Dionisi Davide, Majone Mauro, Papa Viviana, Beccari Mario
Department of Chemistry, University of Rome La Sapienza, P le Aldo Moro 5, 00185, Rome, Italy.
Biotechnol Bioeng. 2004 Mar 20;85(6):569-79. doi: 10.1002/bit.10910.
This article describes a new process for the production of biopolymers (polyhydroxyalkanoates, PHAs) based on the aerobic enrichment of activated sludge to obtain mixed cultures able to store PHAs at high rates and yields. Enrichment was obtained through the selective pressure established by feeding the carbon source in a periodic mode (feast and famine regime) in a sequencing batch reactor. A concentrated mixture of acetic, lactic, and propionic acids (overall concentration of 8.5 gCOD L(-1)) was fed every 2 h at 1 day(-1) overall dilution rate. Even at such high organic load (8.5 gCOD L(-1) day(-1)), the selective pressure due to periodic feeding was effective in obtaining a biomass with a storage ability much higher than activated sludges. The immediate biomass response to substrate excess (as determined thorough short-term batch tests) was characterized by a storage rate and yield of 649 mgPHA (as COD) g biomass (as COD)(-1) h(-1) and 0.45 mgPHA (as COD) mg removed substrates (as COD(-1)), respectively. When the substrate excess was present for more than 2 h (long-term batch tests), the storage rate and yield decreased, whereas growth rate and yield significantly increased due to biomass adaptation. A maximum polymer fraction in the biomass was therefore obtained at about 50% (on COD basis). As for the PHA composition, the copolymer poly(beta-hydroxybutyrate/beta-hydroxyvalerate) with 31% of hydroxyvalerate monomer was produced from the substrate mixture. Comparison of the tests with individual and mixed substrates seemed to indicate that, on removing the substrate mixture for copolymer production, propionic acid was fully utilized to produce propionylCoA, whereas the acetylCoA was fully provided by acetic and lactic acid.
本文介绍了一种生产生物聚合物（聚羟基脂肪酸酯，PHA）的新工艺，该工艺基于对活性污泥进行好氧富集，以获得能够高速率、高产量储存PHA的混合培养物。通过在序批式反应器中以周期性模式（ feast和famine模式）投喂碳源所建立的选择压力来实现富集。每2小时以1天（-1）的总稀释率投喂乙酸、乳酸和丙酸的浓缩混合物（总浓度为8.5 gCOD L（-1））。即使在如此高的有机负荷（8.5 gCOD L（-1）天（-1））下，周期性投喂产生的选择压力仍有效地获得了一种储存能力远高于活性污泥的生物质。通过短期批次试验确定，生物质对底物过量的即时响应特征在于储存速率和产量分别为649 mgPHA（以COD计）g生物质（以COD计）（-1）h（-1）和0.45 mgPHA（以COD计）mg去除底物（以COD（-1）计）。当底物过量存在超过2小时（长期批次试验）时，储存速率和产量下降，而由于生物质适应，生长速率和产量显著增加。因此，在生物质中获得了约50%（基于COD）的最大聚合物分数。至于PHA组成，由底物混合物产生了含有31%羟基戊酸单体的共聚物聚（β-羟基丁酸酯/β-羟基戊酸酯）。对使用单一底物和混合底物的试验进行比较似乎表明，在去除用于共聚物生产的底物混合物时，丙酸被完全用于生产丙酰辅酶A，而乙酰辅酶A则完全由乙酸和乳酸提供。
