【作者】 罗琨；

【导师】 李小明； 杨麒；

【作者基本信息】 湖南大学 ， 环境工程， 2013， 博士

【摘要】 目前,高速城市化进程使污水处理厂产生的剩余污泥量大幅增加,其处理成为污水生物处理过程中面临的一个非常严峻的问题。污水处理厂用于剩余污泥处理和处置的费用大约占整个污水厂投资及运行费用的50%,甚至高达60%。污泥是一种富含有机质的物质,将其资源化利用,就能变废为宝。剩余污泥水解酸化的主要目的是改善污泥的生化降解性能,从而使较多的溶解性COD (SCOD)溶出和较多的短链脂肪酸(SCFAs)产生。SCOD和SCFAs,特别是SCFAs中的乙酸和丙酸,可以作为碳源物质强化生物除磷过程(EBPR)。因此,研究污水厂污泥水解和酸化过程具有重要的现实意义。为了达到此目的,本课题采用外加酶(中性蛋白酶和α-淀粉酶)来强化污泥水解产酸过程,从而为污泥处理过程提供一种新的方法。水解是污泥厌氧消化过程的限速步骤,而污泥中复杂有机质的水解主要取决于水解酶。然而,污泥中的水解酶含量较低,且这些酶一般隐藏、束缚、包埋在污泥基体内,活性没有得到表达,从而导致常规污泥处理过程的水解速率较低。目前,通过外加水解酶促进污泥水解的相关研究还比较少,本研究通过考察厌氧条件下单一酶和复合酶作用时,酶投加量、反应温度、酶配比等对城市污水处理厂剩余污泥破解及减量的影响,优化酶处理过程的指标。结果表明,在厌氧条件下,外加水解酶可以促进剩余污泥中颗粒态有机物的溶解、溶解态大分子有机物(蛋白质和碳水化合物)的水解以及水解后小分子有机物(氨基酸和单糖)的降解过程。该反应在4h内基本完成,淀粉酶比蛋白酶的水解效果好,复合酶的水解效果比单一酶的好。当水解温度为50℃,蛋白酶和淀粉酶的配比为1：3时,水解效果最佳,VSS去除率达68.24%。为了更清楚地了解外加水解酶强化污泥水解过程的本质特征,此过程的动力学分析与物质转化规律极为重要。以淀粉酶为例,对淀粉酶强化污泥水解过程动力学进行了探讨。结果表明,酶催化污泥水解反应在4h内基本完成,在此过程中,反应迅速,此后水解速率变缓。淀粉酶水解过程的阿仑尼乌斯方程为1nk=2429/T+5.57(R2=0.964)。此过程中的反应活化能可由空白组的62.72kJ/mol降低到20.19kJ/mol。污泥水解过程物质转化平衡分析表明：50℃时淀粉酶强化污泥水解过程底物与SCOD的转化系数α为0.266±0.012g SCOD/g VSS,与碳水化合物的转化系数α为0.043±0.001g碳水化合物/g VSS,与NH4+-N的转化系数为0.038±0.002g NH4+-N/g VSS。在酶强化污泥水解的基础上,就外加水解酶对污泥发酵产酸过程作进一步的研究,并从微观和宏观控制上探讨了酶强化污泥水解和酸化过程的机理及影响因素。结果表明,外加水解酶可以促进剩余污泥的发酵产酸过程。经不同水解酶处理后,乙酸始终是产量最大的有机酸,差不多占总有机酸产生量的50%,丙酸和异戊酸次之,正戊酸是产量最少的酸。在整个厌氧发酵过程中,不论是否投加酶,剩余污泥的pH值都随发酵时间的延长而升高；同时,投加水解酶的剩余污泥与空白试验组的pH值的变化趋势相同。探讨外加水解酶强化污泥水解的机理对于此过程内在和本质特征的了解具有重要的意义。目前,运用三维荧光光谱技术识别EPS和DOM的特性已有相关的研究,本研究即运用三维荧光光谱分析法来分析外加酶强化污泥厌氧消化过程中EPS和DOM的光谱特性及物质转化规律,以期从新的角度来探究酶强化剩余污泥水解过程的机理。通过三维荧光光谱分析表明,污泥中的荧光物质主要为蛋白质类物质(芳香蛋白和色氨酸)和腐殖酸类物质,其中色氨酸物质的溶出和转化速率高于芳香蛋白物质。水解酶会严重破坏EPS的结构和功能,同时复杂的DOM降解为低分子量的中间产物,继而促进污泥溶解和污泥降解。通过对比灭菌污泥与不灭菌污泥的有机酸产量和水解酶活力,证实了在外加酶存在的条件下,剩余污泥水解和发酵产酸是污泥中有机物被微生物降解的结果。通过利用PCR-DGGE结合DNA测序和系统发育分析对污泥水解酸化过程中微生物(主要是细菌)的群落结构进行多样性研究,表明原污泥和污泥水解发酵、产酸过程中存在的微生物有部分类似,但在各个阶段也具有各自特有的微生物菌群。投加水解酶的污泥水解产酸过程中梭酸菌群的含量较空白组中的多。外加水解酶和污泥中原有的水解酶会隐藏、束缚、包埋在污泥基体内,从而导致其利用效率较低。表面活性剂可以促进固相物质转化为液相物质,促使大量有机物质溶解于液相中,破坏了污泥絮体结构,将束缚和隐藏于污泥基体和细胞膜上的酶释放出来。同时,污泥中复杂有机物质的水解主要取决于水解酶。鉴于水解酶和表面活性剂两者的特性,表面活性剂和酶的联合作用会对污泥水解过程起到协同作用,其可以用来强化污泥的减量性能。最后,就酶和表面活性剂联合作用对污泥水解和酸化过程的影响进行了研究。结果表明,酶和表面活性剂的联合作用极大地促进了剩余污泥的水解和酸化效率,且两者共同处理的效果明显优于单独处理。SDS+ME厌氧产酸系统生成的有机酸中,乙酸是含量最高的酸,丙酸是含量第二的酸。更多还原

【Abstract】 Rapid urbanization in many areas of the world has resulted in an increasing of waste activated sludge (WAS) from wastewater treatment plants (WWTPs), which has become a serious environmental issue. Costs for traditional treatment and disposal of WAS are quite expensive and would account for up to50%or60%of the total operating cost of WWTPs. Sludge is a kind of substance that are rich in organic matter, and it can be turn into wealth if rational use of the waste. The aim of hydrolysis and acidfication of WAS is to improve its biological degradability in the terms of higher soluble chemical oxygen demand (SCOD) and short chain fatty acids (SCFAs) productions. SCOD and SCFAs, especially acetate and propionate, are recognized as the most suitable carbon substrates for enhanced biological phosphorus removal (EBPR). Therefore, the hydrolysis and acidification of WAS has caused wide public concern, and it has important practical significance for sludge treatment. In