【作者】 胡绍伟；

【导师】 杨凤林；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 博士

【摘要】 由于污水中的氮元素是诱发水体富营养化的主要因素,因此脱氮成为水处理研究领域的热点问题。脱氮过程不仅需要大量专属微生物的协同作用,而且对环境条件的要求十分苛刻,所以高效去除中高浓度有机含氮废水中的含氮污染物更是水处理行业中的难题。目前国内外普遍采用的厌氧、好氧串联方法,不仅工艺流程长、基建费用高、占地面积大,而且需要回流等额外设施。本实验首先分别启动驯化厌氧折流板反应器和膜曝气生物膜反应器,然后利用膜曝气生物膜外层的厌氧状态与厌氧折流板反应器内部环境相融合的特性,将驯化好的膜组件置入运行稳定的厌氧隔室内构成耦合反应器。此工艺所具有的产酸、产甲烷、硝化和反硝化的多相分离特征,不仅避免了不同生化过程中相互竞争和抑制现象的产生,而且充分发挥了不同微生物种群之间的协同互生作用,实现了单一反应器处理中高浓度有机含氮废水的同时去碳脱氮功效。(1)厌氧折流板反应器采用直接接种厌氧颗粒污泥的低负荷同步启动方式,15d后处理效果便趋于稳定。随后两次提高进水有机负荷,COD的去除率始终保持在90%以上。当进水COD浓度为1800 mg/L时三个隔室出水VFA浓度依次为673 mg/L、148 mg/L和24 mg/L,总产气率依次为1.13 L/d,2.57 L/d和0.71 L/d,表明反应器对有机污染物的去除效果良好。通过对各隔室出水水质的分析和颗粒污泥表面生物相的研究,证明反应器内基本实现了产酸相和产甲烷相的分离。(2)通过与其它材质的膜进行对比表明,包裹无纺布的炭膜对微生物具有较强的吸附能力,适宜作为膜曝气组件。实验分别考察了以空气和纯氧为气源的膜曝气生物膜反应器运行效果,前者稳定运行时的COD和TN去除率分别为83.6%和81.6%,而后者分别为82.4%和84.2%,均实现了同时去碳脱氮的功效。不同气源所形成的生物膜均具有特殊的分层结构,生物膜内层具有较高的氧气浓度,微生物种群分布主要以好氧自养菌为主,而外层处于缺氧和厌氧状态,主要以异养菌为主。两组膜组件在高负荷运行时所产生的过厚生物膜,阻碍了底物和氧源在生物膜内的有效传递,降低了处理效果。最后优选出曝空气膜组件与厌氧折流板反应器进行耦合实验研究。(3)耦合反应器对COD具有更好的去除效果,平均出水浓度和去除率分别为51mg/L和96.8%。当进水有机负荷提高50%时,出水COD浓度仍处于60 mg/L以下,具有良好的抗有机负荷冲击能力。反应器对含氮污染物的去除效果明显,稳定运行期间对TN的平均去除率为80.1%。因为流入液体中有机底物的减少和硝态氮的增加,使得3号隔室的沼气产量和甲烷含量均明显减少,但是取而代之的是更为稳定和优良的出水水质。实验结果显示耦合反应器内的生物膜保持了内层好氧、外层缺氧/厌氧的特殊结构,而当内层的硝化细菌活性降低时,脱氮效果随之恶化。(4)基于AQUASIM 2.0所建立的混合生物膜模型,验证了好氧自养菌主要分布在生物膜的内层,而异养菌主要分布在生物膜的外层。灵敏度分析结果表明,微生物的最大比生长速率、细菌对氧的饱和常数和化学计量参数值对模拟中底物变量浓度的计算具有非常重要的影响,而其它常数在预测模型质量方面所起到的作用较弱。模拟结果表明,C/N比值和生物膜厚度对于生物膜的处理功效均有重要的影响,C/N比值较低造成的反硝化碳源不足和C/N比值较高形成的对自养菌的抑制均会使得TN的去除率下降;而生物膜过厚时所造成的对底物传质的阻碍和过薄时形成的缺氧/厌氧环境的缺乏,同样会降低脱氮的效果。数值模拟的应用有助于耦合反应器结构设计的优化及实际工程的应用。更多还原

