间歇曝气对微污染源水生物接触氧化修复系统脱氮性能的影响

针对寡营养生境下生物脱氮过程碳源不足等问题,开展不同间歇曝气方式对微污染源水生物接触氧化修复系统脱氮性能的影响研究,探究修复系统短程硝化反硝化的可行性与过程机理.结果表明:在停曝-曝气时间为8 h-16 h的间歇曝气方式(Ⅰ)下启动的生物接触氧化修复系统,其铵态氮(NH+4-N)、高锰酸盐指数(CODMn)、总氮(TN)的平均去除率分别稳定在93.0%、78.1%、19.4%;而在停曝-曝气时间为16 h-8 h的间歇曝气方式(Ⅱ)下运行修复系统,其NH+4-N、CODMn平均去除率仍能分别维持在81.2%、76.4%,体系内NO-2-N发生积累,TN去除率增至50%以上.对工况Ⅱ下修复系统周期内氮素转化特性分析发现,在确保出水NH+4-N、溶解氧(DO)浓度达标的前提下,缩短曝气时间可将体系DO长时间控制在0.5～1.5 mg·L-1,亚硝酸氧化菌(NOB)生长及其活性受到抑制,NO-2-N明显累积,最终实现了微污染源水生物接触氧化修复系统的短程生物脱氮.     

过表达亚硝酸盐还原酶的重组大肠杆菌辅助污水短程硝化

【目的】为了体现并突出亚硝酸盐还原酶在污水脱氮以及短程硝化中的重要性,对过表达亚硝酸盐还原酶的大肠杆菌进行了污水脱氮的研究。【方法】通过转化带有亚硝酸盐还原酶基因的重组质粒,将亚硝酸盐还原酶在大肠杆菌中过表达,通过分析重组大肠杆菌的产物研究了该酶的表达及还原亚硝酸盐的情况,通过将该重组菌与已报道的硝化-反硝化细菌或生活污水进行混合培养,研究重组菌用于辅助氨氮去除的短程硝化能力。【结果】重组大肠杆菌能正确表达亚硝酸盐还原酶,OD600=2.0的菌悬液在2 h内还原约1 mmol/L的亚硝酸盐,并产生几乎等量的一氧化氮;重组大肠杆菌与Acinetobacter sp.YF14菌株等比例混合时,12 h能够提高氨氮脱氮效率约(36.0±7.4)%,且在4 h时,最大亚硝酸盐的积累量减少37%;重组大肠杆菌(OD600=1.0)12 h内能够提高污水厂活性污泥的脱氮效率约(31.0±5.7)%,且未检测到亚硝酸盐和硝酸盐的积累;溶氧水平对于亚硝酸盐还原酶重组菌辅助脱氮具有明显的影响,中等溶氧量[(6.4?0.7)mg/L]时脱氮效果最好。【结论】过表达亚硝酸盐还原酶的大肠杆菌可以提高污水脱氮的短程硝化能力。     

黄河口不同恢复阶段湿地土壤N2O产生过程对氮输入的响应

以黄河口生态恢复前后未恢复区(R₀)、2007年恢复区(R₂₀₀₇)和2002年恢复区(R₂₀₀₂)的芦苇湿地为研究对象,研究了不同形态氮输入对湿地土壤N₂O产生过程的影响与贡献.结果表明: 硝态氮(NO₃^--N)输入对恢复区湿地土壤N₂O总产生量的影响远远大于铵态氮(NH₄⁺-N),但两者均抑制了R₀土壤的N₂O总产生量.尽管NO₃^--N输入对R₂₀₀₂表层土壤N₂O总产生量的影响明显大于R₂₀₀₇,但二者的N₂O产生量均随氮输入量的增加而增加.恢复区湿地土壤的反硝化作用和硝化细菌反硝化作用受NO₃^--N输入的影响明显,而R₀土壤产生N₂O的生物过程受其影响并不显著.尽管NH₄⁺-N输入对湿地土壤N₂O的总产生量影响不大,但其输入整体促进了R₀ 土壤的硝化细菌反硝化作用、R₂₀₀₇土壤的硝化作用和R₂₀₀₂土壤的非生物作用.比较而言,NO₃^--N输入对R₀、R₂₀₀₇和R₂₀₀₂湿地土壤N₂O产生的非生物作用主要表现为抑制,NH₄⁺-N输入则整体提高了R₀和R₂₀₀₂湿地土壤非生物作用的N₂O产生量,这与不同形态氮输入对土壤pH的调节作用密切相关.研究发现,NO₃^--N输入大大增加了湿地土壤的N₂O总产生量,改变了原有湿地土壤生物作用和非生物作用的贡献模式,故生态恢复工程导致的营养盐输入(NO₃^--N)应受到特别关注.     

