Parametric Evaluation of Heavy Metal Removal from Iron and Steel Wastewater Using Chlorella vulgaris: Linking Operational Conditions to Biomass Composition and Treatment Performance

Abstract

The effects of pH, illumination duration, wastewater dilution, and carbon dioxide addition on heavy metal removal were investigated over seven days of application to real steel mill wastewater. The microalga was isolated from surface water samples obtained from Eflany Lake, which is a freshwater aquatic ecosystem located within the Karabuk Province in Turkey. The isolated strain showed 99% sequence identity to Chlorella vulgaris, confirming its assignment to this species. The molecular composition of biomass under different operating conditions using Fourier transform infrared spectroscopy (FTIR) revealed the biochemical interactions associated with metal concentration. During a period of seven days, the results showed that wastewater concentrations and treatment efficacy were inversely related. An 18-hour light period, pH 8, 30% wastewater concentration, and 500 mL/h CO₂ flow rate was identified as optimal, achieving the highest removal efficiency for metals (As: 45.0 %, Cd: 75.0%, Cr: 82.0%, Cu: 88.0%, Mn: 90.0%, Ni: 65.0%, Pb 94.0%, Fe: 85.0%). Under optimal conditions characterised by high elimination efficiency, an improved protein content was observed with strong Amide I/II extension. Furthermore, correlation of FTIR peak ratios with removal efficiency can produce predictive biomarkers.