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Alternative TitleStudies on the purification technology and flow pattern of Integrated Vertical-flow Constructed Wetland (IVCW)
Thesis Advisor吴振斌
Degree Grantor中国科学院水生生物研究所
Place of Conferral中国科学院水生生物研究所
Degree Discipline环境科学
Keyword复合垂直流构建湿地(Ivcw) 反应动力学 停留时间分布(Rtd) 水流流态 堵塞
Other AbstractConstructed wetland is a kind of low-cost and high-efficiency ecosystem engineering for wastewater treatment and water reuse, which draw more and more attention from China and aboard. Since its purification mechanism is not fully understood and its design is sequentially based mainly on experience, some constructed wetlands do not operate effectively. In this paper a novel constructed wetland, the Integrated Vertical-flow Constructed Wetland (IVCW) with downfiow and upflow is studied. The purification function and its related factors are acquired, and the pollutant removal reaction kinetics is revealed and the parameters of IVCW technological design are obtained. The flow pattern of IVCW is explored and simulated successfully by using no ideal dispersed flow model, and it is declared that the flow pattern is the essential reason for purification efficiency variability. Based on the research on FVCW several constructed wetland projects for wastewater treatment are built. The main results are summarized as following. Five-year operation of small scale plots and medium scale plot of TVCW shows that the removal rates for nutrient, especially nitrogen and phosphorus, are improved and pollutants such as heavy metals, bacteria, algae, toxic microcystins and phthalic acid esters can also be reduced obviously. Adequate purification efficiency is also achieved even in winter. Aesthetic value of the macrophytes in IVCW makes the surroundings more attractive. Utilization of FVCW is favorable for secondary/tertiary treatment of domestic wastewater and for eutrophication control. The pollutant removal kinetics of IVCW is significantly affected by the two factors, pollutant loading rate and hydraulic retention time. Under 0.4m~1.2m~3/m~2·d hydraulic loading rate, the removal loading rate for organic substance and ammonia is in linear correlation with the pollutant loading rate while the mass of organic substance in effluent is in exponent correlation with hydraulic retention time. And the total reaction rate equation for organic pollutant removal is determined. Moreover, based on the oxygen balance in IVCW the value for dissolved oxygen in the effluent is deduced. The flow pattern of IVCW is explored to find that I) the flow rate of outflow and the water level curve follow the pulse type and quick feeding and temporal inundation are beneficial for the substrate to recover from anaerobic condition and promotes purification efficiency of the IVCW system. The dead space, which can avoid the short cut of water flow in constructed wetland, is 48 - 72 % of the whole volume of the substrate under 200-800L/d inflow flow rate. II) In the tracer experiment, the actual retention time and its distribution curve are obtained. The actual retention time is more than 17 hours under 0.2-0.8m~3/m~2 d hydraulic loading rates, and the actual flow pattern can be judged according to the retention time distribution curve and is believed as the state between the ideal plug flow and continuous stir flow. It is stated that the flow pattern is the essential reason for purification efficiency variability and the retention time distribution curve can reflect the extent of deviation of the actual flow from the ideal plug flow, which presents the important information about running of the constructed wetland. III) In terms of the no ideal reactor model in reactor theory, it is found that the dispersed flow model is more accurate than the continuously stirred tank reactor (CSTR) in series model to simulate the actual flow pattern of the IVCW. According to the dispersed flow model, Peclect number is calculated between 11 and 19. This result provides a reasonable explanation for the improved flow pattern and the higher purification efficiency of IVCW in comparison with the other kinds of constructed wetlands, the surface flow constructed wetland and subsurface flow constructed wetland. Furthermore, the outcome of pollutant removal reaction can be predicted by using appropriate reactor model, which is believed as one of the valuable approaches for constructed wetland design. IV) Based on the comparison experiment of the planted and unplanted IVCW, it is revealed that spread of macrophyte rhizomes prolongs the hydraulic retention time of water flow, and is also in favor of water flow to approximate to the ideal plug flow. The parameters of substrate related to clogging, such as the grain size, the filtration rate, the content of water and organic substance in the substrate, are investigated in medium scale plot. The substrate of FVCW is collected by a specific sampling tube in situ and the results demonstrate that the direction of water flow does not affect the penetration of r/CW and the filtration rate of substrate increases with approaching to deeper layer of substrate and the minimum filtration rate exists 15-30cm below the surface of substrate. The amount of organic substances in upper 15cm layer of the substrate is limited and even less in deeper layer after forty two-month running. The relationship between clogging time and TSS in the influent of the small scale plots is reasoned as the equation: t_c = 710000/C_s~(in)·Q·A~(-1). Based on the purification technology and design research on the small scale plots and medium scale plot, several large scale FVCW-based constructed wetlands are built in Central and Southern China, and their appropriate operation provides preliminary confirmation of the above results.
Document Type学位论文
Recommended Citation
GB/T 7714
付贵萍. 复合垂直流构建湿地(IVCW)的净化工艺与水流流态研究[D]. 中国科学院水生生物研究所. 中国科学院水生生物研究所,2002.
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