Effect of recycle on treatment of aircraft de-icing fluid in an anaerobic baffled reactor

Aircraft de-icing fluid at 7 000 mg COD/ l was successfully treated in an anaerobic baffled reactor operated with and without recycle at volumetric organic loading rate of between 4 and 11 g COD/l(reactor)(.)d. Reactor recycle was found to improve reactor performance. The anaerobic baffled reactor operated with a 6: 1 recycle ratio achieved a minimum hydraulic retention time of 17 h with an acceptable COD removal efficiency of 93 % at a volumetric organic loading rate of 9.9 g COD/l(reactor)(.)d. This corresponded to a specific organic loading rate of 0.35 g COD/g VSS(.)d and specific organic removal rate of 0.32 g CODrem/g VSS(.)d. Without recycle similar removal efficiency was achieved; however, the loading rates were about 40 % less. Due to biomass growth specific organic loading rate was not found to vary signicantly through most of the experimental period despite loading rate increases. Hydrodynamically, an anaerobic baffled reactor may be characterised as an in-series continuously stirred tank reactor where the number of continuously stirred tank reactors corresponded to the number of actual compartments. Volatile fatty acid profiles tend to indicate that anaerobic baffled reactor compartmentalisation served to separate acidogenic and methanogenic activities longitudinally through the reactor, with the highest proportion of acidogenic activity in the first compartments. The net accumulated yield within the anaerobic baffled reactor was found to be of 0.007 g VSS/g CODrem when the ABR was operated without recycle and of 0.016 g VSS/g CODrem for the ABR operated with recycle.