Fluourescence as a potential monitoring tool for recycled water systems

Fluorescence spectroscopy has been investigated as a monitoring tool for a range of applications including water quality and pollution monitoring in rivers, process control in sewage treatment works and specific pollutants in industrial wastewater, oil in water and disinfection byproduct formation potentials in drinking water treatment. Organic matter fluorescence occurs when a loosely held electron in an atom or a molecule is excited to a higher energy level by the absorption of energy, for example, a photon, and fluorescence occurs when energy is lost as light as the electron returns to its original energy level (ground state). Some energy is ‘lost’ from the excited electron by collision, non-radiative decay and other processes, prior to emission, so the energy of the emitted photon is lower than the excitation energy. Absorption and excitation will be followed in some instances by relaxation of the electron to a stable configuration, stimulating the emission of a photon termed fluorescence. The precise spectral excitation/emission signature depends on the specific chemical structure as well as other factors including sample matrix and temperature. Organic matter fluorescence was measured on a Varian Eclipse fluorescence spectrophotometer. A series of emission scans from 300 to 600 nm were recorded whilst exciting with light from 240 to 450 nm. The fluorescence measurements resulted in an excitation emission matrix for each sample, representing a map of the fluorescence characteristics of the organic matter in the sample. Fluorescence but have been found to be linked to bacterial activity, sewage treatment process efficiency and therefore organic matter bioavailability. However, high concentration solutions, such as untreated sewage, require dilution prior to fluorescence analysis. A further interference, scatter by particulates and larger colloids, is also reduced by dilution again by reduction in concentration. However scatter is only effectively reduced by filtering, which also ensures that only DOM contributes to the fluorescence signature. The wavelength at which absorption (excitation) and emission occur is specific to the molecule.

Keywords:

Fluorescence , monitoring , pollution , tool