Influence of liquid-phase mass transfer on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass

Abstract

This paper reports on the influence of the liquid-phase mass transfer on the performance of a stirred anaerobic sequencing batch reactor treating low-strength wastewater. The biomass was immobilized in cubical polyurethane foam particles (5 mm per side). The 4.2 l volume reactor was operated at a temperature of 30 °C. A synthetic substrate with a mean chemical oxygen demand (COD) of 560±53 mg/l was treated in 8 h cycles. A mean COD removal efficiency of 78±3% was achieved. Three propeller impellers were used to vary the agitation rate from 300 to 1100 rpm in order to evaluate the influence of the liquid-phase mass transfer on the reactor’s overall performance. The first-order kinetic model was found to represent the degradation of organic matter well, with an apparent constant of 0.54–1.5 h −1 and an agitation rate of 300–900 rpm. The concentration of residual substrate decreased significantly at agitation rates above 800 rpm. Thus, the liquid-phase mass transfer substantially affected both the reactor’s overall performance and the cycle time required for maximum efficiency.