applications of marine red seaweed Pterocladia capillacea biomass in removal of hexavalent chromium and crystal violet dye from several wastewaters.

The potential of Pterocladia capillacea, a marine red seaweed, as a sustainable and eco-friendly adsorbent was investigated for the removal of toxic hexavalent chromium Cr(VI) (or Cr) and crystal violet dye (CVD) from contaminated water. Characterization of P. capillacea using Fourier-Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis revealed a porous structure with a high specific surface area (87.17 m²/g) and a negative surface charge (-29.5 mV), ideal for adsorbent applications. Adsorption studies were conducted to assess the impact of operational parameters, such as pH, adsorbent dose, initial pollutant concentration, and temperature. Optimal removal was achieved at pH 1.0 for Cr and CVD. Increasing the adsorbent dose led to higher Cr adsorption, achieving near-complete removal with 0.4 g. An optimal dose of 0.8 g was selected for subsequent experiments. Cr Cr removal was faster during the initial adsorption stage (within 30-60 min), followed by a slower rate due to saturation and reduced pore diffusion. Adsorption was more effective at lower temperatures and followed pseudo-second-order kinetics, suggesting chemisorption as the dominant mechanism. Six isotherm models were used to describe equilibrium adsorption, with the Freundlich model providing the best fit for both Cr and CVD, indicating multilayer adsorption and heterogeneous surface interactions. P. capillacea showed potential for Cr removal in seawater and real wastewater, although efficiency was reduced due to complex matrix effects. Reusability studies indicated a decline in efficiency over multiple cycles; however, Cr uptake remained above 89.2% for CVD. Similar reusability was observed, with an initial removal efficiency of 87.29% for CFD. Although removal efficiency decreased in subsequent cycles, the material remained effective for repeated CVD adsorption. The study demonstrates the potential of P. capillacea as a readily available, cost-effective, and sustainable material for the bioremediation of Cr and synthetic dyes from water, contributing to the development of environmentally friendly water treatment technologies.