| Biodiesel from micro algae has been gaining national attention. But high cost is one of the major problem restricting the development of algal biodiesel.The feasibility of using paper mill wastewater for oil-riched algae cultivation was studied, hoping to find a new way to reduce the cost of biodiesel from algae. Algae with high oil-content and growth rate was screened, mutagenized by ultraviolet and cutivitation conditions were optimized. Then the composition of wastewater was analyzed. After hydrolysis and detoxification, the hydrolysate was used for algae cultivation.The oil content of six algae used was between 17%～26%. Scenedesmus obliquus was with the highest oil content of 25.77%.C16 and C18 were major fatty acid of these algae. Except Nitzschia closterium, the other five algae were with heterotrophic ability. Hexose and disaccharide(maltose) were good carbon source, but algae could not utilize pentose. Growth rate was highly increased when glucose was added in the medium. Mass growth of Chlorella sp-1,Chlorella sp-2 and S. obliquus cultivated mixtrophically was 4.4, 7.5 and 6.3 times higher than that of autotrophically. Based on growth rate and oil content, S. obliquus was screened for further research.A strain named S.obliquus -1 was screened by UV mutagenesis, the growth rate of which increased by 39% than that of pre-mutagenesis. The strain was with an oil content of 28%. Conditions for lipid productivity were optimized in two stages: fractional factorial design (FFD) and orthogonal experiments. Nitrogen and temperature were selected as significant factors. And the optimal conditions occurred at nitrogen 6.0mM, temperature 25℃,illumination 4500 lux, glucose 10g/L and pH 5.0, with the highest lipid productivity of 75.46mg L-1d-1.The component of pine kraft black liquor was analyzed. Result shows that there were reducing sugar 1.92 g/L and hemicellulose 35 g/L. Dilute acid hydrolysate mainly contained glucose and some cellobiose. S obliquus -1 was cultivated in medium with different proportion of black liquor.Result show that with the increase concentration of black liquor, the influence of black liquor on algae increased. It was observed that the morphology of S.obliquus -1 changed, which means that the black liquor maybe contains some toxic substances for algae.The black liquor was hydrolyzed and reducing sugar content was investigated using different hydrolysis methods. Result shows that compared with acid hydrolysis, enzymatic hydrolysis was with higher reducing sugar content. A reducing sugar content of 9.18g/L was obtained by enzymatic hydrolysis after delignification. And the optimum conditions for delignification was pH 3.0, temperature 75℃,sulfuric acid concentration 6%, when the highest hemicellulose content of 47.61 g/L was obtained in the wupernatant residual.The main sugar in hydrolysate was glucose 3.63 g/L, followed by cellobiose 1.81 g/L, xylose 0.8 g/L and arabinose 0.2 g/L. Meanwhile, 3.10 g/L formic acid and 2.90 g/L acetic acid was detected. After overliming by Ca(OH)2, decompression vacuum concentration and detoxification of activated carbon bleaching, hydrolysate became light yellow and light transmission rate increased. Reducing sugar loss rate was 5.64%.When S.obliquus -1was cultivated in hydrolysate after treatment, its growth yield reached to 1.23 g/L, greatly increased than that of in black liquor medium with glucose, oil content was 24.52 % and lipid productivity was 23.20 mg L-1d-1 , the morphology of S.obliquus -1 returned to normal.Hemicellulose was extracted from black liquor and hydrolyzed. The hydrolysate was used to cultivate S.obliquus -1. It was found that growth yield of S.obliquus -1 greatly increased than that of black liquor medium. By adjusting medium formula, growth yield of S.obliquus -1 increased to 2.7g/L, an increase of 20 % than that of in glucose medium, oil content was 25.7%, the final lipid productivity reached 53.37mg L-1d-1. |
PDF Full Text Request