| Algal blooms caused by eutrophication of water are a great threat to people’s living environment and drinking water safety.Algal cells in algae-laden water have a great influence on the coagulation and filtration process of drinking water treatment.In addition,all kinds of harmful substances released by algae,such as disinfection by-product precursor and microcystins,are stable in the water environment and difficult to be removed by conventional processes.Although ultrafiltration process has a good solid-liquid separation effect and a good purification effect for algal water,the serious membrane pollution caused by algal cell deposition on the membrane surface limits the promotion and development of ultrafiltration process.As an environmentally friendly technology with low pollution,electrochemical oxidation has a good inactivation effect on algal cells.Therefore,this paper introduces electrochemical oxidation technology as the pretreatment process of ultrafiltration to explore the combined process of electrochemical preoxidation coupled ultrafiltration for the treatment of algal water.To investigate the effects of electrochemical strength on the efficacy of two ultrafiltration membranes(PVDF and PES)in treating algal water mixtures,different electrochemical preoxidation time was set in this project.And The mitigation of membrane fouling was investigated by the specific flux curve of filtration and the change of reversible and irreversible resistance.At the same time,the mixed pollution model is introduced to evaluate the filtration process under different working conditions.In addition,through the detection of the modification of algal cell particles before and after electrochemical preoxidation,the interface of ultrafiltration membrane,the change of fluorescent substances in the effluent,and the hydrophilic and hydrophobic classification of the effluent,the paper deeply analyzes and discusses the mechanism of the combined process for the treatment of algal water.Finally,we found the BDD anode will priority to remove hydrophobic organic compounds and fluorescent material in algae-laden wate,makes the algae-laden wate system of hydrophilic gradually strengthen,at the same time it can reduce the algal cells between particles,algal cells and membrane adhesion effect,so as to gain more loose in the ultrafiltration process of filter cake layer,which is beneficial to reduce membrane pollution and improve the water production efficiency of ultrafiltration.In order to further research the contribution of different components to the ultrafiltration membrane pollution,the algal organic matter and algal cell particles in the algae-laden wate were separated in this project,and the combined process was used to treat them under different working conditions.We found that there is a synergistic effect between algal cell granules and extracellular organisms,source of algal organic matter will fill the gap in algal cells and more compact cake layer is formed between pollution,it is an important reason that the improvement of electrochemical preoxidation intensity has no further mitigation effect on membrane contamination in algal water mixing system.At the same time,through the comparison of water quality analysis we can find that the ultrafiltration filter cake layer formed in the process of though can result in serious membrane fouling,but at the same time,it can pass the prefiltering function strengthen ultrafiltration for small molecule organic material removal,but electrochemical oxidation effect to a certain extent,change the nature of the filter cake layer,which make the filtering effect is decreased obviously.After electrochemical treatment for 30 min,the retention rates of the cake layer on the surface of the two ultrafiltration membranes decreased from48.21% and 49.33% to 28.13% and 26.51%.In addition,the effects of electrochemical preoxidation on the morphology and rupture of algal cells in algae-laden wate were analyzed by scanning electron microscopy and flow cytometry.·OH produced by the anode of BDD has a good inactivation effect on algal cells,the inactivated cells increased from 16.5% to 87.85%in a short time.And it can change the permeability of algal cell membrane,causing a large number of algal cells to rupture,while the oxidation in a longer time may destroy its internal structure and increase the content of organic matter in algal water.When the broken algal cells were squeezed during ultrafiltration,they produced more serious organic release.However,the amount of continuous release after inactivation doesn’t exceed the adsorption capacity of ultrafiltration membrane.In this paper,electrochemical technology is proposed as a combined process of ultrafiltration process pretreatment,and different pre-oxidation time is set to explore the membrane pollution mitigation and water purification efficiency of algal water treatment.At the same time a variety of characterization and test results are used to explore the mechanism of the combination process algae-laden wate,and the algal cells in the process of handling broken problem,filter cake layer reinforcement intercept and organic matter to release problem in filter cake layer were analyzed and studied,and the conclusions and suggestions are given,which is instructive to the practical application and operation of the combined process. |
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