Sustainable removal of cadmium from contaminated water using green alga-Optimization, characterization and modeling studies

This research study reported the feasibility of cadmium removal using green algae, Caulerpa scalpelliformis, under controlled environmental conditions. The algal biosorbent could effectively remove cadmium under broad range of test conditions, namely, initial pH (3-6), adsorbent mass (0.5-2.5 gL-1) and shaking speed (60-100 rpm). The best operating conditions were identified using Central Composite Design under Response Surface methodology and found to be pH - 4.9, adsorbent mass - 2.1 gL-1 and shaking speed - 90 rpm. Equilibrium studies were conducted and monolayer sorption was identified as the mechanism, confirmed by Langmuir isotherm (R2 = 0.9920). The maximum Cd uptake achieved at optimal conditions was 111.11 mg g-1. The kinetic constants of the best fit model (pseudo second order) were determined. The thermodynamic feasibility was verified (Delta G>0) and the biosorption process was found to be endothermic (Delta H >0). The mass transfer studies shows that the mass transfer coefficient was inversely related to the temperature. Presence of favorable surface functional groups and enhanced surface area confirmed the suitability of the synthesized biosorbent for effective removal of cadmium.