| Chlorella vulgaris are a type of single-celled green algae which have a wideecological distribution, high photosynthetic efficiency, ease to cultivation and fastgrowth rate.Their cells are important biomass resources which contain large amountsof nutrients, such as protein, fats, pigments, polysaccharides, vitamins, etc. On theother hand, the extensive use of fossil fuels has led to serious problems, such as theenergy crisis and environmental pollution. It is imperative to seek alternative energytraditional fossil energy sources to alleviate issues. The present studies showed thatbio-energy is an ideal renewable energy and probably can partially replace fossilenergy in some way. Chlorella vulgaris was chosen as feedstock for bio-energypurpose due to their high content of fat. Chlorella vulgaris is one of the hottest algaeepecies studied in bio-energy research in recent years. However due to the fact ofrelatively small size and low cell density for Chlorella vulgaris, intensive energywas used for harvest process which limit the large-scale production of algae-basedbio-energy.In this paper, common flocculants were evaluated systematically, then theflocculation process for Chlorella vulgaris harvest is further optimized, and waterand nutrients recycling after harvesting is further explored. The followingconclusions may be made through above experiments:1. The study examined the effect of different flocculants (such as Ferric chloride,ferric chloride, aluminum chloride, aluminum sulfate, zinc sulfate and calcium oxide)with different dosage and incubation time on the recovery efficiency of Chlorellavulgaris, and compared the growth of Chlorella vulgaris in the flocculatedsupernatant media. The results showed that The results showed that the optimizedconditions for ferric chloride, aluminum chloride, aluminum sulfate, zinc sulfate, andcalcium oxide were as follows:1) concentration:150,125,150,300and450mg/L;2) retention time:30,30,30,90, and60min;3) harvesting efficiency92.49%,94.29%,88.06%,88.44%,91.36%. In addition to zinc sulfate, the other four flocculant treated supernatant can be used to stimulate the growth of Chlorellavulgaris. Overall, considerations of cost, environment, water and nutrient recyclingas well as alage paste application, calcium oxide is the most suitable flocculant forChlorella vulgaris harvesting.2. Chlorella vulgaris were harvested in4,8and12days, respectively. followedby flocculation using calcium oxide. The results demonstrated that the optimumprocess was as following conditions: the pH value is8, the dosage of calcium oxideis300mg/L, the stirring speed is250r/min, stirring time is2min and the retentiontime is120min. Compared with the cell bofore flocculation, the cell morphology ofChlorella vulgaris did not changed by a optical microscope which prove thatharvesting process does not result in the loss of intracellular substances of Chlorellavulgaris. Furthermore, the supernatant can also be reused as the culture media ofChlorella vulgaris.3. Using the combination of calcium oxide and γ-PGA to harvest Chlorellavulgaris, the optimum condition were as follows: the concentration of Chlorellavulgaris (OD680) is0.8, the dosage of γ-PGA is60mg/L, the dosage of calcium oxideis120mg/L. The flocculated sample was then filtered by polypropylene materialcarpet, the harvest rate of Chlorella vulgaris can be reached80.25%. Furthermore,the supernatant after harvest can continue to be cultivatedt a new batch withoutinoculation. |
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