Gaby John Christian, Zamanzadeh Mirzaman, Horn Svein Jarle
Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway.
Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, P.O. Box 14155-6446, Tehran, Iran.
Biotechnol Biofuels. 2017 Dec 14;10:302. doi: 10.1186/s13068-017-0989-4. eCollection 2017.
Food waste is a large bio-resource that may be converted to biogas that can be used for heat and power production, or as transport fuel. We studied the anaerobic digestion of food waste in a staged digestion system consisting of separate acidogenic and methanogenic reactor vessels. Two anaerobic digestion parameters were investigated. First, we tested the effect of 55 vs. 65 °C acidogenic reactor temperature, and second, we examined the effect of reducing the hydraulic retention time (HRT) from 17 to 10 days in the methanogenic reactor. Process parameters including biogas production were monitored, and the microbial community composition was characterized by 16S amplicon sequencing.
Neither organic matter removal nor methane production were significantly different for the 55 and 65 °C systems, despite the higher acetate and butyrate concentrations observed in the 65 °C acidogenic reactor. Ammonium levels in the methanogenic reactors were about 950 mg/L NH when HRT was 17 days but were reduced to 550 mg/L NH at 10 days HRT. Methane production increased from ~ 3600 mL/day to ~ 7800 when the HRT was decreased. Each reactor had unique environmental parameters and a correspondingly unique microbial community. In fact, the distinct values in each reactor for just two parameters, pH and ammonium concentration, recapitulate the separation seen in microbial community composition. The thermophilic and mesophilic digesters were particularly distinct from one another. The 55 °C acidogenic reactor was mainly dominated by and , whereas the 65 °C acidogenic reactor was initially dominated by but later was overtaken by . The acidogenic reactors were lower in diversity (34-101 observed OTU, 1.3-2.5 Shannon) compared to the methanogenic reactors (472-513 observed OTU, 5.1-5.6 Shannon). The microbial communities in the acidogenic reactors were > 90% Firmicutes, and the Euryarchaeota were higher in relative abundance in the methanogenic reactors.
The digestion systems had similar biogas production and COD removal rates, and hence differences in temperature, NH concentration, and pH in the reactors resulted in distinct but similarly functioning microbial communities over this range of operating parameters. Consequently, one could reduce operational costs by lowering both the hydrolysis temperature from 65 to 55 °C and the HRT from 17 to 10 days.
食物垃圾是一种大量的生物资源，可转化为沼气，用于供热、发电或作为运输燃料。我们研究了在一个由单独的产酸和产甲烷反应容器组成的分段消化系统中食物垃圾的厌氧消化。研究了两个厌氧消化参数。第一，我们测试了产酸反应器温度为55℃与65℃的效果；第二，我们研究了在产甲烷反应器中将水力停留时间（HRT）从17天减少到10天的效果。监测了包括沼气产量在内的工艺参数，并通过16S扩增子测序对微生物群落组成进行了表征。
尽管在65℃的产酸反应器中观察到较高的乙酸盐和丁酸盐浓度，但55℃和65℃系统的有机物去除率和甲烷产量均无显著差异。当HRT为17天时，产甲烷反应器中的铵水平约为950mg/L NH，但在HRT为10天时降至550mg/L NH。当HRT降低时，甲烷产量从约3600mL/天增加到约7800mL/天。每个反应器都有独特的环境参数和相应独特的微生物群落。事实上，每个反应器中仅pH值和铵浓度这两个参数的不同值，就概括了微生物群落组成中所看到的差异。嗜热和中温消化器彼此特别不同。55℃的产酸反应器主要由 和 主导，而65℃的产酸反应器最初由 主导，但后来被 取代。与产甲烷反应器（观察到472 - 513个OTU，香农指数为5.1 - 5.6）相比，产酸反应器的多样性较低（观察到34 - 101个OTU，香农指数为1.3 - 2.5）。产酸反应器中的微生物群落>90％为厚壁菌门，而广古菌门在产甲烷反应器中的相对丰度更高。
消化系统具有相似的沼气产量和化学需氧量去除率，因此反应器中温度、NH浓度和pH值的差异导致在该操作参数范围内微生物群落不同但功能相似。因此，可以通过将水解温度从65℃降至55℃以及将HRT从17天降至10天来降低运营成本。
