Chlorella Harvesting Methods And Nutrition Analysis For Food Applications

Chlorella has great potential in biodiesel,feed,food and other industry applications.But due to the small size,Chlorella cells are very difficult to be harvested.Traditional microalgae harvest methods have their limitations for commercialization.Chemical flocculation causes contamination to the algae cell,which limits its application in the field of food.Centrifugal method is too costly to be used in large-scale applications,especially when the algae suspension is dilute.In this paper,we studied two kinds of processes:electrolysis flotation method and fungi pellets assisted harvesting method.The effects of processing parameters on harvest rate and the nutrient contents of harvested products were investigated.The main research contents and conclusions are as follows:The effects of parameters related to harvesting of Chlorella vulgaris by electrolytic flotation on harvest rate were studied.With the same current input,the#30 screen electrode required less time to achieve a harvesting rate of 90%,compared to the#10 screen electrode.In both condition of using#30 and#10 screen electrode,less time are needed to achieve a harvesting rate of 90%with increasing current density.The foam concentration of the#30 screen electrode is lower than that of the#10 screen electrode.During the electrolysis flotation process,the voltage on the#10 screen is more stable than that on the#30 screen.Iron electrodes are unsuitable for use as electrodes for continuous culture and harvesting of Chlorella vulgaris because of the problem of severe decoloration.In the range of experimental parameters,higher liquid surface height and larger flow rate have positive effects on increasing harvest rate.There are obvious differences,such as regeneration behavior and lipid content,between the algal cells in the foam and those left in the algae fluid.These differences may lead to different sensitivity to electrolytic flotation.In a pilot scale,the continuous cultivation and recovery of Chlorella were achieved.The medium could be reused because no flocculant was added.Hydrogen bubbles formation process and characteristic were analyzed and discussed.The results show that the hydrogen bubble departure diameter and the surface parameters of the electrode material were related to curvature during the early recovery of Chlorella vulgaris by electrolysis flotation.The smaller the diameter of the electrode,the smaller the bubble formed.With the increase of the liquid height,the greater the pressure of the bubble,the longer the working distance of the bubbles.As the bubble rises,the pressure becomes smaller and the dissolved hydrogen is diffused,so the bubbles become larger eventually.By analyzing the amino acid composition of foam and remaining amino acid composition in algal fluid,it was found that the total amino acid content of Chlorella in foam was relatively high.The essential amino acid coefficient of Chlorella in foam was close to the recommended standard.The indicators of Chlorella vulgaris obtained by electrolysis air flotation method met the requirements of food application in terms of harmful metals and colonies.The pelletization behavior of fungi under different parameters was studied.The results showed that the proper mixing rate is l00rpm under present experimental condition.Low pH,high glucose content and longer fungal culture time had positive effects on harvest rate.The adsorption of Chlorella sp.on the fungus pellets conformed to a second order reaction.Glucose was necessary for the formation of fungi-algae complex.However,when the content of glucose exceeded 10g/L,there was no significant effect on the size of the pellet complex.The pH value was not a decisive factor for the formation of the pellets.The pH value affected the final size of the complex pellets.After one day cultivation,all the samples could form 0.5mm of the pellets.When the initial pH value is higher than 5.5,the pellets stopped growing after one day cultivation.In the condition of pH3.5 and 4.5,the pellets keep growing before the pellets reach 1-2mm.When the number of fungal spores was 7×1O8/L and 7×107/L the fungi-chlorella complex could be formed,which indicated that the spore number should reach a certain extent before pelletization process occurs.The amino acid composition of the edible fungus Chlorella complex was studied.The results showed that cysteine(Cys)wasthe first limiting amino acid of the complex.The ratio between the eight essential amino acids and the total amount of eighteen amino acids was 41.78%,which is very close to the WHO recommended standard(40%).The contents of harmful metals and harmful colonies in the edible fungus Chlorella complex conformed to the requirements of food application.