Modelling of an oil refinery wastewater treatment plant by application of activated sludge model No 3

Activated Sludge Model No 3 (ASM3) was chosen to model an activatedsludge system treating effluents from a full scale refinery industry. The plantconsists of a conventional anoxic/aerobic activated sludge line operating inintermittent mode. During cycles of one hour, the plant operates two phases:40 minutes are devoted to COD and ammonia removal under oxic conditions.The remaining 20 min are used to enhance denitrification by changing the setupto anoxic conditions. Due to the existing plant configuration and the lowCOD/N ratio, denitrification is supported by an external carbon source(methanol in this case). With the adjustment of only three parameters (anoxicyield for heterotrophic biomass, maximum autotrophic growth rate and nitrogencontent of inert biomass) the model proved capable of describing theperformance of the treatment system (for both liquid phase and biomass). Ameasuring campaign and some specific batch tests provided the necessaryinformation for calibration and verification of the biological model. Batch testsyielded crucial information regarding denitrification kinetics based onmethanol. The validated model was used as a simulation supported scenariotool to analyse changes and further upgrading of the plant. Model simulationsshowed gains at methanol level by implementing a lag zone between oxic andanoxic phase. In this way, methanol was prevented to be lost and furtherdegraded to the aerobic zone. Moreover, simulations showed that the most costeffectivesolution for denitrification performance was a combined pre and postdenitrification scheme, which showed optimal aerobic and anoxic conditionswithin the existing rector volumes