[Show abstract][Hide abstract] ABSTRACT: Electrochemical oxidation is a promising technology to treatment of bio-refractory wastewater. Coking wastewater contains high concentration of refractory and toxic compounds and the water quality usually cannot meet the discharge standards after conventional biological treatment processes. This paper initially investigated the electrochemical oxidation using boron-doped diamond (BDD) anode for advanced treatment of coking wastewater. Under the experimental conditions (current density 20-60mAcm(-2), pH 3-11, and temperature 20-60 degrees C) using BDD anode, complete mineralization of organic pollutants was almost achieved, and surplus ammonia-nitrogen (NH(3)-N) was further removed thoroughly when pH was not adjusted or at alkaline value. Moreover, the TOC and NH(3)-N removal rates in BDD anode cell were much greater than those in other common anode systems such as SnO(2) and PbO(2) anodes cells. Given the same target to meet the National Discharge Standard of China, the energy consumption of 64kWhkgCOD(-1) observed in BDD anode system was only about 60% as much as those observed in SnO(2) and PbO(2) anode systems. Further investigation revealed that, in BDD anode cell, organic pollutants were mainly degraded by reaction with free hydroxyl radicals and electrogenerated oxidants (S(2)O(8)(2-), H(2)O(2), and other oxidants) played a less important role, while direct electrochemical oxidation and indirect electrochemical oxidation mediated by active chlorine can be negligible. These results showed great potential of BDD anode system in engineering application as a final treatment of coking wastewater.
[Show abstract][Hide abstract] ABSTRACT: Experiments were conducted to investigate the behavior of the integrated system with biofilm reactors and zero-valent iron (ZVI) process for coking wastewater treatment. Particular attention was paid to the performance of the integrated system for removal of organic and inorganic nitrogen compounds. Maximal removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH(3)-N) and total inorganic nitrogen (TIN) were up to 96.1, 99.2 and 92.3%, respectively. Moreover, it was found that some phenolic compounds were effectively removed. The refractory organic compounds were primarily removed in ZVI process of the integrated system. These compounds, with molecular weights either ranged 10,000-30,000 Da or 0-2000 Da, were mainly the humic acid (HA) and hydrophilic (HyI) compounds. Oxidation-reduction and coagulation were the main removal mechanisms in ZVI process, which could enhance the biodegradability of the system effluent. Furthermore, the integrated system showed a rapid recovery performance against the sudden loading shock and remained high efficiencies for pollutants removal. Overall, the integrated system was proved feasible for coking wastewater treatment in practical applications.
No preview · Article · Mar 2009 · Journal of Hazardous Materials
[Show abstract][Hide abstract] ABSTRACT: Aerobic granules were utilized as an effective biosorbent to remove Cr(3+) from aqueous solution. The results showed that the initial pH, contact time, and Cr(3+) concentration affected the biosorption process significantly. Both Freundlich and Langmuir isotherms were able to describe the equilibrium data reasonably with high correlation coefficients (R(2)>0.95) and pseudo-second-order model best fitted the biosorption process at experimental conditions. Moreover, Environmental Scanning Electronic microscope (ESEM), X-ray energy dispersion (EDX), and Fourier transform infrared (FTIR) analyses revealed that metal complexation, chemical precipitation, and ion exchange were involved in the removal of Cr(3+) with aerobic granules. Further analysis by a metal ion fraction test demonstrated that metal complexation could be the dominant mechanism of biosorption, whereas chemical precipitation and ion exchange appeared only to have minor role in the overall Cr(3+) biosorption process.
No preview · Article · Oct 2008 · Journal of hazardous materials
[Show abstract][Hide abstract] ABSTRACT: In the present work, a biofilm system was developed by combining one anaerobic biofilm reactor with two aerobic ones, all of which were filled with special carriers. Laboratory scale experiments lasting about a year were conducted to investigate the treatment of coking effluent by the biofilm system. Particular attention was paid to the performance of the biofilm system for different hydraulic retention times (HRT) and recirculation ratios (R). Maximal removal efficiencies of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) of 91.0% and 96.8%, respectively were obtained without effluent recirculation at HRT = 60 h. Moreover, 77.5% of total nitrogen (TN) removal was achieved for R = 3 and HRT = 45 h. Simultaneous nitrification and denitrification (SND) occurred. Analysis of the organic compounds revealed that phenolic compounds in the influent were biodegraded effectively within 20 h of aerobic treatment. However, there were still some refractory organic compounds remaining in the biological effluent, which were similar to humic substances (HS). After advanced treatment by coagulation, a significant removal efficiency of 48.3% for COD was achieved and organic compounds in molecular weight ranges of 10,000–30,000 Da and 0–2000 Da were mostly removed. After treatment by the integrated biofilm system, the final effluent met the National Discharge Standard of China with regard to COD and NH3-N content.
No preview · Article · Mar 2008 · PROCESS BIOCHEMISTRY
[Show abstract][Hide abstract] ABSTRACT: Coking wastewater was treated by A/O process of biological filter with a special kind of carrier. The wastewater contained much more phenolic compounds with about 2000 mg/L of COD and 260 mg/L of NH4+ -N. The A/O system could achieve average removal efficiencies of 87.0% and 91.6% for COD and NH4+ -N, respectively, when HRT was 60 h. The NH4+ -N in the effluent could meet the first level of National Discharge Standard at optimal operation condition. The phenolic compounds with low molecular weight could be fully biodegraded by A/O system. The organic compounds in the effluent were in the relative molecular weight range of 10,000-30,000 and contained --OH, C==O, C--O and phenyl group. Based on the support and protection of the carrier, a great number of microorganisms adhered and immobilized on the outer and inner surface of carrier, which contributed to a simultaneous removal of COD, NH4+ -N and TN. The A/O system biological filter showed a characteristic of steady performance and resistance ability during the operation period.
No preview · Article · Jan 2008 · Huan jing ke xue= Huanjing kexue / [bian ji, Zhongguo ke xue yuan huan jing ke xue wei yuan hui "Huan jing ke xue" bian ji wei yuan hui.]
[Show abstract][Hide abstract] ABSTRACT: Advanced treatment of coking wastewater was investigated experimentally with coagulation and zero-valent iron (ZVI) processes. Particular attention was paid to the effect of dosage and pH on the removal of chemical oxygen demand (COD) in the two processes. The results showed that ZVI was more effective than coagulation for advanced treatment of coking wastewater. The jar tests revealed that maximal COD removal efficiency of 27.5–31.8% could be achieved under the optimal condition of coagulation, i.e. 400 mg/L of Fe2(SO4)3 as coagulant at pH 3.0–5.0. On the other hand, the COD removal efficiency could be up to 43.6% under the idealized condition of ZVI upon 10 g/L active carbon and 30 g/L iron being dosed at pH 4.0. The mechanisms for COD removal in ZVI were dominated by coagulation, precipitation and oxidation–reduction. ZVI would also enhance the biodegradability of effluent by increasing BOD5/COD from 0.07 to 0.53. Moreover, some ester compounds could be produced in the reaction. Although ZVI was found more efficient than coagulation in eliminating low molecular weight (<2000 Da) compounds in the wastewater, there were still a few residual contaminants which could hardly be eliminated by either of the process.
No preview · Article · Aug 2007 · Journal of Hazardous Materials