Improvement of biodegradability for coking wastewater by selective adsorption of hydrophobic organic pollutants

• Hydrophobic contaminants in coking wastewater were removed selectively.
• Biodegradability of coking wastewater increased by selective adsorption.
• High TOC removal achieved for coking wastewater after selective adsorption.
• Non-π functional group is critical for selective removal of hydrophobic compound.

As a typical industrial wastewater, coking wastewater is characterized as high organic load, complicated composition and strong biological inhibition. Based on the analysis between organic composition and toxicity contribution of coking wastewater, a selective removal for targeting hydrophobic contaminants was conducted by organic modified acid-vermiculites (Chlorotrimethylsilane modification, CTMS-V; and Chlorotriethysilane modification, CTES-V), powdered activated carbon (PAC) and XAD-16 polymer adsorbent. Binary solution containing hydrophilic (phenol) and hydrophobic (diethyl phthalate, DEP) compounds was employed to evaluate the performance of selective adsorption then coking wastewater was further tested. Results of binary adsorption indicated that the average adsorption percentages of DEP for PAC, XAD-16, CTMS-V and CTES-V were 32.6 ± 11.1%, 50.8 ± 17.4%, 68.7 ± 22.6%, 75.5 ± 27.4% (mean ± standard deviation, n = 5) at varying phenol:DEP ratios (10–100, mol:mol). Coking wastewater treated by PAC, XAD-16 CTMS-V and CTES-V had a decrease of chemical oxygen demand (COD) at 24.6 ± 3.0%, 11.3 ± 1.5%, 4.4 ± 0.08% and 6.8 ± 1.1%. For biochemical oxygen demand (BOD5), PAC and XAD-16 gave a decrease of 47.5 ± 5.6% and 7.8 ± 1.4%, whereas CTMS-V and CTES-V gave an increase of 36.7 ± 4.1% and 57.2 ± 4.6%, respectively. The resulting BOD5:COD were 0.21 ± 0.03, 0.31 ± 0.04, 0.42 ± 0.05 and 0.50 ± 0.05 after treatment by PAC, XAD-16, CTMS-V and CTES-V, respectively. Post incubation of treated coking wastewater showed that the residual TOC after ten-day incubation were 73.1 ± 1.5%, 77.9 ± 3.5%, 73.2 ± 3.7% and 59.2 ± 3.0% for PAC, XAD-16 CTMS-V and CTES-V, respectively. The non-π functional surface (i.e., –CH3 and –CH2CH3) of modified acid-vermiculites played a critical role for capturing hydrophobic compounds from the solution with high concentration of hydrophilic competitive compounds.

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