Study On Microalgae Cultivation Based On Membrane Carbonation Photo-sequence Batch Reactor(MCP-SBR)

Microalgae are used widely in CO₂ gas fixation,sewage treatment and energy recovery,therefore,how to achieve abundant and rapid cultivation of microalgae has attracted much attention.Utilizing CO₂ in industrial waste gas to cultivate microalgae not only reduces costs,but also alleviates greenhouse effect.However,low solubility of CO₂ gas results in gas escape and low availability.Usage of hollow fiber membrane can improve retention time of gas in algae fluid to enhance the utilization ratio.In addition,the normal means of harvesting microalgae,such as centrifugation and sedimentation,can't take advantage of microalgae completely.Besides,membrane fouling existing in membrane filtration,reduces operating efficiency and increases operating costs.The aim of this paper was to establish MCP-SBR?Membrane biofilm-sequence batch reactor?for the continuous cultivation and enrichment of Chlorella.Meanwhile,CO₂ gas,N and P would be consumed to a certain extent.At the same time,along with the alternation of aeration and filtration,the membrane fouling was effectively reduced and the membrane utilization efficiency was improved.Firstly,batch experiments for microalgae cultivation were established.The hollow fiber membrane module was inserted into the vial,so that the CO₂ gas could be injected continuously through the micropores on the surface of membranes.The CO₂ gas could be utilized as the carbon source for the growth of Chlorella.In the vial,the growth index of algae greatly increased,and because of the small bubbles entering the liquid through the membrane,the retention time of CO₂ gas increased,which showed that it was feasible and effective to use membrane aeration to culture microalgae.The influence of pore size,light intensity and CO₂gas concentration on the growth of Chlorella were also investigated.The best experimental conditions were obtained,namely,the diameter of the membrane was 30 nm,the light intensity was 25000 lumens,and the concentration of CO₂ gas was 10%.The optimum condition was used for the continuous cultivation of Chlorella in the subsequent MCP-SBR.Secondly,MCP-SBR,a stable membrane/microalgae cultivation system was established.The reactor was successfully operated for 45 days and harvested high concentration algal fluid twice.In the first stage,the biomass of Chlorella increased from 497.25 mg/L to 2002.39mg/L by continuous cultivation in 22 days,and increased by 3 times than the initial biomass.At the same time,the concentrations of three kinds of pigments were also greatly improved.The concentrations of chlorophyll a,chlorophyll b and carotenoid all increased by 2.30 times,1.79 times and 2.06 times,respectively.After harvesting Chlorella solution,in the second stage,the MLVSS,chlorophyll a,chlorophyll b and carotenoid of Chlorella increased by 2.56,2.78,3.43 and 3.30 times,respectively.Meanwhile,along with the continuous inlet of CO₂gas,the p H was stabilized to 6⁹,which was more beneficial to the growth of Chlorella.In addition,the efficiency of phosphorus and nitrogen treatment reached over 90%and 85%,respectively.Furthermore,in this reactor,the hollow fiber membrane acted as a dual function of aeration and filtration.It not only improved the residence time of microalgae and CO₂ gas,but also reduced the membrane fouling by aeration and filtration alternately?the TMP was only0.034 MPa after continuous cultivation for 45 days?.The use efficiency and service time of the hollow fiber membrane were enhanced greatly,and the cost due to membrane cleaning and replacement was reduced immensely.Thus,it was more feasible for cultivate microalgae consecutively using hollow fiber membrane.