Waste lipids are attractive substrates for co-digestion with primary and activated sewage sludge (PASS) to improve biogas production at wastewater treatment plants. However, slow conversion rates of long-chain fatty acids (LCFA), produced during anaerobic digestion (AD), limit the applicability of waste lipids as co-substrates for PASS. Previous observations indicate that the sulfide level in PASS digesters affects the capacity of microbial communities to convert LCFA to biogas. This study assessed the microbial community response to LCFA loads in relation to sulfide level during AD of PASS by investigating process performance and microbial community dynamics upon addition of oleate (C18:1) and stearate (C18:0) to PASS digesters at ambient and elevated sulfide levels. Conversion of LCFA to biogas was limited (30% of theoretical biogas potential) during continuous co-digestion with PASS, which resulted in further LCFA accumulation. However, the accumulated LCFA were converted to biogas (up to 66% of theoretical biogas potential) during subsequent batch-mode digestion, performed without additional substrate load. Elevated sulfide level stimulated oleate (but not stearate) conversion to acetate, but oleate and sulfide imposed a synergistic limiting effect on acetoclastic methanogenesis and biogas formation. Next-generation sequencing of 16S rRNA gene amplicons of bacteria and archaea showed that differences in sulfide level and LCFA type resulted in microbial community alterations with distinctly different patterns. Taxonomic profiling of the sequencing data revealed that the phylum Cloacimonetes is likely a key group during LCFA degradation in PASS digesters, where different members take part in degradation of saturated and unsaturated LCFA; genus W5 (family Cloacimonadaceae) and family W27 (order Cloacimonadales), respectively. In addition, LCFA-degrading Syntrophomonas, which is commonly present in lipid-fed digesters, increased in relative abundance after addition of oleate at elevated sulfide level, but not without sulfide or after stearate addition. Stearate conversion to biogas was instead associated with increasing abundance of hydrogen-producing Smithella and hydrogenotrophic Methanobacterium. Long-chain fatty acid chain saturation and sulfide level are selective drivers for establishment of LCFA-degrading microbial communities in municipal sludge digesters.

中文翻译：

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市政污泥消化池中的硫化物水平影响微生物群落对长链脂肪酸负荷的反应

废脂是一种有吸引力的底物，可与初级和活性污水污泥 (PASS) 共同消化，以提高污水处理厂的沼气产量。然而，在厌氧消化 (AD) 过程中产生的长链脂肪酸 (LCFA) 的缓慢转化率限制了废脂质作为 PASS 共底物的适用性。先前的观察表明，PASS 消化器中的硫化物水平会影响微生物群落将 LCFA 转化为沼气的能力。本研究通过调查在环境和升高的 PASS 消化器中添加油酸盐 (C18:1) 和硬脂酸盐 (C18:0) 后的工艺性能和微生物群落动态，评估了微生物群落对 LCFA 负荷与 PASS AD 期间硫化物水平的反应硫化物水平。在与 PASS 连续共消化期间，LCFA 向沼气的转化受到限制（理论沼气潜力的 30%），这导致 LCFA 进一步积累。然而，在随后的分批模式消化过程中，累积的 LCFA 转化为沼气（高达理论沼气潜力的 66%），无需额外的底物负载。硫化物水平升高刺激油酸盐（但不是硬脂酸盐）转化为醋酸盐，但油酸盐和硫化物对醋酸碎裂产甲烷和沼气形成具有协同限制作用。细菌和古细菌的 16S rRNA 基因扩增子的二代测序表明，硫化物水平和 LCFA 类型的差异导致微生物群落的改变具有明显不同的模式。测序数据的分类分析表明，Cloacimonetes 门可能是 PASS 消化器中 LCFA 降解过程中的一个关键组，其中不同的成员参与了饱和和不饱和 LCFA 的降解；W5 属 (Cloacimonadales 科) 和 W27 家族 (Cloacimonadales)。此外，通常存在于脂质饲喂消化器中的 LCFA 降解合养单胞菌在添加油酸以提高硫化物水平后相对丰度增加，但在没有硫化物或添加硬脂酸盐后并非如此。相反，将硬脂酸盐转化为沼气与产氢史密斯氏菌和氢营养甲烷杆菌的丰度增加有关。