复合垂直流—水平流人工湿地系统处理二级生化尾水的实验研究

发布时间：2018-07-25 20:08

【摘要】：我国污水处理厂二级尾水排放量大,且氮、磷浓度较高,对自净能力有限或已受到污染的受纳水体来说,排放的尾水中较高的氮、磷浓度仍会造成地表水污染和受纳水体的富营养化现象。尤其在我国西北干旱半干旱地区,由于地域、气候等区域性因素,大多数污水处理厂出水污染物浓度仅能达到《城镇污水处理厂污染物排放标准》(GB18918-2002)中的一级B标准,甚至超出该标准。另一方面,我国水资源呈现出总量多但人均占有量少、水环境污染严重和废水排放逐年快速增长的现状,污水深度处理和尾水资源化利用成为降低受纳水体的污染负荷和缓解水体的自净压力、推进城市化建设进程和解决城市缺水问题的首要选择。人工湿地系统以其投资及运行成本低、运行维护方便、去除氮磷能力强等特点而被广泛应用于各种水体治理,因此研究人工湿地系统对污水厂尾水的深度处理也具有重大意义。针对西北地区某些城镇污水处理厂的实际出水水质中有机物浓度低和氮、磷浓度相对较高的特点,本实验以废砖块和页岩陶粒为人工湿地的基质填料,并将西北地区常见植物芦苇和香蒲作为人工湿地的主要植物,在室外自然条件下构建复合垂直流-水平潜流人工湿地小试装置,研究了系统在启动阶段、稳定运行阶段和植物收割后对二级生化尾水中有机物(COD、BOD5)、氨氮(NH_4~+-N)、总氮(TN)及总磷(TP)等污染物的去除效果。同时,为考察二级生化尾水中较高浓度的氮、磷对两种湿地植物的影响程度,实验于植物移栽初期及收割前期分别检测人工湿地系统下行流池、上行流池和水平流池中两种湿地植物的生长生理指标和光合参数,分析了湿地植物芦苇和香蒲在处理二级生化尾水前后的生理生长特性变化,最终得出了以下结论:(1)在实验的启动阶段,随着移栽的芦苇和香蒲的逐渐成活生长,植物根系输氧能力增强,基质内好氧、兼氧、厌氧微生物数量逐渐增多,系统对COD、NH_4~+-N、TP的去除率由最初的52.94%、37.80%、53.51%分别上升至68.18%、76.61%、81.57%,此阶段芦苇和香蒲植株平均高度由移栽时的32cm、38cm增长到68cm、63cm,复合垂直流湿地床(IVCW段)植物长势好于水平流湿地床(HF段)。(2)稳定运行阶段湿地系统对NH_4~+-N、TN和TP的去除效果随着水力负荷增大而减小,而对COD、BOD5的净化效果受水力负荷影响较小。在0.15m3/(m2·d)的低水力负荷下,进水NH_4~+-N、TN和TP浓度在8.40~14.81mg/L、11.02~18.97mg/L、0.81~1.53mg/L之间时,复合垂直流-水平流人工湿地系统出水COD、BOD5和TP浓度分别低于《地表水环境质量标准》(GB 3838-2002)中的Ⅰ类、Ⅳ类、Ⅲ类水质标准限值,而出水NH_4~+-N、TN浓度虽未达到地表水环境质量标准,但已远远低于《城镇污水处理厂污染物排放标准》(GB18918-2002)的一级A标准。(3)稳定运行阶段复合垂直流-水平流人工湿地对COD、NH_4~+-N、TN和TP的去除负荷随进水负荷的增加而呈线性增加趋势,而且并未表现出减缓的趋势,表明复合垂直流-水平流人工湿地在本实验范围内还能承载更高的进水污染负荷以充分发挥其纳污去污能力。(4)在稳定运行阶段,复合垂直流-水平流人工湿地系统在0.15m3/(m2·d)、0.25m3/(m2·d)、0.35m3/(m2·d)三种水力负荷条件下沿程COD、NH_4~+-N、TN和TP浓度呈现出先迅速降低、后缓慢下降的趋势,且湿地系统表层N、P的去除效率要高于中下层,尤其在复合垂直流湿地床下行流池进水端表层0~30cm范围内污染物均有一个快速降解的过程。(5)不同植物对氮、磷等污染物的吸收富集能力存在一定差异,各湿地床植物吸氮量高于吸磷量,而且植物收割对氮的去除能力有明显影响。因此,在实际应用中应根据耐污性强弱和氮磷吸收量的大小合理选择和配置适宜于不同流程的湿地植物,同时还应选择适当的时机收割湿地植物以强化人工湿地的污染物净化效果。(6)整个实验过程中,芦苇和香蒲长势良好,植物叶片中丙二醛(MDA)和游离脯氨酸(Pro)含量随湿地床污染物浓度升高而不同程度的增加,说明两种植物具有一定的自我防御能力,可以很好的适应二级生化尾水中污染物的胁迫。另外,尾水处理前后两种植物叶片净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)随复合垂直流-水平流人工湿地系统流程加长而增大,表观叶肉导度(AMC)、气孔限制百分率(Ls)则相反,这表明二级生化尾水中适量的有机物、氮素、磷素等可以为香蒲和芦苇提供一定的营养物质而使得植株光合作用能力增强,进一步证明实验选择芦苇和香蒲作为人工湿地植物处理尾水是合理可行的。(7)复合垂直流-水平流人工湿地系统在启动-稳定运行-植物收割后三个阶段均可以有效削减进水污染物负荷,适用于城市污水的深度处理,二级水平流湿地床在一级复合垂直流湿地床处理效率的基础上可以提高15~25%。这表明选择具有发达的根系及通气组织、较强耐污能力的湿地植物和来源广泛、疏松多孔、性质稳定的湿地基质对构建人工湿地强化去污效果具有重要的意义。
[Abstract]:The wastewater treatment plant of China has a large two level tail water discharge, high nitrogen and phosphorus concentration, higher nitrogen and phosphorus concentration in the tailor water discharged from the polluted water body with limited self purification capacity or polluted water. Regional factors, the concentration of effluent from most sewage treatment plants can only reach the first grade B standard in the pollutant discharge standard of urban sewage treatment plant (GB18918-2002), even beyond the standard. On the other hand, the water resources in our country show a large amount but less per capita, the pollution of water environment and the discharge of waste water are increasing rapidly year by year. The advanced treatment of sewage and utilization of tailwater resources have become the primary choice to reduce the pollution load of the received water and relieve the self purification pressure of the water body, promote the process of urbanization and solve the problem of water shortage in the city. It is applied to the treatment of various water bodies, so the study