State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
Hydrochina Huadong Engineering Corporation Limited, 201 Gaojiao Road, Hangzhou 311122, China.
Water Res. 2022 Aug 1;221:118793. doi: 10.1016/j.watres.2022.118793. Epub 2022 Jun 25.
This study proposed that decreasing liquid polarity could weaken the intermolecular polar force at solid-liquid interface of waste-activated sludge (WAS). Accordingly, a process for enhanced sludge dewatering through liquid polarity regulation was established. The liquid polarity was quantified by dielectric constant and the decrease of liquid dielectric constant below 50 was found to significantly improve the solid-liquid separation performance of WAS in terms of filterability by >70%. The differential scanning calorimeter (DSC) coupled with mass spectrum (MS) identified that 60 °C was the appropriate temperature for liquid amendment (i.e., acetonitrile) recovery from filtered sludge cake, and the corresponding energy consumption was calculated to be at most 799.0 J/g, which was substantially lower than that of water evaporation by sludge drying. The NaCl addition with 75% of saturated concentration could non-thermally recover 91.7 ± 4.9% of acetonitrile amendment from filtrate by salting-out. The great potentials in energy saving and recycle of chemicals make the newly proposed approach act as alternatives for the conventional process (i.e., mechanically dewatering + drying). Regarding the mechanism of liquid polarity regulation for enhanced WAS dewatering, the solid-liquid interfacial free energy was found to be reduced by 39.4% with the liquid dielectric constant decreasing from 78.50 to 41.00. Also, Tandem Mass Tags (TMT) proteomics tracked the phase-transfer of amphiphilic proteins with decreasing liquid polarity, which found that the solubilization of proteins involved in the Gene Ontology (GO) classifications of "membrane protein complex" and "membrane protein complex/outer membrane" could facilitate the enhanced solid-liquid separation of WAS. The conformational analysis on those differential proteins was further conducted to reveal the structure attributes of amphiphilic proteins for the phase-transfer feature. The proteins with more exposed amino acid residues (i.e., average solvent accessibility index over 1.8) tended to dissolve in the liquid phase with lower polarity, which was accompanied with the reduced interfacial free energy of WAS. On the contrary, the proteins with buried amino acid residues (e.g., the central hydrophobic β-sheet is surrounded by the hydrophilic α-helix) precipitated in the solid phase with the decreasing liquid polarity. All these findings are expected to create a novel option for dewatering WAS with recyclable liquid conditioning agents, and provide the improved mechanistic insights into the migration of interfacial compositions controlling the dewaterability of WAS.
本研究提出，降低液体极性可以削弱废活性污泥（WAS）固液界面的分子间极性力。因此，建立了一种通过液体极性调节来增强污泥脱水的工艺。通过介电常数来量化液体极性，发现液体介电常数降低到 50 以下可以显著提高 WAS 的固液分离性能，其过滤性能提高了超过 70%。差示扫描量热仪（DSC）与质谱（MS）联用鉴定出，60°C 是从过滤后的污泥饼中回收液体添加剂（即乙腈）的合适温度，相应的能量消耗计算值最高为 799.0 J/g，远低于污泥干燥过程中的水分蒸发。添加 75%饱和浓度的 NaCl 可以通过盐析非热回收滤液中 91.7±4.9%的乙腈添加剂。该方法在节能和化学试剂回收方面具有巨大潜力，使其成为传统工艺（即机械脱水+干燥）的替代方法。关于通过调节液体极性增强 WAS 脱水的机理，发现随着液体介电常数从 78.50 降低到 41.00，固液界面自由能降低了 39.4%。此外，串联质量标签（TMT）蛋白质组学跟踪了随着液体极性降低而发生的两亲性蛋白质的相转移，发现涉及“膜蛋白复合物”和“膜蛋白复合物/外膜”GO 分类的蛋白质的溶解有助于增强 WAS 的固液分离。进一步对那些差异表达蛋白进行构象分析，揭示了两亲性蛋白的结构属性，以阐明其相转移特征。具有更多暴露氨基酸残基（即平均溶剂可及性指数大于 1.8）的蛋白质倾向于溶解在极性较低的液相中，这伴随着 WAS 界面自由能的降低。相反，具有埋藏氨基酸残基（例如，中央疏水性β-折叠被亲水性α-螺旋包围）的蛋白质随着液体极性的降低而沉淀在固相。所有这些发现有望为使用可回收液体调节剂对 WAS 进行脱水创造一种新的选择，并为控制 WAS 脱水性能的界面成分迁移提供改进的机制见解。
