Sharif Digital Repository

The current study is an attempt to contribute for efficient and cost-effective substrates for xanthan gum production. In this context, the sugar cane molasses wastes can be used as a cheap substrate for xanthan gum production. Xanthan biopolymer production by a novel Xanthomonas campestris strain IBRC-M 10644 was optimized with statistical approaches. Based on the results of Response Surface Methodology (RSM) with Central Composite Design (CCD) technique, a second-order polynomial model was developed and evaluated the effects of variables on the maximum xanthan production. Agitation rate (X1: 200-500 rpm), sugar cane molasses concentration (X2: 30-90 g/L) and operation temperature (X3: 25-35... 

The present study was undertaken to investigate a kinetic model for cell growth evaluation and biopolymer production by Xanthomonas campestris in a laboratory-scale batch fermentor. The optimum conditions selected for biopolymer production were 30 °C for media temperature, 500 rpm for agitation rate, 65 g/l for sugarcane concentration and 1.5 vvm for air flow rate. A detailed, unstructured, mathematical kinetic model is presented here for batch production of xanthan biopolymer from X. campestris. Set of ordinary differential equations were developed as logistic model for X. campestris growth and logistic incorporated Luedeking–Piret model for xanthan production. These models would offer more... 

The aim of this research work was to decolorize anaerobically digested (UASB) and aerobically treated distillery wastewater of a process for ethanol production. An Aspergillus species isolated from the soil was used for decolorization. A sequential Plackett-Burman design in three stages was used for optimization of decolorization conditions. Both maximum decolorization and COD reduction under optimized conditions were obtained as 84%. By implementing the optimum values in a pilot scale of an activated sludge system a continuous process for decolorization was conducted. The decolorization efficiency of this system with 48 h retention time was about 75% in a limited period of 4 days. For... 

Nanofluid is the term applied to a suspension of solid, nanometer-sized particles in conventional fluids; the most prominent features of such fluids include enhanced heat characteristics, such as convective heat transfer coefficient, in comparison to the base fluid without considerable alterations in physical and chemical properties. In this study, nanofluids of aluminum oxide and copper oxide were prepared in ethylene glycol separately. The effect of forced convective heat transfer coefficient in turbulent flow was calculated using a double pipe and plate heat exchangers. Furthermore, we calculated the forced convective heat transfer coefficient of the nanofluids using theoretical... 

Refineries are amongst the most energy-intensive and polluting industries in the world. Biotechnology may serve as an alternative low-cost and environmental-friendly tool to the current costly, toxic and hazardous refining processes. In this study, the compositional redistribution of a heavy hydrocarbon cut is investigated under biological conversion using native microbial consortia. The native consortia were obtained by batch enrichment method applied on oil-polluted soil samples from oil refineries of Iran. The bioconversion experiments were conducted with 20% and 40% (v/v) of the heavy cut as the sole carbon source and 10% (v/v) of the consortia broth in 250 ml flasks containing a mineral...