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 m 2 /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 m 3 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.

Excess sludge generated from wastewater treatment plants (WWTPs) can cause negative impacts on human health, water bodies, aquatic plants, and soil quality. However, the produced sludge could be appropriately managed to obtain various economic and environmental benefits. One of the feasible and practical options of sludge management is the synthesize of biochar via oxygen-limited pyrolysis. The use of biochar adsorbent for pollutant removal offers various advantages such as high adsorption capability, low operating and chemical costs, no production of toxins. Hence, this study addresses the applications of sewage sludge-derived biochar for industrial wastewater treatment. The methods of sludge collection, drying, pulverization, and pyrolysis are illustrated. Biochar characterization methods (SEM, EDX, XRD, and FTIR analyses) and mechanisms of the adsorption process are described. The sludge-derived biochar could be used as an adsorptive material for industrial effluent treatment. Recommendations for future studies that could enhance the adsorption capacity of biochar and modified-biochar are given.

Petrochemical industrial wastewater (PIW)contains toluene and xylene (TX), and various organic and inorganic pollutants, causing severe risks to human health if improperly released into the environmental matrices. For the long-term reliability of environmental conservation, this study illustrates the interlinkage between PIW treatment and the three pillars of sustainable development. Sewage sludge biochar was modified with eggshell, showing a relatively high fixed C content (increase in carbonization degree), and small O/C and N/C ratios. The prepared biochar was employed for TX adsorption in mono-component solutions, giving removal efficiencies of 79.1% (T) and 86.6% (X), at pH =10, adsorbent dosage =2 g/L, and Co =40 mg/L within 60 min. The main adsorption mechanism was physisorption, including precipitation/pore-filling, π-π dispersive interaction, and van der Waals force. The modified biochar also treated real PIW under five adsorption/regeneration cycles, providing essential steps toward large-scale applications. According to an economic feasibility estimation, the biochar application for treating 1 m3 of PIW would offer a payback period of 6.9 yr. The study outputs could be linked to the restoration of water-related ecosystems, biochar modification for industrial applications, and climate change mitigation, adopting the 2030 agenda and its sustainable development goals (SDGs).

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