Optimization of coagulant production from Iron oxide waste powder for Phosphorus removal in municipal wastewater treatment

Abstract

Iron oxide waste powder (IOWP) from steel industries is a global challenge and the current disposal methods involving stockpiling or landfilling as solid waste pose a threat to the environment and human health due to its acidic nature. IOWP can be applied as advanced oxidative agents for water treatment and as pigments in paints among others. This study involved synthesis of IOWP-based coagulant for total phosphorus (TP) removal in municipal wastewater treatment. IOWP was characterized by XRF, XRD, SEM, FTIR and Sieve Shaker to evaluate its quality as a precursor for synthesizing IOWP-based coagulant. CCD was used with independent variables; acid concentration, leaching time and IOWP to acid ratio and responses such as iron concentration in leachate and leachate volume. This led to synthesis of the IOWP-based coagulant through the acid dissolution process. The efficacy, applicability and cost-effectiveness of synthesized coagulant in removing TP in municipal wastewater treatment was compared with that of commercial Alum using laboratory jar tests. Findings revealed that IOWP exhibited favorable physicochemical properties including suitable particle size distribution with a pronounced peak at 180 µm, spherical surface morphology, phase composition aligning with those of hematite (α-Fe2O3), high iron oxide content of 98.72% and Fe–O, O–H functional groups conducive for coagulant synthesis. Optimal conditions of the FeCl3 coagulant synthesis included HCl 6M, leaching time of 30 minutes, IOWP to acid ratio of 0.26, stirring speed of 500 rpm and temperature of 90 ℃, yielding 166508 mg/L iron concentration in the leachate. The coagulant demonstrated desirable traits like irregular and agglomerated particles, profile of iron oxychloride lattices, broad absorption attributed to O–H stretching vibrations, and positive zeta potential (+13.52 to −11.18 mV), that enhance phosphate adsorption and complexation in wastewater treatment. Evaluation of the efficacy of the two coagulants in removing TP showed that the IOWP-based (FeCl3) coagulant is more superior at a lower dose of 150 mg/L compared to alum of 200 mg/L as it also improves other water quality parameters such as total suspended solids, turbidity, color, and pH without additional chemical requirement for pH correction before environmental discharge compared to alum. This translates into lower operational costs for municipal wastewater treatment when using the IOWP-based coagulant (0.424 USD/m3) relative to alum (0.767 USD/m3). Therefore, the IOWP based coagulant is a suitable replacement for commercial alum in municipal wastewater treatment contributing to circular economy and import substitution. Key words: IOWP-based coagulant, ferric chloride, alum, optimal dosage, municipal wastewater, optimal conditions.