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Anaerobic fermentation is effective for waste activated sludge (WAS) disposal to realize resource generation and pollutants reduction, and various pretreatments were commonly applied to improve the performance. This work mainly investigated the effects of typical WAS pretreatment approaches on the antibiotic resistance genes (ARGs, as emerging contaminants) removal during anaerobic fermentation processes and unveiled the underlying mechanisms. The results indicated that all the pretreatment strategies exhibited evident effects on the overall ARGs removal with the order of Fe2+ activated persulfate (PS/Fe2+) > pH 10 > Ultrasonication > Heat, and showed selective removal tendency for the specific ARGs (namely easily removed (aadA 1 and sul 1) and persistent ARGs). Mechanistic analysis demonstrated that the pretreatments disrupted the extracellular polymeric substances (EPS) and rose the cell membrane permeability (particularly for PS/Fe2+ and Heat). Then the increased ARGs release benefitted the subsequent reduction of mobile genetic elements (MGEs) and extracellular ARGs (especially for PS/Fe2+ and pH10), resulting the ARGs attenuation. Pretreatments significantly shifted the microbial community structure and the abundances of potential ARGs hosts (i.e., Sulfuritalea , and Denitratisoma). Also, the different pretreatments exhibited distinct effects on the microbial metabolic traits related with ARGs proliferation (i.e., ABC transporters, two-component system and bacterial secretion systems), which also contributed to the ARGs attenuations during WAS fermentation. The partial least-squares path modeling (PLS-PM) analysis indicated that the bacterial community (total effects = 0.968) was key factor determining ARGs fates. [Display omitted] •ARGs removal with different pretreatments followed the order: PS/Fe2+ > pH10 > USp > Heat. • Different pretreatment exhibited selective tendency for the specific ARGs removal. • Pretreatments increased EPS disruption and cell membrane permeability for e-ARGs release and removal. • The bacterial community and metabolic pathways expressions associated with ARGs were altered to various extents. • The predominant contributing factor for the ARGs reduction was distinguished by PLS-PM analysis. [ABSTRACT FROM AUTHOR]

The acesulfame (ACE) degradation in waste activated sludge (WAS) via direct anaerobic fermentation is difficult and the efficient elimination techniques are imperative for the ultimate safe WAS disposal. Persulfate (PS)-based approach was developed to promote the ACE removal during WAS anaerobic fermentation. Results demonstrated the effectiveness of PS-based treatments on ACE degradation, and the ACE removal efficiency was respectively 48.2% and 96.2% in the PS and PS/Fe-treated reactors while it was only 6.0% in the control reactor. Mechanism explorations revealed that the active free radicals (i.e. OH• and SO 4 •−) generated in the PS-based reactors were the key oxidative species for the ACE degradation. However, such effects were interfered by the released soluble substrates (i.e. protein, carbohydrate and inorganic ions) during anaerobic fermentation by competing and/or quenching free radicals, which caused the deceleration of the ACE removal efficiency. Moreover, the PS-based treatment facilitated the enrichment of functional microorganisms (i.e. Phyllobacteriaceae and Bradyrhizobiaceae) and upregulated the critical genes (i.e. pncB and nadE) involved in the ACE degradation. Based on the density functional theory (DFT) and metabolic intermediates analysis, the hydroxylation and oxidative ring-opening were the two main proposed metabolic pathways for ACE degradation. Overall, the combined chemical and biological metabolism effects collectively contributed to the efficient ACE degradation, and it provided a novel and effective strategy for refractory pollutants removal during WAS anaerobic fermentation. [Display omitted] • PS-based treatment is effective for ACE removal during WAS anaerobic fermentation. • The combined chemical and biological effects on the ACE removal are disclosed. • The released fermentation substrates are unbeneficial to ACE removal by PS/Fe treatment. • PS-based treatment induces ACE degraders enrichment and metabolic function upregulation. • Hydroxylation and ring-opening reaction were the main pathways for ACE degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] • PHMG prompt the ARGs spread and alter distribution patterns of ARGs. • PHMG increased cell permeability and MGEs that benefit the ARGs release and HGT. • Potential ARGs hosts (i.e. Burkholderia and Aeromonas) are enriched in PHMG reactor. • PHMG induce to the upregulation of metabolic pathways related with ARGs propagation. • Microbial community was the predominant factor contributing to ARGs propagation. This study mainly investigated the environmental risks of polyhexamethylene guanidine (PHMG) occurred in waste activated sludge (WAS) on the antibiotic resistance genes (ARGs) spread during anaerobic fermentation, and disclosed the critical mechanisms. The total ARGs abundance was increased by 32.2–46.4% at different stressing levels of PHMG. The main resistance mechanism categories of ARGs shifted to the target alternation and efflux pump. PHMG disintegrated WAS structure and increased the cell permeability, which benefitted the mobile genetic elements (MGEs) release and horizontal transfer of ARGs. Besides, PHMG induced the enrichment of potential ARGs hosts (i.e. , Burkholderia , Bradyrhizobium and Aeromonas). Moreover, PHMG upregulated the metabolic pathways (i.e., two-component system, quorum sensing, and ATP-binding cassette transporters) and critical genes expression (i.e., metN , metQ , rpfF , rstA and rstB) related with ARGs generation and dissemination. Structural equation model analysis revealed that microbial community structure was the predominant contributor to the ARGs propagation. [ABSTRACT FROM AUTHOR]

[Display omitted] • PS/Fe treatment attenuated ARGs during WAS fermentation. • Bacterial structure disrupted by PS/Fe treatment favoured ARGs attenuation. • PS/Fe exhibited more devastating effects on the potential ARGs hosts. • ARGs fates were associated with the abundance of functional genes in host bacterial. The occurrence of antibiotic resistance genes (ARGs) in waste activated sludge (WAS) fermentation was investigated with persulfate (PS)-based treatment. ARGs affiliated with multidrug (mex P), macrolide (bla OXA-129), tetracycline (tet B), sulfonamide (sul 1), and vancomycin (van RG) types were significantly decreased by PS/Fe treatment. Mechanistic investigations revealed that PS/Fe possessed oxidating potential and exhibited devastating effects on WAS fermentation. First, PS/Fe promoted cell structure damage, which facilitated ARGs release from potential hosts. A co-occurrence network analysis indicated that Fe/PS suppressed the proliferation of potential host bacteria. In addition, the PS/Fe treatment induced the decreased abundance of certain functional genes involved in pathways associated with ARGs dissemination. Finally, variation partitioning analysis demonstrated that the microbial community structure exhibited more vital effects on ARGs fates than physicochemical factors (i.e., pH and ORP) and gene expression (i.e., two-component system). This work provided a deeper understanding of the critical factors used to determine ARGs fates during WAS fermentation. [ABSTRACT FROM AUTHOR]