Lipid production by Rhodosporidium toruloides using bioethanol wastewater-cassava starch hydrolysates

Abstract:

[Objective] This study was in order to obtain a strain of Rhodosporidium toruloides which can degrade high concentration bioethanol wastewater COD effectively and evaluate the effects of initial COD on the growth of domesticated strain. Especially, the strategy of integrating the treatment of high concentration organic wastewater and microbial lipid production from cassava starch will be explored. Cassava starch hydrolysates was prepared using bioethanol wastewater as water source to obtain a fermentation medium for lipid production. At last, the initial reducing sugar concentration of the medium was optimized for enhancing lipid production and wastewater COD degradation. [Methods] Domestication of the R. toruloides in high concentration bioethanol wastewater was carried out to obtain a strain which could tolerance bioethanol wastewater with high COD concentration; double enzyme hydrolysis method was used to hydrolyze the cassava starch added in wastewater medium; gravimetric method, acid-heating extraction, potassium dichromate method, DNS method, Kjeldahl method and GB 11893-89 were used to determine the biomass concentration, lipid content, COD, reducing sugar concentration, N and P concentration, respectively. [Results] An active oleaginous strain R. toruloides D5 was obtained by domestication in bioethanol wastewater with high COD concentration. With undiluted bioethanol wastewater as cultural medium, the biomass concentration and COD degradation ratio of R. toruloides D5 was 3.8 g/L and 75.0%, respectively; with bioethanol wastewater and cassava starch as the medium, biomass and lipid concentration increased with the initial reducing sugar concentration when it below 30 g/L, the maximum COD degradation ratios were achieved after 120 h; N, P removal ratio was more than 99% and 92%, respectively. [Conclusion] The domesticated strain grew well and reach a high biomass concentration in the bioethanol wastewater without dilution; when the initial reducing sugar concentration was controlled below 30 g/L, the COD degradation ratio did not be affected by the addition of cassava starch, meanwhile the biomass and lipid concentration increased significantly. The strategy recycled the N/P in the wastewater and reduced the cost of microbial lipid production and wastewater treatment. The results of this study could provide useful information for low-cost microbial lipid production.