| Bioretention is one of the most widely used Low-Impact-Development(LID)technology.To improve the quality of surface water,the experiment tried to apply bioretention to the treatment of tail water from wastewater treatment plant.The first experiment was to figure out impacts of different structure and hydraulic load on the processing efficiency.The second experiment was building MFC system by adding wires and electrodes to inhance pollutants removal efficiency.Lastly,a specific plan project estimate was raised.Main work and results are as follows:Saturated zone in bioretention can obviously increase the removal rate of total phosphorous,total nitrogen and nitrate-nitrogen by 29.46%?46.95%and 12.78%respectively.However,removal rate of COD and ammonia-nitrogen was decreased by 9.54%and 21.09%respectively because of the existence of saturated zone.Take removal rate and removal load together into consideration,removal efficiency of each pollutant was high when hydraulic load was 0.5m3/m d.Removal rate of COD,ammonia-nitrogen,total nitrogen,nitrate-nitrogen and total phosphorous were 2.02%?12.95%?67.80%?79.14%?60.00%respectively in devices with saturated zone.Removal rate of COD,ammonia-nitrogen,total nitrogen,nitrate-nitrogen and total phosphorous were 30.33%?32.36%?44.07%?57.36%?52.00%respectively in devices without saturated zone.Bioavailability of MFC could enhance the treatment efficiency of nitrogen,and the average removal rate of ammonia nitrogen was increased by 15.00%,the average removal rate of NO3--N was increased in the experiment of 8.00%,and the average removal rate of total nitrogen increased by 15.00%.The effect of MFC enhanced bioretention pool on the removal of total phosphorus and COD was not improved obviously.The effect of external resistance on MFC is not obvious because experiment time was short and devices were not ideal.Designing the area for bioretention tanks for wastewater treatment plants using total nitrogen and nitrate as target pollutants requires 99 acres of land.In practical application,52.5 acres of green space in the plant area can be fully utilized to construct double-layer bioretention tanks.With reference to the engineering example of the Sponge City Research Center in Kunshan,an investment of 26.6 million yuan will be required for building a 99-acre bioretention pool.Study on treatment of tail water is essential to remitting the pressure of treating wastewater and eutrophication.It also provides a reference value for the natural purification of sewage tailrace. |
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