Study of tramadol removal from water by the electro-Fenton process coupled with biological post-treatment: kinetics and energetic evaluation

Abstract

The pollution of the aquatic environment by the increasing presence of the non-biodegradable analgesic tramadol (TRA) is increasing due to its high consumption and incomplete elimination in conventional wastewater treatment processes. The aim of the present study is, firstly, to evaluate the oxidative degradation of TRA by the ‘electro-Fenton’ process, EF for short, at pH 3 (optimal operating pH) for 6 h at a constant current between 60 and 400 mA. Secondly, the possibility of coupling biological treatment with EF will be investigated in order to minimise energy input and increase the profitability of the treatment process. The experimental results showed a considerable mineralisation rate of TRA of over 94% after 6 h of electrolysis at an applied current of 300 mA and a Fe2+ catalyst concentration of 0.1 mM. The TRA degradation in this process followed pseudo-first order kinetics. Several TRA intermediates were identified by LC-MS/MS analysis. A likely reaction pathway for the process of mineralisation was suggested. Combining the EF process with biological post-treatment reduces the energy consumption by more than 66% and increases the economic viability of TRA mineralisation.