Study On Nitrogen Removal In Partial Nitrification Denitrification Biological Filters

Faced with more and more strict water standards of effluent in waste water plants,it is urge to improve the quality of outflows.Other pollutants but total nitrogen could be removed through biochemical or chemical means.Thus,TN(total nitrogen)is the key index which is hard to remove among most pollutants.At present,the low C/N ratio limits the improvement of nitrogen removal,and the conventional treatment(the activated sludge process)used in most waste water plants can not achieve high nitrogen removal efficiency.Thus,it is significant to find a technology which can achieve higher nitrogen removal efficiency with low C/N ratio.Because partial denitrification can reduce 40% carbon consumption less than total denitrification and biological filters have higher removal efficiency,this paper applied partial nitrification and short-cut denitrification in biological filter to enhance nitrogen removal efficiency.At first,The start-up performance of the clay ceramsite filtering material and volcanic filtering material were performed at the same time.Both nitrification characters and denitrification characters of the clay ceramsite were better than the volcanic filtering material.The clay ceramsite nitrification filter had been started successfully at day 16,the removal rate of COD and ammonia nitrogen were about at82% and 80% at the end of start-up.The clay ceramsite denitrification filter had been started successfully at day 10,the removal rate of COD and total nitrogen were about at90% and 82% at the end of start-up.Using the clay ceramsite filtering material,the influence of C/N ratio of the influent,gas water ratio and hydraulic loading to partial nitrification had been studied.When the gas-water ratio is 4,the C/N ratio is set to the highest of 3,the effluent got the highest nitrite nitrogen concentration of 12.34mg/L.At this experiment,the best partial nitrification had achieved under the condition of gas water ratio of 3.The nitrite nitrogen concentration would decreased when the hydraulic loading was too heavy or small.Increasing C/N ratio caused the shift of nitrification to the upper filtration layer,and increasing the hydraulic loading did the same.This paper also did researches on the influences of nitrite nitrogen proportion,C/N ratio and hydraulic loading to the short-cut denitrification efficiency.The total nitrogen removal efficiency had achieved at 98.9% when the nitrite nitrogen proportion was100%,which was higher than the 85.9% of the total denitrification at the same condition.When the nitrite nitrogen proportion was controlled at 50%,HRT was controlled at 1h,the total nitrogen content could reach the first level A standard only if the C/N ratio was higher than 3.The increase of the hydraulic loading made the COD and nitrate nitrogen of effluents increase,but the nitrite nitrogen concentration remained.Partial nitrification-denitrification biological filters performed well.Theconcentration of nitrite nitrogen was 25.02mg/L on average.Under the condition of COD/N at a value of 3,the concentration of TN in the effluent of denitrifying biofilter was 12.73mg/L on average and the removal efficiency achieved 73.3% on average,which achieved the requirement of first A level.The kinetic model of ammonia nitrogen degradation and denitrification had been established.The kinetic parameters of the nitrification revealed the speed of the degradation of ammonia nitrogen by biofilm.Both the process of short-cut denitrification and denitrification were fit to the first-level reaction kinetic equation.