The remediation performance and mechanism for tetracycline from groundwater using controlled release materials...

Aiming at the effective remediation of antibiotic contaminants in groundwater, in-situ chemical oxidation (ISCO), using controlled release materials (CRMs) as an oxidant deliverer, has emerged as a promising technique due to their long-term effective pollutant removal performance. This study used different microstructures of mesoporous manganese oxide (MnO_x) and sodium persulfate as active components to fabricate CRMs. Following that, a comparative study of tetracycline (TC) degradation and the formation of reactive oxygen species (ROS) by mesoporous MnO_x powder and CRMs were conducted. The ROS formed during peroxodisulfate (PDS) activation by powder catalysts and CRMs differed, but MnO_x powder catalysts and CRMs both had good reaction stoichiometric efficiency (RSE) for PDS, thus completely mineralizing TC. In PDS activation by mesoporous MnO_x powder, oxygen vacancies (OVs) caused by defects in the catalysts contributed to the generation of singlet oxygen (¹O₂). The ¹O₂ and free radicals (·SO₄^- and ·OH) both worked as major ROS participating in TC degradation. Concerning the release of CRMs in static groundwater, the immobilization of catalysts inside CRMs made it difficult to release ¹O₂ in the solution, thus slowing the degradation of TC by CRMs containing MnO_x(1) in static groundwater. In the TC remediation in dynamic groundwater, the water flowing slowly passed through the CRM layer, and TC molecules were trapped. Therefore, ¹O₂ degraded the trapped TC in the CRM layer in dynamic groundwater. Compared to TC, the toxicity of most intermediates during the TC degradation by CRMs has decreased in static and dynamic groundwater.