Effect of aeration on residence time in biological wastewater treatment

Aerobic wastewater treatment requires extensive aeration, which primary function is to provide oxygen to the biomass responsible for degradation of wastewater constituents. Besides the effective oxygen transfer efficiency aeration is responsible for fluid flow created by bubbles. In this research bubbles were released from plate diffusers and the impact on mixing were analyzed. Various aeration flow rates and initial bubble sizes were calculated. Residence time distributions in each scenario were compared applying numerical tracer study. Outcome of the calculations is that the aeration reduces the theoretical residence time significantly and therefore the traditional sizing methods needs to be revisit in wastewater treatment

Analysis of a mechanical mixer performance in anoxic reactor

Denitrification is a key process in wastewater treatment since it is responsible for the effective nutrient removal. It requires anoxic conditions, where only chemically bound nitrogen is used as an oxygen source, and no aeration is applied. In suspended biomass systems the growth and homogenization of biomass is essential, high degree of mixing is required, which is achieved only by using mechanical mixers. Mechanical mixing performance relies on the mixing power determined by the equipment dimensions and rotational speed. In this paper the effect of three different rotational speed (rpm: 100, 400, 900 min-1) on flow field and mixing conditions are evaluated. As a result of the simulations, the acceptable flow field was achieved at 400 rpm. The outcome of this research is that the high degree of energy transfer from mixers to fluid flow deteriorated mixing efficiency

Infrared and microwaves at 5.8 GHz in a catalytic reactor

An improved micro-reactor cell for IR spectroscopic studies of heterogeneous catalysis was built around a 5.8 GHz microwave cavity. The reactor can operate at 20 bars and with conventional heating up to 720 K, with reactant gas flows velocities (GHSV) from 25 000 to 50 000 h−1. The temperature of the sample under microwave irradiation was measured by time resolved IR emission spectroscopy. The first experiment performed was the IR monitoring of the desorption of carbonates induced by irradiating an alumina sample by microwaves at 5.8 GHz