【作者】 岳敏；

【导师】 岳钦艳；

【作者基本信息】 山东大学 ， 环境工程， 2011， 博士

【摘要】 本论文将粉煤灰作为污泥调理剂,首先对城市污水厂污泥进行了脱水预处理效果研究。随后,以污泥、粉煤灰为原料,添加粘土为粘结剂,研究了污泥陶粒的烧制工艺,进行了中试生产,并在水处理实验中考察了其应用性能。在上述实验研究过程中,探讨了粉煤灰对污泥脱水的影响机理；研究了污泥中高含量有机物以及助熔剂对污泥陶粒性能的影响及作用机理,从而揭示了污泥陶粒的膨胀机理。本论文的主要研究内容及结果如下：1.以污泥比阻(SRF)、脱水速度、滤饼含水率等为考察指标,并以阳离子型聚丙烯酰胺(PAM)为对照,通过单因素实验对城市污水处理厂的剩余污泥进行了脱水效果研究。结果表明,随着粉煤灰投加量的提高,污泥比阻持续降低。当粉煤灰投加量达到2g/(100mL污泥)时,污泥比阻从0.92×109s2/g降至0.32×109s2/g,降低了65.2%。单独投加粉煤灰对降低脱水污泥含水率效果最明显,当粉煤灰投加量为3g/(100mL污泥)时,滤饼含水率降至66.9%。PAM的投加,只能将污泥含水率降至80%左右,当继续投加粉煤灰至3g/(100mL污泥)时,滤饼含水率可降为71.8%。PAM与粉煤灰联合投加可使污泥脱水速度提高90%以上。2.通过化学成分分析、微观形貌观察(SEM)、粒径分布、表面电负性(Zeta电位)等表征手段,结合脱水效果实验,认为粉煤灰降低污泥比阻的主要原因在于粉煤灰颗粒结构疏松多孔,分散性好,强度较大,作为骨架均匀分散在污泥絮体结构中,使污泥滤饼形成了透水性更好的多孔结构,降低了压缩程度,水分进出通道比较畅通,从而表现为污泥比阻的降低。粉煤灰和污泥表面都带负电荷,不能对污泥起到电性中和作用,而且粉煤灰的投加不能促进污泥颗粒粒径的长大,因此粉煤灰不会对污泥产生絮凝作用。3.结合污泥、粉煤灰、粘土的化学成分分析,塑性指数测定以及热重-差热(DSC-TGA)分析,分别以硬度、吸水率、密度等为考察指标,对原料配比、预热温度与时间、烧结温度与时间等工艺参数对污泥陶粒性能的影响进行了单因素实验,确定制备污泥陶粒的工艺参数为：原料配比中污泥含量不超过50%,粘土不低于50%；预热温度为400℃,预热时间20min；烧制污泥陶粒滤料时,烧结温度为1050℃,烧结时间为5min；烧制膨胀陶粒时,烧结温度为1150℃,烧结时间10min。实验结果表明,烧结温度是影响陶粒物理性能的最关键因素。随着温度的升高,越来越多的原料成分熔化成为玻璃态物质,使陶粒体积收缩,密度增大,表面增稠而致密,吸水率降低；当温度超过1125℃后,由于产气反应的发生,陶粒体内气压增大,体积膨胀,密度开始降低。4.通过考察预热温度对污泥陶粒密度和吸水率的影响,揭示出污泥中高含量有机物对污泥陶粒的膨胀作用机理为：ⅰ)有机膨胀剂(污泥中的有机物)在预热阶段(<500℃)发生了脱水和碳化,生成还原性的碳；ⅱ)在烧结阶段(1150℃),先是无机膨胀剂中的碳酸盐(主要是CaCO3)、硫酸盐等分解为对应的氧化物和CO2、SO2,然后是Fe2O3在高温下分解为FeO、Fe3O4和O2,产生的这些气体使得陶粒体积产生一次膨胀；ⅲ)由氧化铁分解产生的02与预热阶段产生的还原碳生成CO和CO2,这些二次气体使得污泥陶粒体积产生二次膨胀。5.通过研究不同原料配比及烧结温度对污泥陶粒物理性能和微观结构的影响,揭示了污泥中的助熔剂与烧结温度之间的相互作用机制为：高温下,污泥中较多的碱金属和碱土金属氧化物使得Si-O(桥氧)键断裂,破坏了[SiO4]四面体骨架网络的稳态结构,使其更易解体,从而生成了更多的玻璃态熔融体。故污泥陶粒更容易烧结,即烧结温度更低,烧结时间更短。6.通过对比污泥-粘土陶粒和粉煤灰-粘土陶粒的密度和膨胀率随烧结温度的变化规律,揭示了污泥陶粒的膨胀机理：当温度低于烧胀温度(1150℃)时,熔融物质的数量是决定污泥陶粒物理性能的关键因素。而熔融物质的多少与助熔剂有关,助熔剂越多,则成陶材料的熔点越低,在相同温度下熔化生成玻璃态物质就越多,导致收缩更剧烈,颗粒密度更大。当烧结温度达到膨胀温度后,决定污泥陶粒物理性能的关键因素演变为所产生气体的压力。当气体压力足以克服表面张力时,体积膨胀。1150℃后,开始发生产气反应,在污泥陶粒中,这类反应主要是碳和氧化铁之间的氧化还原反应,而还原碳来自预热阶段污泥中有机物的热解。因此,碳和氧化铁的含量以及它们之间的比例是气体产生量的两个决定因素。污泥陶粒中有机物和铁含量都较高,因此,产气量较大,导致内部的空隙率高从而降低了颗粒密度。7.通过陶粒中矿物成分的X射线衍射(XRD)分析,发现粘土陶粒中主要是钙长石、钠长石等长石类矿物,而污泥陶粒中的矿物成分主要是石英。正是由于高温下原料粉末颗粒之间的熔融烧结,形成了这些长石以及石英等架状硅酸盐晶体和玻璃相无定形物质,才使陶粒具有较高的强度和较大的硬度。8.通过以上污泥陶粒的烧制工艺研究和膨胀机理探讨,认为污泥陶粒滤料的烧结是一个不完全烧结和不完全烧胀的过程。一方面,通过烧结,使颗粒间键合,形成一定的结合力,提高机械强度；另一方面,要在陶粒内部产生气体使其体积膨胀,从而形成多孔的微观结构,降低密度；第三还要通过降低助熔剂等成分的含量,使陶粒表面不易熔融,从而提高表面孔隙率。9.对污泥陶粒的重金属浸出率进行了测定,结果表明,污泥陶粒(污泥：粘土=1：1)的重金属浸出浓度都低于1ppm,对重金属的固化率都超过80%,对总Pb的固化率达到了99.1%。通过高温烧结,污泥中的大部分重金属元素很可能与Si4+、Al3+等网络形成元素发生了类质同象置换,从而被牢牢固定在新的矿物晶体结构中。污泥陶粒作为水处理滤料,其稳定性和安全性符合应用要求。10.分别在实验室旋转电炉和工业回转窑内进行了污泥陶粒动态试验和中试生产,证明污泥陶粒烧制工艺合理,生产过程容易控制,产品性能稳定,具备工业化放大条件。将中试产品应用于曝气生物滤池中,进行了生活污水处理实验,结果表明污泥陶粒滤料有利于微生物生长和繁殖,各项性能不逊于商品陶粒,并在氨氮的去除方面更具优越性,是一种性能良好的水处理填料。通过以上研究,对粉煤灰调理后脱水污泥的处置及资源化途径进行了展望。对于小型污水厂而言,通过投加粉煤灰后压滤脱水使滤饼含水率降至60%以下,可以最经济的卫生填埋方式解决污泥问题。对于大型城市污水厂而言,采用PAM与粉煤灰联合脱水后,添加辅料烧制污泥陶粒,可以同时实现污泥无害化、资源化。更多还原

