Biological treatment by activated sludge of petroleum refinery wastewaters

Abstract

This paper reports on biological treatment by activated sludge of petroleum refinery wastewaters, in a lab-scale reactor constituted by an aeration tank and clarifier provided with sludge recycle system. The main objective of the work includes the optimization of the process efficiency in terms of chemical oxygen demand (COD), total organic carbon (TOC), and total suspended solids (TSS), and modeling of the biological treatment by activated sludge and determination of the main stoichiometry and kinetic parameters for the process, such as, synthesis and decay of biomass, oxygen consumption related to organics oxidation, and endogenous respiration with and without sludge recycle. Laboratory-scale experiments successfully showed high removal efficiencies for COD (94–95%), TOC (85–87%), and TSS (98–99%). The removal of organic matter was well described by a pseudo-first-order kinetic model, with rate constant (k) values of 0.055 and 0.059 L mg−1 VSS day−1, with and without biomass recirculation, respectively. The consumption of oxygen in the biological reactor was calculated according to parameters a′ (0.071/0.069 mg O2 mg−1 COD) and b′ (0.012/0.024 mg O2 mg−1 VSS day−1), experimentally obtained by operating the reactor with and without sludge recycle. The parameters related to the production and destruction of biomass were also determined: a = 0.33/0.32 mg VSS mg−1 COD; b = 0.07/0.03 mg VSS mg−1 VSS day−1, respectively, for the systems with and without sludge recycle.