College of Environmental Science and Engineering, Hunan University, Changsha 410082, PR China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, PR China.
College of Environmental Science and Engineering, Hunan University, Changsha 410082, PR China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, PR China.
Water Res. 2022 Aug 1;221:118742. doi: 10.1016/j.watres.2022.118742. Epub 2022 Jun 14.
Rhamnolipid (RL), one representative biosurfactant, is widely regarded as an economically feasible and environmentally beneficial additive to improve fermentation efficiency and resource recovery from waste activated sludge (WAS). However, its potentially detrimental impact on WAS fermentation such as HS generation was overlooked previously. This study therefore aims to fill the gap through exploring whether and how the presence of RL affects HS generation from WAS anaerobic fermentation. Experimental results showed that when RL increased from 0 to 40 mg/g total suspended solids (TSS), the cumulative HS yield enhanced from 323.6 × 10 to 620.3 × 10 mg/g volatile suspended solids (VSS). Mechanism analysis showed that RL reduced WAS surface tension, which benefited transformations of organic sulfurs (e.g., aliphatic-S and sulfoxide) and inorganic sulfate from solid to liquid phase. The presence of RL not only reduced the ratio of α-helix/(β-sheet + random coil) and damaged the hydrogen bonding networks of organic sulfurs but also promoted substrate surface charges and cell membrane permeability. These facilitated the contact between hydrolase and organic sulfurs, thereby increasing sulfide production from organic sulfurs hydrolysis. Further investigations showed that RL promoted the expression of key genes (e.g., aprA/B and dsrA/B) involved in the dissimilatory sulfate reduction, which accelerated the reaction of adenosine 5'-phosphosulfate (APS)→ sulfite→ sulfide. Meanwhile, RL inhibited the corresponding key genes such as CysH, and Sir, responsible for assimilatory sulfate reduction (APS→3'-phosphoadenosine-5'phosphosulfate→organosulfur), which reduced substrate competition in favor of HS production from dissimilatory sulfate reduction. Besides, RL decreased the fermentation pH, which benefited the transformation of HS to HS.
鼠李糖脂（RL）作为一种有代表性的生物表面活性剂，被广泛认为是一种经济可行且对环境有益的添加剂，可以提高发酵效率并从废活性污泥（WAS）中回收资源。然而，它对 WAS 发酵的潜在不利影响，如 HS 的产生，以前被忽视了。因此，本研究旨在通过探索 RL 的存在是否以及如何影响 WAS 厌氧发酵中 HS 的产生来填补这一空白。实验结果表明，当 RL 从 0 增加到 40mg/g 总悬浮固体（TSS）时，HS 的累积产率从 323.6×10 增加到 620.3×10mg/g 挥发性悬浮固体（VSS）。机理分析表明，RL 降低了 WAS 的表面张力，有利于有机硫（如脂肪族-S 和亚砜）和无机硫酸盐从固相到液相的转化。RL 的存在不仅降低了α-螺旋/（β-折叠+无规卷曲）的比例，破坏了有机硫的氢键网络，而且促进了基质表面电荷和细胞膜通透性。这促进了水解酶与有机硫的接触，从而增加了有机硫水解产生的硫化物。进一步的研究表明，RL 促进了参与异化硫酸盐还原的关键基因（如 aprA/B 和 dsrA/B）的表达，从而加速了腺苷 5'-磷酸硫酸（APS）→亚硫酸盐→硫化物的反应。同时，RL 抑制了负责同化硫酸盐还原（APS→3'-磷酸腺苷-5'-磷酸硫酸→有机硫）的相应关键基因，如 CysH 和 Sir，减少了基质竞争，有利于异化硫酸盐还原产生 HS。此外，RL 降低了发酵 pH 值，有利于 HS 向 HS 的转化。
