循环水产养殖系统中玉米芯介导的反硝化微环境特征研究

Biological denitrification has a pronounced effect on the removal of nitrogen from RAS (recirculating aquaculture system). However, to date, seldom information is available of denitrification mechanism mediated by solid carbon source in RAS.. According to previous study, we have discovered that high nitrate removal rate was found when corncob used as carbon source and biofilm carrier. In order to explore the mechanism of denitrification microenvironment clearly, in present research proposal, we will further investigate the relationship between microbial community structure and substrate transmission within biofilm. Firstly, microelectrode technique will be employed to measure the concentration of characteristic parameters (including oxygen and nitrate) with the increasing depth of biofilm. Based on the profiles, the microenvironment characteristics of exchange flux and utilization rates of oxygen and nitrate will be evaluated. And then, to make clear the change of microbial distribution with the increasing depth of biofilm, high-throughput sequencing technique will be employed to analyze the microbial community structure pretreated by frozen section. Besides, scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) will also be used to explore microbial morphological changes from one-dimensional and three-dimensional, which help reveal the variation of the dominant microbial species on biofilm’s vertical direction. Finally, in order to get a clearer explanation about denitrification microenvironment mediated by corncob, based on the results received, the dynamic balance and internal relations among microorganism, oxygen and nitrate will be evaluated. . The present research can provide theoretical and technical support for denitrification in RAS wastewater treatment. It will be meaningful for water resource reuse and sustainable development of aquaculture.

生物反硝化对循环水产养殖系统氮的去除有重要影响。前期研究发现，以玉米芯同时作为反硝化微生物碳源和载体可有效降低循环养殖水中的硝酸盐浓度，获得较高脱氮效率。本项目拟对玉米芯介导的固相反硝化微环境，特别是基质传递与微生物分布间的关系展开深入研究。借助微电极技术探究生物膜垂直方向上特征参数（氧和硝酸盐）浓度的变化规律，建立扩散-反应方程，获得氧和硝酸盐反应动力学；借助扫描电镜和激光共聚焦显微镜分别从一维及三维角度探究微生物形态变化，在冷冻微切片基础上，借助高通量测序技术分析生物膜不同层面微生物群落结构变化特征，揭示微生物形态及分布动态变化规律；综合以上实验，深入探讨微生物、氧及硝酸盐三者的动态平衡及内在关系，解析三者共同形成的微环境对玉米芯介导的反硝化工艺脱氮效果的影响。本研究将进一步揭示固相反硝化脱氮机理，为固相反硝化工艺的优化提供理论和技术支撑，对推动水产养殖可持续健康发展具有重要意义。

我国的循环水养殖业正处于快速发展期，产业对循环水的关注和需求日益增加。我国的养殖塘普遍存在养殖密度高、投饵及用药过量等问题，使得水环境中的总氮、总磷、TOC等增加迅速。又因养殖水环境中溶解氧普遍较高，不具备反硝化所需的厌氧环境，导致在养殖环境中硝酸盐大量累积，对养殖品种、周边环境及人类健康均造成了较大威胁。未来水产养殖依然是动物源性食品生产增长最快的领域，工厂化循环水养殖模式代表着先进生产力的发展方向，是水产养殖业可持续发展的必经之路。因此，做好循环养殖废水的净化处理工作就显得尤为重要。. 项目组创新性的提出将玉米芯同时作为反硝化碳源和生物膜载体，应用于循环水产养殖废水的生物脱氮处理，以期人为的营造原位反硝化厌氧微环境，促进反硝化脱氮，进一步实现养殖废水循环利用的目标。研究结果表明经人工强化挂膜后，装置运行1天水体硝酸盐和总氮的去除率即可分别达到95% 和85%以上。装置脱氮效果受水温影响较大，水温低于15℃后膜内微生物数量明显下降，装置脱氮效率下降显著。过高的溶解水平同样会对氮的去除产生影响，建议实际应用时将水体溶解氧控制在6mg/L以内。微生物跟踪调查表明，反硝化菌无论是种类还是数量均高于硝化菌，且脱氮微生物的数量和种类随着运行时间的延长会出现下降。微生物空间分布规律为玉米芯中层脱氮微生物种类最为丰富，内层脱氮微生物数量随着运行时间的延长会出现上升趋势，表明反硝化区域有逐步扩大趋势。微电极监测的膜内溶解氧分布规律同样表明，随着运行时间延长，反硝化所需的厌氧微环境有扩张现象。膜内未见N2O累积。装置稳定运行后氧气在基于玉米芯的膜内的扩散系数低于其他载体的扩散系数，表明玉米芯特殊结构更有利于反硝化微环境的营造。本项目的完成为循环养殖废水生物反硝化脱氮工艺的优化提供了理论和技术支撑，对推动循环水产养殖业的可持续发展具有重要的理论和实践意义。