Shakeri Yekta Sepehr, Liu Tong, Axelsson Bjerg Mette, Šafarič Luka, Karlsson Anna, Björn Annika, Schnürer Anna
1Department of Thematic Studies-Environmental Change and Biogas Research Center, Linköping University, 581 83 Linköping, Sweden.
2Department of Molecular Sciences, Uppsala BioCenter, Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden.
Biotechnol Biofuels. 2019 Nov 2;12:259. doi: 10.1186/s13068-019-1598-1. eCollection 2019.
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 (C) and stearate (C) 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 , 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 and hydrogenotrophic .
Long-chain fatty acid chain saturation and sulfide level are selective drivers for establishment of LCFA-degrading microbial communities in municipal sludge digesters.
废弃油脂是与原污水污泥和活性污泥（PASS）共消化以提高污水处理厂沼气产量的有吸引力的底物。然而，厌氧消化（AD）过程中产生的长链脂肪酸（LCFA）转化率低，限制了废弃油脂作为PASS共底物的适用性。先前的观察表明，PASS消化池中硫化物水平会影响微生物群落将LCFA转化为沼气的能力。本研究通过在环境硫化物水平和升高的硫化物水平下向PASS消化池中添加油酸（C）和硬脂酸（C）后，研究过程性能和微生物群落动态，评估了AD过程中微生物群落对与硫化物水平相关的LCFA负荷的响应。
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%），这导致了LCFA的进一步积累。然而，在随后的无额外底物负荷的批次模式消化期间，积累的LCFA被转化为沼气（高达理论沼气潜力的66%）。升高的硫化物水平刺激了油酸（而非硬脂酸）向乙酸盐的转化，但油酸和硫化物对乙酸裂解产甲烷作用和沼气形成产生了协同限制作用。对细菌和古菌的16S rRNA基因扩增子进行的下一代测序表明，硫化物水平和LCFA类型的差异导致微生物群落发生具有明显不同模式的改变。对测序数据的分类分析表明，Cloacimonetes门可能是PASS消化池中LCFA降解过程中的关键菌群，其中不同成员参与饱和和不饱和LCFA的降解；分别是W5属（Cloacimonadaceae科）和W27科（Cloacimonadales目）。此外，通常存在于以脂质为食的消化池中的LCFA降解菌，在硫化物水平升高时添加油酸后相对丰度增加，但在无硫化物或添加硬脂酸后则没有增加。相反，硬脂酸向沼气的转化与产氢菌和氢营养菌丰度的增加有关。
长链脂肪酸链饱和度和硫化物水平是城市污泥消化池中建立LCFA降解微生物群落的选择性驱动因素。
