【作者】 刘晓玲；

【导师】 陈坚；

【作者基本信息】 江南大学 ， 环境工程， 2008， 博士

【摘要】 城市污泥产生总量随着国民经济持续快速发展迅速地增加,因此发展经济有效的污泥处理处置技术迫在眉睫。由于污泥中含有较高的有机质,将这些廉价的有机质转化生产高附加值生物化学品,特别是挥发性脂肪酸不失为污泥资源化的一条新途径。这条新途径不仅可使污泥获得减量化、无害化处理,而且也使得污泥中的有机成分能够得到更好利用。本论文在确立合适底物污泥及最佳预处理技术的基础上,对厌氧发酵产酸的pH和底物初始C/N控制策略开展了研究,通过结合末端限制性片断长度多样性分子技术和荧光原位杂交技术对发酵产酸过程中的微生物种群结构和促使乙酸累积的微生物学机理进行了解析,并在检测形成挥发性脂肪酸的代谢途径中的关键酶的活性基础上,进一步探讨了促使不同单酸累积的主要代谢途径。主要的研究结果如下:(1)直接利用污泥厌氧发酵产酸,发酵结束时蛋白质、碳水化合物和挥发性有机质三者的含量均超过67%。有机质转化率较低,导致挥发性短链脂肪酸的产率难以提高。(2)通过考察热-碱、超声波-碱、热-酸和超声波-酸预处理技术对污泥融胞效果的影响,发现两种碱处理方法能够显著改善高固体浓度的污泥有机质融出效率。污泥中有机质和蛋白类物质融出率分别达到60.2%～61.6%和66.8%～67.5%。此外,在热-碱和超声波-碱预处理后,液相中STOC和STN浓度相对于未处理样增加倍数分别为7.62和4.97。两种碱处理技术不仅分解污泥最外层的絮状结构,而且能够破坏微生物的细胞结构,促使污泥颗粒粒径急剧变小,粒径小于17μm的污泥颗粒占总数50%以上。然而在超声波-酸和热-酸作用下,仅有部分的污泥絮状结构分解,污泥的颗粒粒径变化并不明显。(3)研究了污泥预处理后对厌氧发酵产酸效率的影响。热-碱和超声波-碱预处理后的污泥厌氧发酵生成的总酸分别比未预处理污泥提高59.1%和68.2%,均显著高于两种酸预处理技术。可溶性蛋白质为两种碱处理污泥中VFAs产生的主要来源。此外,分析固相中有机质的含量在发酵过程中的变化,发现超声波-碱和热-碱预处理阶段未融出的有机质在随后的厌氧发酵过程并未进一步水解酸化。不同于两种碱处理技术,热-酸和超声波-酸预处理后污泥的脂肪酸产率却低于未处理污泥。综合考虑预处理成本和产酸效率,确定热-碱为最佳的预处理技术。(4)研究了pH对污泥预处理液中可溶性的蛋白质的沉降影响。结果发现,当pH值从12.0调节到3.0时,可溶性蛋白质的浓度在碱性条件下减小比较缓慢,在酸性条件下则转为迅速。此外,在pH值调节过程中沉降下来的大部分蛋白质在厌氧发酵产酸过程中并未被转化形成VFAs。(5)当调控厌氧发酵过程pH在3.0～12.0时,促使液相VFAs分布特征发生变化的原因是由于pH的调控改变了厌氧微生物的种群结构。厌氧发酵过程pH条件不同,优势菌群也不相同。在pH值为12.0时,优势菌为颗粒链菌属(Granulicatella);pH为10.0时则演变为消化链球菌属(Peptostreptococcus);当发酵过程pH降为7.0和5.0时,梭菌属(Clostridium)却成为优势产酸菌;而pH值为3.0时优势菌则为芽孢杆菌属(Bacillus)。(6)控制厌氧发酵产酸过程pH为10.0时,通过FISH技术检测发现产氢产乙酸菌的数量及其微少,相对丰度仅为总细菌的0.01%。乙酸的累积主要是消化链球菌属通过氨基酸之间的Stickland反应形成的。pH为10.0的条件不仅能够抑制产甲烷菌的活性,而且能够抑制硫酸盐还原菌的生长。同其它pH值条件下厌氧发酵产酸相比,控制厌氧发酵过程在pH值为10.0,可以显著改善污泥预处理的产酸效率,并维持稳定的酸产量。(7)调控发酵底物的初始C/N可实现不同发酵产酸类型。初始C/N在12～44时,形成的是乙酸型发酵类型;当初始C/N在56～69范围内时,可实现丙酸型发酵类型;而当C/N处于156～256时,则形成丁酸型发酵。不同发酵产酸类型的形成是由优势产酸菌群的改变导致的。C/N值在12~69范围内,H2和CO2的增长都较为缓慢,但当C/N值提高到156～256时,二者的产率迅速提高。初始C/N值影响VFAs累积的主要代谢途径。在低C/N值条件下,乙酸的累积主要是通过氨基酸之间的Stickland反应形成,而随着C/N值的增大,导致丙酸和丁酸累积的主要代谢途径转变为糖酵解的丙酮酸途径。更多还原

