Adsorption of UV-quenching substances (UVQS) from landfill leachate with activated carbon

Co-treatment of landfill leachate with sewage at publicly owned treatment works (POTWs) is a common leachate management practice. However, the UV absorbing property of UV-quenching substances (UVQS) present in municipal landfill leachate may significantly reduce the efficiency of disinfection at POTWs that adopt ultraviolet irradiation for disinfection. The UVQS represents an emerging concern in the solid waste and wastewater treatment industries. This study aimed to evaluate the performance of activated carbon (AC) for removal of UVQS from landfill leachate in order to address the leachate UV-quenching issue. Results showed that the abatement of leachate UV254 absorbance with AC followed a pseudo-2nd-order reaction or intra-particle diffusion kinetics model. The adsorption isotherm patterns for leachate UV254 absorbance, dissolved organic carbon (DOC), and chemical oxygen demand (COD) well fit the Freundlich models. AC was capable of effectively adsorbing UV-quenching organic matter, regardless of humic acid (HA), fulvic acid (FA), and hydrophilic (HPI) isolates, via both chemisorption and physical adsorption mechanisms. Of note, after the AC adsorption, the residual UV254 absorbance was linearly correlated with COD remaining in leachate and exponentially correlated with residual DOC in leachate, separately. Furthermore, fluorescence excitation-emission matrix (EEM) analyses could indicate the removal of hydrophobic UVQS during AC adsorption, but could not reflect the presence or variation of hydrophilic UVQS. Findings of this study demonstrate that AC adsorption provides an effective treatment option for mitigation of the leachate-induced UV transmittance impacts on POTWs.