Synergistic Effect of Chemical and Physical Treatments on Azolla pinnata for Cadmium Ions Removal from Synthetic Wastewater Systems

Abstract

Azolla pinnata, an aquatic fern has been utilized as an effective biofiltering and adsorbent agent to complement many conventional treatment methods for the removal of environmental pollutants. This study is designed to develop an effective regime to treat metal pollutants of industrial and urban waste discharge using a novel strategy involving Azolla pinnata. In the present study, cell surface modification by physical treatments that include heating (muffle furnace), and mechanical waves (ultrasonication) and chemical treatments as sulphuric acid and ethanol were employed to enhance the adsorption of metal pollutants. Factors such as biosorbent dose, contact time, initial metal ion concentration, temperature, and solution pH were optimised in batch mode. The point of zero charge of the adsorbent was determined to be at 5.85 pH. The results of surface morphology, elemental analysis, crystallinity, recorded through SEM, FTIR and XRD confirmed the adsorptive properties in both modified and unmodified biomass. The intensity peaks linked to O-H, C-H, C-N, N-H and C=O stretching bands was intense in the treated A. pinnata groups indicating the induction of the active groups. Out of the two chemical pre-treatments, the batch adsorption experiment with ethanol found to chelate Cd+2 metal ions to a higher extent (94.36%) in contrast to the results obtained from H2 SO4 treated biomass. Whereas, the physical treatments exhibited the strong adsorption (83.28 and 96.92±0.55%) for ultrasonicated and muffle furnace pre-treated biomass respectively for the dosage of 0.25g. The adsorption efficiency of physically modified sorbent revealed the cent percent removal of Cd+2 ions from the aqueous phase with the dosage of 1.0g in 15min of contact time which is due to the incorporation of new binding sites. Moreover, these results proved that the highest rate of cadmium adsorption onto A. pinnata is in result of the modifications caused onto surface structure, porosity and the addition of functional groups on the surface of the treated biomass.