【Abstract】 Nitrogen pollution is a key eutrophication factor in receiving water, so the removal of nitrogen has ever been a hot topic in the field of wastewater treatment for years. Generally, the performance of nitrogen removal process not only requires the coupling of large quantities of special microorganisms, but also depends on very strict operation conditions. It accounts for the difficulty in nitrogen removal in high-strength wastewaters with nitrogenous organic pollutants, and this has been particularly emphasized as an important issue in the worldwide wastewater treatment. Recently, the aerobic and anaerobic combination technology has been widely used for municipal and industrial wastewater treatment in the world, which still has problems such as system complexity, large footprint, high operating costs, and requirement of extra water recycling equipments within the process etc.In this study, an anaerobic baffled reactor (ABR) and membrane-aerated biofilm reactor (MABR) were combined for nitrogen removal from synthetic wastewater. Two processes were separately started up. The aerating membrane module was installed into a compartment of anaerobic baffled bioreactor to form the Hybrid MAB-ABR (HMABR) and its construction was based on the consistent anaerobic condition of the outside anaerobic biofilm on the aerated membrane and anaerobic baffled reactor. In this hybrid process, dependent on the biological phase-separation of acidate bacteria and methanogens bacteria in the ABR and the unique stratification of the aerating membrane biofilm into aerobic nitrifying bacteria and anaerobic denitrifying bacteria, the possible coupling was developed, rather than the competition and inhibition in different pollution removal processes. Thus, the improved simultaneous removal of carbon and nitrogen for high-strength nitrogenous organic pollutants was realized in a single reactor.(1) ABR was started up with anaerobic granule sludge as inoculation under low-loading start-up conditions. After the initial start-up phase of 15 days, pseudo-steady state of the ABR was reached. The loading rate was increased by increasing influent organic carbon concentration for two times, and the COD removal efficiency was still kept above 90%. When the influent COD concentration was 1800 mg/L, the effluent VFA concentrations of the three compartments were kept steady, which were 673 mg/L, 148 mg/L and 24 mg/L in average, and the total volumes of biogas produced in these three compartments were 1.13 L/d, 2.57 L/d and 0.71 L/d, respectively. The experiment results show the good performance of pollution removal in the ABR. By the chemical analysis of water quality and the microscope observations of granules surface, the biological phase-separation of acidate bacteria and methanogens bacteria was validated in the ABR. (2) Tubular carbon-membrane, wrapped up with non-woven materials as support media for biofilm was applied as membrane module for the aerating membrane by its virtue of better bacteria adhering capacity than other materials. Either air or pure oxygen was pumped into membrane lumen of the aerating membrane to examine the operation performance of the MABR. When pseudo-steady states were reached, simultaneous nitrogen and carbon removal were realized with highest removal efficiencies of 83.6 % and 81.6 % using air as aerating gas, while 82.4 % and 84.2 % using pure oxygen as aerating gas, respectively. The biomass unique stratification structure was also formed due to the gradient of oxygen concentration. The region near the carbon membrane shell side was favorable for aerobic autotrophic bacteria due to sufficient oxygen supply and organic carbon-depletion conditions; whereas the region near bulk liquid was favorable for growth of heterotrophic denitrifying bacteria. With the increased loading rate, the excess growth of biomass acts as a diffusive barrier for COD and ammonia, and eventually deteriorates nitrogen removal efficiency. Afterward, the air aerating membrane module and anaerobic baffled reactor were coupled to form HMABR for the simultaneous removal of nitrogenous and carbonaceous organic pollutants.(3) The HMABR has excellent COD removal performance, the average effluent concentration and removal efficiency was 51 mg/L and 96.8 %, respectively. When organic loading rate was increased by 50 %, the effluent COD concentration was still below the level of 60 mg/L, indicating its good capability of counteracting influent organic loading fluctuation. The HMABR also demonstrated good nitrogen removal performance with the average TN removal efficiency of 80.1 % during the steady state. At the same time, due to the decreased COD concentration and increased nitrate concentration in the third compartment after installing the membrane module, the biogas volume and methane content in the third compartment were decreased, resulting in the steady and excellent effluent quality. The experiment results show that the biofilm in the hybrid reactor kept the unique configuration of inner aerobic, outer anaerobic. In this case, when the inner aerobic nitrifying bacteria were inactive, the nitrogen removal performance deteriorated correspondingly.(4) A mathematical simulation model of MAB was founded by employing the simulation program of AQUASIM 2.0 to validate that the aerobic autotrophic bacteria were mainly distributed in the inner biofilm, while anaerobic heterotrophic bacteria were mainly distributed in the outer biofilm. Sensitivity analysis results indicated that values of the maximum specific growth rate, oxygen saturation constant and the stoichiometric parameters were the most significant in simulating concentration change of inlet substrates, while other constants were of minor significance in terms of predictive quality of the model. In most runs, the modeling results indicated that the C/N ratio and biofilm thickness were important factors for the biofilm operational regime. When C/N ratio was too low, the amount of COD was not sufficient for heterotrophic bacteria, causing deterioration of nitrogen removal efficiency due to lack of COD. On the other hand, too high C/N ratio resulted in growth inhibition of autotrophic bacteria. Moreover, the high biofilm thickness would be a diffusive barrier for COD and ammonia, and too thin biofilm thickness reduced the aerobic or anaerobic region available for bacteria, which also eventually deteriorated nitrogen removal efficiency. The mathematical modeling has the potential to be used for optimizing configuration design, and practical application of HMABR process.更多还原