Widespread use of nanomaterials raises concerns. The underlying mechanism by which graphene oxide (GO) nanoparticles causes poor settleability of activated sludge remains unclear. To explore this mechanism, three reactors with different GO concentrations were established. Extended Derjaguin-Landau-Verwey-Overbeek theory indicated that GO destroyed the property of extracellular polymeric substances (EPS), increasing the energy barrier between bacteria. Low levels of uronic acid and hydrogen bonding in exopolysaccharide weakened the EPS gelation increasing aggregation repulsion. Lager amounts of hydrophilic amino acid and looser structure of extracellular proteins for exposing inner hydrophilic groups significantly contributed to the hydrophilicity of EPS. Both changes implied deterioration in EPS structure under GO stress. Metagenome demonstrated a decrease in genes responsible for capsular polysaccharide colonization and genes regulated the translocation of loose proteins were increased, which increased repulsion between bacteria. This study elucidated that changes in EPS secretion under GO exposure are the underlying causes of poor settleability.

中文翻译：

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氧化石墨烯引起的活性污泥非丝状膨胀：来自细胞外聚合物的见解

纳米材料的广泛使用引起了人们的担忧。氧化石墨烯（GO）纳米粒子导致活性污泥沉降性差的根本机制仍不清楚。为了探索这一机制，建立了三个具有不同GO浓度的反应器。扩展的 Derjaguin-Landau-Verwey-Overbeek 理论表明，GO 破坏了细胞外聚合物 (EPS) 的特性，增加了细菌之间的能量屏障。胞外多糖中低水平的糖醛酸和氢键削弱了 EPS 凝胶化，增加了聚集排斥力。大量的亲水性氨基酸和暴露内部亲水基团的胞外蛋白结构较松散，显着提高了 EPS 的亲水性。这两个变化都意味着 EPS 结构在 GO 压力下恶化。宏基因组显示，负责荚膜多糖定植的基因减少，而调节松散蛋白质易位的基因增加，从而增加了细菌之间的排斥力。这项研究阐明了 GO 暴露下 EPS 分泌的变化是沉降性差的根本原因。