| Urban sewage and waste water is renewable resource, but most of them is discharged directly without recycling, causing serious pollution and waste. In recent years, with the popularization of concept of circular economy and renewable resources, the recycling of city sewage and waste water has caused more and more concerns. Artificial wetland technology becomes gradually an important technology of urban sewage reusing. Because it has many outstanding advantages, such as low investment and operation cost, strong anti-interference, simple operation, remarkable ecological benefit.In this research, tail water of beijiao sewage purification plant in Taiyuan was advanced treated with the horizontal undercurrent of artificial wetland technology, as the landscape water. The characteristic of tail water is highly nitration and insufficient in carbon source. To solve the problem of low removal efficiency of nitrogen, which is caused by suppressed denitrification as a lack of carbon source. So plant straw harvested from the artificial wetland will be applied to the wetland system, served as carbon source. First of all, three kinds of optional plant straw(reeds, cattails and maize straw) were pretreated in four kinds of different ways respectively. Then their safety, release rule of carbon source and potential impact on water quality along with the decomposition of the plant were analyzed. As a result, the reed straw was chosen as the best carbon source. Secondly, Small-scale experiment was carried out with indoor apparatus simulating artificial wetland. Impact on the running effect of apparatus were analyzed after adding reed straw, which was studied from three stages, they were early operation, sequencing batch operation and continuous running, So as to optimize design parameters, and budget the suitable dosing quantity of straw, laying a foundation for conduct of medium scale experiment. Finally, the medium scale experiment was carried out in the beijiao sewage purification plant of Taiyuan. The running effect of constructed wetland in the same period in 2012 and 2011 were compared, similarly, the bed added reed straw and other beds without carbon source were compared. The influence factors of running effect of the constructed wetland were analyzed, and the conclusion that how much impact it had on the of the denitrification ability to add reed straw was reached, Optimal adding quantity of reed straw applied to artificial wetland were budgeted, so as to lay theoretical basis for the further promotion of engineering.Results showed that:(1)Slow-release effect of crushed reed straw was best, so it was the best carbon. (2) In the initial stage of running of indoor apparatus, release quantity of carbon source was extremely high, The change of COD concentration in effluent of reactor experienced three stages roughly, they were extremely high, falling fast and stable phase, the final concentration was basically stable at about 48 mg/L. With the release of organic matter, N and P in the straw body also dissolved in the water, without affecting effluent quality yet. In the stage of sequencing batch operation, with the extension of time(15h/30h/ 45h), The consumption amount of carbon source for disposing per mg nitrate was 0.046g,0.03g and 0.02g respectively. That is to say, the C/N was 46,30 and 20 respectively. Synthetically considering,30h was regarded as the optimal residence time. By comparing the corresponding denitrification rate of different feed concentrations(20mg/L,30mg/L,40mg/L), the results showed that the increase of nitrate load had a certain inhibitory effect on denitrification reaction.In the stage of continuous running, consumption amount of carbon source was 0.047g for decomposing per mg nitrate, the average removal rate of NO3--N was 81.69%. The concentration of NO2--N, NH4+-N did not affect water quality in entire operation phase. (3)The denitrification efficiency of the bed adding the plant carbon source was better than other bed. When the feed water quality kept the same, the average removal rate of nitrogen in three beds were as follows:the first bed (adding reed straw) 89.61%, the second bed 71.78% and the third bed 61.55%. The removal amount of nitrate was 171.78g every day on average, roughly estimate, the total carbon source consumed was 8.074kg, and the amount of reeding straw was 2.02t.To sum up, It is completely feasible to apply reed straw to artificial wetland as slow-release carbon source. The technology not only realize the recycling of urban sewage, alleviating the shortage situation of water, but also achieve the resource utilization of reed straw, and the purpose of waste used for treating waste. Providing a certain technical support for the recycling of urban sewage and wastewater. |
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