Glycerol-Driven Denitrification: Evaluating the Specialist-Generalist Theory and Partial Denitrification to Nitrite

In order to comply with stringent total nitrogen (TN) limits, supplemental carbon must be added to improve biological nutrient removal (BNR) processes. This research investigated alternatives to methanol that can be used in full-scale applications, such as glycerol (also known as glycerin). The objective was to verify two unusual observations reported for glycerol supplementation for denitrification: increasing COD demand over time (yield) and partial denitrification resulting in nitrite buildup. Three sequencing batch reactors (SBRs) were operated to assess reagent grade methanol, reagent grade glycerol, and a biodiesel glycerol waste. The methanol reactor performed as expected. Over-dosing carbon led to very low levels of residual nitrogen in all the reactors, while under-dosing resulted in incomplete removal of TN. Nitrite accumulation in the glycerol reactors was consistent and significant, whereas the methanol reactor did not exhibit this phenomenon. Increased yield for glycerol over time after startup and anoxic storage of COD were apparent.