Nagamany Nirmalakhandan

Optimization of direct conversion of wet algae to biodiesel under supercritical methanol conditions.

This study demonstrated a one-step process for direct liquefaction and conversion of wet algal biomass containing about 90% of water to biodiesel under supercritical methanol conditions. This one-step process enables simultaneous extraction and transesterification of wet algal biomass. The process conditions are milder than those required for pyrolysis and prevent the formation of by-products. In the proposed process, fatty acid methyl esters (FAMEs) can be produced from polar phospholipids, free fatty acids, and triglycerides. A response surface methodology (RSM) was used to analyze the influence of the three process variables, namely, the wet algae to methanol (wt./vol.) ratio, the reaction temperature, and the reaction time, on the FAMEs conversion. Algal biodiesel samples were analyzed by ATR-FTIR and GC-MS. Based on the experimental analysis and RSM study, optimal conditions for this process are reported as: wet algae to methanol (wt./vol.) ratio of around 1:9, reaction temperature and time of about 255 °C, and 25 min respectively. This single-step process can potentially be an energy efficient and economical route for algal biodiesel production.

Performance evaluation of an activated sludge system for removing petroleum hydrocarbons from oilfield produced water

Abstract During crude oil and natural gas exploration and production, large volumes of petroleum hydrocarbon containing ‘produced water’ are concurrently recovered. Produced water is the largest volume waste stream in the exploration and production processes of oil and gas. During onshore oil recovery, the petroleum hydrocarbon/water mixture is processed through various separation units where the water extract is either discharged into above ground storage facilities, or re-injected into a subsurface formation as a permanent disposal/secondary recovery process. In offshore or coastal oil recovery operations, produced water is either discharged through shore side outfalls or coastal rim releases (within 4 miles from shore). In many cases, current disposal practices such as these have caused severe environmental petroleum hydrocarbon contamination to surface, ground and coastal waterways. Therefore, a research project was conducted to evaluate the performance of a field (continuous-flow) activated sludge treatment system for removing petroleum hydrocarbons from Southwestern US oilfield generated produced water. Petroleum hydrocarbon removal efficiencies were determined using gas chromatography/mass spectrometry (GC/MS) and total petroleum hydrocarbon (TPH) analysis. The activated sludge treatment unit maintained a TPH removal efficiency of 98–99% at a solids retention time (SRT) of 20 days and a mixed liquor suspended solids concentration (MLSS) of 730 mg/l. Incurred energy costs were

Optimization of microwave-assisted transesterification of dry algal biomass using response surface methodology

0.17 per barrel (or

Prediction of aqueous solubility of organic chemicals based on molecular structure

0.004 per gallon) of produced water treated.

Microwave energy potential for biodiesel production

The effect of microwave irradiation on the simultaneous extraction and transesterification (in situ transesterification) of dry algal biomass to biodiesel was investigated. A high degree of oil/lipid extraction from dry algal biomass and an efficient conversion of the oils/lipids to biodiesel were demonstrated in a set of well-designed experimental runs. A response surface methodology (RSM) was used to analyze the influence of the process variables (dry algae to methanol (wt/vol) ratio, catalyst concentration, and reaction time) on the fatty acid methyl ester conversion. Based on the experimental results and RSM analysis, the optimal conditions for this process were determined as: dry algae to methanol (wt/vol) ratio of around 1:12, catalyst concentration about 2 wt.%, and reaction time of 4 min. The algal biodiesel samples were analyzed with GC-MS and thin layer chromatography (TLC) methods. Transmission electron microscopy (TEM) images of the algal biomass samples before and after the extraction/transesterification reaction are also presented.

