Evaluation of the ‘Michigan’ type pure oxygen columns for oxygen addition and nitrogen removal

The gas transfer characteristics of the 61-cm diameter and 76-cm diameter pure oxygen columns used at the Willamette Hatchery were evaluated and compared with similar columns used in Michigan. The change in dissolved oxygen through the columns was directly proportional to the oxygen flowrate. Oxygen transfer efficiencies typically ranged from 30 to 60%. The oxygen transfer performance of the 61-cm column was superior to that of the 76-cm column and of the columns used in Michigan. The effluent nitrogen concentrations were typically less than 100%. The 76-cm column was better at nitrogen removal than the 61-cm column. The 61-cm column increased the ΔP, while the 76-cm column decreased the ΔP. The differences in performance were related to differences in hydraulic loading rate and operating pressure inside the columns.