The respirometer utilized for the study was a BM-T, provided with external thermostatic unit (bath)
This “batch system” respirometer consists of: a single reactor vessel, divided into two interconnected compartments with closed recirculation loop between the two. Both compartments are kept completely mixed by means of paddle stirrers and a peristaltic recirculation A constant air flow is supplied via a ceramic diffuser in the conditioning compartment, and a combined oxygen/temperature sensor in the reaction compartment controls the DO and monitors temperature. The temperature is controlled by means an external thermostatic unit (bath) connected to the reactor vessel.
The BM-T is doted by three different operation modes (Static, Cyclic and Dynamic).
In this study we are only making use of the dynamic R mode for toxicity, biomass yield, rbCOD fraction and nitrification rate. The R mode is based on the addition of one or several small sample doses in the activated sludge previously aerated in the reactor vessel. For R mode the measuring system was previously calibrated to get the corresponding offsets and factors with the purpose to determine the corresponding CO and bCOD results in mg/l units.