Exhaustive Recycling Of The Wastes From Microbial Lipid Producing And Processing With Rhodosproridium Toruloides

The production of microbial lipids will generate major wastes including spent cell mass (SCM), waste water and crude glycerol. It is pivatol to develop technologies for efficient recycling these wastes in order to improve the techno-economics of microbial lipid technology and reduce the risks of resource wasting and environmental pollution. In this dissertation, I focus on developing strategies to utilize the wastes of microbial lipid production by the oleaginous yeast Rhodosporidium toruloides.First, lipid-rich R. toruloides cells were prepared with the fed-batch fermentation stategy. The cells were grinded, extracted by petroleum ether to obtain microbial lipids and SCM. Then, the SCM was subjected to elemental and nutritional compostion analysis, which showed that the carbon, nitrogen, were 47.8%and 3.6%, crude fat and crude protein were 15.5%and 22.5%, respectively. Compositional analysis indicated that the SCM is nutritious for microbial cell growth.Second, R. toruloides, Lipomyces starkeyi, Trichosporon cutaneum and Cryptococcus curvatus were cultivated under nitrogen limited conditions to investigate their capacity of lipid accumulation with glucose, mannose or mixtures of the two as the carbon source. It was found that L. starkeyi can utilize glucose and mannose simultaneously for lipid production. When cultivated in the hydrolysates of spent R. toruloides cell mass, L. starkeyi cells maintained the feature of simultaneous utilization glucose and mannose. This provides a new strategy for exploration of glucose and manose rich materials. R. toruloides achieved a better lipid yield of 0.2 g/g and possess the capacity of synthesizing carotenoids up to 200 μg/g DCW.Third, the SCM hydrolysates (SCH) was found equivalent to the YEPD medium to support cell growth of oleaginous yeasts. The SCH was also explored as nutrients resource in the cultures to convert glucose or corn stalk hydrolysates into lipids. The results showed that lipid and nitrogen recovery yields dropped about 23%and 24%from cycle 1 to cycle 3, indicating that there was nutrients loss in the semi-closed recycling (SCR) mode using glucose as the carbon source. The lipid and nitrogen recovery yields remained stable when the corn stalk hydrolysates applied in the SCR mode, indicated that the nutritions reached a balance. However, the carotenoids content were all below 200 μg/g DCW. For the closed recycling mode, the nutrients in the supernatants were recycled and the water recycling rate was 90%each cycle. The results showed that lipd and nitrogen recovery yields varied within 5%.The two-stage fermentation pattern was conducted to study the effects of inoculation, cultivation time, glycerol concentration, pH, inorganic salts and methanol on lipid and carotenoids production by R. toruloides using glycerol as the carbon source. Lipid yields were obtained up to 0.22 g/g, at least 15% higher than the reported data, indicating that glycerol is a carbon souce comparable to glucose. The carotenoids content were below 200 μg/g DCW.Finally, preliminary analysis of the benefits of recycling the wastes of microbial lipid technology showed that there are major positive impacts in terms of techno-economics and environmental concerns.