【Abstract】 In recent years, the amount of excess sludge produced from municipal and industrial wastewater plants increased very rapidly with the sustainable and fast development of economy in China. The treatment and disposal of sludge have become one of the most important and complex problems. In fact, the main part of sludge is organic biomass, and it can become a source for valuable biochemicals such as volatile fatty acids (VFAs). The bioprocess strategy that results in the production of VFAs not only achieves the objective of controlling pollution and reducing sludge volumes but also efficiently explores the resource of organic substance in sludge.It is known that volatile fatty acids are important intermediate compounds in the metabolic pathway of anaerobic digestion. In this dissertation, using excess sludgs from three different sources, the tests were firstly performed to analyze the relationship between VFAs and consumed organic matter, and to investigate the effects of initial carbon-nitrogen-ratio (C/N) on the acidification efficiency of sludges. And then, hydrolysis and acidogenesis of sludge pre-treated with different techniques was analyzed. Based on the results of the study on those pretreatment techniques, control strategies of pH and initial C/N were investigated in order to achieve the maximum and stable production of total VFAs or different types of anaerobic acidogenesis. The microbial community structure and the dominant microbial population was discovered through the analysis of Terminal-Restriction Fragment Length Polymorphism (T-RFLP). Combining the means of fluorescence in situ hybridization analysis with the analysis of T-RFLP, the reason for accumulating acetic acid was further explored. Furthermore, the main metabolic pathway of different individual VFAs was investigated by analyzing the relative abilities of some key enzymes. Main results of this dissertation were shown as follows:(1) The main component of sludge including proteins and carbohydrates is enclosed in microbial cells. The autolysis bioprocess of microbial cells was slow, which resulted in the relatively low conversion ratio from proteins and carbohydrates into VFAs. Moreover, the results also showed that acetic acid was the main product in total VFAs during the anaerobic digestion. (2) Effects of various pretreatment methods including thermo-acid, thermo-alkaline, ultrasonic-alkaline and ultrasonic-acid on the solubilization of excess sludge were investigated. The results showed that both thermo or ultrasonic -alkaline significantly improved the solubilization of sludge at a high concentration (7.4% of total solid). Solubilization of volatile solids (VS) and total proteins was 60.2%~61.6% and 66.8%~67.5%, respectively. Moreover, STOC and STN concentration increased more than before pretreatment. STOC increased 7.62 times, while STN increased 4.97 times. The ultrasonic- or thermo- alkaline pretreatment significantly decreased the particle size of WAS and account of less than 10μm particles was for 50% and many minute cavities appeared on the surface of particles. They could not only hydrolyze extracellular biopolymer but also destroy some microbial cells. But the thermo- or ultrasonic- acid pretreatment just disintegrated some sludge flocs. On the contrary, the effect of the thermo- or ultrasonic- acid method on the solubilization of WAS was not obvious. They just disintegrated some sludge flocs.(3) Effects of these four pretreatment techniques on the subsequent acidification efficiency of excess sludge were further analyzed. The results showed that the acidification efficiency of sludge was improved in the case of the thermo- or ultrasonic- alkaline pretreatment. Compared with the untreated sludge, the concentration of total VFAs increased by 59.1% for the ultrasonic-alkaline pretreatment, and increased by 68.2% for the thermo-alkaline pretreatment at the final fermentation. Soluble protein was the main source for the total VFAs production in the pretreated WAS slurry with the thermo- or ultrasonic- alkaline methods. On the contrary, the yield of total VFAs from the thermo- or ultrasonic- acid pretreated sludge was lower than that from the untreated sludge. Combining the cost of pretreatment with the acidogenic efficiency of sludge, thermo-alkaline was established the optimal pretreatment technique.(4) Effects of pH on the sedimentation of soluble proteins from the thermo-alkaline pretreated sludge were investigated. The results showed that the concentration of soluble protein decreased slowly with the decrease of pH from 12.0 to 7.0, but it became fast when pH was adjusted from 7.0 to 3.0. The data strongly implied that the most part of insoluble protein deposited after the pH adjustment was not consumed as the substrate for producing VFAs during the fermentation.(5) Bacterial community structure was monitored through T-RFLP at different pHs. The results revealed that the impact of pH on the distribution pattern of VFAs resulted from the varieties of bacterial community structure. The dominant bacterial population varied with the change of pH in the anaerobic process. Granulicatella was the dominant bacterial population at pH 12.0, while Peptostreptococcus dominated at pH 10.0. With the adjustment of pH from 7.0-5.0 to 3.0, the dominant bacterial population evolved from Clostridium to Bacillus.(6) Base on the analysis of fluorescence in situ hybridization, the amount of syntrophic acetogenic bacteria was very small and its relative abundance was only 0.01% in total microorganisms when pH was controlled at 10.0. Peptostreptococcus played an main role on the accumulation of acetic acid. The main metabolic pathway for producing acetic acid was the Stickland reaction between different amino acids. Controlling the pH of fermentation process at 10.0, not only the activity of methanogenic archaea but also the growth of sulfate-reducing bacteria was inhibited. The yield of VFAs could be significantly improved and maintained stable by controlling fermentation pH at 10.0.(7) Control strategy of initial carbon-nitrogen-ratio (C/N) could implement different types of acid-forming fermentation during the anaerobic acidogenesis. Controlling initial C/N in the range of 12~44, the main product was acetic acids, while propionic and acetic acids became the main products under the conditions of initial C/N varied between 56 and 69. With the increase of initial C/N from 156 to 256, butyric acid-type of fermentation appeared in the fermentation process. The change in the different types of acid-forming fermentation was caused by the changes in the dominant microbial populations, from acetic acid-producing bacterial (Peptostreptococcus) to propionic acid-producing bacterial (Propionibacterium), and then to butyric acid-producing bacterial (Clostridium). At the low initial C/N, the increase of H2 and CO2 was slow, but with the increase of initial C/N from 156 to 256, they increased rapidly. Moreover, the main metabolic pathway resulted in the accumulation of predominant VFAs was changed from the Stickland reaction at low initial C/N to the metabolic pathways of pyruvic acid from glycolysis.更多还原