【作者】 郭亮；

【导师】 李小明；

【作者基本信息】 湖南大学 ， 环境工程， 2009， 博士

【摘要】 城市污水处理过程中会产生大量的剩余污泥,污泥的处理是污水处理厂所面临的一个重要问题。污泥中含有大量有机物,如蛋白质、碳水化合物等。目前较常用的污泥处理方法是厌氧消化,一方面能够减少污泥的重量和体积,另一方面能以沼气(主要成分为甲烷)的形式回收污泥中生物质能。但污泥中的有机物大部分为细胞物质,这些有机物为细胞壁所包裹,难以为微生物所利用,微生物要利用这些物质,首先必须水解污泥中微生物的细胞壁,将胞内物质释放出来,使之转化为溶解性物质。正是这个水解过程造成污泥消化过程停留时间长。氢气是污泥厌氧消化的一种中间产物,在厌氧初期的水解酸化阶段产生,随后会迅速被污泥中存在的甲烷菌和硫化菌等耗氢菌所消耗,因此通常很难在污泥的厌氧消化过程中获得氢气。如果通过适当的预处理使污泥融胞、释放有机质,并抑制耗氢菌,则可获得稳定的产氢量。氢气是清洁能源,燃烧时仅产生水。而且氢气燃烧产生的热量(142.35 kJ/g)是碳氢燃料的2.75倍。因此,收获氢气更具有很高的经济价值。本课题立足于国内外最新的研究成果,对污泥水解和污泥发酵产氢进行了较系统的研究。运用热处理、超声波处理和微波处理3种方法预处理污水厂剩余污泥,考察不同预处理方法在不同的处理强度和处理时间下,其对污泥破解效果的影响。结果表明,污泥破解效果随处理强度的增加而增强。超声波处理在能量密度ED=2 W/L条件时,污泥的破解效果最好,其中可溶解性蛋白质和总糖浓度在脉冲辐射10 min时达到最大值分别为1013.7 mg/L和512.6 mg/L,可溶性化学需氧量(SCOD,Soluble Chemical Oxygen Demand)浓度在连续辐射10 min时达到最大为4184.0 mg/L; SCOD/TCOD值较原始污泥升高了41.7%。从经济学角度考虑,低强度长时间的处理往往都能够达到较好的污泥破解效果,即热处理(t=75 min,T=45℃),超声波处理(t=10 min,ED=0.5 W/L),微波处理(t=300 s,P=70 W)。另外,在能耗相同的条件下,污泥的破解效果为:超声波处理>微波处理>热水解处理。研究了嗜热酶污泥溶解(S-TE,Solubilization by Thermophilic Enzymes)技术对污泥水解效果的影响。从土壤中筛选出一株能分泌胞外酶、促进污泥溶解的嗜热菌Bacillus sp. AT07-1(注册号:FJ231108)。在65℃和微曝气条件下,将AT07-1菌液接种到两种不同浓度的剩余污泥中,总悬浮固体(TSS,Total Suspended Solid)浓度分别为14和21 g/L,并与未接种嗜热菌进行对比。结果表明,S-TE污泥溶解存在两种反应:酶催化反应和热水解反应;两个过程:嗜热菌胞外酶(主要是蛋白酶和淀粉酶)首先解聚污泥胶团,然后溶解细菌细胞壁,水解胞内有机物质。接种嗜热菌AT07-1比不接种促进了污泥中悬浮固体的溶解;SCOD和挥发性脂肪酸(VFA,Volatility Fatty Acid)得到最大累积,最大累积量SCOD分别为8222.5 mg/L和11265.8 mg/L;VFA分别为4285.8μg/L和5578.4μg/L,这有利于厌氧消化产气;蛋白质和总糖被嗜热菌先水解后消耗,浓度呈现先升高后降低的趋势。研究了S-TE溶解技术对污泥中固形物的影响。将AT07-1菌液接种入不同浓度(TSS约为7.5、14.5和20.5 g/L)的剩余污泥中,于65℃进行嗜热酶溶解试验,并与未接种试验进行对比,并对挥发性悬浮固体(VSS,Volatile Suspended Solid)的溶解进行了动力学分析。结果表明,接种Bacillus sp. AT07-1比不接种促进了污泥中悬浮固体的溶解。60 h时接种试验不同浓度下VSS的溶解率分别为61.4%、53.8%和41.9%,比不接种试验同期分别提高了27.6%、25.2%和16.3%。试验条件下VSS溶解过程在初始阶段(t=3 d)符合一级反应动力学模型,低浓度下接种嗜热菌溶解速率常数Kd显著提高。为了提高污泥产氢的纯度和产氢率,采用Hungate厌氧培养技术,分别从厌氧颗粒污泥中分离出高效产氢菌Pseudomonas sp. GZ1(注册号: EF551040),从河底泥中分离出高效产氢菌Enterococcus sp. LG1(注册号:FJ231108),并分析其16S rRNA碱基序列,为后面的污泥产氢研究做准备。采用厌氧发酵的方法研究Pseudomonas sp. GZ1利用热处理(灭菌)、微波处理和超声波处理污泥的产氢效果,对3种预处理方法对污泥产氢效果的影响及其原因进行了重点分析,并对污泥发酵过程中底物性质变化(SCOD、可溶性蛋白质、总糖和pH值等)进行了探讨。实验结果显示,产氢菌Pseudomonas sp. GZ1发酵各预处理污泥过程中均只有H2和CO2产生,无CH4产生。3种不同预处理污泥同等条件下发酵,热处理(灭菌)污泥的产氢效果最佳,氢气含量高达81.5%,产氢率为15.0 mlH2/gCOD。超声波处理污泥产氢延迟时间最短(3 h);热处理(灭菌)污泥最长(15 h)。在预处理污泥发酵产氢过程中,各种营养物质变化情况各不相同,尤其是热处理(灭菌)污泥,这说明不同的预处理方法影响Pseudomonaa sp. GZ1发酵过程对污泥中营养物质的利用。其中污泥释放出的重金属浓度和VFA的产生量是影响污泥产氢差异的主要因素。研究了热处理(灭菌)污泥及其滤液作为底物发酵产氢。接种产氢菌Pseudomonas sp. GZ1后,测定两种不同底物发酵反应过程中氢气的产量,以及底物的变化情况。实验结果表明,利用预处理后的污泥滤液作为底物能够有效提高氢气产量。滤液发酵的产氢量达到了4.5 mgH2/gCOD,比使用预处理污泥发酵产氢提高了近3.3倍。本实验证明污泥中的固态物质在发酵过程中能释放出更多的营养物质,但并非所有的底物都能被产氢菌有效地利用来产生氢气。利用一种新型的重金属吸附剂-碳氢磷灰石(CHAP,Carbonate Hydroxylapatite)去除微波处理后污泥中溶解态重金属。以不同CHAP投加量的预处理污泥作为底物,接种产氢菌Enterococcus sp. LG1比较其厌氧发酵产氢效果。研究结果表明,当CHAP的投加量为5 g/L(污泥)时,产氢发酵效果最好,产氢量最大为10.6 mlH2/gCOD,产氢率比未投加CHAP的预处理污泥提高了30%;而当CHAP的投加量≥10 g/L(污泥),产氢发酵开始受到明显的抑制。文章结合重金属、SCOD、可溶性蛋白质、总糖和pH值的变化,分析了产生差异的原因,证实了适当重金属去除能够有效提高污泥氢气产量。利用S-TE水解污泥为底物,考察了在不添加任何外在营养物质的情况下,接种嗜热菌Bacillus sp. AT07-1和不接种嗜热菌(65℃热处理),接种产氢菌(Enterococcus sp.LG1)和不接种产氢菌共四种条件下,研究污泥的发酵产氢效果。同时分析探讨了污泥发酵产氢过程中底物和pH值的变化。结果表明,经S-TE预处理的污泥在未接种外在产氢菌时,产氢效果良好,最大产氢率高达16.3 mlH2/gVS,高出65℃热处理污泥接种产氢菌(Enterococcus sp. LG1)15.6%,高出65℃热处理污泥未接种产氢菌26.4%,发酵气体中只含有H2和CO2,不含CH4,产氢延迟时间短(3~4 h),产氢率达最大值后能较稳定地维持10 h以上;S-TE预处理污泥接种产氢菌后,产氢效果不佳,最大产氢率仅为10.7 mlH2/gVS。说明直接使用S-TE水解污泥发酵产氢,无须接种产氢菌就可以达到非常好的产氢效果。污泥的水解程度和产氢菌对污泥的适应性是造成产氢差异的主要原因。65℃热处理和S-TE预处理污泥发酵产氢,接种产氢菌更有利于污泥的水解。更多还原

