Study on Degradation of Oxytetracycline in Water by PMS Activated by Modified Macadamia Nut Shell Biochar

With a complex molecular structure, oxytetracycline (OTC) has characteristics such as bioaccumulation and poor degradability. As a result, if it accumulates in the environment, it can cause bacteria to develop drug resistance, thereby affecting human health. There is a considerable cultivation area for macadamia nuts in southwestern China. This study mainly focuses on macadamia nut shells, preparing macadamia nut shell biochar (MBC) and cobalt-modified macadamia nut shell biochar (Co-MBC) for activating permonosulphate (PMS) to remove OTC in the water. To determine the optimal preparation conditions for the biochar, the effects of the pyrolysis temperature and the mass ratio of biomass to cobalt sulfate heptahydrate were investigated. The study shows that after modification, the surface roughness of the material increased, transforming into a micro-pore structure; thus, the specific surface area increases significantly and new functional groups appear on the surface. The optimal pyrolysis temperature for the biochar was determined to be 600 °C, and the optimal mass ratio of biomass to cobalt sulfate heptahydrate was 15:1. Under such conditions, the removal rate of OTC by a Co15-MBC600/PMS system in 20 min can reach 95.53%. The reaction mechanism involves pathways of the free radical (SO4−) and non-free radical (1O2), and the Co2+/Co3+ cycle can promote the activation of PMS. Finally, the OTC can be mineralized into CO2 and H2O by reactions such as demethylation and decarboxylation. Co-MBC is highly effective and green and can be reused; therefore, it has good prospects for the removal of OTC in waste water.