Green and low cost tetracycline degradation processes by nanometric and immobilized TiO2 systems

Tetracycline accumulation in surface waters, due to its extensive use and ineffective removal by traditional remediation treatments, represents a major environmental problem, leading e.g. to increasedantibiotic resistance. Here, photocatalysis by TiO2, both as nanostructured powders and macroscopic immobilized systems, is proposed as an efficient procedure to totally degrade tetracycline to harmless compounds. Home-made TiO2 powders were studied to clarify the role of synthetic and process parameters (light pre-treatment, calcination temperature) and to shed light on the role of radical species in promoting the reaction (tests with radical scavengers). The control of phase composition and wetting features appears to be essential in producing photocatalysts able to completely mineralize tetracycline in a short time scale (6 h). The knowledge acquired on the powder system was preparatory to the development of low cost, mechanically robust and highly active TiO2 immobilized systems. Two different substrate geometries (laminas and pellets) were investigated to ease the photocatalyst removal from the treated effluent. Both immobilized systems proved efficient: in particular, the TiO2-coated pellets promoted tetracycline degradation and mineralization on a time scale that is very competitive when compared to similar literature immobilized systems.