Ozone decolorization and mineralization of azo dye Orange II were examined. In order to elucidate the dynamics of the oxidation process by ozone, the rate-based model consisting of the rates of chemical reaction and gas−liquid mass transfer was developed. The overall enhancement factor was introduced to correct the underestimation of mass transfer driving force for fast reactions. In modeling, nonideal mixing characteristics in the gas and liquid phases were described using a tanks-in-series model with backflow. The parameters in the proposed mixing model were determined on the basis of a multiple circulation cell model and a velocity profile of recirculatory flow in a bubble column. Experiments for decolorization and mineralization of Orange II were performed to verify the capability of the proposed model in a semibatch bubble column. The decolorization completed rather quickly. However, the mineralization characterized by the total organic carbon (TOC) was incomplete and its rate was rather slow. It was found that the decolorization rate decreased with the increase in the initial Orange II concentration and increased with increasing ozone gas injection rate, ozone dosage, and solution pH. The proposed model could reasonably describe the present experimental results for the dynamic changes and the steady state of decolorization, mineralization, dissolved ozone concentration, and ozone concentration in the outlet gas. The proposed model might effectively handle the prediction of ozone oxidation process in a semibatch bubble column.

Biodegradation of the pesticides 2,4-D have been investigated in a net draft tube airlift bioreactor at different concentrations (10-160 ppm) and air flow rates (0.75-4 L min −1 ), employing acclimatised activated sludge. A modification for the glass draft tube airlift bioreactor was proposed in which the draft tube is made of non-woven polypropylene textile net. The experiments were carried out as well in a bubble column (BC) for comparison. The results confirmed that immobilising the activated sludge on the net of the draft tube could enhance the substrates mass transfers and improve the biodegradation rate. A mathematical model was developed to simulate the biodegradation process. The simulated results were in good agreement with the experiments.On aétudié la biodégradation des pesticides 2,4-D dans un bioréacteurà agitation par circulation d'airà tube de circulation netà diverses concentrations (10-160 ppm) et divers débits d'air (0,75-4 L min −1 ) en employant une boue activée adaptée. Une modification du bioréacteur a agitation par circulation d'airà tube de circulation en verre aété proposée, dans laquelle le tube de circulation est fait d'un filet textile en polypropylène non tissé. Les expériences ont aussiété réalisées dans une colonneà bulle (CB) aux fins de comparaison. Les résultats ont confirmé qu'immobiliser la boue activée dans le filet du tube de circulation pourrait accroître les transferts de masse de substrats et améliorer le taux de biodégradation. Un modèle mathématique aété créé pour simuler le processus de biodégradation. Les résultats simulés cadraient bien avec les expériences.