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Aerobic granules were utilized as an effective biosorbent to remove Cr3+ from aqueous solution. The results showed that the initial pH, contact time, and Cr3+ 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 Cr3+ 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 Cr3+ biosorption process. [Copyright &y& Elsevier]

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. 400mg/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 10g/L active carbon and 30g/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 (<2000Da) compounds in the wastewater, there were still a few residual contaminants which could hardly be eliminated by either of the process. [Copyright &y& Elsevier]