Comparison of Lactic Acid Productivities at High Substrate Conversions in a Continuous Two-stage Fermenter With Cell Recycle Using Different Kinetic Models

The steady-state performance of a two-stage recycle fermenter with two different types (I and II) of configurations for staging was investigated numerically for the continuous production of lactic acid. In Type I the bleed broth withdrawn from the first stage is supplied to the second fermenter, and in Type II both filtrate and bleed broth from the first stage are introduced to the second stage. Using four different kinetic models taken from the literature, the effects of operating parameters on the overall lactic acid productivities and the overall substrate conversions are examined. At moderate conversions, productivities for Type I operation are found to be higher than those for Type II and for the single-stage system. In the case of high conversions close to complete consumption, Type II operation is more efficient than the Type I and single-stage systems. For 99% conversion and 40 kg m^-3 substrate feed concentration, productivities for Type II are predicted to be 14-74% higher compared to those for the single-stage system at the same bleed ratios.     

高温季节食醋生产中影响酒精发酵的因素及改进措施

该文以镇江香醋生产为例，分析了高温季节食醋生产过程中影响酒精发酵的因素，并提出了改进措施。     

Impact of the addition of an enzyme pool on an activated sludge system treating dairy wastewater under fat shock loads

BACKGROUND: The application of lipase‐rich enzyme pools (such as the crude solid enzymatic preparation (SEP) obtained from Penicillium restrictum solid‐state fermentation of agro‐industrial wastes) to activated sludge systems may be an effective strategy for preventing various operational problems. The continuous addition of SEP to the treatment system can become cost‐prohibitive when in situ production and/or storage are factored in. The application of SEP to high‐fat wastewater treatment would only be justified as an emergency measure, such as a sudden increase in the fat content of the bioreactor influent. Therefore, the primary objective of this work was to investigate the efficiency of a crude SEP during fat shock loads, simulated through the periodic addition of dairy industry waste containing high fat concentrations to the feed stock of an activated sludge system, operated in continuous mode. RESULTS: The test bioreactor exhibited a higher average chemical oxygen demand (COD) removal efficiency than the control bioreactor (83% for control and 90% for test) and the fat accumulation in the biological flocs of the test bioreactor was 3.2 times lower than that in the control bioreactor. Turbidity was also lower in the effluent of the test bioreactor (123 and 66 FTU in control and test, respectively) and it had a shorter recovery time between shock loads, especially when the interval between loads was shorter than one month (biweekly and weekly shock loads). CONCLUSION: The addition of SEP during fat overloads in the reactor feed maintained efficient COD removal in the test bioreactor for 270 days without any operational problems. Copyright © 2008 Society of Chemical Industry     

L-乳酸和聚乳酸的研究进展

综述了乳酸发酵和提取工艺以及聚乳酸的合成进展,分析了L-乳酸及合成聚乳酸两种产品的市场前景,对进一步的技术开发提出了建议。     

城市生活垃圾能源利用探讨

报道了城市有机废弃物转化为能源的几种途径。在管式反应器内甘蔗渣裂解气化制煤气以及在高压釜内湿式裂解气化制煤气液体产品，可得到中值煤气。也研究了甘蔗渣二步法糖化和糖发酵，当ＰＨ为３．６，酵母浓度为１．３３％，乙醇产率可达理论值的６４．８６％。     

KCl与NaCl在低盐固态法酱油发酵中的应用比较

对KCl与NaCl在低盐固态酱油发酵中的应用进行了比较研究。结果表明：用KCl代替NaCl，KCl的浓度要高于NaCl才能抑制发酵期间杂茵的污染，且使用KCl的发酵效果比NaCl要好。     

Acidogenic fermentation of blended food‐waste in combination with primary sludge for the production of volatile fatty acids

The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm^?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm^?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO₂ and CH₄), the organic matter was converted into CO₂ through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFA_produced g^?1 VS_fed day^?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry     

The Use of Biopreservatives in the Control of Bacterial Contaminants of Sugarcane Alcohol Fermentation

ABSTRACT: Efficacy and safety of biopreservatives were studied for microbiological control of alcohol fermentation. Minimum inhibitory concentrations of nisin and lysozyme, and combinations with EDTA and Tween 20, were determined for Lactobacillus plantarum, L. fermentum , and L. confusus. The highest MIC value for nisin was 9.0 ppm for L. fermentum. Lysozyme was efficient against L. plantarum (700 ppm). A 2⁴ factorial design was used to study the effect of biopreservatives and potentiators on the growth kinetics of Lactobacillus fermentum. The combination of 8.6 ppm of nisin plus 0.1% of Tween 20 delayed the lag phase by 12 h. The biopreservatives did not affect the fermentation kinetics of Saccharomyces cerevisiae.     

Cassava retting: Optimisation of a traditional fermentation by an experimental research methodology

Retting, a spontaneous and traditional fermentation of cassava roots in Central Africa, was optimised in terms of time and the quality of the end-product. Optimal conditions were achieved by using an experimental research methodology. Temperature is the most influential factor, with an optimum of 34°C for quicker retting. The roots should be peeled and soaked in water immediately after harvesting to increase the quality of cassava foods. Inoculation of water with juice from a prior retting helps in cassava detoxification but has no influence on the time or the quality of foo-foo. Foo-foo samples had the most favourable organoleptic quality when an incubation temperature of between 28 and 37°C was used. Using optimal conditions, retting time was reduced 3-fold, and foo-foo of high and constant quality could be processed.