order to reach the goal, the additional enzymes (protease and a-amylase) were selected to enhance the hydrolysis and acidification of WAS, thus provided a new technique for the treatment of WAS.Hydrolyis of particulate organic matter to soluble substance is believed to be the rate-limiting step of anaerobic digestion. The hydrolysis of complex organic molecules in the degradation of biodegradable particulate organic matter depends heavily on hydrolytic enzymes. However, the dosages of enzyme in the sludge are low, and they are usually entrapped by, adsorbed by, or bound to the sludge, thus leading to the low hydrolysis efficiency of the conventional sludge treatment. Recently, the enzymatic hydrolysis of sewage sludge has not been conclusively determined, thus the effect of enzyme dosage, operating temperature and the mixture ratio on the solubilisation of WAS were evaluated with additional enzymes used alone or in combination in this investigatin. It was found that during sludge anaerobic fermentation, the solubilization of sludge particulate organic-carbon and the hydrolysis of solubilized substrate (protein and carbohydrate) were all increased in the presence of enzyme. VSS solubilisation process could be almost completed within4h. Single enzyme had less impact on sludge solubilisation, of which amylase treatment displayed higher hydrolysis efficiency than that of protease. The mixture of two enzymes (protease:amylase=1:3) resulted in optimum hydrolysis result, the efficiency of solids hydrolysis could be increased to68.43%at the temperature of 50℃.In order to clearly understand the substantive characteristics of the hydrolysis process enhanced by enzyme, the kinetic analysis and the material transformation rule during this process is very important. The hydrolysis kinetics of WAS hydrolysis process enhanced by additional a-amylase was evaluated. The results showed that VSS solubilisation process could be almost completed within4h, and the rate constants obtained in this study followed the Arrhenius type of behavior. The Arrhenius equation of a-amylase hydrolysis (lnk=2429/T+5.57, R2=0.964), the reaction activation energy for VSS hydrolysis reduced from62.72kJ/mol (control test) to20.19kJ/mol (a-amylase treatment). Kinetics analysis indicated that the conversion coefficients (a) of VSS to soluble chemical oxygen demand (SCOD), carbohydrates and NH4+-N was found to be0.266±0.012,0.043±0.001and0.038±0.002, respectively.Based on the WAS hydrolysis enhanced by enzyme, the effect of enzyme on WAS acidification and the destruction mechanisms of WAS enhanced by additional enzymes was further analyzed and explored. It was found that enzyme could promote the hydrolysis and acidification of WAS. After different enzymes treated, acetic acid was the most prevalent product, which almost accounted for50%of the total SCFAs. The propionic and iso-valeric acids were the second, and the n-valeric acid was the lowest. During the entire fermentation, the pH values kept increasing no matter in the presence or absence of enzyme, and the same pH variations were observed.The study on the