Adsorption characteristics and mechanism of sewage sludge-derived adsorbent for removing sulfonated methyl phenol resin in wastewater

Abstract

Sulfonated methyl phenol resin (SMP) is one of the most popular organic additives in drilling fluid. It is difficult to treat drilling wastewater that contains SMP. Sewage sludge-derived adsorbent (SSA) was prepared by pyrolysis and activation of sewage sludge. Compared to other biochar and bentonitic adsorbents, the SSA possessed the highest adsorption capacity for SMP, with a removal capacity of 39.41 mg g⁻¹. The adsorption of SMP onto SSA was investigated by pH, ionic strength, SMP initial concentration, contact time and temperature. The Langmuir and Freundlich isotherm models were used to describe the adsorption equilibrium. The Langmuir monolayer adsorption capacity of SSA was estimated as 42.97 mg g⁻¹. The pseudo-first-order kinetic, pseudo-second-order kinetic and intra-particle diffusion kinetic model were employed to analyze the adsorption process of SMP onto SSA. The adsorption activation energy (E_a) was 23.95 kJ mol⁻¹ at 25–40 °C, which implied the physisorption was more significant in the SMP–SSA system. The adsorption thermodynamics was evaluated, and the parameters such as the enthalpy (ΔH⁰) was 14.41 kJ mol⁻¹ and entropy (ΔS⁰) was 58.64 J mol⁻¹ K⁻¹ at 100 mg L⁻¹ SMP. The results indicated the SMP adsorption onto SSA was spontaneous and endothermic in nature. The excellent adsorption capacity for SMP indicates that the SSA could be a new promising low cost adsorbent for removal of SMP pollutants in drilling wastewater.