Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering, University of Valladolid, Dr. Mergelina s/n, 47011 Valladolid, Spain; Institute of Sustainable Processes, Dr. Mergelina s/n, 47011 Valladolid, Spain.
Institute of Sustainable Processes, Dr. Mergelina s/n, 47011 Valladolid, Spain; Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Fortaleza, Ceará, Brazil.
Sci Total Environ. 2020 Mar 1;706:135136. doi: 10.1016/j.scitotenv.2019.135136. Epub 2019 Nov 21.
The valorization of biogas as a feedstock for the generation of added-value bioproducts will play a key role on the sustainability of anaerobic digestion. The present work assessed the influence of key environmental parameters (O:CH ratio, temperature and nitrogen source) on the growth and polyhydroxybutyrate (PHB) synthesis under nitrogen limiting conditions of the type II methanotroph Methylocystis hirsuta CSC1 using biogas as a feedstock. The O:CH ratios tested (1:1, 1.5:1 and 2:1) did not affect significantly M. hirsuta CSC1 growth yields (5 g TSS mol CH), although lower CH removal rates were reached under O-limiting conditions (ratio 1:1). The highest PHB content (45 wt%) was achieved at a ratio 2:1 and was threefold higher than those obtained at lower ratios (15 wt%). The increase in temperature from 15 to 25 °C resulted in increases in the growth yield (from 5 to 6 g TSS mol CH) and PHB content (from 32 to 40 wt%). Conversely, the lowest PHB content (30 wt%) was reached at 37 °C, together with a negligible growth under nutrient sufficient conditions. The nitrogen source also played a key role on both M. hirsuta CSC1 growth and PHB synthesis. Thus, ammonium resulted in the highest growth yield (7 g TSS mol CH), although the maximum PHB content was achieved when biomass was previously grown in nitrate as the nitrogen source (41 wt%). Nitrite exerted an inhibitory effect on M. hirsuta CSC1 growth.
沼气作为增值生物制品的原料的增值将在厌氧消化的可持续性方面发挥关键作用。本工作评估了关键环境参数（O:CH 比、温度和氮源）对以沼气为原料的 II 型甲烷营养菌 Methylocystis hirsuta CSC1 在氮限制条件下生长和聚羟基丁酸（PHB）合成的影响。测试的 O:CH 比（1:1、1.5:1 和 2:1）对 M. hirsuta CSC1 的生长产率（5 g TSS mol CH）没有显著影响，尽管在 O 限制条件下（比 1:1）达到了较低的 CH 去除率。在 2:1 的比例下达到了最高的 PHB 含量（45 wt%），比在较低比例下获得的 PHB 含量（15 wt%）高三倍。从 15°C 升高到 25°C 导致生长产率（从 5 增加到 6 g TSS mol CH）和 PHB 含量（从 32 增加到 40 wt%）增加。相反，在 37°C 时达到了最低的 PHB 含量（30 wt%），同时在营养充足的条件下生长几乎可以忽略不计。氮源对 M. hirsuta CSC1 的生长和 PHB 合成也起着关键作用。因此，铵盐导致了最高的生长产率（7 g TSS mol CH），尽管当生物质以前以硝酸盐作为氮源生长时达到了最大 PHB 含量（41 wt%）。亚硝酸盐对 M. hirsuta CSC1 的生长有抑制作用。
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