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Zhen G.,Tongji University | Zhen G.,Tohoku University | Lu X.,Shanghai University | Lu X.,Tohoku University | And 5 more authors.
Frontiers of Environmental Science and Engineering | Year: 2014

In this work, the enhanced dewaterabing characteristics of waste activated sludge using Fenton pretreatment was investigated in terms of effectiveness and statistical optimization. Response surface method (RSM) and central composite design (CCD) were applied to evaluate and optimize the effectiveness of important operational parameters, i.e., H2O2 concentrations, Fe2+ concentrations and initial pH values. A significant quadratic polynomial model was obtained (R 2= 0.9189) with capillary suction time (CST) reduction efficiency as the response. Numerical optimization based on desirability function was carried out. The optimum values for H2O2, Fe2+, and initial pH were found to be 178 mg·g-1 VSS (volatile suspended solids), 211 mg·g-1 VSS and 3.8, respectively, at which CST reduction efficiency of 98.25% could be achieved. This complied well with those predicted by the established polynomial model. The results indicate that Fenton pretreatment is an effective technique for advanced waste activated sludge dewatering. The enhancement of sludge dewaterability by Fenton's reagent lies in the migration of sludge bound water due to the disintegration of sludge flocs and microbial cells lysis. © 2014 Higher Education Press and Springer-Verlag Berlin Heidelberg.

Zhen G.,Tongji University | Lu X.,Shanghai University | Wang B.,Shanghai Tongji Construction Co. | Zhao Y.,Tongji University | And 6 more authors.
Bioresource Technology | Year: 2012

The potential benefits of Fe(II)-activated persulfate (S2O8 2-) oxidation under mild temperature in enhancing the dewaterability of waste activated sludge were investigated. Capillary suction time (CST) was used to characterize sludge dewatering. Zeta potential, particle size distribution, three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, fourier-transformed infrared (FT-IR) spectroscopy and scanning electronic microscopy (SEM) were employed to explore influencing mechanisms. The results indicated that the dewaterability was deteriorated with single thermal treatment, but significantly enhanced in the presence of Fe(II)-S2O8 2- oxidation and further advanced together with thermal treatment. EEM and FT-IR analysis indicated that combined thermal and Fe(II)-S2O8 2- oxidation pretreatment led to degrading of tyrosine and tryptophan protein-like substances in extracellular polymeric substances (EPS) and cleavage of linkages in polymeric backbone. SEM images further revealed the rupture of sludge flocs at the colloidal scale, which contributed to the release of EPS-bound water and interstitial water trapped between flocs, and subsequent enhanced dewaterability. © 2012 Elsevier Ltd.

Zhen G.,Tongji University | Lu X.,Shanghai University | Li Y.,Tohoku University | Zhao Y.,Tongji University | And 5 more authors.
Bioresource Technology | Year: 2012

The potential of Fe(II)-activated persulfate (S2O8 2-) oxidation on enhancing the dewaterability of sludge flocs from 3-full scale wastewater treatment plants (WWTPs) were investigated. Normalized capillary suction time (CST) was applied to evaluate sludge dewaterability. Both extracellular polymeric substances (EPS) and metabolic activity of microorganisms were determined to explore the responsible mechanism. Fe(II)-S2O8 2- oxidation effectively improved sludge dewaterability. The most important mechanisms were proposed to be the degradation of EPS incorporated in sludge flocs and rupture of microbial cells. Three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy confirmed that the powerful SO4 - from Fe(II)-S2O8 2- system destroyed the particular functional groups of fluorescing substances (i.e., aromatic protein-, tryptophan protein-, humic- and fulvic-like substances) in EPS and caused cleavage of linkages in the polymeric backbone and simultaneous destruction of microbial cells, resulting in the release of EPS-bound water, intracellular materials and water of hydration inside cells, and subsequent enhancement of dewaterability. © 2012 Elsevier Ltd.

Zhen G.,Tongji University | Zhen G.,Tohoku University | Lu X.,Shanghai University | Lu X.,Tohoku University | And 7 more authors.
Chemical Engineering Journal | Year: 2013

The activated sludge process of wastewater leads to the production of a substantial amount of excess activated sludge. The increasing interest of Fe(II)-mediated persulfate (S2O82-) oxidation in improving sludge dewatering highlights a need to understand their environmental impacts on subsequent treatment, but the potential effects on sludge anaerobic digestion remains unknown. In this study, the response of waste activated sludge anaerobic digestion to a shock load of Fe(II)/S2O82- oxidation were investigated. It was observed that total suspended solids (TSS) and volatile suspended solids (VSS) removals were considerably lowered when Fe(II) and S2O82- dosages were greater than 0.8 and 1.0mmol/g VSS, respectively, while 34.6-60.5% drop in hydrogen sulfide (H2S) took place. Degradation of extracellular polymeric substances (EPS) of sludge induced by Fe(II)/S2O82- oxidation resulted in their deteriorating protective role on the microorganisms, which may cause the inhibitory effects on the microbial activity, and subsequently reduce digestion efficiency and H2S generation. Then, sludge dewaterability during digestion process was investigated. It was found that dewaterability of sludge, firstly improved by Fe(II)S2O82- pretreatment, was gradually worsened during subsequent digestion because of slightly increased EPS. The visualization of EPS with three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy further revealed that the discernable rise in tyrosine and tryptophan protein-like substances together contributed to poorer dewaterability. © 2013 Elsevier B.V.

Chen Y.,Guangxi University | Yu Z.,Guangxi University | Yu Z.,Guangxi Hualan Design and Consulting Group Co. | Sun L.,Guangxi University | And 3 more authors.
Chinese Journal of Environmental Engineering | Year: 2013

According to landfill leachate's characteristics of high concentration of pollutants, poor biochemical degradability, etc, semi-aerobic aged refuse bioreactor and ultrasound/Fenton process were applied to treat landfill leachate. The removal rates of chemical oxygen demand(COD), ammonia nitrogen(NH3-N), total phosphorus(TP) and colorimetry treated by semi-aerobic aged refuse bioreactor were 80%, 85%, 92%, 85%, respectively. The optimal technical conditions of ultrasound/Fenton process were discovered by single factor and orthogonal experiments. Satisfying treatment effect of the total removal rate of landfill leachate by combined semi-aerobic aged refuse bioreactor and ultrasound/Fenton process could be achieved. The highest removal rates of COD, NH3-N, TP and colorimetry were 96%, 86%, 94% and 95%, respectively. The final effluent was inodorous with color of pale yellow. Its BOD5/CODi increased from 0.16 to 0.35, which met follow-up biological treatment. The effluent of COD, TP could meet the Standard for Pollution Control on the Landfill Site of Municipal Solid Waste (GB 16889-2008).

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