圆红冬孢酵母利用生物乙醇废水-木薯粉水解液发酵产油

【目的】获得能够高效降解生物乙醇废水化学需氧量(COD)的圆红冬孢酵母菌株，评估废水初始COD浓度对驯化菌株生长的影响，将木薯粉生产微生物油脂和高浓度有机废水降解过程整合，以生物乙醇废水为水源制备生物乙醇废水-木薯粉水解液培养基，明确产油效率高、生物乙醇废水COD降解率高的初始还原糖浓度。【方法】采用在高浓度的生物乙醇废水中进行多次驯化的方法，获得能够适应废水环境的圆红冬孢酵母菌株；采用双酶水解法对加入乙醇废水中的木薯粉进行水解；采用重量法监测生物量浓度变化，采用酸热法提取油脂，重铬酸钾法监测COD，DNS法测定废水还原糖浓度，凯氏定氮法测定总氮，钼酸铵比色法测定总磷。【结果】通过驯化筛选得到一株能耐受高浓度生物乙醇废水的优势菌株Rhodosporidium toruloides D5。以未稀释的废水为培养基，驯化菌株的最终生物量浓度和COD降解率分别为3.8 g/L和75.0%。采用生物乙醇废水-木薯粉水解液发酵时，控制初始还原糖浓度低于30 g/L时，生物量浓度和油脂浓度随初始还原糖浓度的升高而升高，均在120 h时达到最高COD降解率，初始还原糖浓度对达到的最大COD降解率无明显影响，废水N、P去除率分别达到99%和92%以上。【结论】在未经稀释的高浓度生物乙醇废水中可获得较高的生物量浓度；采用高浓度生物乙醇废水-木薯粉水解液培养基发酵产油，初始还原糖浓度为30 g/L，可在保证高油脂产量的同时，实现废水COD的高效降解，有效回收利用废水中残余的N、P源，从而降低微生物油脂生产和废水处理成本，研究结果可为开发廉价微生物油脂生产技术提供有用的参考。

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

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.