| Microalgae is the most promising feedstock to support sustainable biofuel development in the near future, however the current algae production cost is too high. The microalgae mass culture cost accounts for an important portion in the production cost of microalgae biofuel. When mass cultivating microalgae as feedstock for producing biofuel, it is very important to select suitable algae strains, mediums and culture conditions in order to improve the productivity of algal biomass and oil, and therefore to reduce the production cost of microalgae biofuel to enhance the economic feasibility of microalgae biofuel and make the microalgae biofuel commericialization become reality. Municipal wastewater (mixture of urban sewage and industrial wastewater) and biomass fermentation slurry is an excellent source of nutrients for commercial mass culture of microalgae for biofuel production, because it contains large amounts of nitrogen, phosphorous, and other nutrients necessary for algae growth. The best way to make the microalgae biomass energy industrialization come ture is to combine the municipal wastewater treatment with the mass culture of microalgae. The purpose of this research is to screen high oil content microalgae in Nanchang municipal wastewater and explore the feasibility of utilizing Nanchang municipal wastewater and biomass fermentation slurry to mass culture microalgae for biofuel production, and the main accomplishment are as following: 1. This paper selected Nanchang QingShanhu municipal sewage plant's wastewater (influent) as the research object, collected the algal samples from the wastewater at fixed-point and fixed-period during each season of the year, and preliminary identified the algae species according to their morphology under microscope after enrichment culturing. The investigation showed that there were many different algal species in the municipal wastewater in all four seasons, and most of them were freshwater general growth species. There were 41 freshwater algae species identified in Spring, which belong to 16 families in 5 phyla; 30 species of freshwater algae indentified in Summer, belong to 14 families in 4 phyla; 29 freshwater algae species identified in Fall, belong to 12 families in 3 phyla; and 44 freshwater algae species identified in Winter, belong to 22 families in 6 phyla. Chlorophyta, Cyanophyta, and Bacillariophyta are the dominant species in the wastewater during all four seasons. During the four seasons, Chlorophyta species has the most changes in phyla and the numbers, the second is Cyanophyta in phyla or Bacillariophyta in total numbers, while the rest of the species did not change much. The investigation aslo showed that Helotism was the common existing form of baacteria in the wastewater, and the dominating algae species in Helotism were Jaaginema pseudogeminatum,Leptolyngbya vaideriana, Microcystis flos-aquae, Chlorococcum in fusionum, Oocystis solitaria, Scenedesmus obliquus, Scenedesmus dimorphus and the primary fungi were Rhodotorula auranliaca (Saito)Lodder, Candida albicans(Robin) Berkhout, Geotrichum candidum LK.ex pers., Trichoderma viride pers.ex Fr.2. This study analysed the characteristics of Nanchang QingShanhu sewage plant municipal wastewater (influent) and after comparing with BG11 medium, it was found that the NanChang municipal wastewater had a higher content of NH4+-N, but less content of TN, TP, and the N/P ratio was also unbalance and the microelements like Co2+, Mo6+, Mn2+, B3+are lacking. The experiment utilized the municipal wastewater as the culture medium for Chlorella vulgaris and monitored the specific growth rate and the biomass yield of Chlorella vulgaris and the associated sewage treatment effects during the 10 day culturing. The experimental results showed that the growth rate of Chlorella vulgaris reached a maximum of OD680nm 2.856 after 8 days culturing and the algae biomass accumulation reached a maximum of 0.0100 g.L-1.day-1(dw). The oil content of Chlorella vulgaris was 180 mg g-1 in dry biomass weight and the average daily oil production rate was 0.0010 g.L-1.day-1. The removal rate of NH4+-N, TP, and COD was 0.6123 mg.L-1.day-1,0.0540 mg.L-1.day-1, and 2.6387 mg.L-1.day-1. The TSS and VSS removal rates were 0.0100mg.L-1.day-1 and 0.0061mg.L-1.day-1 respectively. The investigation showed that the NanChang municipal wastewater can't efficiently support the large-scale microalgae production.3. The biomass fermentation slurry was produced by with anaerobic digestion of duckweed and the characteristics of the slurry were systematicly analysed. The experiment utilized the mixing medium of duckweed fermentation slurry and BG11 as Helotism and Chlorella vulgaris'culture medium and monitored the specific growth rate and biomass yield of Helotism and Chlorella vulgaris and associated nutrients removal in the mixing mediums with different mixing rate. The study showed that compared with BG11 medium, the duckweed fermentation slurry had higher content of NH4+-N and TP, but less TN, and the ratio of N/P was unbalance, also lacked microelements of Co2+, Mo6+, Zn2+, Cu2+, and B3+. When Helotism and Chlorella vulgaris cultivating under three different culture conditions, the removal rate of NH4+-N, TP, COD and the productivity of biomass, oil under normal phototrophic condition were significantly higer than the conditions of adding composite antibiotic and under completely dark condition. There was a syngestic co-growth effect between algae and fungi. Under normal phototrophic condition, fermentation slurry:BG 11=1:1 culture medium had the highest daily algae biomass and oil accumulation rate during 9 day culturing, and they were 0.2456 g.L"1 and 0.0733g.L-1, and the NH4+-N, TP, and COD removal rates were 3.3789mg.L-1.day-1, 0.6422mg.L-1.day-1,91.9600 mg.L-1.day-1, respectively. The total daily biomass productivity and oil content were 0.2567g.L-1(dw),26.80%, respectively. Algae and fungi intergrowth may have the breakthrough potentials of utilizing the organic suspended solids.4. The effect of adding glucose on algae biomass yield, oil productivity, and the corresponding sewage treatment situation when utilized Nanchang municipal wastewater, and the microelements eriched municipal wastewater on cultivate Chlorella vulgaris under mixoterotrophic condition were also studied. The investigation showed that under mixoterotrophic condition, the most favorable culture medium for Chlorella vulgaris was the microelements enriched medium of adding glucose after 3 days according to the growth rate and maximal biomass of Chlorella vulgaris cultivating in 8 different mediums, and the maximal specific growth rate, maximal biomass of Chlorella vulgaris were 0.1777 g.L-1,1.6033 g.L-1, respectively and both happened after cultivating 6 days. During 10 days culturing, the daily average algae biomass and oil accumulation rates, the NH4+-N, TP, and COD removal rates with this medium were up to 0.0836 g.L-1,0.0376 g.L-1,71.35%, 58.09%, and 58.14%, respectively, and its total biomass productivity and oil content were 0.0876 g.L-1 (dw) and 31.86%, respectively. |
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