Microbial fuel cells for sulfide removal

Thus far, microbial fuel cells (MFCs) have been used to convert carbon-based substrates to electricity. However, sulfur compounds are ubiquitously present in organic waste and wastewater. In this study, a MFC with a hexacyanoferrate cathodic electrolyte was used to convert dissolved sulfide to elemental sulfur. Two types of MFCs were used, a square type closed to the air and a tubular type in which the cathode compartment was open to the air. The square-type MFCs demonstrated a potential-dependent conversion of sulfide to sulfur. In the tubular system, up to 514 mg sulfide L(-1) net anodic compartment (NAC) day(-1) (241 mg L(-1) day(-1) total anodic compartment, TAC) was removed. The sulfide oxidation in the anodic compartment resulted in electricity generation with power outputs up to 101 mW L(-1) NAC (47 W m(-3) TAC). Microbial fuel cells were coupled to an anaerobic upflow anaerobic sludge blanket reactor, providing total removals of up to 98% and 46% of the sulfide and acetate, respectively. The MFCs were capable of simultaneously removing sulfate via sulfide. This demonstrates that digester effluents can be polished by a MFC for both residual carbon and sulfur compounds. The recovery of electrons from sulfides implies a recovery of energy otherwise lost in the methane digester.     

Microbial fuel cells generating electricity from rhizodeposits of rice plants

Living plants transport substantial amounts of organic material into the soil. This process, called rhizodeposition, provides the substrate for the rhizospheric microbial community. In this study, a laboratory-scale sediment microbial fuel cell, of which the anode is positioned in the rhizosphere of the rice plants, is used to microbially oxidize the plant-derived organics. An electrical current was generated through the in situ oxidation of rhizodeposits from living rice plants. The electrical power output of a sediment microbial fuel cell was found to be a factor 7 higher in the presence of actively growing plants. This process offers the potential of light-driven power generation from living plants in a nondestructive way. Sustainable power productions up to 330 W ha(-1) could be attributed to the oxidation of the plant-derived compounds.     

微生物发酵竹香鸡加工技术

研究了利用微生物发酵技术,添加益生菌生长促进剂加工竹香鸡的加工工艺和技术要点。     

Microbial ecology and starter culture technology in coffee processing

Coffee has been for decades the most commercialized food product and most widely consumed beverage in the world, with over 600 billion cups served per year. Before coffee cherries can be traded and processed into a final industrial product, they have to undergo postharvest processing on farms, which have a direct impact on the cost and quality of a coffee. Three different methods can be used for transforming the coffee cherries into beans, known as wet, dry, and semi-dry methods. In all these processing methods, a spontaneous fermentation is carried out in order to eliminate any mucilage still stuck to the beans and helps improve beverage flavor by microbial metabolites. The microorganisms responsible for the fermentation (e.g., yeasts and lactic acid bacteria) can play a number of roles, such as degradation of mucilage (pectinolytic activity), inhibition of mycotoxin-producing fungi growth, and production of flavor-active components. The use of starter cultures (mainly yeast strains) has emerged in recent years as a promising alternative to control the fermentation process and to promote quality development of coffee product. However, scarce information is still available about the effects of controlled starter cultures in coffee fermentation performance and bean quality, making it impossible to use this technology in actual field conditions. A broader knowledge about the ecology, biochemistry, and molecular biology could facilitate the understanding and application of starter cultures for coffee fermentation process. This review provides a comprehensive coverage of these issues, while pointing out new directions for exploiting starter cultures in coffee processing.     

Hurdle technology for minimally processed radishes: a response surface methodology approach

Response surface methodology was used to determine the optimum processing conditions that yielded maximum vitamin C content, minimum discoloration and minimum polyphenoloxidase activity after 4 days of refrigerated storage of minimally processed radishes. Ascorbic acid (0–2 %), sodium chloride (0–1 %) and immersion time (0–2 min) at 50 °C were the factors investigated related to polyphenoloxidase activity (PPO), vitamin C (VITC) and total color difference (ΔE). Experiments were conducted according to a Box-Behnken Design with three factors at three different levels. For each response, second order polynomial models were developed using multiple linear regression analysis. Analysis of variance (ANOVA) was performed to check the adequacy and accuracy of the fitted models. The response surfaces showing the interaction of process variables were constructed and analyzed. Based on desirability function, optimum operating conditions were found to be 2 % of ascorbic acid, 0 % of NaCl and 1.5 min of immersion time at 50 °C. At this optimum point, relative PPO activity, relative VITC content and ΔE values were 0.218, 3.227 and 4.929, respectively.     

浅谈燃料乙醇生产技术进展

简述了燃料乙醇－作为一种可再生能源，它可减少环境的污染，被称为“清洁燃料”及它在国外的使用情况；并重点介绍了燃料乙醇的几种生产技术方法。     

Scaling up microbial fuel cells

The goal of this study was to quantify the relation between the surface area of the current-limiting electrode of a microbial fuel cell (MFC) and the power density generated by the MFC. Shewanella oneidensis (MR-1) was grown anaerobically in the anodic compartment of an MFC utilizing lactate as the electron donor. Graphite plate electrodes of various sizes were used as anodes. Commercially available air electrodes, composed of manganese-based catalyzed carbon bonded to a current-collecting screen made of platinum mesh, were used as cathodes, and dissolved oxygen was used as the cathodic reactant. The surface area of the cathode was always significantly larger than that of the anode, to ensure that the anode was the current-limiting electrode. The power density generated by the MFC decreased as the surface area of the anode increased, which fits well with the trend we detected comparing various published results. Thus, our findings bring into question the assertion that the overall power density generated by an MFC with large electrodes can be estimated by extrapolating from an electrode with a small surface area. Our results indicate that the maximum power density generated by an MFC is not directly proportional to the surface area of the anode, but is instead proportional to the logarithm of the surface area of the anode.