Performance Evaluation of Aerated Lagoon in Summer and Winter Conditions

A 1-year study evaluated the performance of a full-scale aerated lagoon, located in a midwest community in the United States. The objective of this study was to evaluate the performance of the lagoon under varied temperature conditions. The main parameters for evaluation were 5-day biochemical oxygen demand, total suspended solids, and ammonia-N. In addition, phosphorus and bacteriological qualities of the effluent were investigated. In general, the facility met 5-day biochemical oxygen demand and suspended solids limits required by the National Pollutant Discharge Elimination System. The lagoon reduced the ammonia-N concentration efficiently during late spring, summer, and fall, with values ranging from 0.3 to 4.2 mg/L. In the winter period the activities of the nitrifying bacteria diminished, resulting in a reduced nitrification rate. The ammonia-N during winter ranged from 8.8 to 23 mg/L. During the spring months (March to May) the nitrification rate slowly increased with the rise in temperature. This reflects the time period and environment necessary to reach an effective nitrification population in the system. The adjustment period was reversed in the fall months with a declining population of nitrifiers and decreased nitrification rates. The effluent total phosphate levels ranged from 0.6 to 4.9 mg/L. Effluent fecal coliform values ranged from 10 to 1,110/100 mL.