Removing Nitrogen and Phosphorus from Slow Moving Surface Water by Layered Multi-media Constructed Floating Islands

In order to increase removal efficiencies of nitrogen and phosphorus from contaminated slow moving surface water,a new type of constructed floating islands with layered multi-media of substrates called the layered multi-media constructed floating island(LMCFI)was proposed.Pilot-scale LMCFI experiment settings were constructed and operated with different conditions,including various hydraulic residence times(HRT),gas water ratios and temperatures.It was observed that the factors such as HRTs,gas water ratios and temperatures had considerable control on removal efficiencies of nitrogen and phosphorus,and removal efficiency of LMCFI was better than those of the other traditional constructed floating islands examined.Gas water ratio around 10:1 offered the highest removal efficiency which was about 2 times as that without aeration.When water temperature was above 13℃,mean removal rates of ammonia nitrogen,nitrate nitrogen,total nitrogen and total phosphorus were 87.6%,63.8%,82% and 83.5% respectively,with HRT equal to 2.5d while mean removal rates of nitrogen and phosphorus were only 70.1% and 69.2% respectively,with HRT equal to 7d when temperature was below 13℃.