The Shortening of Retention Time at the Intermittently Aerated Lagoon

Abstract

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.