Partial nitrification-reactor configurations, and operational conditions: Performance analysis

Abstract

• Essential parameters influencing partial nitrification were evaluated. • Bioreactors configurations and control strategies for nitritation were summarized. • Up-to date full-scale application of partial nitrification was demonstrated. • Research gaps for partial nitrification was presented and discussed. This comprehensive literature analysis evaluated essential partial nitrification (PN) parameters including various reactor configurations, control strategies on dissolved oxygen (DO) and aeration, pH, inhibition via free ammonia (FA) and free-nitrous acid (FNA), and oxidation reduction potential (ORP) in both pilot and full-scale systems. The median growth rates for ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) at 20 °C are 0.74 and 0.65 d −1 , respectively. The median first-order decay coefficient for both AOB and NOB was 0.14 d −1 while the average biomass yields were 0.17 and 0.08 mg chemical oxygen demand (COD) mg N −1 . The COD/N ratio is one of the critical factors for partial nitrification, particularly for attached growth systems. The optimum COD/N ratio for partial nitrification appears to be system-specific, as it is impacted both by system design parameters and operational conditions. The most widely used PN technology is the sequencing batch reactor (SBR) despite significantly lower volumetric nitrogen loading rates due to the ease of NOB suppression by the relatively high FA and FNA concentrations during the early stage of aeration. This review identified several knowledge gaps including better understanding of PN mechanisms in attached growth systems, combination of PN and enhanced biological phosphorous removal (EBPR), and development of process control strategies for technologies other than SBRs. Mainstream low-temperature application and combination with EBPR, particularly in light of the inhibitory impact of nitrites on phosphorus accumulating bacteria, are two major challenges hindering the widespread application of partial nitrification.