Glycerol conversion by Aerobic Granular Sludge

Glycerol is abundantly present in wastewater from industries such as biodiesel production facilities. Glycerol is also a potential carbon source for microbes that are involved in wastewater nutrient removal processes. The conversion of glycerol in biological phosphorus removal of aerobic granular sludge processes has not been explored to date. The current study describes the effect of glycerol on sludge granulation and enhanced biological phosphorus removal (EBPR). Robust granules with good phosphorus removal capabilities were formed in an aerobic granular sludge sequencing batch reactor fed with glycerol. The interaction between the fermentative conversion of glycerol and product uptake by polyphosphate accumulating organisms (PAO) was studied using stoichiometric and microbial community analysis. Metagenomic, metaproteomic and microscopic (Fluorescence in-situ Hybridization) analysis identified a community dominated by fermentative Actinobacteria (Tessaracoccus and Micropruina) and a typical PAO known as Ca. Accumulibacter. Glycerol uptake facilitator (glpF) and glycerol kinase (glpK), two proteins involved in the transport of glycerol into the cellular metabolism, were only observed in the genome of the Actinobacteria. The anaerobic conversion appeared to be a combination of a substrate fermentation and product uptake-type reaction. Initially, glycerol fermentation led mainly to the production of 1,3-propanediol (1,3-PDO) which was not sequestered under anaerobic conditions. Despite the aerobic conversion of 1,3-PDO stable granulation was observed. Over time, 1,3-PDO production decreased and complete anaerobic COD uptake was observed. The results demonstrate that glycerol-containing wastewater can effectively be treated by the aerobic granular sludge process and that fermentative and polyphosphate accumulating organisms can form a food chain in glycerol-based EBPR processes.

甘油（Glycerol）广泛存在于生物柴油生产设施等行业的废水中。同时，甘油也是参与污水营养盐去除过程的微生物的潜在碳源。截至目前，好氧颗粒污泥工艺生物除磷环节中甘油的转化机制尚未得到探索。本研究探讨了甘油对污泥颗粒化及强化生物除磷（Enhanced Biological Phosphorus Removal, EBPR）的影响。在以甘油为底物的好氧颗粒污泥序批式反应器中，成功形成了具备优异除磷性能的稳定颗粒污泥。本研究通过计量学与微生物群落分析手段，探究了甘油发酵转化与聚磷微生物（Polyphosphate Accumulating Organisms, PAO）对产物摄取之间的相互作用。宏基因组学、宏蛋白质组学以及荧光原位杂交（Fluorescence in-situ Hybridization）分析结果显示，群落以发酵型放线菌（Tessaracoccus属与Micropruina属）以及典型聚磷微生物"Ca. Accumulibacter"为主。甘油摄取促进因子（glpF）与甘油激酶（glpK）这两种参与甘油向细胞代谢转运的蛋白质，仅在放线菌的基因组中被检测到。厌氧转化过程表现为底物发酵与产物摄取型反应的结合模式。初始阶段，甘油发酵主要生成1,3-丙二醇（1,3-PDO），该产物在厌氧条件下未被截留。尽管1,3-丙二醇发生了好氧转化，但仍观测到了稳定的颗粒污泥形成。随着反应进行，1,3-丙二醇的生成量逐渐降低，并观测到厌氧阶段化学需氧量（Chemical Oxygen Demand, COD）的完全摄取。研究结果表明，含甘油废水可通过好氧颗粒污泥工艺得到有效处理，且发酵型微生物与聚磷微生物可在以甘油为底物的强化生物除磷工艺中形成食物链。