Monitoring denitrification by means of pH and ORP in continuous-flow conventional activated sludge processes

Luca Luccarini, Dalila Pulcini, Davide Sottara, Roberto Di Cosmo, Roberto Canziani

    Research output: Contribution to journalArticlepeer-review

    11 Scopus citations


    Indirect signal analysis (pH, ORP and DO) are often used in monitoring and control of SBRs (Sequencing Batch Reactors), where operating conditions can be clearly identified during the various cyclic phases. Only few studies applied this methodology to control continuous flow plants, as it is much more difficult to identify operating conditions because of continually variable inflow characteristics. This work applied indirect signal analysis to control pre-denitrification in continuous-flow activated sludge processes: (i) a laboratory-scale plant, fed with synthetic wastewater, simulating real municipal wastewater and (ii) a pilot-scale plant, fed with real sewage. Three different ranges of ORP values identify three operational conditions of the denitrification process. (1) ORP > 0 mV means that nitrates and/or nitrites are present, possibly due to a low C/N ratio. (2) –50 < ORP < –200 mV is typical of normal operating conditions, that is with a balanced C/N ratio. (3) ORP < –350 mV means that oxidized nitrogen load is too low or that C/N exceeds the stoichiometric ratio. The trend of pH, instead, points out if and how the process is evolving from one to another operating condition. The correlation between pH and ORP signals (as well as their derivatives) allows to restore normal operating conditions by acting on the internal recycle flow-rate. Improved denitrification process ensures lower effluent nitrate concentration, and reduce external carbon dosage to achieve stricter nitrogen limits.

    Original languageEnglish (US)
    Pages (from-to)319-325
    Number of pages7
    JournalDesalination and Water Treatment
    StatePublished - Jan 2017


    • Denitrification monitoring
    • ORP signal
    • PH signal
    • Pre-denitrification systems

    ASJC Scopus subject areas

    • Water Science and Technology
    • Ocean Engineering
    • Pollution


    Dive into the research topics of 'Monitoring denitrification by means of pH and ORP in continuous-flow conventional activated sludge processes'. Together they form a unique fingerprint.

    Cite this