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Li X.,Tsinghua University | Wang C.,Tsinghua University | Qian Y.,Tsinghua University | Wang Y.,Tsinghua University | And 2 more authors.
Separation and Purification Technology | Year: 2013

In this study, we investigated the use of an electrochemical oxidation process to simultaneously remove chemical oxygen demand (COD), turbidity, and hardness from biologically treated citric acid wastewater that was non-biodegradable and contained high concentrations of inorganic salts. We employed a Ti/RuO2-IrO2 anode system to analyse the effects of electric voltage and initial chloride concentration on COD, turbidity, and hardness removal as well as on energy consumption. Under optimal conditions (electric voltage of 9 V, initial chloride concentration of 3000 mg L-1), organic pollutants were almost completely mineralised after 60 min of electrolysis. The resulting COD (6 mg L-1) and turbidity (3 NTU) of effluent was within the Water Reuse Standard of China (COD < 30 mg L-1, turbidity < 5 NTU) while energy consumption (Es) and general current efficiency (GCE) were 99 kW h kg COD-1 and 30%, respectively. We also found that electric voltage and initial chloride concentrations increased the rate of hardness removal. Further investigation revealed that organics were mainly degraded by electrochemical oxidation of humic and fulvic acid-like substances, and hardness was primarily removed via the production of CaMg(CO3)2 precipitate on the cathode surface. © 2013 Published by Elsevier B.V.

Li X.,Tsinghua University | Su L.,Tsinghua University | Wang Y.,Tsinghua University | Wang Y.,State Key Joint Laboratory of Environmental Simulation and Pollution Control | And 4 more authors.
Frontiers of Environmental Science and Engineering in China | Year: 2012

Catalytic fast pyrolysis (CFP) of Kraft lignins with HZSM-5 zeolite for producing aromatics was investigated using analytical pyrolysis methods. Two Kraft lignins were fast pyrolyzed in the absence and presence of HZSM-5 in a Curie-point pyrolyzer. Without the catalyst, fast pyrolysis of lignin predominantly produced phenols and guaiacols that were derived from the subunits of lignin. However, the presence of HZSM-5 changed the product distribution dramatically. As the SiO2/Al2O3 ratio of HZSM-5 decreased from 200 to 25 and the catalyst-to-lignin ratio increased from 1 to 20, the lignin-derived oxygenates progressively decreased to trace and the aromatics increased substantially. The aromatic yield increased considerably as the pyrolysis temperature increased from 500°C to 650°C, but then decreased with yet further increase of pyrolysis temperature. Under optimal reaction conditions, the aromatic yields were 2. 0 wt.% and 5. 2 wt.% for the two lignins that had effective hydrogen indexes of 0. 08 and 0. 35. © 2012 Higher Education Press and Springer-Verlag Berlin Heidelberg.

Yu Y.,Tsinghua University | Li X.,Tsinghua University | Su L.,Tsinghua University | Zhang Y.,Tsinghua University | And 3 more authors.
Applied Catalysis A: General | Year: 2012

Catalytic fast pyrolysis (CFP) of lignin with four different zeolite catalysts was investigated to determine the role of shape selectivity of zeolites in CFP. These zeolites included ZSM-5, mordenite, beta, and Y zeolites, which have various crystallographically determined static pore sizes between 5.6 and 7.6. The molecular dimensions of pyrolysis products, including lignin-derived oxygenates and aromatics, were calculated using quantum chemical computations. The effective pore sizes of the four zeolites at 650 °C were then determined by analyzing the molecular size and conversion behavior of the pyrolysis products in CFP. Results suggest that thermal distortion of the zeolite pore structure under high-temperature conditions of CFP effectively enlarge the crystallographically determined pore sizes of the zeolites by 2.5-3.4. Therefore, many lignin-derived oxygenates with a molecular size considerably larger than the static pore size were able to enter the pores of the zeolites and become effectively converted in our CFP tests. Bulkier monolignols derived from syringyl lignin, however, could not be effectively converted by ZSM-5 and mordenite zeolites due to size exclusion or pore blockage. Among the four zeolites, ZSM-5 produced the highest aromatic yield, followed in order by beta, mordenite, and Y zeolites. Beta and Y zeolites were the most effective catalysts for deoxygenating lignin-derived oxygenates. This analysis indicates that for CFP of softwood, ZSM-5 is the optimal catalyst because it can achieve satisfactory deoxygenation and aromatic production simultaneously, whereas for hardwood feedstock, beta zeolite may be used to convert bulky oxygenates derived from syringyl lignin. © 2012 Elsevier B.V.

Wang Y.,Tsinghua University | Wang Y.,State Key Joint Laboratory of Environmental Simulation and Pollution Control | Li X.,Tsinghua University | Zhen L.,Tsinghua University | And 3 more authors.
Journal of Hazardous Materials | Year: 2012

The electro-Fenton (E-Fenton) treatment of landfill leachate concentrates was investigated in this study. The concentrates were generated from nanofiltration of biologically pretreated landfill leachate, and contained high concentrations of refractory organics and inorganic salts. During the E-Fenton treatment, H2O2 was electrochemically produced at a carbon-polytetrafluorethylene (PTFE) cathode with oxygen feeding. The in situ generated H2O2 then reacted with Fe2+ that was added into the concentrates to bring about Fenton oxidation of the refractory organics in the concentrates. The effectiveness of the E-Fenton treatment of the concentrates was appraised in terms of its removal efficiency of total organic carbon (TOC) of the concentrates. The effects of FeSO4 dosage, current density, initial pH of the solution, and cathode area on the process performance were also evaluated. Under optimal reaction conditions that included a current density of 30mAcm-2, FeSO4 dosage of 10mM, initial pH of 3, and cathode area of 20cm2, the TOC and total nitrogen (TN) removal efficiencies were 82% and 51% after 6h of the E-Fenton treatment. The results indicated that the E-Fenton technology could produce sufficient amounts of advanced oxidants in situ to effectively degrade the refractory organic pollutants in high-strength leachate concentrates. © 2012 Elsevier B.V.

Shi H.-C.,Tsinghua University | Qiu Y.,Tsinghua University | Qiu Y.,State Key Joint Laboratory of Environmental Simulation and Pollution Control | He M.,Tsinghua University
International Journal of Chemical Engineering | Year: 2010

Surface water environment in China was degraded rapidly in the last two decades, resulting in increasingly tighten criteria issued for municipal wastewater treatment plants (WWTPs). This paper reviewed the recent advances of process design and operational optimization for nutrients removal. Three major processes, as anaerobic-anoxic-oxic (AAO) process, oxidation ditch (OD), and sequencing batch reactor (SBR) occupied 65 of WWTPs amounts and 54 of treatment volumes of China in 2006. However conservative process designs and operational faults often impaired the process performances and energy efficiency. Therefore, typical processes were modified, combined, and innovated to meet the requirements of the diverse influent characteristics and lower energy consumptions. Furthermore, operational optimization techniques by modeling, simulation, and real-time control were also developed and applied in China to improve the process operation. Although great efforts had been contributed to improve the WWTPs performances in China, attentions should be continuously paid to the introduction, instruction, and implementation of advanced techniques. At last, the technical demands and appropriated techniques of WWTPs in China were briefly discussed. Copyright © 2010 Yong Qiu et al.

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