Variation Characteristics of Different Fractions of Dissolved Organic Matter in Landfill Leachate during UV-TiO2 Photocatalytic Degradation

Fractionation was performed to investigate the variation characteristics of dissolved organic matter (DOM) in leachate during UV-TiO2 photocatalytic treatment process. Experimental results showed that the leachate from Erfeishan landfill with low COD was relatively steady after long-time natural environmental evolution. DOM dominating the main organic component of the leachate was up to 90% of TOC. Biodegradation was comparatively poor due to low BOD/COD (0.09) as an index meaning that the main component was refractory organics in the leachate. DOM in the leachate was separated into six fractions: hydrophobic acid (HOA), hydrophobic base (HOB), hydrophobic neutral (HON), hydrophilic acid (HIA), hydrophilic base (HIB), and hydrophilic neutral (HIN). The content of different DOM fractions were in descending order as: HOA > U HON > U HIA > U HIN > U HOB > U HIB. The photocatalytic removal efficiency of COD was up to 60%, more than 74% for DOC, respectively. BOD/COD continued to increase from initial 0.09 to about 0.39 during the whole photocatalytic treatment process, which indicated that biodegradation ability of leachate was improved by photocatalysis. The DOM content was reduced sharply after photocatalytic treatment. However, the HIA fraction kept almost steady in all treatment samples, the HOA fraction changed slowly in 24 h, and changed obviously after 36 h treatment, the HIB fraction increased slowly in 36 h, and decreased obviously after 36 h, and the HOB fraction decreased sharply in 6 h, increased from 6 h to 24 h, after 24h decreased,. The other two fractions (HON and HIN) decreased steadily during all treatment process. The predominant fraction in the raw leachate was HOA (30.5% of DOC), while the dominant fraction in the final effluent was HIA (69.4% of DOC).