|Abstract||复合垂直流湿地是一种独特的污水生态处理设施, 具有除污效率较高, 投资少, 管理简单, 运行费用低等优点, 同时拥有较高的脱氮能力。
一般认为湿地的脱氮能力主要依靠湿地微生物的硝化反硝化作用, 而微生物的反硝化作用需要有机质提供电子, 因而有机质成为影响湿地脱氮效果的一个重要因素。然而如今的污水往往具有低碳高氮的特征, 使得湿地的脱氮能力面临严峻考验。本论文研究了湿地在低碳氮比条件下的除氮效果及其变化, 对于了解湿地的脱氮机理及提高系统的净化效果具有重要意义。
本研究采用复合垂直流湿地的下行池为对象, 通过有无植物湿地的脱氮效果对比及出水中各种形态氮的浓度变化, 研究了植物对硝化反硝化作用的影响。对湿地进水的碳氮浓度进行控制, 并监测出水中几种形态氮的浓度, 以探讨湿地在不同浓度条件下的除氮效果。通过考察湿地在进水碳氮比小于1时的脱氮效果, 监测硝化反硝化细菌数量和硝化反硝化作用强度以及各种形态氮在湿地内部的变化趋势, 结合碳源的量化分析, 推导出湿地中除了传统的硝化反硝化途径外, 极可能存在一种不需要消耗碳源的反硝化脱氮途径, 即厌氧氨氧化途径。本论文研究结果如下:
植物对污染物质的直接吸收作用有限, 湿地的脱氮能力主要通过微生物的硝化反硝化作用。有无植物对氨氮的去除效果没有影响, 但是对总氮及硝态氮的去除率影响极为明显。无植物湿地的硝态氮累积现象显著, 进水总氮浓度在6.4 mg/L时, 其出水硝态氮浓度可高达2.83 mg/L, 比相应的有植物系统高一个数量级。湿地植物对硝化率没有显著影响, 但能够提高湿地中的反硝化率。有植物湿地的反硝化率和总氮去除率比无植物湿地分别高1.4倍和1.7倍左右。植物通过根系传输到基质内部的氧气有限, 不足以对湿地的硝化作用产生实质性的影响。植物根系能够显著增加基质的透水能力, 提高湿地的稳定性, 根系表面还为湿地微生物提供了巨大的栖息场所。
湿地在夏季对较高浓度的氨氮有很好的去除效果, 且去除率基本不受有机质以及有无植物的影响。进水氨氮浓度在50.5 mg/L左右时, 出水浓度一般可在1.5 mg/L以下, 去除率达95％以上。进水浓度高达100.5 mg/L时, 出水浓度也可保持在10 mg/L左右, 去除高达90％以上, 这也说明硝化反硝化菌对高浓度氨氮的毒性有较强的忍耐能力。进水氨氮浓度处于5.5－50.5 mg/L范围内时, 出水浓度与其呈线性关系(R2值为0.9971)。进水氨氮浓度处于0.5－50.5 mg/L范围内时, 湿地对总氮的去除量与进水浓度也成线性关系(R2值为1)。
进水碳氮比小于1时湿地也能取得较好的脱氮效果, 总氮去除率高达86.3％,与碳源充足的系统相当, 但湿地中的硝态氮变化大为不同。碳源充足的系统出水硝态氮一直较低, 波动也小。碳源不足的湿地出水硝态氮浓度在初期很高, 较碳源充足的系统高一个数量级, 之后才逐渐下降至碳源充足系统的含量水平。通过湿地反硝化作用的监测和碳源的量化分析, 发现无论是全程反硝化还是短程反硝化都无法解释实验结果, 因此推断湿地中极可能存在一种不消耗碳源的反硝化途径, 即湿地中的氨氮被氧化成亚硝态氮, 亚硝态氮又直接氧化剩下的氨氮为氮气, 称之为厌氧氨氧化。本反硝化途径既可解释本实验结果, 又不与传统硝化反硝化理论冲突。
碳源对湿地中的硝化作用无显著影响, 但对反硝化有显著的抑制作用。厌氧氨氧化途径存在于湿地中, 此途径不需要消耗碳源, 而且难以通过传统方法测量。|
|Other Abstract||Integrated Vertical flow Constructed Wetland is a special kind of ecological establishment for wastewater treatment which has fine removal efficiency, little investment, simple management, low cost for running and high ability for nitrogen removal.