of the artificial wetland system is also of great significance to the depth treatment of the tail water of the sewage plant. In this paper, the waste brick and shale ceramsite are used as the matrix of the constructed wetland for the low concentration of organic matter and the relatively high concentration of nitrogen and phosphorus in the actual effluent quality of some municipal wastewater treatment plants in Northwest China. The common plant reeds and cattails in Northwest China were used as the main plants in the artificial wetland. Under the outdoor natural conditions, a compound vertical flow horizontal subsurface constructed wetland was constructed. The system was studied at the starting stage, the stable operation stage and the two grade biochemical tail water (COD, BOD5), and ammonia nitrogen (NH_4~+-N) after the plant harvest. The effect of total nitrogen (TN) and total phosphorus (TP) on the removal of pollutants. At the same time, in order to investigate the effect of nitrogen and phosphorus on the two kinds of wetland plants in the two grade biochemical tail water, the growth physiological index of two wetland plants in the artificial wetland system, the upstream pool and the horizontal flow pool were tested at the early stage of plant transplanting and the early harvest. The physiological characteristics of reeds and cattails of wetland plants and cattails were analyzed before and after the treatment of two grade biochemical tail water. The following conclusions were concluded: (1) in the starting stage of the experiment, with the gradual survival of reed and cattail, the oxygen transport capacity of plant roots increased, and the number of aerobic and anaerobic microbes in the substrate was increased. Gradually increasing, the removal rate of COD, NH_4~+-N and TP increased from 52.94%, 37.80%, 53.51% to 68.18%, 76.61%, 81.57% respectively. The average height of reeds and cattail plants from the transplanted 32cm, 38cm to 68cm, 63cm, and the compound vertical flow wetland bed (IVCW section) was better than the horizontal flow wetland bed (HF section). (2) stable operation order. The removal effect of the segment wetland system on NH_4~+-N, TN and TP decreases with the increase of hydraulic load, while the purification effect for COD, BOD5 is less affected by the hydraulic load. In the low hydraulic load of 0.15m3/ (M2 d), the influent is NH_4~+-N, TN and TP concentration is between the 8.40~14.81mg/L, the vertical flow and the horizontal flow. The concentration of COD, BOD5 and TP in the effluent of the ground system is lower than that of category I, type IV, and class III water quality standard in the environmental quality standard of surface water (GB 3838-2002), while the NH_4~+-N and TN concentration of the effluent has not reached the standard of surface water environmental quality, but it is far below the first grade A standard of the pollutant discharge standard of urban sewage treatment plant (GB18918-2002). (3) stability. The removal load of COD, NH_4~+-N, TN and TP of the composite vertical flow and horizontal flow constructed wetland in the fixed operation stage increases linearly with the increase of the influent load, and does not show a slow trend. It shows that the composite vertical flow horizontal flow constructed wetland can