Control of nitrate recirculation flow in predenitrification systems

Abstract

The control of the nitrate recirculation flow in a predenitrification system is addressed. An elementary mass balance analysis on the utilisation efficiency of the influent biodegradable COD (bCOD) for nitrate removal indicates that the control problem can be broken down into two parts: maintaining the "anoxic" zone anoxic (i.e. nitrate is present throughout the anoxic zone) and maximising the usage of influent soluble bCOD for denitrification. Simulation studies using the Simulation Benchmark developed in the European COST program show that both objectives can be achieved by maintaining the nitrate concentration at the outlet of the anoxic zone at around 2 mgN/L. This setpoint appears to be robust towards variations in the influent characteristics and sludge kinetics.

Nutrient removal performance of an anaerobic–anoxic–aerobic process as a function of influent C/P ratio

“…It is well known that the anoxic environments would become anaerobic environments if nitrate was consumed completely in the anoxic zone, it was unavoidable for phosphorus release to occur and take up organic substrate at a slow rate, either due to a conversion reaction (hydrolysis, fermentation) or due to incoming readily degradable substrates not being taken up in the anaerobic zone. To improve the nitrogen removal efficiency, meanwhile, to enhance the function of anoxic P uptake in the anoxic zone so as to reduce the operation cost, the experiments maintained the nitrate concentration at the end of the anoxic zone at 1-3mg L −1 by adjusting the internal recirculation flow rate according to the nitrate recirculation control strategies reported by Yuan et al 16 Figures 7 and 8 show the variations of PO 4 3− -P and NO 3 − -N concentration in the anoxic zone versus C/P ratio as well as the variations of NO 3 − -N concentration at each compartment with C/P ratio, respectively. It can be observed that nitrate was available as an electron acceptor in the second anoxic reactor by PAOs for the oxidation of stored PHB to realize P uptake simultaneously.…”

Control en Estaciones Depuradoras de Aguas Residuales: Estado actual y perspectivas

“…Idealmente, la concentración a la salida del reactor anóxico debe ser baja pero no zero. En Yuan et al (2002b), por ejemplo, se derivan las condiciones para un controlador simple pero que asegure una determinada robustez, mientras que en Peng et al (2005) se presenta un controlador fuzzy para esta misma tarea. En Baeza et al (2004) se analizan los efectos de la recirculación interna en el grado de eficiencia para una planta con una configuración A 2 /O.…”

Feedforward control for nitrogen removal in a pilot-scale anaerobic-anoxic-oxic plant for municipal wastewater treatment

“…When used in process control, the COD entering anoxic section and the nitrate in internal recycle gave more direct information about denitrification [18]. However, installing extra nitrate and COD probes in the anoxic reactor was probably difficult to afford for many WWTPs.…”