Elfrida M. Carstea

Determination of changes in wastewater quality through a treatment works using fluorescence spectroscopy.

Fluorescence spectroscopy was used to characterize municipal wastewater at various stages of treatment in order to understand how its fluorescence signature changes with treatment and how the signal relates to biochemical oxygen demand (BOD) and chemical oxygen demand (COD). The impact of size fractionation on the fluorescence signal was also investigated. Fluorescence measurements were taken for unfiltered and filtered (0.45 and 0.20 μm) samples of crude, settled and secondary treated wastewater (activated sludge and trickling filter), and final effluent. Good correlations were observed for unfiltered, diluted wastewater samples between BOD and fluorescence intensity at excitation 280 nm, emission 350 nm (Peak T1) (r=0.92) and between COD and Peak T1 intensity (r=0.85). The majority of the T1 and T2 signal was found to be derived from the<0.20 μm fraction. Initial results indicate that fluorescence spectroscopy, and changes in Peak T1 intensity in particular, could be used for continuous, real-time wastewater quality assessment and process control of wastewater treatment works.

Characterisation of dissolved organic matter fluorescence properties by PARAFAC analysis and thermal quenching

The fluorescence intensity of dissolved organic matter (DOM) in aqueous samples is known to be highly influenced by temperature. Although several studies have demonstrated the effect of thermal quenching on the fluorescence of DOM, no research has been undertaken to assess the effects of temperature by combining fluorescence excitation - emission matrices (EEM) and parallel factor analysis (PARAFAC) modelling. This study further extends previous research on thermal quenching by evaluating the impact of temperature on the fluorescence of DOM from a wide range of environmental samples, in the range 20 °C - 0 °C. Fluorescence intensity increased linearly with respect to temperature decrease at all temperatures down to 0 °C. Results showed that temperature affected the PARAFAC components associated with humic-like and tryptophan-like components of DOM differently, depending on the water type. The terrestrial humic-like components, C1 and C2 presented the highest thermal quenching in rural water samples and the lowest in urban water samples, while C3, the tryptophan-like component, and C4, a reprocessed humic-like component, showed opposite results. These results were attributed to the availability and abundance of the components or to the degree of exposure to the heat source. The variable thermal quenching of the humic-like components also indicated that although the PARAFAC model generated the same components across sites, the DOM composition of each component differed between them. This study has shown that thermal quenching can provide additional information on the characteristics and composition of DOM and highlighted the importance of correcting fluorescence data collected in situ.

LIGHT-INDUCED FLUORESCENCE SPECTROSCOPY AND OPTICAL COHERENCE TOMOGRAPHY OF BASAL CELL CARCINOMA

Many up-to-date optical techniques have been developed and applied recently in clinical practice for obtaining qualitatively and quantitatively new data from the investigated lesions. Due to their high sensitivity in detection of small changes, these techniques are widely used for detection of early changes in biological tissues. Light-induced fluorescence spectroscopy (LIFS) is one of the most promising techniques for early detection of cutaneous neoplasia. Increasing number of recent publications have suggested that optical coherence tomography (OCT) also has potential for non-invasive diagnosis of skin cancer. This recent work is a part of clinical trial procedure for introduction of LIFS technique into the common medical practice in National Oncological Medical Center in Bulgaria for diagnosis of non-melanoma skin cancer. We focus our attention here on basal cell carcinoma lesions and their specific features revealed by LIFS and OCT analysis. In this paper we prove the efficiency of using the combined LIFS-OCT method in skin lesions studies by integrating the complimentary qualities of each particular technique. For LIFS measurements several excitation sources, each emitting at 365, 385 and 405 nm maxima are applied. An associated microspectrometer detects in vivo the fluorescence signals from human skin. The main spectral features of the lesions and normal skin are discussed and their possible origins are indicated. OCT images are used to evaluate the lesion thickness, structure and severity stage, when possible. The obtained results could be used to develop a more complete picture of optical properties of these widely spread skin disorders. At the same time, our studies show that the combined LIFS-OCT method could be introduced in clinical algorithms for early tumor detection and differentiation between normal/benign/malignant skin lesions.

