CONTINUOUS ESTIMATION OF SHORT-TERM OXYGEN-DEMAND FROM RESPIRATION MEASUREMENTS

The Short Term Oxygen Demand /STOD/ is a valuable parameter for monitoring the influent wastewater and is particulary important in control of activated sludge processes. In this paper, a method for the continuous estimation of the STOD is described. The method is based on the measurement of three different oxygen uptake rates of the activated sludge: endogenous respiration rate, momentary respiration rate and actual respiration rate. Measurement of the latter needs special experimental conditions. The respirometer used is a Wazu respiration meter which is capable of continuous and on-line measuring the oxygen uptake rate. The method was applied to a completely mixed continuous-flow pilot plant which was fed with domestic wastewater. The results show a varying STOD with significant peaks at about noon, indicating higher concentrations of readily biodegradable compounds. The STOD of the examined wastewater appears to be mainly caused by ammonia being oxidized by nitrifiers.