Identifying the critical activated carbon properties affecting the adsorption of effluent organic matter from bio-treated coking wastewater

Activated carbon is widely used to remove effluent organic matter (EfOM) from bio-treated coking wastewater. However, the critical carbon properties affecting adsorption performance are still unclear. Nine commercial powdered activated carbons (PACs) with different pore structures, surface functional groups, and surface charges were used to adsorb EfOM from bio-treated coking wastewater, which was fractionated according to their molecular weight (MW) and hydrophobicity. Good correlations were observed between the adsorption of biopolymers (MW > 20,000 Da, 7 %) and macropore volume (>50 nm), as well as between the adsorption of humics (MW = 1000 ~ Da, 36 %) and mesopore volume (2-50 nm), suggesting that the adsorption sites of EfOM depended on their molecular size. Higher isoelectric points and fewer acidic groups promoted the adsorption of the most negatively charged hydrophobic acids (HPOA, 39.5 %). According to variation partitioning analysis (VPA), mesopore-macropore greatly contributed to the adsorption capacities of EfOM (71.3 %), whereas the sum of phenolic hydroxyl and carboxyl (26.3 %) and isoelectric point (12.2 %) affected the normalized adsorption capacities of EfOM. In conclusion, PAC with a higher mesopore volume, fewer acidic groups, and a higher isoelectric point was desirable for removing EfOM from bio-treated coking wastewater. This study provides guidance for the selection of PAC for the removal of EfOM from bio-treated coking wastewater.