The bottle was closed air-tight, placedback into the water bath, stirred and the O2 concentration was then measured/recorded. O2concentrations in the measurement bottleswere always kept above 1 mg/L. When O2 concentrations droppedbelow 3 mg/L, a second bottle was filled with sludge from the mainincubation and the measurement was continued in the second bot-tle after equilibration of the oxygen probe. This procedure allowedfor an almost continuous measurement of oxygen consumptionrepresentative for the main incubation. After the switch, the sludgefrom the first bottle was poured back into the main incubation.The measurement bottles were kept stirred at 250 rpm in the samewater bath as the main incubation.