Application of sludge-based activated carbons for the effective adsorption of neonicotinoid pesticides

Abstract

The amount of sludge produced in wastewater treatment plants (WWTPs) has increased over the years, and the methods used to reduce this waste, such as incineration, agricultural use, or disposal in landfills, cause problems of secondary pollution. For this reason, it is necessary to find sustainable and low-cost solutions to manage this waste. Additionally, emerging and priority pollutants are attracting attention from the scientific community as they can generate health problems due to inadequate removal in conventional WWTPs. In this work, a pharmaceutical industry sludge was used as a precursor in the synthesis of four activated carbons (ACs) using different activating agents (ZnCl2, FeCl3·6H2O, Fe(NO3)3·9H2O, and Fe(SO4)3·H2O), to be used for the removal by adsorption of three neonicotinoid pesticides included in latest EUWatch List (Decision 2018/840): acetamiprid (ACT), thiamethoxam (THM), and imidacloprid (IMD). The prepared ACs showed micro-mesoporous properties, obtaining relatively slow adsorption kinetics to reach equilibrium, but despite this, high values of adsorption capacity (qe) were obtained. For example, for AC-ZnCl2 (SBET = 558 m2/g), high adsorption capacities of qe = 128.9, 126.8, and 166.1 mg/g for ACT, THM, and IMD, respectively, were found. In most cases, the adsorption isotherms showed a multilayer profile, indicating an important contribution of the mesoporosity of the activated carbons in the adsorption process.