An innovative approach to the control of sequencing batch reactors used for nitrification and denitrification

Abstract

This study investigated the potential of pH, redox and DO to act as monitoring tools for the nitrification and/or denitrification processes, in a sequencing batch reactor (SBR) type process. In addition, the SBR activated sludge protozoan and metazoan communities were observed as nitrification and/or denitrification progress, to determine their use in plant control. The laboratory set-up consisted of two equal and independent SBR configurations coupled together to a data aquisition and control (DA & C) system. Each reactor was provided with lateral electrode ports such that pH, redox and DO probes could be placed directly into the reactor environment. A personal microcomputer was used to command the DA & C system. After a long period of time designing, assembling, correcting electric influences and performing initial tests, four separate experiments were carried out, including nitrification only, nitrification/denitrification and nitrification/enhanced biological phosphorus (EBP) removal. The SBR system achieved organic carbon removal, nitrification and denitrification on a regular basis. Removals of 84% COD, 91.5% SS and 99.9% ammonia-nitrogen, were observed. SVIs averaging 110 mL/g were achieved, confirming the inherent good settling ability of sludges from SBRs. Nitrite was routinely found as the predominant oxidized nitrogen specie, an observation connected to the presence of free-ammonia at inhibitory levels in the mixed liquor. Only sporadic EBP removal occurred. All three measurements (pH, redox and DO), in particular pH and redox, showed great promise as control parameters for the nitrification and/or denitrification processes. Nitrification and denitrification end point features were identified, among others. The application of such a system can improve general efficiency and provide for large cost savings. The study on the reactor microfauna corroborated some of the results showed in the literature with, for example, ciliated protozoa increasing as the effluent improved. An inverse correlation was found for flagellates.