Biomedical subjects

N Nirmalakhandan

Publications and source records attributed to N Nirmalakhandan.

6 recordsLinked to original sources

PubMed2006

Anaerobic fermentation of cattle manure: modeling of hydrolysis and acidogenesis.

A mathematical model for the hydrolysis and acidogenesis reactions in anaerobic digestion of cattle manure is presented. This model is based on the premise that particulate hydrolysable fraction of cattle manure is composed of cellulose and hemicellulose that are hydrolyzed at different rates according to a surface-limiting reaction; and, that the respective soluble products of hydrolysis are utilized by acidogens at different rates, according to a two-substrate, single-biomass model. Batch experimental results were used to identify the sensitive parameters and to calibrate and validate the model. Results predicted by the model agreed well with the experimentally measured data not used in the calibration process, with correlation coefficient exceeding 0.91. These results indicate that the most significant parameter in the hydrolysis-acidogenesis phase is the hydrolysis rate constant for the cellulose fraction.

Acids↗

PubMed2004

Computer-aided tutorials and tests for use in distance learning.

Compared to the traditional on-campus students, remote students in distance education courses find it more difficult to develop problem-solving skills. In this paper, we propose the use of computer-aided tutorials and tests (CATTs) as convenient tools for remote students to practice and improve problem-solving and test taking skills at their own pace. Example of CATTs developed with Authorware software for use in distance education is presented.

Ecology↗

PubMed2001

Evaluation of an ozonation system for reduced waste sludge generation.

The ultimate disposal of biosolids has been and continues to be one of the most expensive problems faced by wastewater utilities. Previous work has shown that the waste sludge generation in an activated sludge plant can be reduced by promoting cryptic growth conditions (i.e., biomass growth on intracellular products). For this purpose, excess biosolids from a continuous flow activated sludge system were solubilized using ozone as the cell lysing agent, and then returned to the aeration tank. The results of these preliminary studies indicate that the proposed process configuration has the potential to reduce the waste sludge production by 40% to 60%. In the present research, the details of the ozonation process is further investigated to determine the maximum solubilization efficiency. For this purpose, a number of variables such as the solids concentration in the excess sludge, ozonation time, and ozonation dosage rate are studied.

Oxidants, Photochemical↗

PubMed1998

Microbial toxicity in soil medium.

A laboratory procedure using the respirometer was developed to measure microbial toxicity in soils of organic chemicals. The procedure was tested with Polytox, a commercial microbial test culture, on 35 organic chemicals. The test protocol was reproducible with a mean standard deviation of 0.08 mg chemical/g of soil for eight chemicals. The assays were also carried out at different moisture-holding capacities of soil. Correlation between toxicity tests done in aqueous medium and soil for Polytox test culture was statistically significant and yielded an r2 of 0.816. Details of the laboratory procedure and test results are presented together with comparisons of toxicity of chemicals in the soil medium with that in aqueous medium for the same test organism. A few practical applications are discussed.

Bacteria, Aerobic↗

PubMed1998

Structure- and property-activity relationship models for prediction of microbial toxicity of organic chemicals to activated sludge.

Two quantitative structure-activity relationship (QSAR) and two quantitative property-activity relationship (QPAR) models reported in the literature for predicting toxicity of synthetic organic chemicals to activated sludge microorganisms are summarized and compared. The QSAR models were developed using solvatochromic parameters and molecular connectivity indices; the QPAR models, using octanol-water partition coefficient and aqueous solubility. Experimental data on 16 chemicals not used in developing the above models are used to compare and evaluate the predictive ability of these QSAR/QPAR models. Based on the quality of the original models, their predictions, ease of application, and availability of model parameters, molecular connectivity indices and log P appear to be the most suitable in toxicity predictions.

1-Octanol↗

PubMed1997

Additivity in microbial toxicity of nonuniform mixtures of organic chemicals.

Microbial toxicity of nonuniform mixtures of selected synthetic organic chemicals in several proportion is evaluated. Toxicity is quantified by the inhibition of oxygen uptake rate of a surrogate microbial text culture as measured by a respirometer. The joint toxic effects of the chemicals are analyzed for simple addition using toxic units (TU) and similarity parameters (lambda). A new approach is proposed to assign acceptance limits to sigma(TU)i and lambda to account for experiment errors and variances. Based on this approach, the joint toxic effects of 16 chemicals evaluated in this study in 14 different mixtures were found to be simply additive. Predictions of component concentration based on simple additivity agreed with the measured values within an average factor of error of 1.4.

Bacteria↗