A Study On Continuous Wastewater Treatment By Wet Air Oxidation In A Trickle-Bed Reactor

As one of the advanced oxidation technologies, wet air oxidation (WAO) is studied in this thesis on its potential application in continuous wastewater treatment process. WAO refers to the process where aqueous organic pollutants are oxidized by oxygen at elevated pressure (0.5-20 MPa) and temperature (125-320 0C). Through addition of catalyst into the reactive system the same results of removing pollutants can be achieved at relatively low pressure and temperature and hence the operational costs can be lowered. A pilot scale trickle bed reactor (TBR) was manufactured as the appropriate reactor configuration for a study on continuous catalytic WAO process. The objective of this study is therefore to investigate the capability of this TBR system in continuously oxidizing organic pollutants.First of all, we developed and characterized various types of heterogeneous catalysts, including using a recently discovered mesoporous material: MCM-41 as the catalyst support, and evaluated them in batch WAO of phenol solution at 150 0C and 200 0C. Activated carbon supporting-copper (CU/AC) catalyst was finally selected as the most ideal type, with regards to its advantageous physical properties and catalytic reaction performances. Approximate 6.0 liters of CU/AC catalysts were prepared and loaded into the TBR. and its applicability was investigated in continuously oxidizing phenol solution at much milder conditions (temperature of 1 500C and pressure less than 1.0 MPa). The outstanding result that more than 90% of phenol and total organic carbon (TOC) were removed by oxygen at a wide range of liquid flow rate and phenol feeding concentration, inevitably drew our attention to further analysis the details of each of mass transfer processes involved. It is different from most of other relevant studies, a non-steady state adsorption method was employed to estimate mass transfer coefficient and wetting efficiency. In complete wetting region the mass transfer coefficient was obtained and correlated by Sb = 1.868 Re0 ~" Sc"3 , while in incomplete wetting region the wetting efficiency was measured and found around 0.8. All the results were compared with some other reports and studies and concluded invigood agreement. In respect of gas-liquid mass transfer study, initially oxygen solubility was regressed for the normal operational range of catalytic WAO process as H(T) = 761.l-108.9ln(T)-40785.5/T , MPaI(mmolO2/molH2O), based on the survey on a broad spectrum of available data. Subsequently by means of physical absorption the mass transfer coefficient were measured and correlated as k,a up030 p___ = 193.6(-) (.)1/2 The interfacial area was found to be roughly 4- 5 m2/m3.DppDTo obtain the intrinsic kinetics of catalyzed oxidation of phenol, we chose the batch reactor where the mass transfer effects were sufficiently eliminated. On basis of the experimental data at 150 0C a model was established that is able to simulate the rate of phenol degradation by either homogeneous or heterogeneous catalyst very well.In the end, we prospected what is expected on the future work of this study. A mathematical model integrating all the aforementioned processes can therefore be established to optimize the TBR system. It was also recommended that another study needs to be carried out on evaluating the ability of TBR system in treating practical industrial wastewater.