Effect of seawater intrusion using real wastewater on an attached biomass system operating a nitrogen and phosphorus removal process

Abstract

Wastewater treatment plants that are close to the coast and sea level often have problems with seawater intrusion. Because of this, three saline intrusions of 2%, 5% and 10% in volume (socks 1, 2 and 3 respectively) were carried out using actual wastewater. As a technology, a sequential biofilm batch reactor operating an enhanced biological phosphorus removal process was studied. The main focus of the study lies in the impact on the plant's nutrient removal performance during these seawater intrusion events until achieving system recovery. During the study a constant salinity profile was observed without large variations in the reactor after reproducing the seawater intrusions. The COD removal rate decreased below 80% and 65.4% for shock 2 and 3 respectively. In a seawater intrusion of 2% and 5% in volume, corresponding to shocks 1 and 2, TN removal decreased to 66.4% and 71.5%, respectively, and was subsequently restored to previous removal rate values (> 80%) 4 days after the shocks, in both cases. TP removal was negative after every shock due to increased concentrations in the effluent resulting from deficient PAO activity. This situation lasted for 9, 10 and 14 days for shocks 1, 2 and 3, respectively, until recovery of performance to the same levels as prior to the shocks.