Calicioglu Ozgul, Shreve Michael J, Richard Tom L, Brennan Rachel A
1Department of Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, University Park, 16802 USA.
2Department of Agricultural and Biological Engineering, The Pennsylvania State University, 132 Land and Water Research Building, University Park, PA 16802 USA.
Biotechnol Biofuels. 2018 Oct 8;11:275. doi: 10.1186/s13068-018-1278-6. eCollection 2018.
Duckweeds (Lemnaceae) are efficient aquatic plants for wastewater treatment due to their high nutrient-uptake capabilities and resilience to severe environmental conditions. Combined with their rapid growth rates, high starch, and low lignin contents, duckweeds have also gained popularity as a biofuel feedstock for thermochemical conversion and alcohol fermentation. However, studies on the acidogenic anaerobic digestion of duckweed into carboxylic acids, another group of chemicals which are precursors of higher-value chemicals and biofuels, are lacking. In this study, a series of laboratory batch experiments were performed to determine the favorable operating conditions (i.e., temperature and pH) to maximize carboxylic acid production from wastewater-derived duckweed during acidogenic digestion. Batch reactors with 25 g/l solid loading were operated anaerobically for 21 days under mesophilic (35 °C) or thermophilic (55 °C) conditions at an acidic (5.3) or basic (9.2) pH. At the conclusion of the experiment, the dominant microbial communities under various operating conditions were assessed using high-throughput sequencing.
The highest duckweed-carboxylic acid conversion of 388 ± 28 mg acetic acid equivalent per gram volatile solids was observed under mesophilic and basic conditions, with an average production rate of 0.59 g/l/day. This result is comparable to those reported for acidogenic digestion of other organics such as food waste. The superior performance observed under these conditions was attributed to both chemical treatment and microbial bioconversion. Hydrogen recovery was only observed under acidic thermophilic conditions, as 23.5 ± 0.5 ml/g of duckweed volatile solids added. More than temperature, pH controlled the overall structure of the microbial communities. For instance, differentially abundant enrichments of were observed in acidic samples, whereas enrichments of were found in the basic samples. Acidic mesophilic conditions were found to enrich acetoclastic methanogenic populations over processing times longer than 10 days.
Operating conditions have a significant effect on the yield and composition of the end products resulting from acidogenic digestion of duckweed. Wastewater-derived duckweed is a technically feasible alternative feedstock for the production of advanced biofuel precursors; however, techno-economic analysis is needed to determine integrated full-scale system feasibility and economic viability.
浮萍（浮萍科）因其高养分吸收能力和对恶劣环境条件的适应能力，是用于废水处理的高效水生植物。结合其快速生长速率、高淀粉含量和低木质素含量，浮萍作为热化学转化和酒精发酵的生物燃料原料也受到欢迎。然而，关于浮萍产酸厌氧消化生成羧酸（另一组高价值化学品和生物燃料的前体化学品）的研究却很缺乏。在本研究中，进行了一系列实验室批次实验，以确定在产酸消化过程中使源自废水的浮萍羧酸产量最大化的有利操作条件（即温度和pH值）。固体负荷为25 g/l的批次反应器在中温（35°C）或高温（55°C）条件下，于酸性（5.3）或碱性（9.2）pH值下厌氧运行21天。在实验结束时，使用高通量测序评估了各种操作条件下的优势微生物群落。
在中温和碱性条件下，观察到浮萍-羧酸的最高转化率为每克挥发性固体388±28毫克乙酸当量，平均产率为0.59 g/l/天。该结果与其他有机物（如食物垃圾）产酸消化的报道结果相当。在这些条件下观察到的优越性能归因于化学处理和微生物生物转化。仅在酸性高温条件下观察到氢气回收，添加量为23.5±0.5 ml/g浮萍挥发性固体。pH值比温度更能控制微生物群落的整体结构。例如，在酸性样品中观察到不同丰度的 富集，而在碱性样品中发现 富集。发现酸性中温条件在处理时间超过10天时会富集乙酸分解产甲烷菌种群。
操作条件对浮萍产酸消化的最终产物产量和组成有显著影响。源自废水的浮萍是生产先进生物燃料前体的技术可行替代原料；然而，需要进行技术经济分析以确定综合全规模系统的可行性和经济可行性。
