Adsorption of tylosin in wastewater by iron-rich farmland soil and the effect of iron reduction and common cations

Livestock wastewater reused in farmland may cause tylosin to stay in farmland soil. Under the influence of some factors, such as irrigation and fertilization, tylosin may desorb and diffuse into the water environment. Batch adsorption experiments and soil column flooding experiments were set up to investigate the effects of several cations and iron reduction on the adsorption, desorption and oxidation removal of tylosin in iron-rich farmland soils (red soil). The results showed that tylosin can be adsorbed by the red soil. The coexistence of these cations significantly reduced its adsorption capacity. The order of influence was as follows: Ca2+ > Mg2+ > K+ > > Na+. This means that some agricultural farming measures, such as the application of chemical fertilizers, would release the adsorbed tylosin into the farmland. Anaerobic iron reduction and massive production of ferrous ions did not affect the adsorption and desorption of tylosin in the red soil column. Moreover, the ferrous iron could activate persulfate to generate hydroxyl radicals and sulfate radicals which oxidized and removed the tylosin adsorbed in the soil column. Therefore, the iron reduction that occurred during flooding was not a factor causing tylosin release, which provided a way for tylosin in iron-rich farmland soils to be oxidized and removed.