Connection between oxygen uptake rate and carbon dioxide evolution rate in aerobic thermophilic sludge digestion

Abstract

The main aim of studying the relation of carbon dioxide evolution rate CER to oxygen uptake rate (OUR) is the possible application of CER in mathematical modelling of aerobic biodegradation processes instead of OUR. Biodegradation tests using glucose and sewage sludge as feed were performed to compare the OUR and CER. The respiratory quotient (RQ) was 0.9 mol CO₂ × mol O₂^-1 in endogenous stage while its value was increased to 1.2 mol CO₂ × mol O₂^-1 during glucose degradation. At higher F/M ratios and high respiration rates RQ values up to 2.95 were observed which may indicate the appearance of anaerobic degradation pathways. These results prove that there is no direct, simple relation between OUR and CER in case of sewage sludge degradation so direct substitution of OUR with CER in modelling studies is not feasible.