Filamentous bacteria-induced sludge bulking can alter antibiotic resistance gene profiles and increase potential risks in wastewater treatment systems.

Sludge bulking caused by filamentous bacteria is a prevalent issue in wastewater treatment systems. While previous studies have primarily concentrated on controlling sludge bulking, the biological risks associated with it have been overlooked. This study demonstrates that excessive growth of filamentous bacteria during sludge bulking can significantly increase the abundance of antibiotic resistance genes (ARGs) in activated sludge. Through metagenomic analysis, we identified specific ARGs carried by filamentous bacteria, such as Sphaerotilus and Thiothrix, which are responsible for bulking. Additionally, by examining over 1,000 filamentous bacterial genomes, we discovered a diverse array of ARGs across different filamentous bacteria derived from wastewater treatment systems. Our findings indicate that 74.84% of the filamentous bacteria harbor at least one ARG, with the occurrence frequency of ARGs in these bacteria being approximately 1.5 times higher than that in the overall bacterial population in activated sludge. Furthermore, genomic and metagenomic analyses have shown that the ARGs in filamentous bacteria are closely linked to mobile genetic elements and are frequently found in potentially pathogenic bacteria, highlighting potential risks posed by these filamentous bacteria. These insights enhance our understanding of ARGs in activated sludge and underscore the importance of risk management in wastewater treatment systems.

Physicochemical characteristics and pyrolysis performance of corn stalk torrefied in aqueous ammonia by microwave heating.

The physicochemical characteristics and pyrolysis performance of corn stalk (CS) torrefied in water and aqueous ammonia by microwave heating were investigated. Physicochemical characterization revealed that both microwave water torrefied CS (MCS) and microwave ammonia torrefied CS (MACS) showed low hemicellulose content, disrupted macrostructure, improved porous properties, and low ash content. MACS exhibited a significantly lower crystallinity degree of 44.34% than CS (79.55%) and MCS (89.50%). MACS also showed increased methyl/methylene groups intensity, and complete acetyl groups disrupture. Pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) revealed that compared with CS and MCS, MACS exhibited higher peak areas for ketones, aldehydes, furans and esters, and significantly lower peak areas for acids and phenols. A possible mechanism was proposed for the effects of wet torrefaction with aqueous ammonia on changes in physicochemical structure and pyrolysis behavior of corn stalk.