Removal of antibiotic resistance genes from secondary effluent by processes combining nano-iron, ultrasound-activated persulfate, and ultrafiltration

Abstract

Antibiotic resistance genes (ARGs), as a new type of environmental pollutant that threaten human health, have been detected in the effluent of sewage treatment systems. In this study, the removal from water of ARGs, 16S rRNA, class 1 integron (intI1), and dissolved organic carbon (DOC) were investigated using processes combining nano-iron (nFe), ultrasound (US), activated persulfate (PS) and ultrafiltration (UF). The oxidation mechanism was also studied. The results showed that both nFe and US activation could improve the oxidative effect of PS, and the effect of nFe was better than that of US. Compared with PS-UF, nFe/PS-UF and US/PS-UF significantly enhanced the removal of various ARGs and DOC. nFe/PS-UF was the most effective treatment, reducing cell-associated and cell-free ARGs by 1.74–3.14-log and 1.00–2.61-log, respectively, while removing 30% of DOC. Pre-oxidation methods using PS, nFe/PS, and US/PS significantly enhanced the efficacy of UF for removing DOC with molecular weights above 50 kDa and below 10 kDa, but the removal of DOC between 10 and 50 kDa decreased. The free radicals SO4·− and ·OH were shown to participate in the process of ARGs oxidation. HIGHLIGHTS Persulfate oxidation pretreatment significantly improved the removal effect of ultrafiltration on ARGs due to release of SO4·−.; Nano-iron forms a loose and porous oxide shell on the surface of the particles, which can adsorb ARGs.; Cavitation during ultrasound treatment can lyse the cell structure, transforming cell-associated ARGs into the free state;

Keywords

• antibiotic resistance genes
• nano-iron
• persulfate
• ultrafiltration
• ultrasound