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Li X.,Tsinghua University | Zhu W.,Tsinghua University | Wang C.,Tsinghua University | Zhang L.,China University of Mining and Technology | And 3 more authors.
Chemical Engineering Journal | Year: 2013

In this study, we constructed a continuous-flow three-dimensional electrode reactor (CTDER) to remove organic compounds from biologically-treated citric acid wastewater. We analyzed the effects of the residence time, current density, initial pH, and airflow rate on the reactor's energy consumption (Es), general current efficiency (GCE), and ability to remove the chemical oxygen demand (COD). We determined that the optimal operation conditions for the reactor included a residence time of 5min, a current density of 40mAcm-2, and an initial pH of 5. Under these conditions, we determined that 55.7% of COD was removed. The resulting COD of the effluent was within the National Discharge Standard of China (COD<100mgL-1), and the Es and GCE were 274.8kWhkgCOD-1 and 16.2%, respectively. We also found that aeration in the CTDER negatively affected COD removal due to the short-circuiting of the fluid. Further investigation revealed that the CTDER could produce a steady effluent quality where the organic compounds were degraded primarily via the indirect electrochemical oxidation of humic acid-like substances in the citric acid wastewater. Our results demonstrate that the CTDER is a highly efficient system for the electrochemical treatment of biologically-treated citric acid wastewater. © 2013 Elsevier B.V. Source


Zeng R.,Tsinghua University | Zhang H.,Tsinghua University | Huang D.,Tsinghua University | Wu C.,Tsinghua University | Cheng L.,Guohuan Tsinghua Environment Engineering Design and Research Institute Co
Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae | Year: 2013

In order to study the influences of influent concentration, hydraulic retention time (HRT) and air flow on the filtering performance of active medium filter, a series of performance experiment schemes were designed, with the siliceous sand (SS) as lifting medium and the suspending liquid of kaolin as the target, to analyze the removal efficiency of SS under different conditions. The results showed that the cyclic period of sand was within 24 h while the height of the bed was 700 mm and HRT=10 min & SS=45 mg·L-1. Influent concentration and air flow didn't affect the filtering performance of active medium filter, with the increase of the HRT, the removal efficiency of SS increased gradually. While active medium filter used for upgrade and reconstruction of SS from Standard B to Standard A, the reasonable HRT was 7.5~10 min and the optimal air flow range was 7.96~26.53 L·m-2·min-1. Source


Zeng R.,Tsinghua University | Zhang H.,Tsinghua University | Cheng L.,Guohuan Tsinghua Environment Engineering Design and Research Institute Co | Gao L.,Tsinghua University | And 3 more authors.
Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae | Year: 2013

The performance of the air-lift filtration system in Nordic Water filters is particularly affected by air flow rate, water head and the size of sand-lifting tube. This paper tests the impacts of air flow rate and diameter of tube on the volume of the lifted water and sand at fixed water head in an air-lift sand filter (ALF). It is shown that the amount of lifted sand and lifting efficiency both have an increasing-then-decreasing trend with the increasing air flow. The diameter of sand-lifting tube mainly determines the maximum amount of lifted sand and the lifting efficiency, which has no effect on the ratio of lifted water to sand. There is also a linear relationship between water head and the amount of sand lifted per unit air flow volume under the condition of constant air flow. As a consequence, the diameter of the sand tube and air flow rate are suggested to be well designed in order to maximize the efficiency of the air-lift sand filter (ALF) system. Source

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