The effect of recycle ratio on nitrogen removal in the combined pre-denitrification/nitrification biofilter system

Previous research has shown that nitrogen in municipal wastewater could be eliminated by a biofilter system. This study investigates the effect of the recycle ratio on total nitrogen removal and the nitrogen component in the effluent. In this study, a system combining pre - denitrification/nitrifica tion biofilters was set up. The experiments which varied the recycle ratio of the nitrifying solution to the influent were carried out in order to det ermine the amount of the total nitrogen removal and the form of nitrogen in the effluent. These experimental results show that total nitrogen removal might be dependent on nitrification but not on denitrification. Although th e operation at a low recycle ratio would result in a lower value of total n itrogen removal, the NH3-N content of the effluent would be lower and the f low condition would be more stable. In comparison, operation at a higher re cycle ratio would result in a lower NO3-N content in the effluent, while th e NH,-N content in the effluent would be higher. At a recycle ratio of 2.5, the total nitrogen removal is at its maximum. The relationship between spe cific nitrification rate and recycle ratio is also discussed. (C) 2001 Soci ety of Chemical Industry.