Surfactants Aggravated the Biotoxicity of Fe₂O₃ Nanoparticles in the Volatile Fatty Acids’ Biosynthesis during Sludge Anaerobic Fermentation

Abstract

Exogenous contaminants often co-occur in waste-activated sludge (WAS), but their potential mutual interactions and joint effects on the WAS treatment are less concerning. This work revealed that surfactants induced and aggravated the toxicity of Fe 2 O 3 nanoparticles (NPs) in volatile fatty acids (VFAs)' biosynthesis during WAS anaerobic fermentation. The VFA production exhibited a 40.1 and 20.3% inhibition compared to the individual LAS and CTAB reactors, respectively. A mechanistic exploration implied that the WAS solubilization, hydrolysis, and acidification steps during VFA generation were restrained. Moreover, the Fe 2 O 3 NPs' and surfactants' coexistence suppressed the acid-forming bacteria (i.e., Saprospiraceae_uncultured, Bacteroidetes vadinHA17_norank) and the homologous metabolic functions responsible for substrate hydrolysis (e.g., malZ and pepD), intracellular metabolism (e.g., pf kA and gdhA), VFAs' biosynthesis (e.g., bkdA and ackA), and ATP generation (e.g., atpE and atpH), resulting ultimately in VFAs' reduction. Furthermore, the surfactants contributed to the dispersibility of coexisting Fe 2 O 3 NPs to maintain the high reactivity of NPs. Besides, the WAS disintegration triggered by surfactants increased the interactions between Fe 2 O 3 NPs and microorganisms, thereby aggravating toxicity. Our study provides novel insights into environmental behaviors of co-occurring contaminants in the anaerobic environment and provides in-depth guidance for practical WAS treatment.

Predicting and Evaluating Different Pretreatment Methods on Methane Production from Sludge Anaerobic Digestion via Automated Machine Learning with Ensembled Semisupervised Learning

“…The difference might be mainly attributed to the various data sources. The mixed data set included the data from previous studies that focused on the effect of diverse contaminants (i.e., surfactants and NPs (CeO 2 and Fe 2 O 3 ) on the anaerobic digestion efficiency). , WAS anaerobic digestion was a primarily biological process, and the microbial metabolism was readily affected by various environmental factors, such as pH, temperature, and exogenous toxic pollutants (e.g., antibiotics, nanoparticles (NPs), surfactants, etc.). Their presence in the WAS anaerobic digesters might lead to changes of variable importance.…”

Effects of Mixtures of Engineered Nanoparticles and Cocontaminants on Anaerobic Digestion

“…In previous studies, the variations in ATP, NADH, and lactate dehydrogenase (LDH) release are typically used to assess general microbial activity and cell membrane disruption. For example, the presence of surfactants resulted in extracellular polymeric substances disintegration, which made ENPs and their metal ions interact with the previously captured anaerobes, and further exacerbated the inhibition of AD by ENPs. , This was confirmed by the increase in LDH release as well as the decrease in ATP in the copresence of ENPs and surfactants. Moreover, Fe 3 O 4 NPs, TiO 2 NPs, and cPAM were all found to have the potential to restore the inhibition of ATP and NADH expression or increase the LDH release induced by ZnO NPs. ,− This suggested that these cocontaminants are advantageous for preventing or restoring the inhibited intracellular metabolism, laying the foundation for the subsequent methanogenic reaction.…”

“…35 Similarly, another study reported that, the co-occurrence of nano-Fe 2 O 3 and surfactants (linear alkyl benzenesulfonates (LAS) and cetyltrimethylammonium bromide (CTAB)) also caused a reduction in VFAs' biosynthesis (40.1% and 20.3% inhibition by LAS + Fe 2 O 3 and CTAB + Fe 2 O 3 compared to the single LAS and CTAB digesters, respectively). 150 Both studies highlighted that specific fermentation steps such as acidogenesis, hydrolysis, and solubilization were significantly restrained under coexistence conditions. The abundance of Proteobacteria and Bacteroidetes significantly decreased when CeO 2 NPs and surfactants cooccurred.…”

“…152−154 Luo's team successively found that surfactants could improve the stability and dispersity of Fe 2 O 3 NPs and CeO 2 NPs through adjusting the Zeta potential with enhanced repulsion force, which may help to maintain a high specific surface area and catalytic activity, and thus increase the toxicity to anaerobes in AD. 35,150 Conversely, the adsorbed SDS or Fe 3 O 4 NPs altered the positively charged surface of ZnO NPs. 40,115 Meanwhile, the particles were agglomerated and precipitated, therefore decreasing the inhibiting effect of ZnO NPs on microbial cells.…”

“…However, their coexistence with surfactants counteracts the positive effect of surfactants on the activity of these enzymes, synchronously inhibiting the solubilization, hydrolysis, and acidogenesis processes in AD and ultimately leading to a decrease in VFAs. 35,150 Given that previous studies were mainly limited to the effects on several key enzymes mentioned above, the generation of byproducts during AD should include more enzymatic pathways to more comprehensively reflect the changes in different biochemical reactions, especially considering that the activity of coenzyme F 420 may not accurately represent the acetoclastic methanogenic activity. Consequently, future studies should consider other biomarkers such as cofactor F 430 .…”