Optimization Of Operational Conditions During Leachate Treatment By Coagulation And FENTON Processes And DOM Analyses

Landfill leachate contains the higher content of dissolved organic matter (DOM), and the composition and characteristics of DOM can affect the leachate treatment options. Therefore, this paper focus on two typical advanced treatment processes: coagulation and Fenton. Effluent of the SBR was treated by Fenton and coagulation processes, and after that the effluent from both processes was fractionated into five classes using non-ionic adsorption resin, in order to characterize the removal of DOC during Fenton and coagulation. Fluorescence EEMs was applied to characterize the transformations of DOM fractions and IR spectroscopy was used for gross characterization of DOM and can provide valuable information on the structural and functional properties of DOM molecules.The optimum operational conditions for coagulation was dosage of poly-ferric chloride (PFC) 0.772 mmol/L (Fe) without adjusted pH (8.89). DOC removal rate was 67.21%. The maximum amount of DOC that could be removed by the Fenton's post-treatment was about 64% of the initial value. Such a maximum removal was achieved with dosages of H2O2 and Fe2+ respectively 1.2 mL/L and 6.44 mmol/L, pH=3.5 and reaction time=30 min. The residual COD of both effluents from coagulation and Fenton were less than 100 mg/L, which meet the correlative discharge standard (GB 16889-2008). Compared with Fenton process, coagulation showed a better performance for using less precipitant and producing less sludge. The cost of leachate treatment was lower and environmental benefit was obvious in coagulation process.Fenton process was good at removing organics of small molecules, thus the residual organics in the effluent of Fenton were of large molecular weight. In the coagulation process, complex organic matters of large molecular weight were removed, because mechanism of coagulation was adsorption and interception. The removal rates of different fractions during coagulation process in decreasing order was as following: HPO-N (83.47%), TPI-A (78.55%), HPO-A (72.22%), TPI-N (60.89%), HPI (0.49%); so was Fenton process: HPO-N (84.78%), TPI-A (73.99%), TPI-N (67.57%), HPO-A (60.43%), HPI (17.10%).The peaks in the fluorescence EEMs of HPO-A were the highest ones, which showed that there were more fluorescing materials in HPO-A, while SUVA of HPO-A was also higher than other fractions, which meant that its internal components containing more aromatic substances. HPI, mainly composed of hydrophilic material which is not in the range of humus, was properly derived from carbohydrate and amino acids and contained mainly of aliphatic hydrocarbons. There were more aromatic proteins in HPO-N and TPI-N, and these organic matters were with large molecular weight.The IR spectrum effectively indicated that carboxylic acids existed as a major functional group in the influent HPO-A and TPI-A. The FT-IR spectra of the HPO-N and TPI-N were very similar, with greater hydrocarbon character and less carboxylic acid character than other fractions. Moreover, both contained a significant amide-1 or amide-2 peaks. HPO-N and TPI-N were enriched in hydrocarbon and amide-1 or amide-2 functional groups, indicating bacteria-derived glycoprotein material.