2 research outputs found
Effect of chromium (VI) on the multiple nitrogen removal pathways and microbial community of aerobic granular sludge
<p>The frequent appearance of Cr(VI) significantly impacts the microbial metabolism in wastewater. In this study, long-term effects of Cr(VI) on microbial community, nitrogen removal pathways and mechanism of aerobic granular sludge (AGS) were investigated. AGS had strong resistance ability to 1.0 mg/L Cr(VI). 3.0 mg/L Cr(VI) increased the heterotrophic-specific ammonia uptake rate (HSAUR) and heterotrophic-specific nitrate uptake rate (HSNUR) transiently, whereas 5.0 mg/L Cr(VI) sharply decreased the specific ammonia uptake rate (SAUR), specific nitrate uptake rate (SNUR) and simultaneous nitrification denitrification rate (SNDR). It was found that Cr (VI) has a greater inhibitory effect on autotrophic nitrification (ASAUR), and the maximal inhibition rate (IR) was 139.19%. Besides, the inhibition of Cr (VI) on nitrogen removal process belongs to non-competitive inhibition. Cr(VI) had a weaker negative impact on heterotrophic bacteria compared with that on autotrophic bacteria. Denaturing gradient gel electrophoresis analyses suggest that <i>Acidovorax</i> sp., <i>flavobacterium</i> sp., <i>uncultured soil bacterium</i>, <i>uncultured nitrosospira</i> sp., <i>uncultured prokaryote</i>, <i>uncultured β-proteobacterium</i> and <i>uncultured pseudomonas</i> sp. were the dominant species. The inhibition of Cr(VI) on nitrite-oxidizing bacteria was the strongest, followed by ammonia-oxidizing bacteria and denitrifying bacteria. Linear correlations between bacterial count and biomass-specific uptake rate were observed when the Cr(VI) concentration exceeded 3 mg/L. This study revealed the effect of Cr(VI) on nitrification is more serious than that on denitrification. Autotrophic and heterotrophic nitrification, heterotrophic denitrification and simultaneous nitrification denitrification played a significant role on nitrogen removal under Cr(VI) stress.</p
Response of Aerobic Granular Sludge to the Long-Term Presence of CuO NPs in A/O/A SBRs: Nitrogen and Phosphorus Removal, Enzymatic Activity, and the Microbial Community
The
increasing use of cupric oxide nanoparticles (CuO NPs) has raised
concerns about their potential environmental toxicity. Aerobic granular
sludge (AGS) is a special form of microbial aggregates. In this study,
the removal efficiencies of nitrogen and phosphorus, enzyme activities
and microbial community of AGS under long-term exposure to CuO NPs
(at concentrations of 5, 20, 50 mg/L) in aerobic/oxic/anoxic (A/O/A)
sequencing batch reactors (SBRs) were investigated. The results showed
the chronic toxicity caused by different concentrations of CuO NPs
(5, 20, 50 mg/L) resulted in increases in the production of ROS of
110.37%, 178.64%, and 188.93% and in the release of lactate dehydrogenase
(LDH) of 108.33%, 297.05%, 335.94%, respectively, compared to the
control. Besides, CuO NPs decreased the activities of polyphosphate
kinase (PPK) and exophosphatase (PPX), leading to lower phosphorus
removal efficiency. However, the NH<sub>4</sub><sup>+</sup>-N removal
rates remained stable, and the removal efficiencies of TN increased
due to the synthesis of nitrite and nitrous oxide (N<sub>2</sub>O)
reductases. In addition, CuO NPs at concentrations of 0, 5, 20 mg/L
increased the secretion of protein (PN) to 90, 91, 105 mg/gVSS, respectively,
which could alleviate the toxicity of CuO NPs. High-throughput sequencing
showed that CuO NPs increased the abundance of nitrogen-removal bacteria
and reduced the abundance of phosphorus-removal bacteria, which is
consistent with the results of pollutant removal upon long-term exposure
to CuO NPs