A new penalized nonnegative third‐order tensor decomposition using a block coordinate proximal gradient approach: Application to 3D fluorescence spectroscopy

In this article, we address the problem of tensor factorization subject to certain constraints. We focus on the canonical polyadic decomposition, also known as parallel factor analysis. The interest of this multilinear decomposition coupled with 3D fluorescence spectroscopy is now well established in the fields of environmental data analysis, biochemistry, and chemistry. When real experimental data (possibly corrupted by noise) are processed, the actual rank of the “observed” tensor is generally unknown. Moreover, when the amount of data is very large, this inverse problem may become numerically ill‐posed and consequently hard to solve. The use of proper constraints reflecting some a priori knowledge about the latent (or hidden) tracked variables and/or additional information through the addition of penalty functions can prove very helpful in estimating more relevant components rather than totally arbitrary ones. The counterpart is that the cost functions that have to be considered can be nonconvex and sometimes even nondifferentiable, making their optimization more difficult and leading to a higher computing time and a slower convergence speed. Block alternating proximal approaches offer a rigorous and flexible framework to properly address that problem since they are applicable to a large class of cost functions while remaining quite easy to implement. Here, we suggest a new block coordinate variable metric forward‐backward method, which can be seen as a special case of majorize‐minimize approaches to derive a new penalized nonnegative third‐order canonical polyadic decomposition algorithm. Its interest, efficiency, robustness, and flexibility are illustrated thanks to computer simulations performed on both simulated and real experimental 3D fluorescence spectroscopy data.

Quality assessment of Romanian bottled mineral water and tap water

This study reports the evaluation of bottled mineral water characteristics using fluorescence spectroscopy (synchronous fluorescence scans and emission spectra) and physico-chemical analyses. Samples from 14 still mineral water brands were compared to 11 tap waters collected from two Romanian cities. Correlation and factor analyses were undertaken to understand the relationships between the individual components. The concentration of major and minor ions showed great variation between the bottled mineral water samples highlighting the diversity of the water intakes, while in the case of tap water the chemical composition was relatively similar for samples collected in the same city. Fluorescence data showed that the mineral water contained low quantities of organic matter. The humic fraction was dominant in all samples, while the microbial fraction was low in most samples. Synchronous fluorescence scans provided more information, regarding the composition of organic matter, compared to emission spectra. The study evidenced the correlation between fluorescence parameters and major elements and highlighted the potential of using fluorescence for qualitative evaluation of the bottled mineral water quality, as a screening method before undertaking complex analyses.

Seasonal Variation of Eutrophication in Some Lakes of Danube Delta Biosphere Reserve.

  To understand the trophic state of lakes, this study aims to determine the dynamics of phytoplankton assemblages and the main factors that influence their seasonal variation. Sampling campaigns were carried out in three lakes from the Danube Delta Biosphere Reserve. Spectral analysis of specific phytoplankton pigments was applied as a diagnostic marker to establish the distribution and composition of phytoplankton taxonomic groups. Fluorescence spectroscopy was used to quantify changes in dissolved organic matter (DOM). The relative contribution of the main phytoplankton groups to the total phytoplankton biomass and the trend of development during succession of the seasons showed that cyanobacteria could raise potential ecological or human health problems. Moreover, fluorescence spectroscopy revealed that Cryptophyta and cyanobacteria were the main contributors to the protein-like components of DOM. It was concluded that fluorescence could be used to provide a qualitative evaluation of the eutrophication degree in Danube Delta lakes.

REAL-TIME MONITORING OF AN URBAN RIVER CONTAMINATED WITH PETROLEUM PRODUCTS

Fluorescence spectroscopy is a promising approach to the characterization of natural aquatic components and organic pollutants, due to its rapid analysis and high sensitivity. Petroleum products had been studied, using fluorescence technique, in numerous occasions, as seawater and soil contaminant or as raw sample. Nevertheless, no complex assessment has been made on fluorescence real–time spectra of freshwater diesel oil contamination. This study reports a 5–days experiment on an urban river, where water samples were collected and measured automatically for fluorescence. Also, measurements of standard water quality parameters (pH, conductivity and total organic carbon) were performed. During the experiment, the river was accidentally polluted with diesel oil from containers disposed directly into the river. Fluorescence spectra presented 2 intense peaks with excitation wavelengths at 235 nm and 275 nm and emission wavelength at 340 nm. The data revealed that 2 and 3 aromatic rings hydrocarbons were dominant in the sample. Real-time measurements were compared with laboratory analyses performed on samples of diesel oil and gasoline. Based on this investigation, it has been evidenced that fluorescence spectroscopy is an effective tool in monitoring oil pollution in water systems, identifying the type of contaminant and estimating the quantity of the pollutant.