脱氮微生物及脱氮工艺研究进展

脱氮是大部分污水处理系统中不可缺少的一环。由于具有经济高效、工艺简单和无二次污染等显著优势,生物脱氮工艺在最近数十年中备受关注。根据脱氮微生物的生理特性和脱氮机制不同,文中分类综述了近年来生物脱氮工艺的研究进展,重点对比分析了硝化菌、反硝化菌和厌氧氨氧化菌以及以这些菌为基础的不同生物脱氮工艺的优缺点,为复杂污水环境的脱氮工艺选择提供参考。基于微生物脱氮机制,通过合成生物学技术开发高效脱氮菌株,结合不同工艺优点并应用自动化模拟最佳条件,从而建立经济高效的脱氮工艺将是未来发展的重要方向。     

Nitrite reduction by a mixed culture under conditions relevant to shortcut biological nitrogen removal

Dissimilative reduction of nitrite by nitrite-acclimated cellswas investigated in a batch reactor under various environmental conditions that can beencountered in shortcut biological nitrogen removal (SBNR: ammonia to nitrite andnitrite to nitrogen gas). The maximum specific nitrite reduction rate was as much as 4.3 times faster than the rate of nitrate reduction when individually tested, but the reaction was inhibited in the presence of nitrate when the initial nitrate concentration was greater than approximately 25 mg-N/l or the initialNO ₃ ^- N/NO ₂ ^- N ratio was larger than 0.5. Nitrite reduction was also inhibited by nitrite itself when theconcentration was higher than that to which the cells had been acclimated. Therefore, it was desirable to avoid excessively high nitrite and nitrate concentrations in a denitrification reactor. Nitrite reduction, however, was not affected by an alkaline pH (in the range of 7–9) or a high concentration of FA (in the range of 16–39 mg/l), which can be common in SBNR processes. The chemical oxygen demand (COD) requirement for nitrite reduction was approximately 22–38% lower than that for nitrate reduction, demonstrating that the SBNR process can be economical. The specific consumption,measured as the ratio of COD consumed to nitrogen removed, was affected by the availability of COD and the physiological state of the cells. The ratio increased when the cells grew rapidly and were storing carbon and electrons.     

急诊快捷护理流程应用于急性脑卒中的效果分析

目的：探讨急诊快捷护理流程对急性脑卒中的临床效果,为改善患者预后提供有效措施。方法：回顾性分析2007年6月-2011年6月我院收治的319例急性脑卒中患者的临床资料,按照其就诊时期分为对照组（n=166）及观察组（n=153）,对比两组患者的急诊效果。结果：观察组接诊至确诊时间、确诊至接受专科治疗时间均显著低于对照组（P〈0．05）,两组抢救费用无明显统计学差异（P〉0．05）;观察组致残19例,病死7例,致残、致死率分别为12．4％及4．6％,对照组致残35例,病死13例,致残、致死率分别为21．1％及7．8％,观察组致残、致死率均低于对照组（P〈0．05）;观察组共出现30例并发症,并发症率19．6％,对照组出现55例并发症,并发症率33．1％,观察组并发症率明显低于对照组（P〈0．05）。结论：急诊快捷护理流程可有效缩短急诊各环节消耗的时间,使患者得到最准确、最及时的干预、治疗,能够有效保证其治疗效果,从而保证其顸后,提高急救效率,值得临床广泛推广。     

三江平原典型小叶章湿地土壤硝化反硝化作用与氧化亚氮排放

应用C₂H₂抑制原状土柱培育法研究了三江平原典型小叶章湿地土壤N₂O排放速率及反硝化速率的变化,分析了它们与环境因子的关系,并估算了N₂O排放量及反硝化损失量.结果表明：草甸沼泽土和腐殖质沼泽土N₂O排放速率的变化基本一致,其范围分别为0.020～0.089 kg N·hm^-2·d^-1和0.012～0.033 kg N·hm^-2·d^-1,前者的N₂O排放速率均明显高于后者(平均为1.79±1.07倍),且其差异达到显著水平(P＜0.05);二者反硝化速率的变化并不一致,其范围分别为0.024～0.127 kg N·hm^-2·d^-1和0.021～0.043 kg N·hm^-2·d^-1,前者的反硝化速率一般也要高于后者(平均为1.67±1.56倍),但其差异并未达到显著水平(P＞0.05);硝化作用在前者N₂O排放和氮素损失过程中发挥了重要作用,而反硝化作用则是导致后者N₂O排放和氮素损失的重要过程;氮素物质基础不是影响二者硝化-反硝化作用的重要因素;温度对前者硝化 反硝化作用的影响比后者更为明显,其反硝化速率与5、10和15 cm地温均呈显著正相关(P＜0.05);二者所处湿地水分条件的差异是导致其N₂O排放速率及反硝化速率差异的重要原因.生长季内,前者的N₂O排放量和反硝化损失量分别为5.216 kg N·hm^-2和6.166 kg N·hm^-2,而后者分别为3.196 kg N·hm^-2和4.407 kg N·hm^-2;在二者的反硝化产物中,N₂O/N₂的比率最高,分别为5.49和3.76,表明N₂在后者反硝化产物中所占的比例明显高于前者,说明季节积水条件会导致N₂O/N₂比例降低.     

