Anoxic conditions are beneficial for abiotic diclofenac removal from water with manganese oxide (MnO2)

Abstract

This is the first study examining pharmaceutical removal under anoxic conditions with MnO2. This study compares the abiotic removal of seven pharmaceuticals with reactive MnO2 particles in the presence of oxygen (oxic conditions) and in the absence of oxygen (anoxic conditions). Due to the novelty of pharmaceutical removal under anoxic conditions, the influence of phosphate buffer, pH, and MnO2 morphologies is also examined. Results show that over 90% of diclofenac is removed under anoxic conditions. Additionally, we found that (1) anoxic conditions are beneficial for diclofenac removal with MnO2, (2) phosphate buffer affects the pharmaceutical removal efficiencies, (3) higher pharmaceutical removal is obtained at acidic pH compared to that at neutral or alkaline conditions, and (4) amorphous MnO2 removes pharmaceuticals better than crystalline MnO2. The pharmaceutical molecular structure and properties, MnO2 properties especially reactive sites of the MnO2 surface, are important for degradation kinetics. This study provides a fundamental basis towards understanding pharmaceutical degradation with MnO2 under anoxic conditions, and development of a cost-effective, sustainable technology for removal of pharmaceuticals from water.