Performance Research Of Electro-Fenton Membrane In Microalgae Harvesting

Microalgae biofuel is a kind of environment-friendly renewable energy,which has been considered as one of the best alternative resources of fossil fuels in recent years.It can meet human demand for primary energy and has a broad development prospect.However,the current microalgae harvesting methods have the problem of higher cost or lower efficiency,which is a major bottleneck restricting the development of microalgae biomass energy.Membrane separation technology can achieve high efficiency recovery of microalgae and has low energy consumption,but serious membrane fouling will occur during the filtration process.In view of the above situation,the electro-Fenton coupling membrane filtration technology was applied to microalgae harvesting in this study,aiming to alleviate the membrane fouling during microalgae harvesting by electro-Fenton effect,and finally realize the low cost and high efficiency recovery of microalgae.Firstly,the iron-porous carbon-carbon nanotube(Fe-PC-CNT)hollow fiber membrane was prepared by a wet spinning process and its properties were characterized.The prepared membrane was microfiltration membrane(the pore size was 207 nm)with uniform morphology,good hydrophilicity(contact angle was 29.38°),high porosity(87.8%)and high permeate flux(～1751.6 L/(m~2·h·bar)).Furthermore,in-situ formation of hydroxyl radical(·OH)could be detected when the voltage of-1 V was applied on the membrane,which provided a theoretical support for subsequent experiments.Secondly,Fe-PC-CNT hollow fiber membrane capable of in situ production of·OH was used as the basic separation unit to perform short-term filtration of microalgae in both continuous and intermittent modes.In continuous filtration,under the optimal voltage of-1 V,electro-Fenton effect significantly delayed the increase of transmembrane pressure(TMP)and enhanced the harvesting ability of microalgae by 2.5 times.Moreover,the reversible and irreversible fouling rates decreased by 20.1%and 9.9%,respectively.In intermittent filtration,microalgae was concentrated from 1.05 g/L to 7.45 g/L after Fe-PC-CNT membrane filtration,and the membrane flux could be restored to the initial level after electro-Fenton cleaning for 30min.In addition,due to the electrochemical rejection and strong oxidation of·OH,electro-Fenton enhanced Fe-PC-CNT hollow fiber membrane could not only reduce the reversible fouling,but also effectively restrain irreversible fouling,and presented excellent antifouling and the microalgae harvesting ability without obvious damage to membranes and microalgae cells.The electro-Fenton membrane has good usability.Finally,an electro-Fenton enhanced membrane photobioreactor integrating microalgae cultivation,wastewater treatment and microalgae harvesting was constructed.During the53-day operation(four cycles),microalgae could grow from～100 mg/L to 1 g/L in each cycle.Moreover,after the carbon to nitrogen ratio of the influent was increased to 15:1,the average growth rate of microalgae could reach about 75 mg/(L?d),and the culture cycle was shortened from 18 days to 12 days.The secondary effluent of the municipal sewage treatment plant was used as the treatment object,the removal rates of nitrogen and phosphorus were higher than93%and 90%.Moreover,electro-Fenton enhanced Fe-PC-CNT hollow fiber membrane presented good antifouling performance.It was cleaned for only 3 times during the whole operation period,and the flux recovery was close to 100%;while polyvinylidene fluoride(PVDF)hollow fiber membrane of control group was cleaned up to 8 times,and the final flux recovery was less than 50%.Moreover,the concentration factor of electro-Fenton enhanced system was 1.6,2.1,3.4 and 4.8 times of that of the control group.Finally,the high-efficiency and economical microalgae cultivation,the efficient and stable removal of pollutants in wastewater,the effective control of membrane fouling,and the efficient of microalgae harvesting were realized.