【Abstract】 At first, this paper used fly-ash as conditioner to study the dewatering pretreatment of sewage sludge. Then, the preparation and mechanisms of ceramsite were investigated by taking sludge and fly-ash as the raw material and clay as binder. A pilot-scale production was carried out based the process parameters of bench-scale. And the application performance of sludge ceramsite was investigated by the experiments of sewage treatment in biological aerated filter (BAF). In these experiments, the fly-ash influence mechanism to sludge dewatering was explored; the effects of high content of organic and flux in sludge on ceramsite were studied, which revealed the expansion mechanism of sludge ceramsite. The main contents and results are as follows:1. Through the single-factor experiments, contrast to cationic polyacrylamide (PAM),the effects of fly-ash on dewatering of sewage sludge were studied according to specific filtration resistance (SRF), dehydrated speed, and filter cake moisture content (FCMC) as investigation indexes. The results showed that with the rising of fly-ash dosage, SRF kept decreasing. When the dosage of fly-ash achieved 0.02g/mL, SRF fell from 0.92×109 s2/g to 0.32×109s2/g,65.2% was dropped, and so it was easy to filter. The most obvious effect on FCMC is addition of fly-ash only. When the fly-ash dosage is 0.03g/mL, FCMC fell to 66.9%. FCMC could only drop to 80% when adding PAM into sludge. But when adding fly-ash as 0.03g/mL at the same time, FCMC could be reduced to 71.8%. When adding PAM combined with fly-ash, the dehydrated speed will be increased more than 90%.2. By chemical composition analysis, microstructure observation (SEM), and surface electrical behavior (Zeta potential), combined with the dehydration experiments, it was thought that the improvement on SRF by fly-ash was because fly-ash particles were loose and porous, which evenly dispersed in sludge floc structure as skeleton to maintain the permeability of the filter cake during compression dewatering. The surface of fly-ash and sludge are both negatively charged, so there is no electrostatic charge neutralization. Fly-ash cannot promote the sludge size to grow up. Fly-ash won’t produce flocculation to sludge.3. The raw materials, sludge, fly-ash and clay, were tested by chemical composition plastic index, and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). Taking the physical properties of ceramsite, including hardness, water absorption, and density, as the indexes, the effects of mass ratio of raw materials, preheating temperature and time, and sintering temperature and time on the performance were investigated by some single-factor experiments. The preparation parameters of sludge ceramsite were as follows:the mass ratio of sludge should not be more than 50% and clay not be less than 50%; preheating temperature is 400℃and time is 20min; for making sludge ceramsite filter materials, sintering temperature is 1050℃and sintering time is 5min; for making expansion ceramsite, sintering temperature is 1150℃, and time is 10min. The results showed that the sintering temperature is the most key factor in ceramsite preparation. As