EFFECTS OF FLOW VELOCITY CHANGES ON NITROGEN TRANSPORT AND CONVERSIONIN AN OPEN-CHANNEL FLOW

This study demonstrates that short-term changes in flow velocity affec t nitrogenous compounds' transport and conversion in a shallow, slow-f lowing channel. Two different flow conditions controlled by varied how velocities, including laminar and turbulent flow, are proposed to des cribe soluble and particulate nitrogenous compounds transported betwee n the water column and biofilms. The incipient turbulent flow was sugg ested to design a flowing channel which will induce a high rate of nit rification and a low rate of resuspension. A series of well-controlled batch tests were carried out to investigate nitrogenous compound tran sformations in an artificial channel at varied flow velocities. The re sults of the batch tests show that a particular type of water motion w ill control the fate of nitrogen, while organic matter concentration i s low in the water column. When laminar flow occurs in the flowing cha nnel, total kjeldahl nitrogen (TKN) removal rate is held approximately constant; oxidized nitrogen generation rate increased when how veloci ty increased; nitrate and ammonium nitrogen converted slowly; organic nitrogen and total nitrogen concentration gradually decreased with the test time. In contrast, when the flow condition transferred from lami nar dow to turbulent flow, the TKN removal rate decreased when flow ve locity increased; the oxidized nitrogen generation rate increased more than it did during the laminar flow, and it maintained a constant rat e when flow velocity became higher; nitrate concentration increased an d ammonium nitrogen concentration decreased quickly; total nitrogen an d organic nitrogen concentration gradually decreased and later increas ed. The primary pathways of nitrogenous compounds' conversion and tran sport can be recognized when organic substance concentrations and flow conditions are known. Copyright (C) 1996 Elsevier Science Ltd