Interaction-sedimentation strategy for highly efficient removal of refractory humic substances in biologically treated wastewater effluent: from mechanistic investigation to full-scale application

Based on the accurate characterization of the binding sites of humic substances (HS) and their binding coefficients with ferric ions (Fe(III)), a coupled interaction-sedimentation (CIS) technology was proposed for dealing with HS in the biologically treated wastewater effluent (BTWE) from a full-scale antibiotic production wastewater treatment plant. The infrared spectral and carbon-13 nuclear magnetic resonance characteristics showed that (i) protonated carboxyl groups in HS were the main binding sites for Fe(III) and HS, (ii) one carboxyl group of HS interacted with one ferric ion, (iii) the Fe(III)-binding ability of fulvic acids (FA) was 2.8 times as much as that of humic acids (HA) when FA and HA coexisted, and (iv) the presence of non-humic substances in the effluent organic matter (EfOM) amplified the Fe(III)-binding ability difference between FA and HA to 4.9 times. Afterwards CIS technology was successfully optimized and applied in engineering-scale and superior HS and EfOM removal efficiencies of 94.2% and 84.0% were reached, respectively. The CIS technology and its engineering application in this study not only fulfill the direct discharging standard for antibiotic production wastewater, but also have the potential for replication in broader advanced treatments for BTWE. [Display omitted] •71.6% of the EfOM was identified to be humic substances (HS).•84.0% of the EfOM was removed at pH 4.6 using a CIS technology in full-scale.•High EfOM-removal efficiency benefited mainly from 94.2% of HS-removal.•Strong interactions between HS and ferric ions dominated the CIS technology.•Protonated carboxyl groups in HS were the main binding sites with ferric ions.