ABSTRACT
Although humic substances (HSs) are among the most valuable compounds in the environment, they often constitute nuisance factors for wastewater treatment plants (WWTPs). However, their recovery from by-products of WWTPs opens up opportunities for their utilization. Therefore, this study aimed to evaluate the suitability of selected analytical methods for determining the structure, properties, and possible utilization of HSs originating from WWTPs based on model humic compounds (MHCs). As a consequence, the study proposed separate approaches for the initial and in-depth characterization of HSs. The results demonstrate that UV-Vis spectroscopy may be recognized as a cost-effective approach for the preliminary characterization of HSs. Such a method indeed gives similar information on the degree of complexity of MHCs as X-EDS and FTIR, and similarly to them allows for the differentiation of their particular fractions. In turn, X-EDS and FTIR techniques were recommended to be used for in-deep analysis of HSs due to their ability to detect heavy metals and biogenic elements in their structure. Contrarily to other studies, the presented research indicates that only selected absorbance coefficients - A253/A230, Q4/6, and ΔlogK may help to distinguish particular humic fractions and evaluate changes in their behavior, independently of their concentration (coefficient of variation < 20%). Herein, the fluorescence capacities of MHCs were found to be equally affected as their optical properties by the changes in their concentration. Focusing on the obtained results, this study recommends that the quantitative comparison of the properties of HSs should be proceeded by the standardization of their concentration. Herein, the stability of other spectroscopic parameters characterizing solutions MHCs was achieved within a concentration from 40 to 80 mg L-1. Among them, the analyzed MHCs were differentiated the most by the SUVA254 coefficient, which value was almost 4 times higher for SAHSs (8.69) than for ABFASs (2.01).
ABSTRACT
The ability to measure and control the composition of activated sludge is an important issue, aiming at evaluating the effectiveness of changes occurring in the sludge, what determines its usefulness to treat wastewater. In this research, diffuse reflectance infrared Fourier transform (FTIR-DRIFT) technique was used, which relies on measuring the reflectance of the powdered substance's surface layer and capturing spectra in range of infrared wave. First, spectra correlation table of the substances mostly occurring in wastewater was developed to assess the main components of the tested samples of activated sludge. The simplest compounds containing functional groups characteristic for particular chemical classes were chosen: peptides (peptone and albumin), fats (glycerin and fatty acids), carbohydrates (glucose and sucrose), nitrogen compounds (NaNO3 and NH4SO4), sulfur compounds (Na2SO4 and Na2S2O3), silicate, etc. The spectra of those substances were captured and characteristic absorption bands for respective bonds in the function groups were assigned. Second, samples of activated sludge from lab-scale membrane bioreactors (MBRs), which purifies petroleum wastewater, were taken. Samples were properly prepared (lyophilization and homogenization) and their spectra were captured. During spectra analysis, previously developed correlation table was used. In obtained spectra of activated sludge, absorption bonds characteristic for amides, peptides, carbohydrates, fats, and aliphatic was identified. The spectra profile of the sludge sample from MBR feed with petroleum wastewater was slightly different from the control MBR sample's spectra. Intensity of bands in the area characteristic for aliphatic compounds and phenols was clearly higher. This study proves the usefulness of FT-IR technique to observe changes in the chemical composition of activated sludge.
