Study On Water Disinfection By Ozone In A Rotating Packed Bed

Ozone disinfection is a promising water disinfection technology.The existing study on ozone disinfection reactor lies on the optimization for the structures of conventional disinfection contactors,but the development of efficient and non-conventional disinfection reactors is scarce.This study employed a rotating packed bed(RPB)as an ozone contactor for water disinfection and the performance of the RPB on the inactivation of E.coli was evaluated.Futhermore,the artifical neural network was used to establish the model for the prediction of mass transfer coefficients in ozone-water absoption process in RPB.Also,RPB was adopted for the efficient production of ozone water.In addition,the performance of the RPB ozone disinfection reactor was evaluated through the treatment of two types of actual wastewater.The main contents are as follows:1.The effect of various operation parameters on the mass transfer coefficient was investigated by serial experiments.The results show that the increase of rotational speed increases the gas-liquid interface area for mass transfer,but also reduce the contact time of gas and liquid.The rise and decline of the mass transfer coefficient result from the competing effect of these two factors.The increase of gas flow is beneficial because it causes the disturbance to liquid phase and thus the turbulence between gas and liquid was enhanced,which is favourable for ozone absorption.The effect of liquid flow on the mass transfer coefficient of the ozone-water process is significant.The increase of liquid flow boosts liquid and gas turbulence,and increase droplet number and liquid film area,resulting in a significant increase in the mass transfer coefficient.Futhermore,the RPB was used for the efficient production of ozone water.The effects of rotational speed,gas and liquid flow rates,gas ozone concentration and treatment capacity of packing on the quality of ozone water were investigated,and the optimal operation parameters were obtained.2.The validity of artificial neural network(ANN)modeling approach in predicting overall mass transfer coefficient was demonstrated for ozone absoption process in RPB.Serial experiments were conducted and the effect of rotation speed,gas and liquid flow rates on KLa was investigated.Further,an artificial neural network was developed to predict KLa.The input variables including Reynolds number of gas(ReG)and liquid(ReL),Froude number(FrL)and Weber number(WeL)of liquid were used because they can demostrate the flow characteristics of fluids in RPB and eliminate the effect of irrelevant factors.Random grid search method was used to optimize the model hyperparameters.The model was trained with 50000 epochs based on the optimal hyperparameters,and the final model contains three hidden layers and 15,25,25 neurons in each layer,respectively.The model exhibits a satisfying prediction performance with R2 of 0.9896 on the training set and 0.9877 on the test set with a variation of 15%.These results show that ANN model can be employed as an efficient approach for the mass transfer study on ozone absorption process in RPB.3.The inactivation of E.coli was studied by employing RPB as an ozone disinfection contactor.Hatta number for the inactivation of E.coli in RPB reached 7.72,which further revealed that RPB is a suitable ozone contactor for the inactivation of E.coli.The RPB exhibits a fair performance on the inactivation of E.coli with a lower Ct value compared to those in the conventional disinfection contactors.It was found that RPB can achieve a 1-2 Log inactivation,which is higher than that in the bubble reactor with the same treatment capacity.The end zone in the packing can be identified as the efficient dissolving region for ozone absorption,and the residual packing and cavity zone as the contacting region for uniform mixing and microorganism inactivation.Due to the unique fluid flow characteristics,there are a huge gas-liquid interface and violent interface renewal rate in RPB.It is thus possible to achieve a good inactivation effect of E.coli at a low Ct value,which means that RPB can find application in the disinfection of water with the advantage of low cost and small volume of equipment.4.RPB was employed to treat two actual wastewaters to evaluate the performance on the inactivation of target microorganisms.The results of disinfection on the river water show that the increase of rotational speed improves the Log inactivation of total coliform the river water,and the inactivation performance of RPB is 0.5-1.5 Log higher than that achieved in the stirred aeration reactor under the same experimental condition.The trials on the disinfection of secondary municipal wastewater were conducted and the inactivation of total coliform and E.coli in water reached the water discharge standard in Beijing district.