It is generally considered that the competence of nitrogen removal in wetlands mostly depends on the nitrification-denitrification of microorganisms, but microbial denitrification needs electrons from organic matter, so organic matter becomes an important factor influencing the removal efficiency. Now much wastewater presents the characteric of low carbon but high nitrogen, which means that the removal ability of wetlands for nitrogen faces baptism. This paper investigated the removal efficiency and variation of nitrogen on the condition of low carbon but high nitrogen in influent, which will bring realism significance to understand the mechanism of nitrogen removal and to enhance the removal efficiency of wetlands.
This study took the down pond of Integrated Vertical flow Constructed Wetland as the object, via contrasting the removal efficiency and concentration of different nitrogen in effluent between the wetland with macrophytes and without, to study the influence of macrophytes to nitrification and denitrification. By controlling the concentration of carbon and nitrogen in influent and measuring the nitrogen concentration in effluent to probe into the removal efficiency of wetlands under the condition of different nitrogen concentration in influent. Via observing the removal efficiency to nitrogen under the condition of C/N less than 1, measuring the intension
of nitrification and denitrification, variation tendency of different nitrogen, combining with quantity analysis of carbon, educed that it was likely to exist a denitrification approach needing no carbon in wetlands except the traditional nitrification and denitrification approach, which is the ANAMMOX approach. The results of this paper were as follows:
That pollutants directly absorbed by macrophytes were limited in wetlands, so the ability of nitrogen removal mostly depends on the nitrification and denitrification of macroorganisms. Macrophytes had no obvious influences to removal efficiency of ammonia nitrogen, but the influences to total nitrogen was very notable. Cumulation phenomena of nitrate nitrogen in wetlands without macrophytes was remarkable. When total nitrogen concentration was 6.4 mg/L around, nitrate nitrogen concentration in effluent could reach 2.83 mg/L, higher a magnitude than that in wetland with macrophytes. Macrophytes had no obvious influences to nitration rate while the influences to denitration rate was very obvious. Denitration rate and removal efficiency of total nitrogen in wetlands with macrophytes were more 1.4 and 1.7 times than that in wetlands without macrophytes respectively. Only limited oxygen was transmited to substrate inner via macrophytes radicle, so no material influences to the nitrification appeared in wetlands, but radicle could enhance the permeability of substrate and improve the stability of wetlands, and it also provides huge surface for macroorganisms to inhabit.
Wetlands presented better removal efficiency to high concentration ammonia in summer, and which was not influenced by organic matter or macrophytes. When concentration of ammonia nitrogen was 50.5 mg/L around, which in effluent could reduce to 1.5 mg/L with removal efficiency of 95%; When concentration of ammonia nitrogen rose to 100.5 mg/L, concentration in effluent could maintain about 10 mg/L with removal efficiency of 90%, which means that bacterias for nitrification and denitrification have strong tolerance to high concentration ammonia. When ammonia concentration in influent ranged from 5.5 mg/L to 50.5 mg/L, concentration in effluent behaved linearity relation with it(the value of R2 reaching 0.9971). When ammonia concentration in influent ranged from 0.5 mg/L to 50.5 mg/L, the quantity of total
nitrogen removed by wetlands behaved linearity relation with it(the value of R2 reaching 1).
Removal efficiency of nitrogen highly achieved 86.3% when value of C/N was less than 1, as much as which in wetlands with ample carbon source, while concentration variation of nitrate nitrogen had great difference. Concentration of nitrate nitrogen in effluent from wetlands with ample carbon was evidently low and the fluctuation was also little. Concentration of nitrate nitrogen in effluent from wetlands with scant carbon was very high early, even higher a magnitude than that from wetlands with ample carbon, then it played down to the level of former gradually. Via detection of denitrifing rate in wetlands and quantity analysis of carbon, it was found that neither full-denitrification nor short-denitrification could explains the results of experiment, so a denitrification approach needing no carbon was deduced to exist in wetlands. Ammonia nitrogen was oxidized to nitrite nitrogen, then nitrite nitrogen oxidized ammonia nitrogen into nitrogen gas, which was called ANAMMOX. This approach could not only explain the result of experiment, but also does not conflict with traditional nitrification and denitrification theory.
Carbon source had no obvious influences on nitrification, but which restricted the dinitrification observably. The ANAMMOX approach was very possible to exist in wetlands, which needs no carbon source and is difficult to be measured via traditional method.|