the temperature increases, more and more materials become melted glass phase, which made the ceramsite shrank, density increased, the surface thicken and dense, and water absorption decreased. When the sintering temperatures is above 1125℃, the reactions of gas producing occurred which increased the internal pressures, made the sludge ceramsite expanded, and the density began to decrease.4. The influences of preheating temperature on density and water absorption revealed the expansion mechanism of sludge ceramsite about the high content of organic composition:i) dehydration and carbonation occurred in organic foaming agent (organic content in sludge) and generated reducing carbon in the preheating process (<500℃); ii) in the sintering process (1150℃), carbonate (CaCO3) and sulfate in inorganic foaming agent firstly decomposed into corresponding oxides and CO2, SO2, and then Fe2O3 decomposed at high temperature into FeO, Fe3O4 and O2, and these gases bloated the body of sludge ceramsite; iii) the O2 produced by ferric oxide decomposition reacted with reducing carbon produced CO and CO2, these secondary gas made the ceramsite expanded again.5. Interaction mechanism about the flux in sludge and sintering temperature was revealed by the affection of mass ratio of raw materials and sintering temperature on ceramsite properties and microstructure observation:at high temperature, many alkali and alkaline metal oxides in sludge made Si-O (bridging oxygen) bond broken, which destroyed the steady structure of [SiO4] tetrahedron skeleton network, made it easier to collapse to generate more glass phases. For this reason, sludge ceramsite was easier to be sintered than fly-ash ceramsite, which meaned a lower sintering temperature and shorter sintering time.6. Expansion mechanism about sludge ceramsite was revealed by comparing the density and expansion rate of sludge-clay ceramsite and fly-ash-clay ceramsite varies with the sintering temperature:when temperature is below the bloating temperature (1150℃), the critical factor is the quantity of molten materials to determine the sludge ceramsite physical properties, which related to flux, the more flux, the lower melting point of framework material, the more glass phase materials melted at the same temperature, which lead to shrink harder and form a denser body. When reached bloating temperature, the gas pressure generated from reaction mentioned above turned to be the critical factor. When the gas pressure could overcome the surface tension, the body of cemamsite would expand. When the temperature is above 1150℃, the reaction of gas producing occurred. This kind of reaction in sludge ceramsite was mainly redox reactions between carbon and ferric oxide, and the reducing carbon was from the pyrolysis product of organic matters in preheating process. Therefore, the content of carbon and ferric oxide and their ratio were the factors determining the gas producing. For