Degassing Column

A degassing column is a packed-bed stripper that removes excess dissolved carbon dioxide and nitrogen gas from RAS water by cascading it over high-surface-area media while forcing large volumes of low-CO2 air through the column in counter-current. Fish respiration produces about 1 kg of CO2 per kg of oxygen consumed, and in closed systems CO2 can climb past the 15–25 mg/L comfort threshold for salmonids, causing acidification of the blood (reduced blood oxygen affinity) and reduced growth even when dissolved oxygen looks adequate. Typical design air-to-water ratios are 10:1 to 30:1, with target effluent CO2 below 10–12 mg/L for sensitive species; warm-water species tolerate 20–30 mg/L. Degassers also strip excess dissolved nitrogen supersaturation that causes gas bubble disease. They are sized from the system's total CO2 production rate, which scales with feed intake and fish biomass, and often integrate into the trickling filter or a dedicated tower. Neglecting degassing is one of the most common design errors in new RAS, since standard oxygen probes give no warning of elevated CO2.