The influence of a particulate substrate on filamentous bulking and phosphorus removal in activated sludge systems

Abstract

Particulate substrates comprise all forms of solid and colloidal particles and soluble organic molecules with complex structure and high molecular weight. According to the IAWPRC Hydrolysis Hypothesis, the particulate substrate cannot be utilized in anaerobic zones of nutrient removal activated sludge systems because the rate of its hydrolysis (i.e. solubilization) is zero under anaerobic conditions. The particulate substrate is enmeshed in the flocs of activated sludge and transferred from an anaerobic zone to an oxic zone where hydrolysis occurs and hydrolysis products become available for filamentous microorganisms. The influence of a particulate substrate on the activated sludge system with an anaerobic zone has been studied in two laboratory systems. The systems consisted of a three-compartment anaerobic zone followed by an oxic completely-mixed tank or by a three-compartment oxic cascade. The systems were fed by artificial wastewater. The soluble fraction of substrate was simulated by glucose, ethanol and acetic acid, the particulate fraction with peptone and the suspension prepared from hard-boiled eggs. It has been demonstrated that filamentous bulking caused by oxic zone growers (e.g. Types Sphaerotilus and 021N) occurred when the oxic zone was supplied either with the soluble substrate generated by fermentation in the preceding anaerobic zone; or with the products of the hydrolysis of the enmeshed particulate substrate. The compartmentalization of the oxic zone significantly reduced the bulking problems and improved the phosphorus removal with all substrates used in this study.