Synthesis of sludge-derived biochar modified with eggshell waste for monoethylene glycol removal from aqueous solutions

Abstract

Abstract: In this study, the pyrolysis of sewage sludge was employed to prepare a biochar (BC) adsorbent that was modified using eggshell wastes, obtaining eggshell-modified biochar (EMBC). The adsorbent material was used for the removal of monoethylene glycol (MEG) from aqueous solutions under various adsorption conditions. Results showed that the specific surface area of EMBC (i.e., 3.95 m2/g) was approximately twofold higher than that of BC, implying that the application of eggshell waste would improve the surface adsorption performance. The optimum adsorption pH value was 7, achieving MEG removal efficiencies of 29.9% for BC and 89.9% for EMBC using adsorbent dosage = 2 g/L, initial MEG concentration = 100 mg/L, and 25 °C within 60 min. The adsorption mechanisms were illustrated regarding XRD, FTIR, and SEM, demonstrating that surface adsorption, pore-filling, precipitation, and complexation contributed to the adsorption process. The adsorption data fitted well to the Langmuir isotherm model with the maximum monolayer adsorption capacity of 12.20 mg/g, implying a reversible physisorption mechanism. Based on a techno-economic feasibility assessment, the preparation of BC and EMBC adsorbents for the treatment of 1 m3 of wastewater-containing ethylene glycol would require capital costs of 4.80 and 6.50 US$, respectively. The selling of adsorbents and the economic benefit of tertiary treated water showed adequate annual profitability with payback periods of 12.97 and 6.79 years for the BC and EMBC scenarios, respectively. Hence, the study succeeded in preparing efficient and low-cost adsorbents that could be used for the tertiary treatment of petrochemical industrial wastewater containing toxic environmental pollutants. Graphic abstract: [Figure not available: see fulltext.]