Simplified empirical model for phosphorous removal in a facultative wastewater lagoon

Nutrient removal in a facultative lagoon in Manitoba, Canada, was monitored from May 2015 to April 2016. According to the 12-month data, phosphorous concentration in the effluent did not meet the regulatory requirement. Various models have been developed to predict nitrogen removal from lagoon through the years; however, not much effort has been deployed to model phosphorous removal from lagoons. Therefore, this research aims to relate the lagoon phosphate removal to the volatile suspended solids (VSS), metal concentration, and detention time. A simple empirical equation was derived by observing the one-year data, which considers assimilation into biomass as a major mechanism of phosphorous removal. The metals' concentration was found to be very low in the facultative lagoon studied. Hence, phosphorous precipitation by metals was neglected. The model relates assimilation directly to VSS which is simple to evaluate practically unlike other models that require individual algae and bacteria concentration. The correlation coefficient (R²) between the observed and the predicted effluent VSS was 0.92, which indicates excellent fit. The R² between observed and predicted effluent orthophosphate was 0.83, which indicates moderate fit. The trend of modeled effluent phosphate is similar to the observed effluent phosphate concentration, which approves the validity of this model. The model developed in this research can be used to predict the average effluent VSS and phosphorous concentration in similar facultative lagoons.