Studies On Culture And Harvesting Of Dunaliella Salina Cells

Dunaliella Salina is a unicellular species of green alga noted for itshalotolerance. It's a valuable mircoalga in many fields, including food,health care, chemical engineering and culture. Currently, it's mainly usedto produce natural β-carotin for commerce. In many countries, the cultureof it has become a large-scale microalga industry. The culture method isthe open racetrack poor, but the concentration of Dunaliella Salina is verylow, which is usually (4～5)×105cells/mL, under this condition. Also,because its body size is rather small (about 14×22μm) and its density issimilar to water's, the harvesting of it is difficult. There are someshortcomings in traditional separation methods between solid and liquid.For instance, flocculation-precipitation could pollute the production andthe efficiency of filtration separation would be much too low. Todaycentrifugation is the most frequently adopted method for cells harvestingin the big-scale cultivation of Dunaliella Salina. But the energy cost israther high and cell broken is inevitable during centrifugation, which isdisbeneficial to the down-stream process. According to actualities,harvesting methods, such as foam separation and dissolved air flotationwithout flocculating agent were studied at length in this paper in order toprovide some valuable basic data for industry. In the experiment of batch foam separation, by determining theenrichment factor and total yield of Dunaliella salina cells, the effects ofdifferent operational conditions, such as gas flow rate, pH, initial cellconcentration, average hole diameter of distributing board andconcentration of cracked cells on the feasibility of foam flotation ofDunaliella salina cells were investigated. The experimental results showedthat correlativity between performances, including total yield andenrichment factor and gas flow rate exhibited peak value, viz. Lorents orGuass equation. The same phenomena existed between the performancesand other influential factors, for example the pH, initial cell concentration,and concentration of cracked cells. Otherwise, the phenomenon betweenperformances and average pore diameter of distributing board showedexponent descending correlativity. In addition, math models matchedexperimental results well. Operation factors, such as the pH, rate of feeding water, volume ratioof saturation water to feeding Dunaliella Salina, saturation time andsaturation pressure have important effects on harvesting performances ofbatch dissolved air flotation. The curves of performances versus the pH orthe rate of feeding water showed peak value, viz. Lorents equation. Butthe curves of performances versus the ratio of saturation water volume tofeeding volume, saturation time and saturation pressure indicated theminus exponent ascending correlativity. According to these conclusions,math models were set up, which match experimental results well. In addition, the effects of the pH on hydrophobicity and Zetapotential of cells were studied. The experimental results revealedpreliminarily micro mechanism of the influence of the pH on flocculationof Dunaliella Salina cells. And these results indicated that the method ofchanging pH to flocculate the cells was feasible.