Insights into endocrine-disrupting Bisphenol-A adsorption from pharmaceutical effluent by chitosan immobilized nanoscale zero-valent iron nanoparticles

Abstract

Bisphenol A (BPA) in the aquatic environment have adverse effects on human health and other living organisms. BPA at low traces can lead to cardiovascular disease, type II diabetes, and impaired hepatic enzymes. For efficient BPA removal, chitosan immobilized nanoscale zero-valent iron (nZVI-chitosan) nanoparticles were synthesized and used as adsorbent. Since the BPA removal efficiency depends on independent process variables like nZVI-chitosan dosage, initial BPA concentration, pH and contact time, experiments were conducted systematically. To characterize the interaction effect of these variables, the experimental matrix is designed using response surface methodology (RSM). The isothermal and kinetic model parameters are estimated using differential evolution optimization (DEO), and these parameters better represent adsorption behaviour. The batch adsorption experiments indicated that the BPA adsorption on to nZVI-chitosan follows pseudo 1st order kinetic models. The maximum extent of BPA adsorption was 65.16 mg/g based on the Langmuir isotherm model. DEO based model parameters better fit the non-linear models with high R2 and lower RMSE. The regenerability experiments indicate that synthesized nZVI-chitosan adsorbent can be used up to three cycles with removal efficiency over 50%. The thermodynamic studies indicated that ΔG° is negative signifying a favourable and spontaneous adsorption process. The inhibition effects of coexisting ions on BPA adsorption followed the order of Mn2+ > Ca2+ > Mg2+ > Fe2+ for cations and of SO42− > NO3− > Cl− for anions. The BPA removal from real pharmaceutical wastewater is 93.8% obtained for optimal initial BPA concentration of 6 mg/L, an adsorbent dosage of 1.5 g/L, with solution pH of 3 and adsorption time of 1 h, whereas this removal efficiency is 95% for synthetic wastewater.