Sharif Digital Repository

In this study low-grade sphalerite has been treated by the bioleaching process using native cultures of Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfido-oxidans in order to determine the ability of these bacteria to the leaching of zinc. The effects of bacterial strain, pH, temperature, pulp density, iron precipitation, and initial concentration of ferric iron on the zinc leaching were evaluated. The bioleaching experiments were carried out in shake flasks at pH 1.5, 180 rpm, 33 °C and 60 °C for mesophilic and thermophilic bacteria, respectively. Compared with the use of laboratory reference strains or control conditions, zinc recovery from the respective concentrate was... 

In water treatment processes, because of complicated and nonlinear relationships between a number of physical, chemical and operational parameters, using analytical models with the ability to capture underlying relationships using examples of the desired input-output mapping is quite suitable. Artificial Neural Networks (ANN) has been increasingly applied in the area of environmental and water resources engineering. The main advantage of Artificial Neural Networks over physical-based models is that they are data-driven. The purpose of this research is to study the performance of pressure filters on turbidity removal from water according to several parameters such as turbidity, filtration... 

The Jajrood River watershed is on of the main drinking water resurces of Tehran, the capital city of Iran. In addition it provides many recreational usages. However, a variety of microbial pollutions is commonly perecived in the Jajrood River, among them a high concentration of coliform group bacteria that has caused strong concerns. In this article, different aspects of microbial pollution as well as the main microbial pollution sources in the region are discussed. Coliform group bacterial die-off rates have been evaluated as the key parameters that govern bacterial fate in the watershed and were estimated using both laboratory and field data investigations. The high values of the bacterial... 

The effect of up velocity and influent COD concentration on the activity of sulphate-reducing bacteria (SRB) in UASB reactors is discussed. To study these effects, four UASB reactors were built and utilized in parallel. Examinations were carried out in two different concentrations of molasses (500 mg COD/l and 1000 mg COD/l) and four different upward flow velocities. It was observed that at velocities greater than 1 m/h, SRB bacteria were easily washed out from the reactors due to lower density and lack of ability to form dense and firm granules. It was found that in low-strength wastewaters with a COD to sulphate ratio of 2, an upward velocity in the range of 1.5-2.5 m/h could be... 

There is a need to find cheaper and simpler techniques for rural water filtration system in developing countries. Using a filter made of blocks for the water treatment enables one to make vertical filters. It is expected that the amount of land utilized would decrease by more than 70 % if vertical filters were used. The operation and washing would be simpler than using horizontal sand filters as filters made of blocks would be used instead. The feasibility study focused on finding adequate materials, compositions and methods of making a block with enough resistance to water pressure, sufficient porosity for water transformation, and using inexpensive, readily available materials. A pilot... 

Multi-component photocatalysts based on apatite-coated Ag/AgBr/TiO(2) were prepared by the deposition method. The effects of various kinds of apatites, with hydroxyl and fluoro substituents, on photocatalytic activity were investigated. The antibacterial processes in the dark, and under visible light, on two types of bacteria indicate that the multi-composites can inhibit the growth of bacteria by two different mechanisms. TEM images and optical microscopic data demonstrate that by attaching the nanosize catalyst to the outer membrane of the cell, the bacteria could not derive nourishment from surrounding media, i.e. this component acts as bacteria-static. The mechanism for deactivation of... 

The remarkable rotational symmetry of the photosynthetic antenna complexes of purple bacteria has long been thought to enhance their light harvesting and excitation energy transport. We study the role of symmetry by modeling hypothetical antennas whose symmetry is broken by altering the orientations of the bacteriochlorophyll pigments. We find that in both LH2 and LH1 complexes, symmetry increases energy transfer rates by enabling the cooperative, coherent process of supertransfer. The enhancement is particularly pronounced in the LH1 complex, whose natural geometry outperforms the average randomized geometry by 5.5 standard deviations, the most significant coherence-related enhancement... 

The purpose of this study is to evaluate an anaerobic system (ABR) cultured by chemoautotrophic bacteria for biodesulfurization of natural gas. In this study anaerobic baffled reactor with five compartments and active volume of 10 l was used. For increasing solid retention time, reactor was packed by pumice with 0.5-2 cm diameter which active volume decreased to 9 l. Inoculation was performed by activated sludge from municipal sewage treatment, which was kept in anaerobic condition for 1 year. The synthetic wastewater which contains S2O32- ion was used in start-up and S -2 for running of ABR. Performance of the reactor was evaluated at three equivalent hydraulic retention times (HRT) of 50,... 