【Abstract】 Large amounts of waste sludge are produced from the biological processes of sewage plants, and the disposal of waste sludge is becoming an important and complex question to many sewage plants. The sludge contains many organic matters, for example, proteins and carbohydrates. Anaerobic digestion has traditionally been employed to reduce the volume and weight of sludge and to recover the biomass energy from sludge by producing methane. Most of the organic matters in sludge are microbial cytoplasm, the microbial cell walls must be disrupted or hydrolyzed before those organics can be used and this process is very slow and is the key of sludge utilization. On the other hand, hydrogen is an intermediate product of anaerobic sludge digestion, which is rapidly taken up and conversed into CH4 by methanogens or H2S by sulfate-reducing bacteria. It is difficult to harvest hydrogen during the anaerobic digestion of sludge. However, hydrogen is a clean, environmentally‘friendly’fuel that produces water instead of greenhouse gases when combusted. Furthermore, hydrogen has a high energy yield (142.35 kJ/g) that is about 2.75 times that of hydrocarbon fuels, hydrogen has more economic value than methane, and it is more advantaged to harvest hydrogen than to harvest methane. Basing on the latest researches in both domestic and abroad, the waste sludge solubilization and hydrogen production were investigated in this paper systematically.Three kind methods of thermal treatment, ultrasonication and microwave treatment were used to pretreat the waste sludge. The influence on sludge solubilization was inspected through detecting different pretreatments at different treating strength and time. The sludge solubilization was enhanced with treating strength. When ultrasonication at energy density (ED)=2 W/L conditions, the sludge solubilization effect was excellent, the maximal value of soluble protein and total sugar were 1013.7 mg/L and 512.6 mg/L at continuous radiation 10 min; the maximal value of soluble chemical oxygen demand (SCOD) concentration was 4184 mg/L at pulse radiation 10 min. SCOD/TCOD value increased 41.73% compared to the raw sludge. Considering from the economics, low strength and long time waste sludge treatment could reach relatively good solubilization effect, namely thermal treatment (t=75 min, T=45℃), ultrasonic treatment (t=10 min, ED=0.5 W/L), microwave treatment (t=300 s, P=70 W). In addition, under the same energy consumption, the solubilization effect of sludge is: ultrasonic treatment > microwave treatment > thermal treatment.The effect of hydrolization by thermophilic enzymes (S-TE) pretreatment on waste sludge solubilization was investigated. A thermophilic bacterium Bacillus sp. AT07-1 (registration number: FJ231108) was isolated from soil and shown that it could produce extracellular enzyme to accelerate solubilization of excess sludge. At 65℃and microaeration, the strain of AT07-1 was inoculated in the waste sludge with different concentration (TSS were 14 g/L and 21 g/L respectively). The result showed that two reaction mechanisms of enzyme-catalyzed and thermal-hydrolyzed were involved in the S-TE process, which began