Optimization of Phosphates , Nitrates and Turbidity Removal from Handwashing Wastewater Using Char Byproducts from Sponge Iron Production.

Abstract

Dolochar, a solid waste generated during direct reduction of iron ore in the sponge iron industry, was explored as an adsorbent in wastewater treatment. The dolochar was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), Scanning electron microscopy (SEM), and X-ray diffraction (XRD). The adsorption process was optimized using response surface methodology based on central composite design (CCD) by considering three key input parameters: adsorbent dose (4–14 g/L), contact time (25–90 min), and particle size (100–600 µm). Twenty experimental runs were used to probe the impact of these variables on removal of phosphates, nitrates, and turbidity from handwashing wastewater. Regression analysis was applied to the experimental data, revealing a strong fit to quadratic models for both nitrate and phosphate removal, with R2 values of 0.99 and 0.98, respectively. A linear model was appropriate for turbidity, with an R2 value of 0.98. The optimal conditions for achieving effective removal of phosphate, nitrate, and turbidity were adsorbent dose 9 g/L, contact time 57.5 min, and particle size 100.2 µm. Adsorption data fitted well on the pseudo-second-order kinetic model and the Langmuir isotherm proving the formation of inner-sphere complexes and monolayer adsorption. These findings confirm that dolochar can be used as a suitable material for treatment of handwash wastewater for onward safe disposal.