Effects of organic matter on the conversion rates of nitrogenous compounds in a channel reactor under various flow conditions

Abstract

This study investigated the effects of organic matter on the conservation rates of nitrogenous compounds in a deep mixed films channel reactor under high dissolved organic (DO) and various flow conditions. A series of batch tests was performed to examine the effects of organic matter, with and without the addition of glucose, on variations of the nitrogenous compounds. Experimental results indicated that increasing the organic matter concentration under all flow conditions decreased the concentrations of nitrate and total nitrogens; however, an enormous build-up of nitrite occurred in the water column. Also, the conversion pathways of nitrogenous compounds changed from ammonification and nitrification to assimilation, ammonium oxidation and denitrification. Moreover, changing the flow velocity significantly influenced the conversion rates of nitrification and denitrification. When adding organic matter, the rate of nitrite to gaseous products became greatly enhanced if the flow velocity increased within the turbulent regime; increasing velocity seemed only to inhibit the rate of conversion from nitrate to nitrite. In contrast, when organic matter was not added, the rates of ammonium oxidation exceeded those of nitrite oxidation within all flow regimes. Experimental results further demonstrated that nitrite oxidation was the rate-limiting process of nitrification under the low organic matter conditions. On the other hand, when sufficient amounts of organic matter were present, the processes of nitrite to gaseous products and nitrate to nitrite dominated the rate of denitrification under the laminar and turbulent regimes, respectively.