with depolymerization of sludge flocs by extracellular enzyme (including proteases and amylases), followed by cell-walls and organic matters disintegration and hydrolyzation, the inoculation was advantage for solubilization compared with non-inoculation. It was revealed that under microaeration and inoculation operation, the maximal accumulation of SCOD in the waste sludge were 8222.5 mg/L and 11265.8 mg/L respectively, and the maximal accumulation of volatile fatty acid (VFA) were 4285.8μg/L and 5578.4μg/L respectively, which was beneficial for the followed anaerobic digestion and biogas generation. Moreover, the protein and total sugar released from the sludge was hydrolyzed and consumed by thermophilic bacterium rapidly, which resulted in an increase first and then a decrease at the later. The effect of S-TE method to the solid material in waste sludge was also investigated. The strain of AT07-1 was inoculated in the waste sludge of different total suspended solid (TSS) concentrations (7.5, 14.5, 20.5 g/L) at 65℃and the dynamic analysis of VSS was also made. The result showed that the solubilization process with Bacillus sp. AT07-1 inoculation was enhanced comparing to those with non-inoculation. The volatile suspended solid (VSS) solubilization rate reached to 61.4%, 53.8% and 41.9% at 60 h after the inoculation at different concentration, 27.6%, 25.2% and 16.3% higher than the non-inoculation respectively. The VSS dissolving process (at the first 3 days) accorded with first-order reaction dynamic model, and low concentration and inoculation, the dissolving rate constant Kd (t=3 d) increased evidently.In order to enhance the yield of hydrogen production and hydrogen concentration, hungate method was used to separate hydrogen bacteria. An effective hydrogen production bacteria of Pseudomonas sp. GZ1 (registration number: EF551040) was separated from anaerobic granular sludge, the other one of Enterococcus sp. LG1 (registration number: FJ231108) was separated from river sediment, and the 16s rRNA gene sequence was also analysis. The two kinds of bacteria were used for hydrogen production from waste sludge.Batch tests of anaerobic fermentative hydrogen production by Pseudomonas sp. GZ1 were investigated using thermal treatment(sterilization), microwave and ultrasonication pretreated sludge as substrate.The changes of SCOD, protein, total sugar and pH value during the fermentation process were monitored, and the impact of different pretreatments on hydrogen production using waste sludge was also analysed. The results showed that only H2 and CO2 were produced and CH4 was not observed during the process. A maximal hydrogen yield (15.0 mlH2/gCOD) and hydrogen content (81.5%) were obtained from the sterilization pretreated sludge. The shortest lag time for hydrogen production was obtained for using ultrasonication pretreated sludge (3 h), while the longest one was obtained from thermal (sterilization)pretreated sludge (15 h). It was found that the changes of sludge substrates were various with diferent pretreated sludge during the fermentation process, especially in the thermal (sterilization) sludge run, which implied that the pretreatment method could affect substrate utilization by Pseudomonas sp. GZ1. The heavy metal