Characterization Of Isolated Fractions Of Dissolved Organic Matter In The Wastewater Treatment Process

Dissolved organic matter (DOM) in municipal wastewater which has a wide rangevariety and complex structure is one of the removal objects in wastewater treatment. Inorder to clarify the transformation and biochemical conversion of organic matter intreatment process, we get the dissolved organic matter from A2O process in municipaltreatment plant as the study object and the component of humic acid (HA), fulvic acid(FA) and hydrophilic (HyI) were concentrated and fractionated by the DAX-8resin.The results showed that: microbe played a major role in DOM removal processes,the concentration of HyI, FA, HA fractions’ in the influent respectively were15.26mg/L,17.94mg/L,6.83mg/L, whereas in the effluent were respectively decreasedto1.44mg/L,2.14mg/L,0.24mg/L, the removal rate respectively reached90.56%,88.07%,96.49%. Moreover, the composition of the organic matter had changed afterthe biological treatment, the percentage of HyI, FA, HA fractions were33.50%,39.40%,15.00%in the influent, but in the effluent they varied to31.73%,47.34%,5.23%, this results showed that HA decreased9.77%in percentage of total TOC.However, the percentage of HyI increased7.94%, while the percentage of HyIdecreased slightly.At the same time, the gel chromatography was used to analysis the molecularweight distribution of the separated organic fractions. Study shown that the molecularweight of influent HyI fraction concentrated in2kDa，0.7kDa and also had a weakabsorption in10kDa;the effluent HyI molecular weight was relative concentrated,mainly in1.1kDa,and had a weak absorption in8kDa.However,the influent FAmolecular weight mainly concentrated in6kDa and10-12kDa, the effluent FAmolecular weight increased to10kDa,13.5kDa.Moreover, the influent and effluent HAmolecular weight showed a two peaks characteristic at12kDa and10kDa,but after the biological treatment the relative intensity changed, overall, the molecular weight of HAhad an increasing trend.In order to further understand the changes of dissolved organic matter inwastewater treatment processes, the fluorescence, ultraviolet, organic acidic functionalgroup and the FTIR spectra characteristics of organic fractions were analyzed andevaluated.Among them, the UV results showed that after biological treatment theoxygen-containing functional groups in the aromatic rings substituents decreased, thearomaticity and the degree of humification grade of organic matter gradually increasedwith the treatment processing, and the degree of humification grade was HA>FA>HyIin all influent and effluent fractions. Fluorescnce analysis showed that: humic acidproduced by microbial metabolism was the primary source of humic acid inwastewater, and fluorescent components in wastewater DOM were mainly protein-like(Peak A and Peak B) and humic-like fluorescence peaks (Peak C), the location were A:230/340-342nm, B:285-290/342nm, C:325-335/410-418nm, where A, B related toreadily biodegradable protein while C peak related to refractory fulvic acid. After thebiological treatment, the protein-like fluorescence peaks were disappeared, while thefulvic fluorescence intensity was just reduced by25%.The results of acidic functionalgroup showed that HA, FA and HyI fractions of DOM samples from influent andeffluent had similar total acidity whose range was10.87-18.74meq/g, and the effluentwas larger than influent. Combined the FTIR spectra and molecular weight distributionof fractions we can see that high molecular weight HA had more complex structuresand more fat chains, and relatively low molecular weight FA, HyI componentscontained more oxygen-containing functional groups.