| As a kind of algae with high scale of cultivation in China,Chlorella vulgaris has been widely used in the production of bioenergy,food and medical.In the process of large-scale culture of C.vulgaris in China,the culture medium after recycling for several times inhibits the algae growth significantly.In view of this phenomenon,the accumulated growth inhibitors for C.vulgaris was analyzed and a series of methods for the inhibitors remcoval were evaluated.Finally,ozone oxidation and activated carbon adsorption were combined to treat C.vulgaris aging solution under the optimum operating conditions,and C.vulgaris was cultured in the aging solution after treatment,and the growth ability and intracellular material contentt of C.vulgaris were analyzed.Firstly,after recycling the culture medium of C.vulgaris for 4 to 5 cycles?about 30 days one cycle?,the aging liquid with high inhibition degree was obtained.Then,qualitative analysis was carried out on the inhibitor of C.vulgaris aging solution by gas chromatography?GC?,and C.vulgaris was cultured after adding nutrients to the diluting aging solution of different multiples.Growth inhibition test was conducted on at different concentrations of the inhibitor.It was found that the growth inhibitors of C.vulgaris were mainly c16:0,c17:0 and c18:0 saturated fatty acids,which accounted for about 83%of the total fatty acids.It was found that the relationship between the effects of fatty acid content on biomass inhibition rate and specific growth rate inhibition rate found was more in line with the quadratic polynomial.Secondly,the effects of dosage of granular activated carbon(020 g·L-1),adsorption time?0180 min?,pH value?59?of aging solution and adsorption temperature?1535??on fatty acids treatment by granular activated carbon were studied.With the increase of dosage of granular activated carbon,adsorption time,pH value and the decrease of adsorption temperature,the removal rate of fatty acids from activated carbon increased gradually.At the same time,the optimum technological parameters were determined as follows:the temperature range was 1525?,the dosage was 10 g·L-1,the pH value was 9,the adsorption time was 2 h,and the removal of fatty acids by activated carbon was the best under this condition,the removal rate was?42.87±4.01?%.In addition,the intra-particle diffusion model reveals?Webber-Morris Dynamics Model?that the intra-particle diffusion was not the only step to control the adsorption rate of fatty acids on activated carbon,but may also be affected by membrane diffusion and surface adsorption.By calculating the activation energy of arenius on activated carbon,it was shown that the adsorption of fatty acids by activated carbon belongs to physical adsorption,and Ea=12.5 kJ·mol-1.Thirdly,the effects of ozone dosage(1025 mg·L-1)and reaction time?060 min?and pH value?59?of aging solution on the treatment of fatty acids by ozonation technology were studied.It was found that with the increase of ozone dosage,the reaction time and pH value of aging solution,the removal rate of fatty acids by ozone increased gradually.The optimal condition for ozone oxidation was pH=9,the dosage of ozone was 25 mg·L-1,and the optimal reaction time was 45 min,the removal rate of fatty acids was?47.99±11.83?%at the optimium condition.It was also found that the removal of 85%of fatty acids by ozonation was caused by hydroxyl radicals,and there was no significant difference between saturated fatty acids and unsaturated fatty acids by ozonation.Finally,based on the optimal operating conditions of activated carbon adsorption and ozonation,three experimental groups were conducted and compared,which were activated carbon adsorption,ozonation and"ozonation+activated carbon"Combined process were set up to analyze the cultivation capacity of C.vulgaris after the treatment of C.vulgaris aging solution and the addition of nutritients.The results revealed that the biomass(OD680)of chlorella of"ozonation+activated carbon"combined process experimental group was significantly increased by?16.1±3.2?%??27.0±5.2?%compared with activated carbon adsorption group and ozonation group,reaching 83%of the density of chlorella in fresh culture.In addition,compared with Chlorella vulgaris cultured in fresh medium,the lipid content of Chlorella vulgaris in the experimental group treated with ozone activated carbon combination technique was significantly increased by about 12%.,but the content of polysaccharide and protein and chlorophyll decreased significantly,decreased by?11.7±2.1?%??14±4.3?%??17.0±5.8?%,respectively.The results showed that the presence of fatty acids was beneficial to the accumulation of lipids and was not conducive to the accumulation of polysaccharides,proteins and chlorophyll. |
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