Performance of wastewater sludge modified with zinc oxide nanoparticles in the removal of methylene blue from aqueous solutions

The presence of chromogenic substances in water can potentially be carcinogenic and mutagenic, and thus, it may be hazardous to public health. This study was carried out with the objective of investigating the feasibility of using wastewater sludge, modified with zinc oxide nanoparticles, in the removal of the methylene blue (MB) dye from aqueous solution. The stabilization of nanoparticles onto the sludge was performed using the thermal method in order to increase the active adsorption surface. The effects of the operational parameters (including pH, contact time, MB dye concentration, and adsorbent dosage) on the adsorption of MB by the modified sludge were studied in batch mode. The sludge coated with zinc oxide nanoparticles had higher MB dye removal efficiency (%) than that of raw sludge. The MB adsorption amount (Qe) increases with a reduction in the adsorbent dosage, an increase in pH, and an increase in the initial concentration of the MB dye. At equilibrium, the amount of MB dye adsorbed onto sludge coated with zinc oxide nanoparticles was 6.6 mg/g, while the amount of adsorbed MB dye onto raw sludge was 2.9 mg/g. The adsorption reached equilibrium after 120 min and the adsorption data fitted the Langmuir isotherm model (R2 = 0.99). The modification of sludge with zinc oxide nanoparticles can provide an appropriate substance to function as the adsorbent in the removal of MB dye from aqueous solution.