Modeling effect of remaining nitrate on phosphorus removal in SBR

Nitrate shock loading experiments were conducted in a bench scale SBR to in vestigate the effect of nitrate on phosphorus removal. After achieving sati sfactory phosphorus removal under steady state operation, initial NO3-N con centration amounting to 10 and 20 mg /L was fed at the beginning of the cyc le. It was observed that, 10 mg/L of NO3-N suppressed phosphorus release du ring the feed and mix phases. Organic consumption for denitrification lead to limited PHA storage by phosphorus removing bacteria, resulting in less P O4-P removal. For 20 mg/L, influent organic substrate was not sufficient ev en for complete denitrification, thus leading to the presence of higher NO3 -N and PO4-P in effluent. To explain the dynamics of the nutrient removal s ystem under the transient loading, a SBR model based on IAWQ ASM2 was imple mented. After adjusting PHA contents, model simulations well predicted dyna mic changes of nitrate and phosphate concentrations during a cycle. Based o n the model simulations, competition of COD substrate among denitrification , fermentation and oxygen respiration were investigated by calculating thei r consumption rates during mixing phase. In addition, a nitrate disappearan ce model was proposed and implemented in conjunction with a settling model to predict remaining and effluent nitrate in a cycle of SBR. Furthermore, i ntegrated model simulations highlighted the effect of remaining nitrate on phosphorus release considering different options of reactions in settling p hase.