Traditional bioenergy recovery in the form of short chain fatty acids (SCFAs) from waste activated sludge (WAS) is generally limited by economic unattractiveness and complexity of products separation. Herein, a novel biotechnology process of two-stage anaerobic fermentation for converting the WAS into high energy density, easy-separated medium chain fatty acids (MCFAs) and long-chain alcohols (LCAs) was evaluated. In this process, the WAS was first converted to WAS alkaline fermentation liquid (WASAFL), serving as electron acceptors (EAs) and inoculum, then adding ethanol as electron donor (ED) for chain elongation (CE). The co-production of MCFAs and LCAs during CE were studied under three different ED to EA ratios, i.e., 3:1, 4:1 and 5:1. Experimental results demonstrated that when the ratio of ED to EA increased from 3:1 to 5:1, the production of MCFA and LCAs respectively increased from 5.57 ± 0.17 and 2.58 ± 0.18 to7.67 ± 0.48 and 4.21 ± 0.19 g COD/L. A similar observation was made in the total product electron efficiency, increasing from 59.9% to 72.1%. However, the highest total product selectivity (i.e., 68.0%) and highest products production yield (i.e., 59.77%) were not achieved at the ED to EA ratio of 5:1 due to toxicity caused by higher accumulation of n-caproate. The kinetic analysis further confirmed that high ratio of ED to EA induced improvement in product maximum yield, production rate for both MCFAs and LCAs. Microbial community analysis indicated that Clostridium, Caproiciproducens, Acinetobacter, Exilispira, and Oscillibacter were clearly enriched in the CE reactor and had positive correlation with MCFAs and LCAs production.

从废物活性污泥（WAS）中以短链脂肪酸（SCFA）形式进行的传统生物能源回收通常受到经济上缺乏吸引力和产品分离复杂性的限制。本文中，评估了将厌氧发酵转化为高能量密度，易分离的中链脂肪酸（MCFAs）和长链醇（LCA）的两阶段厌氧发酵的新生物技术工艺。在此过程中，首先将WAS转化为WAS碱性发酵液（WASAFL），用作电子受体（EA）和接种物，然后添加乙醇作为电子供体（ED）进行链延长（CE）。在三种不同的ED与EA比率（即3：1、4：1和5：1）下研究了CE期间MCFA和LCA的联产。实验结果表明，当ED与EA的比例从3：1增加到5：1时，MCFA和LCAs的产量分别从5.57±0.17和2.58±0.18增至7.67±0.48和4.21±0.19 g COD / L。在总产品电子效率方面也有类似的观察，从59.9％增加到72.1％。然而，由于正己酸较高的积累引起的毒性，在ED与EA的比例为5：1时，没有达到最高的总产品选择性（即68.0％）和最高的产品产量（即59.77％）。动力学分析进一步证实，高比例的ED与EA可以提高MCFA和LCA的产品最大产率，生产率。微生物群落分析表明 9％至72.1％。然而，由于正己酸较高的积累引起的毒性，在ED与EA的比例为5：1时，没有达到最高的总产品选择性（即68.0％）和最高的产品产量（即59.77％）。动力学分析进一步证实，高比例的ED与EA可以提高MCFA和LCA的产品最大产率，生产率。微生物群落分析表明 9％至72.1％。然而，由于正己酸较高的积累引起的毒性，在ED与EA的比例为5：1时，没有达到最高的总产品选择性（即68.0％）和最高的产品产量（即59.77％）。动力学分析进一步证实，高比例的ED与EA可以提高MCFA和LCA的产品最大产率，生产率。微生物群落分析表明梭菌，己生菌，不动杆菌，Exilispira和Oscillibacter在CE反应器中明显富集，并且与MCFA和LCA的产生呈正相关。