Treatment Of Chromium Containing Wastewater In EGSB Reactor Optimized By CFD

Chromium-containing wastewater,having widespread sources and high toxicity,is harmful to natural environment and human being health.Among the approaches used to remove chromium from wastewater,adsorption is the most popular one,due to the low operating cost,the easiness of operation and excellent removal efficiency of pollutants.Recently,many researchers began to focus on inexpensive biosorbent.In present study,the structure of three-phase separator of the expanded granular sludge bed(EGSB)reactor was optimized using computational fluid dynamics(CFD).The optimized reactor was started up and used to remove Cr(VI)continually.The main contents and conclusions of the thesis were described as follows:(1)The impact of baffle angle(θ)on separation efficiency and hydraulic characteristics in the three phase separation zone were analyzed using CFD.The results show that when θ was 40°,the sludge loss rate was the smallest and the reflux condition was the best.(2)The start-up of the EGSB reactor was carried out and a neural network model was developed based on the experimental data.Some model parameters were optimized using response surface methodology.The result indicated that the proposed network model predicted effluent COD concentration of the reactor within ± 20% deviation.(3)Anaerobic granular sludge was used as a novel adsorbent for hexavalent chromium removal from aqueous solutions and the process was analyzed by many methods.The experimental isotherm date was successfully described by the Freundlich isotherm and the pseudo-second-order kinetic model was more suitable for explaining the kinetics process of adsorption.The results of the Fourier Transformed Infrared and the X-ray Photoelectron Spectroscopy analyses suggested that Cr(VI)adsorption most likely involved electrostatic adsorption,redox reaction and complexation.The obtained model predicted maximum Cr(VI)removal efficiency(99.1%)at pH 2.0,150 min of contact time and a sludge dosage of 1.67 g,while verification experimental value was about 99.9%.(4)EGSB reactor was used to treat chromium containing wastewater continually.The removal rate of total chromium was above 97% during the whole operation of 35 d.When the Cr(VI)concentration was up to 50 mg/L,the removal rate of COD was still above 76%.