Abstract Proper pretreatment of waste activated sludge is commonly needed before biohydrogen fermentation due to its complex floc structure. Considering that the outer-layer extracellular polymeric substances (EPS) could restrict the disintegration of inner-layer microbial cells during the pretreatment of sludge, this study firstly applied sodium citrate pretreatment (0.3 g/g-TSS) for removing EPS from sludge flocs, followed by ultrasonic pretreatment (2 W/mL, 15 min), which aimed to enhance the disintegration efficiency. The subsequent hydrogen fermentation performance was tested in batch mode at 37 °C and initial pH 7.0. Results showed that the combined sodium citrate-ultrasonic pretreatment significantly disrupted the sludge floc structure and promoted soluble COD concentration by 157.5 times, which synergistically enhanced the biohydrogen fermentation performance. The maximum hydrogen yield of 38.8 mL/g-VSadded was achieved with the combined pretreatment, which was 604.2%, 155.1%, and 92.6% higher compared to the control, individual ultrasonic pretreatment, and individual sodium citrate pretreatment, respectively. Correspondingly, the energy conversion efficiency increased from 7.4% to 32.8% through the combined pretreatment. The combined pretreatment also enhanced the organics utilization, induced a more efficient fermentative pathway, and shortened the hydrogen-generating lag phase. More enrichment of hydrogen-producing bacteria, especially the genera Clostridium sensu stricto and Paraclostridium, was responsible for the synergistic enhancement in hydrogen yield and energy conversion efficiency. The present work puts forward an effective and eco-friendly pretreatment approach for enhancing bioenergy recovery from waste activated sludge.

中文翻译：

---

柠檬酸钠联合超声预处理废弃活性污泥制氢：能量转换与微生物群落

摘要 废活性污泥絮体结构复杂，在生物制氢发酵前通常需要对其进行适当的预处理。考虑到外层胞外聚合物（EPS）在污泥预处理过程中会限制内层微生物细胞的分解，本研究首先采用柠檬酸钠（0.3 g/g-TSS）预处理去除污泥絮体中的EPS，随后进行超声预处理（2 W/mL，15 分钟），旨在提高崩解效率。随后的氢发酵性能在 37 °C 和初始 pH 值 7.0 下以分批模式进行测试。结果表明，柠檬酸钠-超声联合预处理显着破坏了污泥絮体结构，将可溶性COD浓度提高了157.5倍，协同提高了生物氢发酵性能。联合预处理的最大氢气产量为 38.8 mL/g-VS，分别比对照、单独超声预处理和单独柠檬酸钠预处理高 604.2%、155.1% 和 92.6%。相应地，通过联合预处理，能量转换效率从7.4%提高到32.8%。联合预处理还提高了有机物的利用率，诱导了更有效的发酵途径，并缩短了制氢滞后期。产氢细菌的更多富集，特别是狭义梭菌属和副梭菌属，负责协同提高产氢率和能量转换效率。