their higher organic matters and iron content in sludge ceramsite, the quantity of gas generated was more than fly-ash ceramsite, which lead to a higher porosity inside and a lower density.7. The results of X-ray diffraction (XRD) analysis showed that the main mineral compositions were anorthite, albite, and potassium feldspar, and in sludge ceramsite was mainly quartz. But for these melted and sintered materials between powder particles at high temperature, formed tectosilicate, such as feldspar and quartz, and amorphous substances, which made ceramsite with high strength and higher hardness.8. It was thought that the sintering of sludge ceramsite filter material was an incomplete sintering process by the investigation of preparation and expansion mechanism of sludge ceramsite. On the one hand, certain bonding force between power partical formed by sintering to improve the mechanical strength of sludge ceramsite. On the other hand, the body could be expanded and porous inside by gas production in order to have a lower density. And at the same time, it must to make the ceramsite surface melted not so easy by reducing the content of flux composition so as to improve the surface porosity.9. The heavy metal contents leached from sludge ceramsite (sludge:clay=1:1) were lower than lppm, and the solidified rates were all above 80%, even the curing rate of Pb was 99.1%. Most heavy metals were likely to replace with network forming elements, such as Si4+ and Al3+ as isomorphism state sintering at high temperature, thus were firmly fixed in the new crystal texture. The stability and security of sludge ceramsite were conformed to be satisfactory for wastewater treatment as filter material.10. The preparation procedure of sludge ceramsite was proved to be reasonable, easy to control, having industrialized amplification conditions, and the performance of products was stable by production testing in a bench-scale rotating furnace and pilot-scale rotary kiln respectively. The results of sewage treatment in biological aerated filter (BAF) showed that, the sludge ceramsite filter material was fit for bacteria growth, and its performance was no less than the commercial ceramsite. Moreover, it had advantage on ammonia nitrogen removal over the commercial ceramsite. So sludge ceramsite had good performance in wastewater treatment as filter material.From above researches, the disposal of dewatering sludge and recycling approaches after fly-ash condition were prospected. For small wastewater treatment plant, if only the moisture content of filter cake could be below 60% through pressure filtration dehydration by dosing fly-ash, it could choose sanitary landfill, the most economical way, for sludge disposal. For large municipal sewage treatment plant, adding auxiliary materials to prepare sludge ceramsite after dehydration by PAM joint with fly-ash, could achieve the aim of harmless and recycling of sludge simultaneously.更多还原