Evaluation of nutrients in effluent from wastewater treatment lagoons discharging to surface water in the United States.

Wastewater treatment lagoons (WTLs) are one of the most widely used wastewater treatment technologies in the world; yet, questions remain about the best strategies to improve WTL performance, particularly for nutrient removal. In this study, 1,412 facultative and upgraded WTLs were analyzed for their average effluent quality for biochemical oxygen demand (BOD), total suspended solids (TSS), ammonia (NH3), total nitrogen (TN), nitrate (NO3), and total phosphorus (TP). The geometric means of BOD, TSS, NH3, TN, NO3, and TP facility average effluent concentrations for facultative WTLs were 11.2, 19.3, 2.5, 8.8, 0.95, and 1.9 mg/L, respectively. WTLs upgraded with sand or rock filters had a lower geometric mean of average effluent BOD and TSS compared with facultative systems (Tukey-Kramer test). WTLs upgraded with moving bed-biofilm reactors, aerated gravel filters, and complete mix converted ponds showed a significant reduction in NH3 concentrations comparable to similar-sized activated sludge systems. A multi-variable regression analysis (n = 764, R2 = 0.35) found that temperature had a nonlinear effect on the average NH3 concentration. The nitrogen surface loading rate also had a significant, but smaller, effect. Finally, the seasonal NH3 variation observed in WTLs was reduced with the addition of nutrient upgrades.