Optimal operational factors for nitrite accumulation in batch reactors

The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture. A batch reactor with 50 mg-N/l of ammonia was used. The pH, temperature and dissolved oxygen concentration were varied. The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature. The accumulation of nitrite was affected sensitively by pH and temperature. A higher nitrite concentration was observed at pH 8-9 or temperature around 30 °C. The dissolved oxygen also affected, giving the highest nitrite accumulation at around 1.5 mg/l. These were the favoredconditions for nitrite production. The free ammonia concentration influenced thenitrite accumulation also, by inhibiting nitrite oxidation. The inhibition becameapparent at a concentration of approximately 4 mg/l or above, but insignificant atbelow 1 mg/l. Thus, simultaneously high free ammonia concentration and maximumspecific ammonia-oxidation rate (above 15 × 10^-3 mg-N/mg-VSSh)were needed for a significant nitrite accumulation. When the two conditions were met, thenthe highest accumulation was observed when the ratio of the maximum specific oxidationrate of ammonia to the maximum specific oxidation rate of nitrite (k_a/k_n) was highest.Under the optimal operating conditions of pH 8, 30 °C and 1.5 mg/l of dissolvedoxygen, as much as 77% of the removed ammonia accumulated in nitrite.     

消落带生态系统氮素截留转化的主要机制及影响因素

消落带是陆地与水体(河流、湖泊、水库、湿地以及其他特殊水体)之间的生态过渡带,具有独特的生态水文学和生物地球化学过程,是截留和转化NH₄⁺、NO₃^-等非点源氮素进入水体的最后一道生态屏障.整合已有相关研究成果发现: 1)植物固持作用改变氮素在土壤-植被-土壤-大气中相对存在位置;2)微生物反硝化作用将氮素从系统内永久性地去除,是消落带生态系统氮素截留转化的主要机制,但其相对贡献率仍有很大的不确定性.在不同流域背景条件下,影响消落带生态系统氮素生物地球化学循环的主要生态因子变化较大,很难确定地下水位高低、植被状况、微生物属性和土壤基质等哪一个生态因子是驱动消落带生态系统氮素循环的关键因子.研究方法的局限性、大的时空尺度数据的缺乏及对植被宽度认识的模糊性,是导致消落带生态系统氮素截留转化结果变异性大的主要原因.因此,应在消落带生态系统具体研究区位环境因子基础上,利用数学模型、GIS、RS等分析方法及同位素示踪和气体联用测定等定量分析技术,从不同时空尺度研究消落带生态系统氮素的循环与转化规律,以实现消落带生态系统氮素截留转化最优化,为消落带生态系统的科学管理提供理论基础.     

Factors Affecting Nitrous Oxide Production: A Comparison of Biological Nitrogen Removal Processes with Partial and Complete Nitrification

Nitrous oxide (N₂O) emission from biological nitrogen removal (BNR) processes has recently received more research attention. In this study, two lab-scale BNR systems were used to investigate the effects of various operating parameters including the carbon to nitrogen (C/N) ratio, ammonia loading, and the hydraulic retention time on N₂O production. The first system was operated in a conventional BNR mode known as the Ludzack–Ettinger (LE) process, consisting of complete denitrification and nitrification reactors, while the second one was operated in a shortcut BNR (SBNR) mode employing partial nitrification and shortcut denitrification, which requires less oxygen and carbon sources. As the C/N ratio was decreased, a significant increase in N₂O production was observed only in the anoxic reactor of the LE process, indicating that N₂O was released as an intermediate of the denitrification reaction under the carbon-limited condition. However, the SBNR process did not produce significant N₂O even at the lowest C/N ratio of 0.5. When the SBNR process was subjected to increasing concentrations of ammonia, N₂O production from the aerobic reactor was rapidly increased. Furthermore, the increasing production of N₂O was observed mostly in the aerobic reactor of the SBNR process with a decline in hydraulic retention time. These experimental findings indicated that the increase in N₂O production was closely related to the accumulation of free ammonia, which was caused by an abrupt increase of the ammonium loading. Consequently, the partial nitrification was more susceptible to shock loading conditions, resulting in a high production of N₂O, although the SBNR process was more efficient with respect to nitrogen removals as well as carbon and oxygen requirements.