Biomedical subjects

E R Blatchley

Publications and source records attributed to E R Blatchley.

4 recordsLinked to original sources

PubMed2001

Chlorination of pure bacterial cultures in aqueous solution.

The fate and distribution of chlorine in aqueous solutions containing four pure bacterial cultures was studied. Solutions were subjected to chlorination at different initial free chlorine concentrations. Resulting concentrations of residual chlorine were determined by both DPD/FAS titration and membrane introduction mass spectrometry (MIMS). In all cases, false-positive breakpoint chlorination curves, probably attributable to the formation of chloroorganic-N compounds, were observed by DPD/FAS titration, while little or no inorganic residual chloramine was found by MIMS. Free chlorine was observed in similar quantities by both methods after chlorine demand by bacterial cellular materials in solution was satisfied. These results indicated the residual chloramines existed in the form of organic chloramines; these compounds are generally recognized as being poor antimicrobial agents. Further investigation confirmed that the bacterial cells were the source of organic-N compounds. The kinetics of chlorination of pure bacterial suspensions was also studied. The pattern of residual chlorine decay following chlorination of the bacterial suspensions indicated rapid initial free chlorine consumption, followed by slow free chlorine consumption, with trace quantities of inorganic chloramine being formed.

Chloramines↗

PubMed2001

Bacterial responses to ultraviolet irradiation.

The UV dose-response behavior of laboratory cultures of waterborne bacteria were examined for UV doses ranging from ca. 0-100 mW.s/cm2 using a collimated-beam reactor. Specific physiological responses measured in these tests included viability (ability to reproduce) and respiration (oxygen uptake rate). The results of these exposures indicated that resistance to UV-imposed loss of viability in E. coli cultures can be partially attributed to agglomeration during the irradiation process. From these results, it is conjectured that a bacterial population may be comprised of two sub-populations: one with low resistance (discrete or paired cells) and a second with high resistance (bacterial aggregates). A small fraction of the high-resistance portion of the population appears to be essentially unaffected by UV irradiation, thereby causing a discontinuity in the measured dose-response behavior. Moreover, the dose-response behavior of the highly resistant fraction is variable and difficult to describe quantitatively. The basis of these statements and most information in the literature is microbial viability as quantified by the membrane filtration assay. In contrast to these findings, the results of analyses for bacterial activity (respiration) suggest that comparatively little change in the population can be found to result from UV irradiation. This suggests that UV radiation accomplishes inactivation of the bacteria, but does not "kill" the bacterial cells per se, thereby highlighting the importance of considering bacterial repair processes in the design of UV disinfection systems.

Bacteria↗

PubMed2001

UV dose distribution characterization using fractal concepts for system performance evaluation.

This paper presents a mathematical model for estimating the UV dose distribution delivered by continuous-flow UV disinfection processes. The model adopts fractal concepts and a stochastic method to simulate microorganism (particle) trajectories through the irradiation zone of an open-channel UV system. The irregularity of particle trajectories attributable to random movements was characterized by fractal dimension. In turn, trajectory-specific doses were calculated by integrating UV intensity over travel time. Results of these simulations indicated that radiation intensities along the trajectories could be highly variable. Therefore, microorganisms are expected to receive a broad range of radiation doses as a result of variations in radiation intensity along their trajectories and spatial heterogeneity in the radiation intensity field. This supports previous assertions that the conventional averaged-dose approach will result in substantial deviations between predicted and actual system performance. Implications of the results in terms of treatment efficiency and system design are discussed. The presented approach is found to be useful as a tool for rapid estimation of the dose distribution delivered by UV processes.

Bacteria↗

PubMed1999

Determination of 3,3'-dichlorobenzidine and its degradation products in environmental samples with a small low-field Fourier transform ion cyclotron resonance mass spectrometer.

3,3'-Dichlorobenzidine (DCB) and its degradation products, 3-chlorobenzidine (MCB) and benzidine, are of environmental concern because of their carcinogenic nature. The suitability of a small Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer for the analysis of these environmental contaminants in different types of matrices was explored. All the measurements were carried out by depositing the sample solution directly on a disk that was introduced into the mass spectrometer. This approach is very fast and simple because it requires no prior chromatographic separation or derivatization. Calibration curves determined by collecting 70-eV electron ionization mass spectra of neat samples yielded lower limits of detection of 29 and 17 pg (total amount on the solids probe) for DCB and benzidine, respectively (based on a signal to noise ratio of > or = 2:1), while chemical ionization with ammonia resulted in lower limits of detection of 21 pg for DCB and 9 pg for benzidine (total amount on the solids probe). FT-ICR analysis of sediments collected from Lake Macatawa (Holland, MI) verified the presence of DCB in this complex, environmentally significant sample matrix. Laboratory experiments designed to probe biodegradation and photodegradation pathways showed that DCB undergoes sequential dehalogenation to yield MCB and then benzidine under exposure to microorganisms and under simulated tropospheric solar radiation. The ability of the FT-ICR to determine elemental compositions of compounds introduced as described above was demonstrated for one of the degradation products.

3,3'-Dichlorobenzidine↗