Efficiency And Parameter Optimization Of A Novel Rotating Multi-column Adsorption Reactor Treatment For Removing Algal Toxins From Water

Although China had achieved remarkable results in water pollution control in recent years,the process involved many complicated factors,and it still needs a long-term process to completely solve the water environmental problems.At present,the outbreak of cyanobacteria in some major water bodies such as Chaohu Lake is still frequent.When cyanobacteria breaked out,it was one of the important means to quickly remove cyanobacteria through physical and chemical methods to prevent the water body from becoming black and smelly after cyanobacteria corruption.However,the secondary pollution problems such as the dissolution of algae toxins in the rapid algae removal process had not been fully paid attention to and effectively solved.In particular,the research on the in-situ removal of algae toxins in the process of algae removal was relatively blank.In response to this problem,this research designed a rotating multi-column adsorption reactor to achieve rapid in situ removal of algal toxins from water.It was considered that MC-LR was a kind of algae toxin that existed more widely and was more harmful.This thesis mainly investigates the removal efficiency of the developed reactor for MC-LR through simulation experiments,and optimizes the operating parameters of the reactor with the aid of single factor and response surface method,laying a foundation for the further research and application of the reactor.The main conclusions of the study are as follows:（1）From the perspective of adsorption kinetics,the adsorption performance of three kinds of granular activated carbon（GAC）of coconut shell,fruit shell and tar on MC-LR was compared.The results showed that both pseudo-first order kinetics and pseudo-second-order kinetics could describe the adsorption process of three activated carbons on MC-LR.Comparing the kinetic adsorption rate constants,the adsorption effect of coconut shell GAC was the best.The effect of NOM on the adsorption performance of medium coconut shell granular activated carbon was analyzed with the help of adsorption isotherms.The results showed that the presence of NOM could significantly reduce the maximum adsorption capacity q_m of coconut shell activated carbon for MC-LR.In this test,there were and no NOM.In this case,q_m is 7.15μg/g and 49.92μg/g,respectively.（2）Firstly,a single factor experiment was used to investigate the influence of the four main design parameters(A_j/A_w,the device speed,m_c,A_f/A_w)on the MC-LR removal effect of the studied adsorption reactor.The results show that within a certain range（5095.5g/m²～8493g/m²）,increasing m_c could significantly improve the removal effect of MC-LR,but when it exceeded this range,continuing to increase the effect of m_c on the removal of MC-LR was less;Under the test conditions,when A_j/A_w exceeded 2.12,increasing this value had a certain promoting effect on MC-LR.In the experiment,it was found that in the range of 8r/min～60r/min,increasing the speed could obviously promote the removal effect of the reactor on MC-LR,but when it exceeded 60r/min,continued to increase the device speed,the MC-LR removal rate would decrease instead.Trend:A_f/A_whad a significant influence on the removal effect of MC-LR,and the removal rate of MC-LR decreased with the decrease of A_f/A_w,indicating that the smaller the distribution range of the adsorption column in the active area,the less conducive to the removal of MC-LR.（3）Based on the single-factor test results,the variation range of each parameter was determined.With the help of Box-behnken center group test design and response surface analysis,a mathematical model of the relationship between the removal rate of MC-LR and the response of each parameter was obtained.The results of variance analysis showed that the model obtained was extremely significant（F=24.65,P=0.0002）,the lack-of-fit term was not significant（P=0.1816）,and Adeq Precision（AP）was 20.322.In the regression model,B,C,B²,and BC had significant effects on the removal rate of MC-LR（p<0.05）.A,AB and AC terms had little effect on the response value（A:m_c;B:speed;C:A_f/A_w）.It showed that the speed and A_f/A_w were two relatively important influencing factors,and there was a certain interaction between they.Based on the mathematical model,the design-Expert 11 software was used to optimize the optimal operating parameters:m_c=8492.99 g/m²,speed=35.69 r/min,A_f/A_w=0.25,under this operating condition,the predicted MC-LR removal rate was 33.15%,which was closed to the test value under this condition（the average value was 32.61%）,and the relative error was only 1.65%.（4）The experiment revealed the adsorption kinetics and mass transfer characteristics of the developed reactor（coconut shell GAC as the adsorbent）for MC-LR,and the results showed that the removal process of MC-LR by this reactor was more in line with pseudo-second-order kinetics equation.The intra-particle diffusion model showed that the intra-particle diffusion was not the only speed-controlling factor of the MC-LR mass transfer process.The outer wall resistance of the reactor and the liquid film diffusion may have an impact on the MC-LR mass transfer process.The adsorption process of MC-LR by GAC in the reactor could be divided into three stages,namely the rapid diffusion stage of MC-LR from the liquid phase to the outer surface of the activated carbon,the internal diffusion stage of the activated carbon particles,and the adsorption approaching equilibrium stage.