A kinetic study of a combined anaerobic–aerobic system for treatment of domestic sewage

Monod, zero and first order kinetic models have been used to represent the biodegradation of domestic sewage in a combined treatment system. This consisted of one UASB reactor, 750 l working volume, followed by two serial RBC reactors, each having a working volume of 55 l. First order model is the only one that adequately represents biodegradation in both aerobic and anaerobic parts of the system. In anaerobic unit the first order kinetic constant is 0.31 h−1 in summer temperatures (around 19°C) and 0.20 h−1 in winter temperatures (around 12.5°C). In aerobic units the values are higher (around 2.0 h−1), using, in all these cases, BOD units for substrate concentration