Activated sludge recovered from wastewater provides a sustainable approach for removing dyes and heavy metals from effluents.

Industrial wastewater is one of the most widespread sources of water pollution that cause increasing problems with heavy metals and dyes, which at the same time implies the find of sustainable and cost-effective treatment solutions. The current research was centred on the use of activated sludge that is obtained from the natural wastewater to remove both methylene blue (MB) dye and lead (Pb) ions from contaminated water. The SEM, EDS, FTIR, BET, XRD, and TGA analysis were used to characterize the structure and function of the activated sludge. The effect of pH, contact time, initial concentration, and sludge dosage on the removal efficiency was studied using the batch experiments. The activated sludge was most efficient at pH 6, 120 min contact time with 2 g/L sludge dosage. The steps of adsorption process have been best described by the pseudo-second-order kinetic model, in which physical attachment was found to be the major route. The results of isotherm studies showed that the best fitting model for the adsorption data was the Langmuir model, with the maximum adsorption capacities of 78.6 mg/g for MB and 52.3 mg/g for Pb. The sludge also showed appreciable regeneration, with over 80% of the adsorption capacity left after it had completed the fifth cycle. The findings thus put forward the idea of using naturally occurring activated sludge from wastewater as a sustainable, low-cost, and efficient biosorbent for the treatment of water polluted with dyes and heavy metals.