Studies on the high rate removal of nitrogen in a lagoon with intermittent aeration - V. The shortening of retention time at the intermittently aerated lagoon.

With an intention to shorten the retention time of treatment water in the lagoon with high rate removal of nitrogen, a bench scale experiment of intermittent aeration was done. Using artificial wastewater with approx. 50 mg-N/l as total N and approx. 300 mg/l as COD three 150lvolumetric tanks with 1 day, 1.6 days and 3.3 days retention time were run at around 20°C. After 1 month of acclimation, the effluent NH4+-N, NO2--N, NO3--N, Organic N and Total N, and COD were around 0.4, 0.1, 1.0, 4.0 and 5.5 mg-N/l, and 15 mg/l, respectively. The removal rates of nitrogen in the tanks with 1 day, 1.6 days and 3.3 days were 87, 90 and 87%, respectively, and the removal rates of COD were 94, 95 and 93%, respectively. The degree of DO saturation in the tanks changed from 0 to around 50%. During most of off-aeration time it was kept at zero. By the achievement of the shortening of retention time, the intermittent aeration techniques would find a wide applications to the various fields of wastewater treatment.