also carry the higher influent pollution load in this experiment. (4) in the stable operation stage, the compound vertical flow and horizontal flow constructed wetland system in 0.15m3/ (m2. D), 0.25m3/ (m2. D), 0.35m3/ (m2. D) under three kinds of hydraulic loads, the COD, NH_4~+-N, TN, and the concentration of TN and decreased slowly decline, and the removal efficiency of the wetland system is higher than that of the middle and lower levels. There is a rapid degradation process in the 0~30cm range of the surface layer of the influent end of the downflow pool of the compound vertical flow wetland. (5) there is a certain difference in the absorption and enrichment ability of different plants to nitrogen and phosphorus, and the uptake of nitrogen in the wetland bed plants is higher than that of the phosphorus uptake, and the plant harvesting has a significant influence on the removal of nitrogen. Therefore, in practical application, we should choose and configure wetland plants suitable for different processes according to the strength of the resistance to pollution and the amount of nitrogen and phosphorus absorption. At the same time, we should choose the appropriate time to harvest the wetland plants to strengthen the purification effect of the pollutants in the constructed wetland. (6) in the whole experiment, the reed and the cattail are in good growing trend and in the leaves of plants. The content of malondialdehyde (MDA) and free proline (Pro) increased with the increase of the pollutant concentration in the wetland bed, indicating that the two plants have a certain self defense ability and can adapt to the stress of the pollutants in the two grade biochemical tail water. In addition, the net photosynthetic rate (Pn), the stomatal conductance (Gs), and the stomatal conductance (Gs) of the two plant leaves before and after the tail water treatment The CO2 concentration (Ci) increased with the lengthening process of the composite vertical flow horizontal flow constructed wetland system. The apparent mesophyll conductivity (AMC) and the stomatal limit percentage (Ls) were the opposite. This showed that the proper amount of organic matter, nitrogen and phosphorus in the two grade biochemical tail water could provide a certain nutrient for the cattail and reed, which could enhance the photosynthesis ability of the plant. It is further proved that the experimental selection of reeds and cattails as artificial wetland plants is reasonable and feasible. (7) the composite vertical flow horizontal flow constructed wetland system can effectively reduce the influent load in the three stages after the starting - stable operation - plant harvest. It is suitable for the deep treatment of municipal sewage and the two level horizontal flow wetland bed. On the basis of the treatment efficiency of the first grade compound vertical flow wetland bed, 15~25%. can be improved, which indicates that the selection of developed roots and aeration tissues, the strong pollution resistant wetland plants and the wide and porous, porous and porous wetland matrix are of great significance to the construction of the artificial wetland to strengthen the pollution removal effect.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703

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