Optimization of media composition for the production of biohydrogen from waste glycerol

Enterobacter aerogenes has a known ability to convert glycerol during a fermentative process to yield hydrogen and ethanol as the main products. A Box-Behnken design and response surface methodology were used to determine the optimal concentration of some media constituents and oxygen to maximize the yield of biohydrogen. Results indicated that the concentration of the salts studied: NH₄NO₃, FeSO₄, and Na₂HPO₄ and; the presence of oxygen in the pre-culture significantly influence the production of biohydrogen. Optimal conditions were determined to be 7.5% O₂ in the inoculum transfer step, ratio of inocula 18%, 8 g/L of Na₂HPO₄, 0.00625 g/L of FeSO₄ and 1.5 g/L of NH₄NO₃. These optimal conditions resulted in a measured yield of 0.85 mol H₂/mol glycerol at a substrate concentration of 15 g/L and a maximum predicted yield of 0.95 mol H₂/mol glycerol at a substrate concentration of 21 g/L. These results were obtained using lower concentrations of salts than in previous studies, corresponding to a 76% cost savings. These experimental results also demonstrated the importance of optimizing the amount of oxygen present in the biological system rather than maintaining complete anaerobic conditions.     

Adsorption of Reactive Red 141 from wastewater onto modified chitin

This research involved the adsorption of synthetic reactive dye wastewater (SRDW) by chitin modified by sodium hypochlorite and original chitin in batch experiments. The comparison of maximum adsorption capacity used the Langmuir model to describe SRDW adsorption onto chitin and modified chitin under a system pH of 11.0. Maximum dye adsorption by chitin increased from 133mgg(-1) to 167mgg(-1) at temperatures of 30-60 degrees C, respectively. For modified chitin, the capacity decreased from 124mgg(-1) to 59mgg(-1) when the temperature increased from 30 degrees C to 60 degrees C, respectively. Both Na(2)SO(4) and Na(2)CO(3) increased in dye adsorption. The spectra of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometry confirmed the hydroxyl groups as functional groups of modified chitin, which affected the modification and the SRDW adsorption. The adsorbed dyes were eluted by distilled water and 1M NaOH to confirm the dye adsorption mechanism. Total elution of modified chitin and chitin were 92.76% and 55.29%, respectively. Although modified chitin had a maximum adsorption capacity less than chitin, elution of the dye from modified chitin was easier than chitin. Therefore, modified chitin could be suitable in a column system for dye pre-concentration as well as wastewater minimisation. In addition, the column study showed that modified chitin could be used for more than four cycles of adsorption and elution by distilled water.     

Biohydrogen and Bioethanol Production from Biodiesel-Based Glycerol by Enterobacter aerogenes in a Continuous Stir Tank Reactor

Crude glycerol from the biodiesel manufacturing process is being produced in increasing quantities due to the expanding number of biodiesel plants. It has been previously shown that, in batch mode, semi-anaerobic fermentation of crude glycerol by Enterobacter aerogenes can produce biohydrogen and bioethanol simultaneously. The present study demonstrated the possible scaling-up of this process from small batches performed in small bottles to a 3.6-L continuous stir tank reactor (CSTR). Fresh feed rate, liquid recycling, pH, mixing speed, glycerol concentration, and waste recycling were optimized for biohydrogen and bioethanol production. Results confirmed that E. aerogenes uses small amounts of oxygen under semi-anaerobic conditions for growth before using oxygen from decomposable salts, mainly NH₄NO₃, under anaerobic condition to produce hydrogen and ethanol. The optimal conditions were determined to be 500 rpm, pH 6.4, 18.5 g/L crude glycerol (15 g/L glycerol) and 33% liquid recycling for a fresh feed rate of 0.44 mL/min. Using these optimized conditions, the process ran at a lower media cost than previous studies, was stable after 7 days without further inoculation and resulted in yields of 0.86 mol H₂/mol glycerol and 0.75 mol ethanol/mole glycerol.     

Interactive Effects of Ascophyllum nodosum Seaweed Extract and Silicon on Growth,Fruit Yield and Quality,and Water Productivity of Tomato under Water Stress

Silicon - Agricultural crops including tomato (Solanum lycopersicum L.) are severely affected by drought, which is a critical abiotic stress. Biostimulants, such as Ascophyllum nodosum seaweed...