Monitoring denitrification by pH-Stat titration

An improved pH-stat titrimetric procedure was developed, validated, and extensively applied to monitor biological heterotrophic denitrification in a lab-scale sequencing batch reactor (SBR). So far, titrimetric procedures were not successful in monitoring denitrification processes in full-scale wastewater (WW) treatment plants, mainly because the stoichiometric ratio between proton production and nitrate reduction is highly variable due to variability of both biomass and influent WW characteristics. In this article, a new titration procedure is proposed where a simple calibration step is performed before each experimental test. This procedure allows for the assessment of (i) nitrate content in a sample of mixed liquor; (ii) the maximum denitrification rate of sludge when fed on acetate; and (iii) the denitrification potential (DNP) of different substrates. As for (i), validation by comparison with spectrophotometric measures indicated an average discrepancy of less than 3% on more than 40 samples; as for (ii) and (iii) collected values compared well with literature data. The titrimetric method proposed here is also capable of assessing the biomass anoxic yield in a very simple way, since it does not require any analytical nitrate determination. According to the results of this experimentation, titrimetry appeared to be a simple, inexpensive, and powerful tool for monitoring and operating denitrification processes in WW treatment plants.