In order to improve nitrogen and phosphorus removal efficiencies at low water temperature, intermittent aeration batch activated sludge process combined with biofilm process (media-added batch activated sludge process) was applied and its treatment performance was investigated for a different packing rate of string contact media with range of 0-21%. With the increase of packing rate of contact media, successful nitrification occurred. However, the dentrification efficiency decreased at the packing rate of 21%. This is because the relatively high DO concentration at the packing rate of 21% was not suitable for the denitrification condition. The optimal packing rate of media was 13% for simultaneous removal of BOD and nitrogen at 10°C.
Removal efficiencies of BOD, DTN (disoluble total nitrogen) and DTP (disoluble total phosphorus) were 90%, 31% and 20%, respectively under operating condition of 3cycle a day at 10°C. Moreover, removal efficiencies of BOD, DTN and DTP increased to 94%, 64% and 22%, respectively by combining with biofilm process. Nitrogen removal efficiency was significantly enhanced.
In spite of introduction of biofilter process, removal efficiency of phosphorus was not improved. It was observed that anaerobic phosphorous release and aerobic phosphorous uptake was significantly affected by low water temperature.
As a biological removal of phosphorus cannot be expected at low water temperature, it is necessary to consider the combination with a physical treatment method.