Toxicity of mixtures of organic chemicals to microorganisms

Correlations for aqueous solubility of a range of 200 environmentally relevant chemicals are derived from molecular connectivity indexes and a polarizability factor, calculated solely from molecular structure. The quality and reliability of the correlations are shown to be high enough for environmental applications, even with the minimum number of variables in the equations and without excluding any data to improve the correlations. The robustness and validity of these correlations are demonstrated by use of appropriate statistical techniques. A generalized predictive equation for aqueous solubility is recommended, which employs easily calculable molecular descriptors.

Feasibility of microalgal cultivation in a pilot-scale airlift-driven raceway reactor.

Microwave energy based chemical synthesis has several merits and is important from both scientific and engineering standpoints. Microwaves have been applied in numerous inorganic and organic chemical syntheses; perhaps, from the time their ability to work as heat source was discovered. Recent laboratory scale microwave applications in biodiesel production proved the potential of the technology to achieve superior results over conventional techniques. Short reaction time, cleaner reaction products, and reduced separation-purification times are the key observations reported by many researchers. Energy utilization and specific energy requirements for microwave based biodiesel synthesis are reportedly better than conventional techniques. Microwaves can be very well utilized in feedstock preparation, extraction and transesterification stages of the biodiesel production process. Although microwave technology has advanced in other food, pharmaceutical and polymer chemistry related research and industry, it has yet to prove its potential in the biodiesel industry at large scale applications. This paper reviews principles and practices of microwave energy technology as applied in biodiesel feedstock preparation and processing. Analysis of laboratory scale studies, potential design and operation challenges for developing large scale biodiesel production systems are discussed in detail.

Use of QSAR models in predicting joint effects in multi-component mixtures of organic chemicals

Abstract Approaches developed by toxicologists in analyzing joint effects of two or more chemicals on fish were used to analyze and predict joint effects on microorganisms. Based on the results, the joint toxic effects of the 50 chemicals tested in this study can be considered simply additive. A quantitative structure-activity relationship (QSAR) technique is proposed for predicting the concentrations of the components of a mixture that would cause 50% inhibition by joint action. The concentrations predicted by the proposed QSAR method are shown to agree well with those experimentally measured with r2 = 0.8 at a level of significance, P = 0.0001.

PREDICTING HENRY'S LAW CONSTANT AND THE EFFECT OF' TEMPERATURE ON HENRY'S LAW CONSTANT

A Scenedesmus sp. was cultivated in a 23-L airlift-driven raceway reactor under artificial lighting and laboratory conditions, in batch and continuous modes. In batch mode, a maximum volumetric biomass productivity of 0.085 dry g L(-1) day(-1) was achieved under sparging at a CO(2)-to-air ratio of 1%, and a maximum CO(2) utilization efficiency of 33% was achieved at a CO(2)-to-air ratio of 0.25%. In continuous mode, the maximum volumetric biomass productivity was 0.19 dry g L(-1) day(-1). Biomass productivities per unit power input achieved in this reactor configuration (0.60-0.69 dry g W(-1) day(-1)) were comparable to or better than those reported in the literature for different photobioreactor designs (0.10-0.51 dry g W(-1) day(-1)). Based on the energy-efficient productivity and the high CO(2) utilization efficiency demonstrated in this study, the proposed airlift-driven raceway design holds promise for cost-effective algal cultivation.

Comparison of predictive methods for Henrys Law Coefficients of organic chemicals

The application of Quantitative Structure Activity Relationship (QSAR) models in predicting joint toxicity of mixtures of organic chemicals to microorganisms is presented. In the proposed approach, QSAR models derived from single chemical toxicity assays are used to predict concentrations of components in mixtures that would jointly cause 50% inhibition of microbial respiration. Experimental joint toxicity data from several different binary and multi-component, uniform and non-uniform mixture assays on two microbial cultures are used to validate the proposed approach. The predictions made from QSAR models agreed well with the experimental data with r2=0.80 at p=0.0001 for a total of 610 data points. The factor of error of the predictions ranged from 1.00 to 4.79, averaging 1.82. Validation tests with 16 chemicals not used in the QSAR model derivation yielded predictions of similar quality.