Simple methods for the determination of the denitrifying activity of sludges

In this work, the conditions for measuring the specific denitrifying activity (SDA) of sludges were established as simple batch tests based on the measurement of N2 production. The effects of carbon to nitrogen ratios (C/N=1.3 and 2.0), sludge concentrations (0.35, 0.73, 1.5 and 3.0 g volatile suspended solids (VSS) l−1) and shaking (0–180 rpm) on SDA were studied by means of the application of two factorial designs. A very simple method (Method A), based on the displacement of an alkaline solution by the N2 generated, was used. In the 0.35–0.73 g VSS l−1 range, the SDA was strongly affected by variable VSS, but not in the range 1.5–3.0 g VSS l−1. The optimum conditions to obtain the SDAs, evaluated by means of a statistical tool, were a C/N=1.3, 1.5 g VSS l−1 and shaking at 180 rpm. Method A was statistically compared to a second method (Method B), based on the measurement of partial pressure and composition of the gas produced in the same conditions.