| In order to solve the problem of cross-linked enzyme aggregates(CLEAs)that are highly viscous and difficult to reuse,CLEAs-hollow fiber membrane reactor is prepared.Based on the characteristics of hollow fiber membranes with large specific surface area and on-line separation,lipase CLEAs are immobilized on its inner wall,thus the influence of enzyme immobilization on mass transfer performance of membrane may be reduced.This paper includes three parts.The first part is to discuss the factors affecting CLEAs activity through meta-analysis.The second part is to prepare enzymatic reactor of CLEAs-hollow fiber membrane,and optimizes the preparation conditions;moreover,characteristics of CLEAs immobilized on hollow fiber membrane are observed.The third part is to investigate the application of the CLEAs-hollow fiber membrane enzyme membrane reactor in the treatment of oil wastewater.The main results are as follows:(1)Searching papers using keywords "CLEA*","cross-linked enzyme aggregate*" and "cross linked enzyme aggregate*" in Web of Science and CNKI databases,there are 141 valid documents(10 in Chinese and 131 in English),2611 data.Meta-analysis showed that CLEAs enzymes activities were significant lower than those of free enzymes.In various enzymes species,CLEAs activity of ligase was the lowest relative to the free enzyme(ln R=-1.85),while CLEAs activity of transferase was the highest(lnR=-0.35).As for precipitant and cross-linking agent,ammonium sulfate(n=1087)and glutaraldehyde as the cross-linking agent(n=1857)were mostly used.The optimal conditions for preparing the CLEAs-hollow fiber membrane reactor were the precipitant concentration 40-60%(lnR=-0.6),the precipitation time>720min(LnR=-0.25),precipitation temperature 5-20℃(lnR=-0.11),cross-linking agent concentration≤50mM(lnR=-0.825),cross-linking time>4h(lnR=-0.82),cross-linking temperature 21-30℃(lnR=-0.76),stirring speed≤100 r/min(lnR=-0.64),centrifugation speed≤5000g(lnR=-0.86),and centrifugation time>10min(lnR=-0.76).In addition,the addition of protective agents such as BSA,Tween80(lnR=-0.53)or the introduction of immobilized carriers,such as magnetic mesoporous silica beads,magnetic Fe3O4,etc.could increase CLEAs activity(lnR=-0.77).(2)Preparation of CLEA-Hollow Fiber Membrane Enzyme Membrane Reactor:Under the conditions lipase enzyme concentration 20g/L,precipitant acetone concentration 60%(v/v),crosslinking agent glutaraldehyde concentration 2.5mmol/L,the cross-linking time 60s,and the immobilization time 60min,catalytic activity of CLEAs immobilized on hollow fiber membrane reactor was the highest as 1.90 U/cm2.(3)The performance of CLEAs immobilized on the hollow fiber membrane:Compared with free lipase immobilized on immobilized on the hollow fiber membrane,immobilized CLEAs had wider range,and higher temperature tolerance increased by 10-38%at-20,4,20,40,60,and 80℃after 2 h incubation,especially at-20℃ 38%increment was observed.The storage stability experiment(21d)showed that at a low temperature of 4℃,the residual enzyme activity of the free enzyme immobilized on the hollow fiber membrane was 25%,but the residual enzyme activity of the CLEAs immobilized on the hollow fiber membrane was 85%.The reaction kinetics experiment of CLEAs immobilized on the hollow fiber membrane showed higher Km as 238%and higher Vmax relative to the free lipase immobilized on hollow fiber membrane,indicating that immobilized CLEAs had lower affinity of substrate and higher catalytic efficiency.(4)Application of CLEAs-hollow fiber membrane reactor in treating oil wastewater:The results showed that low flow rate(60-30ml/min),high temperature(4-20℃),and high pH value(5-7)facilitate the treatment of oil wastewater.The highest removal rate of oil was 78%under the optimal conditions20℃,pH=7,flow rate is 30ml/min,and reaction time 12 hours.In addition,treatment effect was slightly affected by salt ion(Na+)in oil wastewater. |
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