Biomedical subjects

Thomas E Clevenger

Publications and source records attributed to Thomas E Clevenger.

5 recordsLinked to original sources

PubMed2006

Prediction of N-nitrosodimethylamine (NDMA) formation as a disinfection by-product.

This study investigated the possibility of a statistical model application for the prediction of N-nitrosodimethylamine (NDMA) formation. The NDMA formation was studied as a function of monochloramine concentration (0.001-5mM) at fixed dimethylamine (DMA) concentrations of 0.01mM or 0.05mM. Excellent linear correlations were observed between the molar ratio of monochloramine to DMA and the NDMA formation on a log scale at pH 7 and 8. When a developed prediction equation was applied to a previously reported study, a good result was obtained. The statistical model appears to predict adequately NDMA concentrations if other NDMA precursors are excluded. Using the predictive tool, a simple and approximate calculation of NDMA formation can be obtained in drinking water systems.

Dimethylnitrosamine↗

PubMed2006

Element concentrations of dry-grind corn-processing streams.

The dry-grind corn process is one of two technologies used to convert corn into ethanol. In this process, all kernel components are processed through several sequential steps, including fermentation. Only one coproduct (distillers' dried grains with solubles [DDGS]) is available for marketing. DDGS provide income to offset costs of processing; issues that affect marketing have implications in the economic viability of dry-grind plants. Two issues relate to elements in DDGS: high concentrations and excessive variation. Data on element concentrations in dry-grind processing streams could be helpful in addressing these concerns. The objective of this study was to determine element concentrations in primary process streams from dry-grind plants. Samples of corn, ground corn, beer, wet grains, syrup, and DDGS were obtained from nine dry-grind plants, and element concentrations were determined. The concentrations of most elements in corn were not different among processing plants and were similar to published data. However, for the processing streams, there were differences in several element concentrations among processing plants. The concentrations of most elements in beer were about three times those of corn, due to the disappearance of starch during fermentation. Syrup had the highest element concentrations. Variations in element contents of DDGS and parent streams were due to processing conditions and not corn. Appropriate processing of thin stillage (the parent stream of syrup) could reduce the element content of DDGS.

Beer↗

PubMed2005

Effects of alum coagulation on speciation and distribution of trihalomethanes (THMs) and haloacetic acids (HAAs).

The impacts of alum coagulation on the distribution of disinfection by-products (DBPs), trihalomethanes (THMs), and haloacetic acids (HAAs) were evaluated under controlled chlorination conditions using four surface waters. Among the nine HAAs found in waters, dihaloacetic acids (X2AAs) have been found to be the dominant species in all of the raw and alum treated waters. Alum coagulation tends to remove more monohaloacetic acids (XAAs) and trihaloacetic acids (X3AAs) precursors than that of dihaloacetic acids (X2AAs). Alum coagulation treated water had a lower HAA9/TTHM ratio compared with that of the raw water. The increase of THM bromine incorporation factors (BIFalpha) value of alum treated water was statistically significant in comparison with the raw water. On average, BIFalpha increased by 54% after the alum coagulation process in these four different waters. This indicated that THM speciations shifted in favor of the more brominated compounds. However, alum coagulation treatment process had less effect on HAA bromi ne incorporation factors (BIFbeta)than it did on BIFalpha. Bromine incorporation factor (BIF) values decreased with time in the THM and HAA formation processes, especially within the first 10 h of the reaction time. This suggested that brominated THMs or HAAs formed faster than the chlorinated species in the initial period.

Acetates↗

PubMed2004

Environmental factors influencing microcystin distribution and concentration in the Midwestern United States.

During May-September 2000-2001, physicochemical data were collected from 241 lakes in Missouri, Iowa, northeastern Kansas, and southern Minnesota U.S.A., to determine the environmental variables associated with high concentrations of the cyanobacterial hepatotoxin microcystin (MC). The study region represents a south-north latitudinal gradient in increasing trophic status, with total phosphorus (TP) and total nitrogen (TN) values ranging between 2-995 and 90-15870 microg/L, respectively. Particulate MC values, measured by ELISA, ranged from undetectable to 4500 ng/L and increased with increasing latitude. Despite latitudinal trends, environmental variables explained < 50% of the variation in MC values. Inspection of MC-TN and MC-Secchi bivariate plots revealed distinctly nonlinear trends, suggesting optima for maximum MC values. Nonlinear interval maxima regression indicated that MC-TN maxima were characterized by a unimodal curve, with maximal (> 2000 ng/L) MC values occurring between 1500 and 4000 microg/L TN. Above 8000 microg/L TN all MC values were < 150 ng/L. MC-Secchi maxima were characterized by exponential decline, with maximal MC values occurring at Secchi depths < 2.5 m. The development of empirical relationships between environmental variables and MC values is critical to effective lake management and minimization of human health risks associated with the toxin. This study indicates MC values are linked to the physicochemical environment; however, the relationships are not traditional linear models.

Carcinogens↗

PubMed2003

Relationship of chlorine decay and THMs formation to NOM size.

Because of increasing concern about balancing health risks for pathogen control and disinfection by-product (DBP) formation in water supplies, utilities are forced to closely examine and optimize their disinfection practices. A better understanding of the relationship between the molecular weights of the natural organic matter (NOM), chlorine decay kinetics and THMs formation can help the utilities to minimize the DBP concentrations, providing healthier and microbially safer water. The authors present data on chlorine decay kinetics and total trihalomethanes (TTHM) formation kinetics and modeling with different molecular weights NOM fractions of Mississippi River water. TTHM modeling results indicated that the TTHM formation in fractionated NOM was a function of chlorine consumption. TTHM yield coefficients ranged from 31 to 42 microg-TTHM/mg-Cl2. As the molecular weight of the fractions decreased, TTHM yield coefficients increased.

Chlorine Compounds↗