A lab scale externally illuminated photobioreactor was used to evaluate the lipid productivity (LP) of microalga Chlorella protothecoides (SAG-211-10C) cultivated in municipal secondary waste water supplemented with CO2. Experiments were conducted in two stages: growth phase (GP) and nitrogen starvation phase (NSP). The influence of five environmental factors (light intensity [LI], photoperiod, temperature, concentration of CO2, pH) on LP of Chlorella protothecoides under both phases was studied and the parameters were individually optimized. Under optimum operating conditions in GP (LI 6 klux, photoperiod 12 h:12 h, temperature 25°C, 6% concentration of CO2), the total nitrogen was completely consumed after 8 days of operation and highest LP of 64.7 mg/(L.day) was obtained. This value was further enhanced to 106.65 mg/(L.day) by operating the photobioreactor in NSP under its optimum conditions (LI of 4 klux, photoperiod of 16 h:8 h, temperature 25°C, pH 8, 4% concentration of CO2). Under optimum operating conditions, removal efficiency of total phosphorous and Chemical Oxygen Demand were 100 and 70.19%, respectively, and highest carbon fixation rate of 549.16 mg CO2/(L.day) was observed.
In the design of chemical equipments, thermodynamic properties of pure forms and mixtures are very important. For the systems selected, the experimental works were carried out in two phases - experiments of enthalpy of mixing, and heats of vaporization were conducted. From the various designs available for the experimental determination of enthalpy of mixing, the apparatus described by Tanaka et al. (1972), Patel (1974) and Nirguna Babu (2003), was selected, modified and fabricated. Experiments were conducted in the equipments designed for the mixtures of Ethyl alcohol with n-Hexane and n-Heptane. Data on heats of vaporization were obtained by using a static apparatus similar to the one used by Rao and Viswanath (1973). The apparatus selected was modified, fabricated and tested for accuracy. Experiments were conducted for the mixtures of Ethyl Alcohol with n-Hexane and n-Heptane.
The present work was carried out in two phases. First, enthalpy of mixing was measured and then the heat of vaporization for the same mixtures was obtained. The data are useful in the design of separation equipments. From the various designs available for the experimental determination of enthalpy of mixing, and heat of vaporization, the apparatus was selected, modified and constructed. The apparatus of enthalpy of mixing was tested with a known system Benzene - i-Butyl Alcohol and the data obtained was in very good agreement with literature values. Experiments were then conducted for mixtures of Ethyl Acetate with Benzene and Toluene. The experimental data was fitted to the standard correlations and the constants were evaluated. Heat of vaporization data were obtained from a static apparatus and tested for accuracy by conducting experiments with a known system Benzene - n-Hexane and the data obtained were found to be in agreement with literature values. Experiments were then conducted to measure heat of vaporization for the mixtures of Ethyl Acetate with Benzene and Toluene. Using experimental data of enthalpy of mixing from the first phase, and heat capacity data, the heat of vaporization were calculated.
In the present study, 100% centrate (wastewater generated in the sludge centrifuge of a municipal wastewater treatment plant) was used for the cultivation of microalga Nannochloropsis oculata in a lab scale externally illuminated photobioreactor. Cells were harvested at the end of the exponential phase and the resulting wet algal biomass (80 wt % moisture) was subjected to direct saponification in a low-cost microwave reactor using ethanolic KOH to convert the algal lipids to soap. The soap was separated from other unsaponifiable matter by precipitation using saturated KCl and subjected to simultaneous acidulation and esterification to form biodiesel of high purity (97.04% FAME in final biodiesel). Optimum values of esterification of fatty acids in microwave reactor were: microwave power-450 W, molar ratio of methanol to fatty acids -80:1, concentration of sulphuric acid-2.5 wt %, reaction time-11 min and reaction temperature-60 °C. Kinetics studies of esterification conducted under these conditions revealed that the rate constant was high (0.452 min−1). The final yield of biodiesel was 97.11%. Cetane number and oxidation stability index of biodiesel were evaluated to be 59.349 and 3.298 h respectively. Removal rates of Chemical oxygen demand (COD), total nitrogen and total phosphorous were 82.65%, 62.25% and 52.65% respectively.
In the present work, a lab scale photobioreactor was used to evaluate lipid productivity and carbon dioxide fixation rate of microalgae Chlorella protothecoides under nitrogen deplete conditions. Effect of environmental conditions such as pH, temperature, light intensity, photoperiod (light to dark cycle ratio), CO2 concentration in air and aeration rate on lipid productivity and carbon fixation rate of microalga was studied. Response surface methodology was adopted to optimize these conditions. All the parameters were found to be statistically significant. Best operating conditions were evaluated to be: pH-6.51, Temperature-28.63 °C, light intensity-5.31 klux, Photoperiod-15.36 h:8.64 h, CO2 concentration in air-6.26% (v/v), Aeration rate −2.92 lpm. Lipid productivity under these conditions was found to be 274.15 mg/(L day) which was 3.94 times higher than the value obtained in N+ experiment (69.46 mg/(L day)). Carbon fixation rates under N+ and N− conditions were 286.12 and 273.66 mg/(L day) respectively.
In the present study, the non living biomass of cyanobacteria Spirulina platensis was used for biosorption of Zn +2 in column mode. Polyurethane foam (PUF) cubes were used for immobilizing the biosorbent. A maximum biomass loading of 0.2 g dry S. platensis /(g of PUF cubes) could be achieved. The effect of parameters (such as pH of feed solution, flow rate of feed solution to column, bed height and initial concentration of metal ion in feed solution )on uptake capacity of biosorbent was studied. A maximum uptake capacity of 87.3 mg Zn +2 /(g S. platensis) was observed under optimum conditions. The column was regenerated using 0.1 M HCl and sorption-desorption studies were carried out for four cycles. Both % removal of Zn +2 and uptake capacity of biosorbent were found to progressively decrease with increase in the number of cycles. The biomass was characterized by Fourier transform infrared Spectroscopy (FTIR) and Scanning Electronic Microscopic (SEM) images before and after biosorption.
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