The power law logistic model was utilized to investigate the growth of a hydrocarbon assimilating bacterium on a water-insoluble substrate. To achieve this end, population dynamics of Bacillus licheniformis MS3 in a medium containing n-decane as the sole carbon source was monitored for 30 h. Different initial biosurfactant concentrations and shaking rates were employed to examine the role of mass transfer in the cell growth and the consequent hydrocarbon biodegradation. The amount of n-decane degraded in the system was detected by gas chromatography at the end of the incubation period. The results revealed that when mass transfer limitations were lessened through addition of an initial... 

Optimization based on appropriate parameters can be applied to improve a process. Mazut degradation as a critical issue in environment requires optimization to be efficiently done. To provide biodegradation conditions, experiments were designed on the least interactions among levels of parameters consisting of pH, Tween 80, glucose, phosphorous source, nitrogen source, and time. Kinetic constants and biomass were calculated based on 16 assays, designed using Taguchi method, which constructed various mazut biodegradation conditions. Kinetics of mazut degradation by newly isolated bacteria Enterobacter cloacae closely followed second order kinetic model. Results of the 16 experiments showed... 

For the first time, the simultaneous effects of sulfate reducing bacteria (SRB), soil type and moisture content on corrosion behavior of a pipeline steel were investigated. Corrosion weight loss measurements were performed in abiotic control and SRB-active conditions, at three different moisture contents, and in two types of soils. Results showed that the presence of SRB in the soils, although increased the corrosion rate and aggravated pitting corrosion at low moisture contents, had a protective effect at high moisture contents. The corrosion rates showed a maximum at the saturation moisture content (SMC) of the soils. Soil physicochemical analyses showed that the corrosion rate and soil... 

The selective plugging effect of hydrophobic bacteria cell on secondary oil recovery performance was investigated. Water and aqua solution of purified Acinetobacter strain RAG-1 were injected into an oil-saturated heterogeneous micromodel porous media. Pure water injection expelled oil by 41%, while bacterial solution injection resulted in higher oil recovery efficiency (59%). In the simulation section, a smaller part of the heterogeneous geometry was applied as a computational domain. A numerical model was developed using coupled Cahn-Hilliard phase-field method and Navier-Stokes equations, solved by a finite element solver. In the non-plugging model, approximately 50% of the matrix oil was... 

The current study was undertaken to compare four analytical methods including drop collapse, oil spreading, surface tension (SFT) measurements, and blood agar lysis tests for detection of biosurfactant-producing bacteria. Among 32 biosurfactant-producing bacteria isolated from Ahvaz oil fields, in south of Iran, 16 isolates (50%) exhibited highest biosurfactant production. Eleven isolates (MASH.1 to MASH.11) demonstrated a reduction in surface tension from 65 mN/m to less than 41 mN/m. The results showed that about 91% of these highly biosurfactant producers had the same response levels of "++++" and "+++" in the case of both SFT and oil spreading methods. Among these, seven isolates had the... 

Most sulfide oxidizing bioreactors are based on pure cultures or artificial mixes of microorganisms with strict requirements for growth, which make the system unstable and do not guarantee their long term performance. The ultimate goal of this study is to develop a natural mix of chemotrophic bacteria that may be applied anaerobically for the treatment of sour gas. Activated sludge from local municipal wastewater treatment plant that was maintained in endogenous anaerobic conditions for one year was used in this study. Total suspended solids (TSS) and volatile suspended solids (VSS) of the sludge was 22 gl-1 and 14.3 gl-1, respectively. A glass culture vessel had a volume of 0.65 L was used... 

The effects of several variables on zinc recovery in column bioleaching have been investigated. The ore contained sphalerite and pyrite as the main sulfide minerals and chalcopyrite and galena as minor minerals. Tests were carried out using a bench-scale column leach reactor which was inoculated with mesophilic (Acidithiobacillus ferrooxidans) and thermophilic (Sulfobacillus) iron oxidizing bacteria; initially isolated from the Sarcheshmeh chalcopyrite concentrate (Kerman, Iran) and Kooshk sphalerite concentrate (Yazd, Iran), respectively. In the inoculated column, jarosite and elemental sulfur were formed. The leaching rate of sphalerite tended to increase with dissolved ferric ion... 

In this paper the effect of the COD/SO4 ratio on the performance of an anaerobic baffled reactor (ABR) was investigated. Synthetic wastewater (3000 mg-COD/l) was used as the sole organic substrate. ABR was maintained at a hydraulic retention time (HRT) of 1 day and at a temperature of 35 °C. The results of this study showed that when COD/SO4 ratios were changed from 16.7 to 6 with increasing sulfate concentration from 180 to 500 mg/l, COD conversion was not decreased, but a slight increase in COD removal was observed. These phenomena indicated that both methanogenic bacteria and sulfate reducing bacteria (SRB) could exist in the system as synthrophism. Maximum COD and sulfate removal were 86...