Analysis Of Biological Wastewater Treatment Processes Using UV And Fluorescence Spectra

The biological wastewater treatment reactors with various pollutants and microorganisms are complex systems. Conventional chemical analysis can not meet the requirement of real-time and on-line monitoring of bioreactors. Spectrometry method is a non-invasive and regent-free one, and can be performed on-line and in situ. Thus, it is a promising method for monitoring the bioreactor.In this study the chemometrical method was introduced to decompose the spectra of microorganisms and the effluents from various bioreactors, including aerobic, anaerobic, and nitrifying bioreactors and a microbial fuel cell (MFC). The information was drawn and related to the bioreactor process parameters. The main objective of this work was to develop a new method of characterizing the parameter and status of bioreactors, based on UV/Vis and fluorescence spectra. Main contents and results are as follows:In Chapter 2, the correlation model was established between the UV spectra and the concentrations of nitrate and nitriate from a mtrifying reactor. The feasibility of decomposing the overlapped spectra by partial least squares (PLS) was verified. Taking the four biogenic fluorophores as an example, the feasibility of decomposing the severely overlapped fluorescence spectra by parallel factor analysis (PARAFAC) was verified. The information about the relative concentration, the excitation and emission spectra was obtained.In Chapter 3, the excitation-emission matrix (EEM) fluorescence spectra were used to characterize the soluble microbial products (SMP), intracellular substances and extracellular polymer substances (EPS). PARAFAC was applied to extract the pure spectra from the overlapped spectra. Results show that proteins and nicotinamide adenine dinucleotide, reduced form (NADH), were identified as the two main intracellular fluorophores in the intracellular substances. The fluorescence intensity scores of the intracellular fluorophores were closely related to the bioreactor performance. The profiles of the intracellular proteins were similar to those of volatile suspended solids (VSS), and the intracellular NADH was correlated to the specific substrate degradation rate. Three main components, i.e., proteins, fulvic- and humic-like substances, were identified from the SMP. Their fluorescence intensity scores of the three fluophores in the SMP could be connected with process parameters through the Leudeking-Piret equation. The extracellular proteins and humic-like substances were substrate-utilization-associated, and that the fulvic-like substances were non-growth-associated. Proteins and fulvic-like substances were identified as the two main fluorophores in the EPS. The on-line monitoring data of the mixture in the reactor were able to reflect the variation of the sludge concentration, but failed to reflect the effect of substrate addition. The voltage of the photomultiplier tube (PMT), the coupling efficiency of the fiber optics and the influence of the circumstance lightshould be taken into account.In Chapter 4, the EEM of an anaerobic H₂-producing batch reactor were explored,and the main fluorophores of the reactor effluents were proteins and NADH. The ratio of the fluorescence intensity scores of the two fluorophores was related to the H₂ partial pressure, and the relationship between them could be expressed using a non-liner equation. The EEM fluorescence spectra of the effluents from a thermophilic upflow anaerobic sludge bed (UASB)H₂-producing reactor were also explored. Proteins, NADH and riboflavin were the main fluorophores. The effects of hydraulic retention time, substrate concentration and temperature on the bioreactor performance were evaluated, and the response of the three fluorophores scores was also explored. The profiles of the NADH scores were related to the variation of the H₂ partial pressure. Standard addition method was used to quantitatively determinate the concentration of these three fluorophores from the UASB effluents.In Chapter 5, the variation of the UV and fluorescence spectra from an MFC was investigated. Accompanied with the reaction in the microbial fuel cell, the microorganisms released some microbial products, which led to an increase in UV₂₅₄. Proteins and fulvic-like substances were identified as the main fluorophores by decomposing the EEM fluorescence spectra of the MFC with PARAFAC. The protein fluorescence was attributed to the tryptophane residues of the proteins, while the fulvic-like substances might be attributed to the coenzyme and fulvic acid. The dose of Fe²⁺ promoted the electrogenesis of the MFC, and the profiles of the fluorophores were different from those of the control.In Chapter 6, Mie scattering theory was used to calculated the extinction coefficient as a function of dimensionless radius at different reflection indexes. The extinction spectra produced by the macrostructure and internal structure were also calculated as a function of wavelength. Taking the polystyrene pellet as an example, levenberg-marquart least squares coupled with the Mie theory were used to calculate the extinction spectrum, and the radius and concentration were estimated. The UV/Vis spectra of Bacillus megaterium was explored.