An investigation of recalcitrant organic compounds in leachates

Recalcitrant organic compounds remain a key challenge in landfill leachate management as they are resistant to microbial degradation and have potential to damage the water environment. Conventional leachate characterisation methods are time consuming and limited by their inability to provide compositional analysis. This research therefore investigates the characteristics of recalcitrant organic compounds in leachates and undertakes a feasibility study of the possible use of UV absorption and fluorescence spectroscopy for a rapid and economical compositional analysis of recalcitrant organic compounds. Two laboratory experiments are carried out in this regard. In one experiment, a laboratory scale aerobic biodegradation is carried out on four untreated and two treated leachate samples collected from two UK MSW landfills (Pitsea and Rainham), and leachates are characterised using conventional methods (COD and DOC) as well as UV absorption and fluorescence spectroscopy. It is found that the leachates which have low organic content are easily biodegradable whereas the leachates which have high organic content are not easily biodegradable. UV and fluorescence spectroscopy allow compositional analysis of recalcitrant organic compounds and show that humic and fulvic compounds are the key components of the recalcitrant organic compounds. A rapid biodegradability assessment of different leachates using these novel techniques is in agreement with conventional method showing that a rapid characterisation of leachates using spectroscopic methods is feasible. It is also found that organic compounds in these leachates are aromatic in nature and the leachates containing large amounts of aromatic compounds, condensed aromatic structures are difficult to degrade. In another experiment, the influence of the solid waste component on the development of recalcitrant organic compounds in leachates is investigated by carrying out an anaerobic biodegradation experiment for fresh waste, composted waste, newspaper waste and synthetic waste. Composted waste contributes significantly to the development of the recalcitrant compounds due to the removal of readily biodegradable organic compounds during composting and hence the increased proportion of biologically resistant compounds during the subsequent anaerobic biodegradation. Newspaper waste also contributes significantly to the presence of recalcitrant organic compounds due to the relatively less resistant cellulose and high lignin present in this waste. This research validates the application of UV and fluorescence spectroscopy for rapid on-site monitoring of landfill leachates that would help scientist and engineers to assess leachate quality, identify various organic compounds and to optimise leachate treatment processes. The analysis performed on Pitsea and Rainham leachates is a promising step towards developing a database of representative information of characteristics of recalcitrant organic compounds in leachates for different UK landfills. This research also provides an understanding of the composition of leachates from different wastes and it can be conclude that disposals enriched with composted and newspaper waste would favour the development of leachates with high concentrations and condensed aromatic structures of recalcitrant organic compounds in a landfill system