destruction mechanisms of WAS during anaerobic digestion is helpful for the understanding of substantive characteristics of the hydrolysis enhanced by enzyme. The Excitation-emission matrix (EEM) fluorescence spectroscopy has been applied in the distinguishing of the characteristics of extracellular polymeric substances (EPS) and dissolved organic matter (DOM), thus the objectives of this research were to obtain the EEM fluorescence characteristic of the EPS and DOM during WAS anaerobic digestion enhanced by enzymes and attempt to well understand this process from a novel insight. It was found that the protein-like (aromatic and tryptophan protein-like substances) and humic acid-like substances were the mainly fluorophores in the sludge, of which the release and transformation of tryptophan protein-like substances was more rapidly than that of aromatic protein-like substances. The EPS could be seriously disrupted by the action of hydrolytic enzymes, and the complex DOM was also broken down into low molecular-weight intermediates, thus the hydrolytic enzyme could enhance WAS solubilization and destruction. The comparisons of SCFAs production and hydrolytic enzymes activities between autoclaved and unautoclaved sludge showed that the production of SCFAs was the result of organics degraded by microbial. The diversity of microbial community structure (mainly bacterium) was studied through the application of16S rDNA-PCR amplification, DGGE fingerprinting and phylogenetic analysis. The results showed that the microbial existed in the enzymatic treatment and the raw sludge was partially similar, and each stage also had their special microbial. The amount of Clostridiaceae bacterium for the enzyme systems were much more than the blank during WAS hydrolysis and acidificationThe enzyme added or originally exist in the sludge are usually entrapped by, adsorbed by, or bound to the sludge, thus leading to the low hydrolysis efficiency of the conventional sludge treatment. Surfactant can cause an apparent increase in the aqueous solubility, thus accelerate the rate of nonaqueous phase substance dissolution into the aqueous phase, which may be able to compromise the floc integrity, liberate the trapped enzyme (within the floc matrix and on the cell-surface) and also expose more substrate. In addition, the hydrolysis of complex organic molecules in the degradation of biodegradable particulate organic matter depends heavily on hydrolytic enzymes. In consideration of the special characteristics of both enzyme and surfactant, the combination of surfactant and enzyme might exhibit a positive synergetic effect on waste solids hydrolysis, which could be used in the treatment of WAS to enhance its reduction. Thus, the combined effect of SDS and enzyme on WAS hydrolysis and acidification was investigated. It was found that the combined system was more effective in the promotion of sludge hydrolysis than sole SDS and sole enzyme. The composition analysis of SCFAs produced in SDS+mixed-enzymes (ME) system indicated that acetic acid was the most prevalent product and propionic acid was the second one.更多还原