Humification phenomenon and its application for the transformation of refractory organic pollutants by oxidoreductive catalyst-mediator systems

Abstract

Humic substances (HS), which are a naturally occurring mixture of organic compounds, play an important role in both pollutant chemistry and the biogeochemistry of natural waters and soils. HS may undergo various interactions with xenobiotic chemicals, which result in a removal or detoxification of the toxic pollutants. One of the prominent interactions is oxidative covalent binding that incorporates xenobiotics into HS. In addition, organic pollutants can also be involved in the humification process with naturally occurring lignin derivatives through oxidative coupling reaction in the presence of appropriate reaction catalysts. Therefore, both humic substances and humification process are currently being considered as a promising candidate for pollution remediation. The interaction reaction may be affected by the characteristics of HS, which again strongly depend on the degree of humification and its source. Waste landfill can be considered as a huge bioreactor that produces a relatively high amount of HS during organic degradation process. The terrestrial environments contaminated by leachate from unsanitary or improperly designed or operated sanitary landfills can be significantly affected by the composition of the leachates. From the fact that leachate contains a relatively high amount of HS as well as other organic pollutants, the understanding of the characteristics and role of the HS in the contaminated aquifer is critical to estimate the degree and effect of the pollution and, in turn, to establish an optimal remediation strategy. Therefore, in this study, humic and fulvic acids extracted from several landfill leachates with different landfill ages were characterized using elemental analysis and various spectroscopic methods. Molecular size distribution of the HS was also determined using batch ultrafiltration technique and permeation coefficient model. The element analysis and spectral features obtained from UV/Vis., IR, and $1^H$ and ${13}^C$ NMR sho...