and VFA released from waste sludge were the key factor influencing the hydrogen production from waste sludge. The sludge after thermal (sterilization) pretreatment and their filtrate were used as the substrates for hydrogen production. After inoculated Pseudomonas sp. GZ1, the hydrogen yield and the changes of SCOD, protein, total sugar and pH value during the fermentation processes were analyzed and measured. The results showed that using filtrate could produce more hydrogen gas than using the bio-solid waste sludge. It could produce a hydrogen yield of 4.5 mgH2/gCOD, approximately 3.3 times higher than the pretreated sludge. It was demonstrated that the solids matter in waste sludge could release more nutrients during fermentation, and not all the substrate could be used for producing hydrogen. A new style of heavy metals sorbent-carbonate hydroxylapatite (CHAP) was utilized to remove the dissolved heavy metals from microwave pretreated waste sludge. Then the pretreated sludge in which different dosages of CHAP added was used as the substrates for anaerobic fermentive hydrogen production by Enterococcus sp. LG1. The results showed when the dosage of CHAP in the sludge was 5 g/L (sludge), the hydrogen yield reached to 10.6 mlH2/gCOD and improved nearly 30% camparing pretreated sludge without adding CHAP. However, when the dosage of CHAP in the sludge was more than 10 g/L (sludge), the anaerobic fermentation was obviously restrained. In this study, the hydrogen yield and the changes of heavy metals, SCOD, protein, total sugar and pH value during the fermentation processes were measured, and it was demonstrated that the hydrogen yield could be effectively improved though removing the appropriate heavy metals from waste sludge.Four batch tests were carried out to analyse the effects of anaerobic fermentative hydrogen production using waste sludge pretreated by S-TE method with and without inoculateion of thermophilic bacteria Bacillus sp. AT07-1 (65℃thermal treatement) , and with and without inoculation of hydrogen producing bacteria (Enterococcus sp. LG1). The changes of substrates and pH value during the fermentation process were also monitored. The results showed that sludge pretreated by S-TE without inoculation could make good bio-hydrogen production. The maximal hydrogen yield was 16.3 mlH2/gVS, 26.4% higher than the sludge pretreated by 65℃thermal treatement inoculated Enterococcus sp. LG1 and 15.6% than 65℃thermal treatement without inoculation. H2 and CO2 were only produced and CH4 was not observed during the process. The lag time for hydrogen production was only 3~4 hours, and after reaching its maximum, the hydrogen production was able to maintain stable for about 10 h with little consuming. The hydrogen yield of the S-TE pretreated sludge inoculated Enterococcus sp. LG1 was very low, only 10.7 mlH2/gVS. It implied that using S-TE pretreated sludge directly could produce hydrogen well, and the solubilization effect and the adaptability of hydrogen production bacterial in the waste sludge were the main reasons of hydrogen production diversity. Using 65℃thermal treatement and S-TE pretreated sludge to produce hydrogen, it was benefical for hydrolization of sludge which inoculated hydrogen production bacteria.更多还原