Treatment Of Membrane Concentrated Landfill Leachate By Cu-Based Fenton-Like Process Coupled With Active Sludge Method

Membrane concentrated landfill leachate（MCLL）is a kind of highly concentrated organic wastewater with high salt content,very low biodegradability and strong biological toxicity,which is produced in the treatment of landfill leachate through the integration of biochemical method with membrane filtration.As a degradation-efficient and condition-mild technology,advanced oxidation processes have been considered as the most application-promising techniques,especially for the Fenton oxidation method.However,the narrow p H range and iron sludge generation limit its widespread application.In view of the above problems,this dissertation aimed to treat MCLL based on the Cu-based Fenton-like method,which has a wider working p H range.A new approach that integrates Cu-based Fenton-like and active sludge methods for the treatment of MCLL was proposed.Moreover,spectroscopic technologies and high-resolution mass spectrometry were employed to provide a molecular insight into the structural transformation of dissolved organic matter in MCLL.The primary contents and results are listed as follows:（1）Taking the typical pollutant humic acid（HA）in MCLL as the treatment object,the degradation efficiencies of Cu-based Fenton-like and Fenton methods were compared.The results showed that Fenton method was suitable for acid condition,while Cu-based Fenton-like process was more suitable for neutral/alkaline condition.The removal of HA followed pseudo-first-order kinetics and the reaction rate can be significantly accelerated at higher temperatures.The reaction rate can be increased by18.3 times with reaction temperature increasing from 30 ^oC to 70 ^oC.The addition of Cl^-can also accelerate the reaction rate and the reaction rate constant for HA degradation with 21000 mg/L Cl^-was 20.1 times higher than that without Cl^-.This study confirmed that Cu-based Fenton-like method was suitable for treating MCLL,which possessed alkaline condition and high Cl^-concentration.Fluorescence regional integration results showed that the removal of HA experienced a two-stage process,i.e.,oxidation followed by degradation.（2）The degradation of real MCLL by Cu-based Fenton-like process was systematically studied.DOM can be effectively removed under the condition:H₂O₂ dosage of 440.6 mmol/L,H₂O₂/Cu（II）molar ration of1000,p H of 5.0,temperature of 60 ^oC,and time of 3 h,and the removal rates of COD and TOC were 81.9%and 71.8%,respectively.Compared with the Fenton method,the optimal reaction p H shifted from 3 to 5 for the Cu-based Fenton method,and the dosage of Cu（II）was only 3/1000 of that of Fe（II）.Moreover,the BOD₅/COD ratio of the effluent and the removal rates of COD also increased（from 0.11 to 0.16 and from 78.9%to 81.9%,respectively）.In addition,multi-stage Cu-based Fenton-like treatment can significantly improve the biodegradability of the effluent.After the two-stage and three-stage treatment,the BOD₅/COD ratio increased from 0.01to 0.31 and 0.64,respectively.（3）The feasibility of combining multi-stage Cu-based Fenton-like process with activated sludge process to treat MCLL was confirmed.The COD concentrations of the influent from the two-stage and three-stage oxidation effluents during the domestication of activated sludge were 117-262 mg/L and 50-188 mg/L,respectively.The final COD in the effluent was less than 100 mg/L.During the domestication process,the effluent was clarified and the settling performance of activated sludge settling performance was good.（4）The degradation characteristics of DOM in MCLL during the Cu-based Fenton-like process were studied based on UV-Vis and fluorescence spectroscopies combined with chemometric methods.Two fluorescent DOM components were identified according to the parallel factor analysis,i.e.,terrestrial HA and microbial HA.Combined with two-dimensional correlation analysis and kinetic studies,the degradation degree,degradation rate and degradation order of DOM followed the order:FDOM（terrestrial HA>microbial HA）>chromophore DOM（CDOM）.The aromatic structure was degraded preferentially over the conjugated unsaturated structure in CDOM.（5）The transformation characteristics of DOM in MCLL during the multi-stage Cu-based Fenton-like combined activated sludge process were unveiled at the molecular level based on Fourier transform ion cyclotron resonance mass spectrometry（FT-ICR MS）.The results showed that the single-stage Cu-based Fenton-like process tended to remove CHOS and CHONS-like organic matter,the multi-stage Cu-based Fenton-like process tended to remove CHON-like organic matter,and the activated sludge process tended to remove CHOS-like organic matter.The molecular weight of the refractory DOM in the multi-stage Cu-based Fenton-like process and activated sludge process was mainly 300-400 Da,which was distributed in lignins/carboxylic rich alicyclic molecules with large O/C ratio and tannin structures in the VK diagram.In this study,a new process of multi-stage Cu-based Fenton-like combining with activated sludge was proposed to treat MCLL,addressing the problem that MCLL could not be treated biologically due to its low biodegradability and strong biotoxicity,and achieving the goal of MCLL treatment to meet the discharge standards.Meanwhile,the degradation and transformation mechanism of DOM in MCLL was revealed by molecular spectroscopy and high resolution mass spectrometry.