Advanced treatment of biologically pretreated coking wastewater by intensified zero-valent iron process (IZVI) combined with anaerobic filter and biological aerated filter (AF/BAF)

Abstract

Experiments were conducted to investigate the behavior of the sequential system of intensified zero-valent iron process (IZVI) and anaerobic filter and biological aerated filter (AF/BAF) reactors for advanced treatment of biologically pretreated coking wastewater. Particular attention was paid to the performance of the integrated system for the removal of chemical oxygen demand (COD), ammonia nitrogen (NH₃-N) and total nitrogen (TN). The average removal efficiencies of COD, NH₃-N and TN were 76.28%, 96.76% and 59.97%, with the average effluent mass concentrations of 56, 0.53 and 18.83 mg/L, respectively, reaching the first grade of the national discharge standard. Moreover, the results of gas chromatography/mass spectrum (GC/MS) and gel permeation chromatography (GPC) analysis demonstrated that the refractory organic compounds with high relative molecular mass were partly removed in IZVI process by the function of oxidation-reduction, flocculation and adsorption which could also enhance the biodegradability of the system effluent. The removal efficiencies of NH₃-N and TN were achieved mainly in the subsequent AF/BAF reactors by nitrification and denitrification. Overall, the results obtained show that the application of IZVI in combination with AF/BAF is a promising technology for advanced treatment of biologically pretreated coking wastewater.

Keywords

advanced treatment / coking wastewater / intensified zero valent iron / biofilter

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