Cold weather nitrogen removal deficiencies of aerated lagoons

Aerated lagoons are widely used throughout the state of Iowa, USA by small communities, due to their relatively low costs and maintenance requirements. Although aerated lagoons were not initially designed for ammonia removal many of these facilities have been assigned effluent ammonia limits in recent years Since widespread monitoring began, it has been found that aerated lagoons tend to have problems with high effluent ammonia concentrations during the winter and early spring. This study collected and analyzed data from 10 aerated lagoon facilities in central Iowa to determine the factors governing cold weather nitrogen removal in aerated lagoons. The factors found to affect performance were temperature and detention time. None of the following factors were found to significantly affect performance: dissolved oxygen (DO), pH, CBOD5 loading, total nitrogen loading, aerated cell depth and design standards governing the design. It should be noted that DO and pH were relatively constant and generally favorable for nitrification. Increased mixing energy was correlated with poorer performance, but this correlation may not be correct as the expected benefit of more intense mixing conditions may masked by the overwhelming benefit of long detention times.