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Evaluation of characteristics and microbial community of anaerobic granular sludge under microplastics and aromatic carboxylic acids exposure
Summary
Researchers exposed anaerobic granular sludge to polyether sulfone microplastics combined with aromatic carboxylic acids and found that both contaminants impaired sludge granule stability, reduced methane production, and shifted microbial community composition toward less efficient fermenters.
The influences of polyether sulfone (PES) microplastics and different structures aromatic carboxylic acids such as benzoic acid (BA), phthalic acid (PA), hemimellitic acid (HA), and 1-naphthoic acid (1-NA) on the performances and characteristics of anaerobic granular sludge as well as the microbial community were investigated. The chemical oxygen demand (COD) removal efficiency was the highest in the experimental group with 40 mg/L BA, reaching 90.1%. The inhibitory effect of aromatic carboxylic acids addition on the 2,3,5-triphenyltetrazolium chloride (TTC) activity was more obvious than that on 2-para (iodo-phenyl)-3(nitrophenyl)-5(phenyl) tetrazolium chloride (INT) activity. Compared with the control group (only 0.5 g/L PES microplastics, 60.6 mg TF·g TSS·h), the inhibition effect of TTC activity was 32.5 mg TF·g TSS·h and 44.3 mg TF·g TSS·h in the 40 mg/L HA and 40 mg/L 1-NA experimental groups, respectively. When aromatic carboxylic acids were added, the activities of acetate kinase and coenzyme F in the anaerobic granular sludge decreased. The excitation-emission matrix (EEM) fluorescence spectra indicated that loosely bound extracellular polymeric substances (LB-EPS) began to decay. After the addition of different aromatic carboxylic acids, the CC and CH functional groups of the anaerobic granular sludge increased, suggesting that aromatic carboxylic acids migrated to the surface of anaerobic granular sludge, such a transfer would lead to changes in anaerobic granular sludge performance. High-throughput sequencing technology showed that the dominant microbial communities in the anaerobic granular sludge were Proteobacteria, Methanothrix, and Methanomicrobia. After the addition of aromatic carboxylic acids, the relative abundances of Proteobacteria, Methanobacterium, and Methanospirillum increased. In the presence of PES, 1-NA had the most serious toxicity to the anaerobic granular sludge.